Method for synthesizing SiO2Al2O3-containing sol solution and method for forming porous alumina film

Abstract

A method for synthesizing a sol solution is provided for forming a porous alumina film with high heat resistance and a high specific surface area, which has excellent adhesion to various substrate surfaces. An alkoxysilane solution and an aluminum solution are separately prepared in advance. A precipitate containing a silicon compound adsorbed on aluminum hydroxide is precipitated in a mixed solution of the alkoxysilane and aluminum solutions. The precipitate separated from the mixed solution is washed with water and filtered to produce a precipitate cake. Water is added to the precipitate cake to prepare a slurry solution. The slurry solution is pH-adjusted and then autoclaved to prepare a SiO2Al2O3-containing sol solution. The pH adjustment of the slurry solution controls the pH of the slurry solution within a specific pH range where the SiO2Al2O3-containing sol solution after autoclaving becomes a sol state. This sol solution is suitable for forming a porous alumina film with high heat resistance and a high specific surface area, which has excellent adhesion to various substrate surfaces.

Description

Technical Field

[0001] The present invention relates to a method for synthesizing a SiO2Al2O3-containing sol solution for forming porous alumina to which silicon dioxide is added, and a method for forming a heat-resistant porous alumina film. Background Art

[0002] Porous alumina materials having a large specific surface area, such as γ-alumina, can be used as catalyst supports for supporting catalyst substances, filters, etc., and research has been conducted to improve their properties (for example, see Patent Documents 1 to 5).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2004-203654

[0006] Patent Document 2: International Publication No. 2014 / 051091

[0007] Patent Document 3: International Publication No. 2012 / 096386

[0008] Patent Document 4: International Publication No. 2013 / 111457

[0009] Patent Document 5: Japanese Patent Application Laid-Open No. 2009-061383

[0010] Patent Document 6: International Publication No. 2021 / 192752 Summary of the Invention

[0011] Problems to be solved by the invention

[0012] Catalyst supports must be subjected to harsh conditions such as high temperature, high pressure, and the presence of steam, minimizing the reduction in specific surface area and the compositional changes associated with hydration reactions. The inventors of this application have demonstrated that Al2O3, doped with SiO2 and Ba, maintains a high specific surface area even after calcination at 1200°C for dozens of hours, and no evidence of the formation of α-Al2O3 associated with the migration of Al2O3 has been confirmed (see Patent Document 6 above). This highly heat-resistant alumina powder, molded into pellets, can be used as a catalyst support for reactions requiring high heat resistance, such as steam reforming.

[0013] However, pelletized catalyst supports experience increased pressure loss under high SV conditions. As an example of efficiently promoting reactions on the catalyst surface layer under high SV conditions, automobile exhaust purification catalysts are known, which utilize a cordierite honeycomb coated with a carrier component such as alumina to form an alumina layer, supporting precious metals. However, the alumina layer obtained using existing technologies lacks heat resistance, making it prone to sintering in the high-temperature, high-pressure, steam-vapor atmosphere of steam reforming reactions, significantly reducing catalytic activity.

[0014] The present invention is proposed in view of the above-mentioned problems, and its purpose is to provide a method for forming a porous alumina film with excellent adhesion, high heat resistance and high specific surface area on the surface of various substrates (for example, cordierite, quartz glass, α-Al2O3, etc.), and to provide a method for synthesizing a sol solution as an alumina precursor when making such a porous alumina film.

[0015] Means of solving the problem

[0016] The inventors of the present application have conducted in-depth research on the preparation conditions of the sol solution serving as the above-mentioned aluminum oxide precursor and the method of forming the above-mentioned aluminum oxide film on the surfaces of various substrates. As a result, they have discovered a method for forming a catalyst carrier layer on the surface of the substrate that exhibits high performance in terms of adhesion, heat resistance, and specific surface area, and have achieved the invention shown below.

[0017] The first feature of the method for synthesizing a sol solution of the present invention is that it is a method for synthesizing a SiO2Al2O3-containing sol solution for forming porous alumina to which silicon dioxide is added, comprising the following steps:

[0018] A process for preparing an alkoxysilane solution containing alkoxysilane, water, alcohol and inorganic acid;

[0019] A process for preparing an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride and aluminum sulfate and water;

[0020] A step of precipitating a precipitate having a silicon compound adsorbed on aluminum hydroxide in a mixed solution of the alkoxysilane solution and the aluminum solution;

[0021] The process of filtering and separating the precipitate from the mixed solution, and washing the filtered and separated precipitate with water to prepare a precipitate cake;

[0022] The process of adding water to the precipitate cake to prepare a slurry solution, adjusting the pH of the slurry solution, and then subjecting the slurry solution to an autoclave treatment to prepare the SiO2Al2O3-containing sol solution,

[0023] By the pH adjustment treatment of the slurry solution, the pH value of the slurry solution is controlled within a specific pH range in which the solution state of the SiO 2 Al 2 O 3 -containing sol solution after the autoclave treatment becomes a sol state.

[0024] According to the sol solution synthesis method of the first characteristic, the autoclave treatment in the step of preparing the SiO₂Al₂O₃-containing sol solution can produce a SiO₂Al₂O₃-containing sol solution containing sol particles in a highly dispersed state with silica bonded to boehmite particles. Since this sol solution is in a sol state, applying the sol solution to a substrate surface and drying it produces a gel film, a homogeneous film-like coating in which the sol particles are uniformly dispersed. This gel film, upon calcination, can form a porous silica-added alumina film with excellent adhesion to various substrate surfaces, high heat resistance, and a high specific surface area.

[0025] In a preferred embodiment of the method for synthesizing the sol solution of the first characteristic, in the step of precipitating the precipitate,

[0026] When the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, the mixed solution is heated under reflux and then subjected to pH adjustment to coprecipitate the precipitate.

[0027] When the aluminum compound is sodium aluminate, the aluminum solution is heated to reflux, subjected to pH adjustment treatment, and then mixed with the alkoxysilane solution to prepare the mixed solution, in which the precipitate of the silicon compound adsorbed on the precipitate of aluminum hydroxide precipitated during the pH adjustment treatment is precipitated.

[0028] In addition, in a preferred embodiment of the method for synthesizing the sol solution of the above-mentioned first feature, the specific pH range changes according to the SiO2 concentration defined as the mass concentration of SiO2 relative to SiO2Al2O3 in the prepared SiO2Al2O3-containing sol solution, and when the aluminum compound is any one of the aluminum nitrate, the aluminum chloride and the aluminum sulfate, it is in the range of greater than 2.8 and less than 7.8, and when the aluminum compound is sodium aluminate, it is in the range of greater than 1.0 and less than 6.2.

[0029] In addition, in a preferred embodiment of the method for synthesizing the sol solution of the first characteristic, in the process of preparing the SiO2Al2O3-containing sol solution,

[0030] The treatment temperature of the autoclave treatment is controlled to a specific treatment temperature within a range of 100° C. to 200° C.,

[0031] The treatment time of the autoclave treatment is controlled within a specific time range in which the solution state after the autoclave treatment becomes a sol state.

[0032] The specific time range varies according to the specific processing temperature, the SiO2Al2O3 content in the prepared SiO2Al2O3-containing sol solution, and the SiO2 concentration defined as the mass concentration of SiO2 to SiO2Al2O3 in the prepared SiO2Al2O3-containing sol solution, and is within the range of more than 1 hour and less than 100 hours.

[0033] Furthermore, the second characteristic of the method for synthesizing a sol solution of the present invention is that it is a method for synthesizing a SiO2Al2O3-containing sol solution for forming porous alumina to which silicon dioxide is added, comprising the following steps:

[0034] A process for preparing an alkoxysilane solution containing alkoxysilane, water, alcohol and inorganic acid;

[0035] A process for preparing an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride and aluminum sulfate and water;

[0036] A step of precipitating aluminum hydroxide in the aluminum solution;

[0037] The process of filtering and separating the precipitate from the aluminum solution, and washing the filtered and separated precipitate with water to prepare a precipitate cake;

[0038] A process of adding water to the precipitate cake to prepare a slurry solution, adjusting the pH of the slurry solution, and then subjecting the slurry solution to an autoclave treatment to prepare an Al2O3 sol solution;

[0039] The process of adding the alkoxysilane solution to the Al2O3-containing sol solution to prepare the SiO2Al2O3-containing sol solution,

[0040] By the pH adjustment treatment of the slurry solution, the pH value of the slurry solution is controlled within a specific pH range in which the solution state of the Al 2 O 3 -containing sol solution after the autoclave treatment becomes a sol state.

[0041] According to the synthesis method of the sol solution of the second characteristic, an Al2O3-containing sol solution containing highly dispersed boehmite sol particles can be obtained by autoclaving in the step of preparing the Al2O3-containing sol solution. After the alkoxysilane solution in which the alkoxysilane obtained in the alkoxysilane solution preparation step is uniformly dissolved is added to the above-mentioned Al2O3-containing sol solution, a hydrolysis reaction proceeds at a certain temperature and over time to generate silica particles. A SiO2Al2O3-containing sol solution containing highly dispersed sol particles with silica particles adsorbed on boehmite sol particles can be obtained in the same manner as the synthesis method of the sol solution of the first characteristic. Then, because the sol solution is in a sol state, by applying the sol solution to the surface of a substrate and drying it, a gel film of a homogeneous film-like coating in which the sol particles are uniformly dispersed can be obtained. After firing, the gel film can form a porous alumina film with added silica that has excellent surface adhesion to various substrates, high heat resistance, and a high specific surface area.

[0042] In a preferred embodiment of the method for synthesizing a sol solution of the second characteristic, in the step of precipitating the precipitate, the aluminum solution is heated under reflux and then subjected to a pH adjustment treatment to precipitate the precipitate.

[0043] In a preferred embodiment of the method for synthesizing the sol solution of the above-mentioned second feature, when the aluminum compound is any one of the aluminum nitrate, the aluminum chloride and the aluminum sulfate, the specific pH range is within the range of greater than 3.8 and less than 7.8, and when the aluminum compound is sodium aluminate, the specific pH range is within the range of greater than 2.0 and less than 6.2.

[0044] In a preferred embodiment of the method for synthesizing the sol solution of the second characteristic, in the step of preparing the Al2O3-containing sol solution,

[0045] The treatment temperature of the autoclave treatment is controlled to a specific treatment temperature within a range of 100° C. to 200° C.,

[0046] The treatment time of the autoclave treatment is controlled within a specific time range in which the solution state after the autoclave treatment becomes a sol state,

[0047] The specific time range varies according to the specific treatment temperature and the Al 2 O 3 content in the prepared Al 2 O 3 -containing sol solution, and is within the range of 1 hour to 100 hours.

[0048] Furthermore, in a preferred embodiment of the method for synthesizing the sol solution of the first or second characteristics, the alkoxysilane is tetraethoxysilane (TEOS).

[0049] Furthermore, the method for synthesizing a sol solution of the present invention, in addition to the first or second feature described above, has a third feature that further comprises a step of adding a barium compound to the SiO2Al2O3-containing sol solution prepared in the step of preparing the SiO2Al2O3-containing sol solution to prepare a Ba-added SiO2Al2O3-containing sol solution.

[0050] According to the method for synthesizing the sol solution of the third characteristic, the heat resistance of the porous alumina film obtained by adding barium, applying the sol solution to the surface of the substrate, and drying and firing can be further improved.

[0051] In addition, the method for synthesizing a sol solution of the present invention, in addition to the third feature mentioned above, has a fourth feature that further comprises a step of adding an organic solvent having a boiling point higher than water and a surface tension lower than water to the Ba-added SiO2Al2O3 sol solution prepared in the step of preparing the Ba-added SiO2Al2O3 sol solution.

[0052] Furthermore, the method for synthesizing a sol solution of the present invention, in addition to the first or second feature described above, has a fifth feature that further comprises a step of adding an organic solvent having a higher boiling point than water and a lower surface tension than water and a barium compound to the SiO2Al2O3-containing sol solution prepared in the step of preparing the SiO2Al2O3-containing sol solution, thereby preparing a Ba-added SiO2Al2O3-containing sol solution.

[0053] According to the method for synthesizing the sol solution of the fourth or fifth characteristics, the heat resistance of the porous alumina membrane obtained by adding barium, coating the sol solution on the surface of the substrate, and drying and firing can be further improved. Moreover, by adding an organic solvent having a higher boiling point than water and a lower surface tension than water, the reduction in the total pore volume of the sol solution during drying can be suppressed, thereby further increasing the specific surface area of ​​the porous alumina membrane.

[0054] In addition, according to the synthesis method of the sol solution of the present invention, in addition to the first or second feature mentioned above, its sixth feature is that it also has a process of adding an organic solvent having a boiling point higher than water and a surface tension lower than water to the SiO2Al2O3-containing sol solution prepared in the process of manufacturing the SiO2Al2O3-containing sol solution.

[0055] According to the synthesis method of the sol solution of the sixth characteristic, by adding an organic solvent having a higher boiling point than water and a lower surface tension than water, the reduction in the total pore volume of the sol solution during drying can be suppressed, and the specific surface area of ​​the porous alumina membrane obtained by coating the sol solution on the surface of the substrate and drying and firing can be further improved.

[0056] In a preferred embodiment of the method for synthesizing the sol solution according to the third to fifth features, the barium compound is at least one selected from the group consisting of barium nitrate, barium hydroxide, barium chloride, and barium acetate.

[0057] In a preferred embodiment of the method for synthesizing the sol solution according to the fourth to sixth features, the organic solvent is ethylene glycol or N,N-dimethylformamide.

[0058] Furthermore, the method for forming a porous alumina film of the present invention is characterized in that it is a method for forming a porous alumina film, comprising the following steps:

[0059] A step of preparing a SiO2Al2O3-containing sol solution or a Ba-added SiO2Al2O3-containing sol solution as a final sol solution synthesized by the synthesis method using the sol solution synthesis method described in any one of the first to sixth features;

[0060] The process of coating the sol solution on the surface of the substrate;

[0061] a step of drying the coating film of the sol solution;

[0062] The dried sol solution coating film is then fired.

[0063] Effects of the Invention

[0064] According to the sol solution synthesis method of the present invention, a SiO2Al2O3-containing sol solution containing sol particles in a highly dispersed state with silica bonded to boehmite particles can be obtained. Therefore, by applying the sol solution to the surface of a substrate, drying and firing, a porous alumina film containing silica added thereto, which has excellent adhesion to the surface of various substrates, high heat resistance, and a high specific surface area, can be formed. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] Figure 1 This is a process transition diagram showing an overview of the synthesis method (first synthesis method) of the SiO2Al2O3-containing sol solution of the first embodiment.

[0066] Figure 2 TEM photos of SiO2Al2O3 sol solutions in four states: sol, gel, first semi-sol, and precipitate.

[0067] Figure 3 This is a scatter diagram showing the relationship between the solution state of the SiO2Al2O3 sol solution synthesized by the first synthesis method and the pH value of the slurry solution and the SiO2 concentration.

[0068] Figure 4 This is a scatter diagram showing the relationship between the solution state of the SiO2Al2O3 sol solution synthesized by the first synthesis method and the sol solution concentration and SiO2 concentration.

[0069] Figure 5 This is a scatter diagram showing the relationship between the solution state of the SiO2Al2O3 sol solution synthesized by the first synthesis method and the heating conditions (treatment temperature, treatment time) of the autoclave treatment.

[0070] Figure 6 This is a scatter diagram showing the relationship between the solution state of the SiO2Al2O3 sol solution synthesized by the first synthesis method and the sol solution concentration and the processing time of the autoclave treatment.

[0071] Figure 7 The graph shows the measurement results of the specific surface areas of the main powder sample S1 after the initial heat treatment, the first heat treatment, and the second heat treatment, which were prepared by drying and sintering the SiO2Al2O3 sol solution synthesized by the first synthesis method.

[0072] Figure 8 Graph showing the measurement results of the specific surface areas of Comparative Example C1 produced by the precipitation method after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0073] Figure 9 XRD patterns showing the crystal structure of the main powder sample S1 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining a SiO2-containing Al2O3 sol solution synthesized by the first synthesis method, after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0074] Figure 10 This is an XRD pattern showing the crystal structure of Comparative Example C1 with a SiO2 concentration of 1 mass% produced by the precipitation method after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0075] Figure 11 This is an XRD pattern showing the crystal structure of the main powder sample S1 (main dried sample S1D) before the initial heat treatment of the SiO2Al2O3 sol solution synthesized by the first synthesis method.

[0076] Figure 12 This is an XRD pattern showing the crystal structure of Comparative Example C1 (Comparative Dry Sample C1D) before the initial heat treatment.

[0077] Figure 13 BJH plot showing the pore distribution of the main powder sample S1 and the comparative sample C1B after the first heat treatment with a SiO2 concentration of 3 mass %.

[0078] Figure 14 BJH plot showing the pore distribution of the main powder sample S1 and the comparative example C1 after the first heat treatment with a SiO2 concentration of 10% by mass

[0079] Figure 15 This is a process transition diagram showing an overview of the synthesis method (second synthesis method) of the SiO2Al2O3-containing sol solution according to the second embodiment.

[0080] Figure 16 This is a scatter diagram showing the relationship between the solution state of the SiO2Al2O3 sol solution synthesized by the second synthesis method and the pH value of the slurry solution and the SiO2 concentration.

[0081] Figure 17 This is a scatter diagram showing the relationship between the solution state of the SiO2Al2O3 sol solution synthesized by the second synthesis method and the sol solution concentration and SiO2 concentration.

[0082] Figure 18 XRD patterns showing the crystal structure of the main powder sample S2 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining a SiO2-containing Al2O3 sol solution synthesized by the second synthesis method, after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0083] Figure 19 This is an XRD pattern showing the crystal structure of Comparative Example C2 with a SiO2 concentration of 1 mass% produced by the precipitation method after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0084] Figure 20 Graph showing the results of measuring the specific surface areas of the main powder sample S2 after the initial heat treatment, the first heat treatment, and the second heat treatment, which was prepared by drying and sintering the SiO2Al2O3 sol solution synthesized by the second synthesis method.

[0085] Figure 21 Graph showing the results of measuring the specific surface areas of Comparative Example C2 produced by the precipitation method after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0086] Figure 22 A process transition diagram showing an overview of a method for synthesizing a SiO2Al2O3-containing sol solution (third synthesis method) according to a third embodiment.

[0087] Figure 23Graph showing the results of measuring the specific surface areas of the main powder sample S1, main powder sample S3, and comparative example C1 after initial heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the first synthesis method, the third synthesis method (Example 5), and the precipitation method, respectively.

[0088] Figure 24 Graph showing the results of measurement of specific surface areas of main powder samples S1 and S3, prepared by drying and calcining SiO2Al2O3 sol solutions synthesized by the first synthesis method, the third synthesis method (Example 5), and the precipitation method, respectively, and comparative example C1 after the first heat treatment.

[0089] Figure 25 Graph showing the results of measuring the specific surface areas of the main powder samples S1, S3, and comparative example C1 after the second heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the first synthesis method, the third synthesis method (Example 5), and the precipitation method, respectively.

[0090] Figure 26 The XRD patterns of the crystal structure of the main powder sample S3 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the third synthesis method (Example 5), after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0091] Figure 27 Graph showing the results of measurement of specific surface areas after initial heat treatment of main powder sample S2, main powder sample S4, and comparative example C2, which were prepared by drying and calcining SiO2Al2O3 sol solutions synthesized by the second synthesis method, the third synthesis method (Example 6), and the precipitation method, respectively.

[0092] Figure 28 Graph showing the results of measurement of specific surface areas after the first heat treatment of main powder sample S2, main powder sample S4, and comparative example C2, which were prepared by drying and calcining SiO2Al2O3 sol solutions synthesized by the second synthesis method, the third synthesis method (Example 6), and the precipitation method, respectively.

[0093] Figure 29 Graph showing the results of measuring the specific surface areas of the main powder sample S2, main powder sample S4, and comparative example C2 after the second heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the second synthesis method, the third synthesis method (Example 6), and the precipitation method, respectively.

[0094] Figure 30XRD patterns of the crystal structure of the main powder sample S4 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the third synthesis method (Example 6) after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0095] Figure 31 A process transition diagram showing an overview of a method for synthesizing a SiO2Al2O3-containing sol solution (fourth synthesis method) according to a fourth embodiment.

[0096] Figure 32 BJH plots showing the pore distribution of the main powder sample S5 to which the specific additive EG and DMF with a SiO2 concentration of 3 mass% were added and the main powder sample S1 to which no specific additive was added after the first heat treatment.

[0097] Figure 33 BJH plot showing the pore distribution of the main powder sample S5 to which the specific additive of EG and DMF with SiO2 concentration of 10 mass% was added and the main powder sample S1 without the specific additive after the first heat treatment.

[0098] Figure 34 Graphs showing the results of specific surface area measurements after initial heat treatment of the main powder samples S5, S11, and Comparative Example C1, which were prepared by drying and calcining SiO2Al2O3 sol solutions synthesized by the fourth synthesis method (Example 7), the fourth synthesis method (Example 9), and the precipitation method, respectively.

[0099] Figure 35 Graph showing the results of measurement of the specific surface areas of the main powder sample S5, the main powder sample S11, and the comparative example C1 after the first heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the fourth synthesis method (Example 7), the fourth synthesis method (Example 9), and the precipitation method, respectively.

[0100] Figure 36 Graph showing the results of measurement of the specific surface areas of the main powder sample S5, main powder sample S11, and comparative example C1 after the second heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the fourth synthesis method (Example 7), the fourth synthesis method (Example 9), and the precipitation method, respectively.

[0101] Figure 37 Graph showing the results of measurement of specific surface areas after initial heat treatment of main powder sample S6, main powder sample S12, and comparative example C2, which were prepared by drying and calcining SiO2Al2O3 sol solutions synthesized by the fourth synthesis method (Example 8), the fourth synthesis method (Example 10), and the precipitation method, respectively.

[0102] Figure 38 Graph showing the results of measurement of the specific surface areas of the main powder sample S6, the main powder sample S12, and the comparative example C2 after the first heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solution synthesized by the fourth synthesis method (Example 8), the fourth synthesis method (Example 10), and the precipitation method, respectively.

[0103] Figure 39 Graphs showing the results of the measurement of the specific surface areas of the main powder samples S6, S12, and Comparative Example C2 after the second heat treatment, which were prepared by drying and calcining the SiO2Al2O3 sol solutions synthesized by the fourth synthesis method (Example 8), the fourth synthesis method (Example 10), and the precipitation method, respectively.

[0104] Figure 40 This is a process transition diagram showing an overview of the synthesis method of the Ba-added SiO2Al2O3 sol solution (fifth synthesis method) of the fifth embodiment.

[0105] Figure 41 XRD patterns showing the crystal structure of the main powder sample S7 after the initial heat treatment, the first heat treatment, and the second heat treatment, which was prepared by drying and calcining the SiO2Al2O3 sol solution containing Ba added by the fifth synthesis method and having a SiO2 concentration of 1% by mass and a BaO concentration of 6.5% by mass.

[0106] Figure 42 This is an XRD pattern showing the crystal structure of Comparative Example C7 prepared by the precipitation method with a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass% after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0107] Figure 43 XRD patterns showing the crystal structure of the main powder sample S8 after the initial heat treatment, the first heat treatment, and the second heat treatment, which was prepared by drying and calcining the SiO2Al2O3 sol solution containing Ba added by the fifth synthesis method and having a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass%.

[0108] Figure 44 This is an XRD pattern showing the crystal structure of Comparative Example C8 prepared by the precipitation method with a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass% after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0109] Figure 45 This is a process transition diagram showing an overview of the synthesis method of the Ba-added SiO2Al2O3 sol solution (sixth synthesis method) according to the sixth embodiment.

[0110] Figure 46XRD patterns showing the crystal structure of the main powder sample S9 having a SiO2 concentration of 1 mass % and a BaO concentration of 6.5 mass % produced by drying and calcining a Ba-added SiO2Al2O3 sol solution synthesized by the sixth synthesis method (Example 13) after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0111] Figure 47 XRD patterns showing the crystal structure of the main powder sample S10 having a SiO2 concentration of 1 mass % and a BaO concentration of 6.5 mass % prepared by drying and calcining a Ba-added SiO2Al2O3 sol solution synthesized by the sixth synthesis method (Example 14) after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0112] Figure 48 A process transition diagram showing an outline of a method for forming a porous aluminum oxide film (main forming method) according to a seventh embodiment.

[0113] Figure 49 This is a FE-SEM photograph of a 6.5% BaO-1% SiO2Al2O3 porous alumina film formed on the surface of glass cloth and silica cloth.

[0114] Figure 50 FE-SEM images of the cross section and surface of a porous alumina film containing 1% SiO2Al2O3 formed on a glass plate using sol solutions containing 1% SiO2Al2O3 at concentrations of 2.5% and 3.75% by mass.

[0115] Figure 51 XRD patterns showing the crystal structures of 6.5% BaO-1% SiO2Al2O3 formed on the surface of silica cloth and silica cloth alone after initial heat treatment, first heat treatment, and second heat treatment.

[0116] Figure 52 A process transition diagram showing an outline of the synthesis method (seventh synthesis method) of the eighth embodiment of the SiO2Al2O3 sol solution

[0117] Figure 53 This is a process transition diagram showing an overview of an example of a synthesis method of a Ba-added SiO2Al2O3 sol solution according to the eighth embodiment (Example 20 of the seventh synthesis method).

[0118] Figure 54 This is a process transition diagram showing an overview of an example of a synthesis method of a Ba-added SiO2Al2O3 sol solution according to the eighth embodiment (Example 21 of the seventh synthesis method).

[0119] Figure 55This is a process transition diagram showing an overview of an example of a method for synthesizing a SiO2Al2O3 sol solution having a high sol solution concentration according to the eighth embodiment (Example 22 of the seventh synthesis method).

[0120] Figure 56 XRD patterns showing the crystal structure of the main powder sample S11 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining the SiO2Al2O3 sol solution synthesized in Example 18 of the seventh synthesis method, after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0121] Figure 57 XRD patterns showing the crystal structure of the main powder sample S12 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining the SiO2Al2O3 sol solution synthesized in Example 19 of the seventh synthesis method, after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0122] Figure 58 XRD patterns showing the crystal structure of the main powder sample S13 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining the SiO2Al2O3 sol solution containing Ba added in Example 20 of the seventh synthesis method, after the initial heat treatment, the first heat treatment, and the second heat treatment.

[0123] Figure 59 XRD patterns showing the crystal structure of the main powder sample S14 with a SiO2 concentration of 1% by mass, which was prepared by drying and calcining the SiO2Al2O3 sol solution containing Ba added in Example 21 of the seventh synthesis method, after the initial heat treatment, the first heat treatment, and the second heat treatment. DETAILED DESCRIPTION

[0124] With reference to the accompanying drawings, preferred embodiments of the method for synthesizing a SiO2Al2O3-containing sol solution (hereinafter appropriately referred to as the "main synthesis method") and the method for forming a porous alumina film of the present invention are described in detail.

[0125] [First embodiment]

[0126] Hereinafter, a first embodiment of the main synthesis method (first synthesis method) will be described.

[0127] [1] Basic structure of the first synthesis method

[0128] The first synthesis method, such as Figure 1 As shown in the process conversion diagram, if roughly divided, it is composed of the following steps #11 to #15.

[0129] First, an alkoxysilane solution containing alkoxysilane, water, alcohol, and an inorganic acid is prepared (step #11), and an aluminum solution containing an aluminum compound selected from aluminum nitrate, aluminum chloride, and aluminum sulfate and water is prepared (step #12). It is noted that either step #11 or step #12 can be performed first. Next, in a mixed solution obtained by mixing the alkoxysilane solution obtained in step #11 and the aluminum solution obtained in step #12, a precipitate having the silicon compound adsorbed on aluminum hydroxide is precipitated (step #13). Next, the precipitate obtained in step #13 is filtered and separated from the mixed solution, and the filtered precipitate is washed with water to form a precipitate cake (step #14). Next, water is added to the precipitate cake obtained in step #14 to prepare a slurry solution. This slurry solution is subjected to a pH adjustment treatment and then autoclaved to prepare a SiO2Al2O3-containing sol solution (step #15). Through the above steps #11 to #15, a SiO2Al2O3-containing sol solution is synthesized.

[0130] In step #15, as described later, under the temperature and pressure of the autoclave treatment, the aluminum hydroxide (Al(OH)3) in the slurry solution is partially dehydrated to form boehmite (AlOOH), and a SiO2Al2O3-containing sol solution is synthesized in which sol particles of silica are bonded to the boehmite particles in a highly dispersed state.

[0131] Hereinafter, the synthesis method of synthesizing a SiO₂Al₂O₃-containing sol solution after autoclaving, as in the first synthesis method, is referred to as the first AC (autoclave) method. In other words, the first synthesis method corresponds to the first AC method when the aluminum compound is selected from aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0132] In step #11, the alkoxysilane is preferably tetraalkoxysilane. Furthermore, the tetraalkoxysilane is preferably selected from tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetra-n-butoxysilane. In the examples described below, tetraethoxysilane (TEOS) is preferably used. Alcohols such as methanol, ethanol, n-propanol, and isopropanol can be used. In the examples described below, ethanol is preferably used. Inorganic acids such as hydrochloric acid and nitric acid can be used. In the examples described below, hydrochloric acid is preferably used.

[0133] The mass concentration of SiO2 relative to SiO2Al2O3 in the SiO2Al2O3-containing sol solution prepared in step #15 (expressed in mass %, hereinafter referred to as "SiO2 concentration") is determined by the amount of the alkoxysilane raw material in the alkoxysilane solution prepared in step #11, the amount of the aluminum compound raw material in the aluminum solution prepared in step #12, and the mixing ratio of the alkoxysilane solution and the aluminum solution mixed in step #13. Therefore, in order to set the SiO2 concentration in the SiO2Al2O3-containing sol solution to a desired value, the mixing ratio of the two solutions is adjusted in step #13 based on the respective raw material amounts in steps #11 and #12.

[0134] As one embodiment of step #13, after heating and refluxing the mixed solution, aqueous ammonia is added dropwise to the mixed solution and stirred to adjust the pH. The heating and refluxing and pH adjustment allow the mixed solution to be hydrolyzed, and aluminum hydroxide and the silicon compound are co-precipitated.

[0135] As an embodiment of step #15, the amount of water added to the precipitate cake is adjusted, and the sol solution concentration (mass %) represented by the synthesized SiO2Al2O3 content relative to the total mass of the SiO2Al2O3 sol solution is controlled to be below a specific concentration at which the solution state after autoclaving becomes a sol state, and the slurry solution is subjected to pH adjustment treatment to control the pH value of the slurry solution within a specific pH range at which the solution state after autoclaving becomes a sol state.

[0136] In addition, in this embodiment, in order to make the total mass of the synthesized SiO2Al2O3 sol solution a fixed value relative to the content of the autoclave used for autoclave treatment, the concentration of the sol solution is controlled by adjusting the respective raw material amounts of alkoxysilane and aluminum compound in steps #11 and #12 and the amount of water added to the precipitate cake in step #15.

[0137] Here, as described later, the specific concentration varies depending on the SiO 2 concentration and the heating conditions (treatment temperature, treatment time) of the autoclave treatment, and the specific pH range varies depending on the SiO 2 concentration within the range of 2.8 to 7.8.

[0138] Furthermore, as one embodiment of step #15, the autoclave treatment temperature is set to a specific treatment temperature within the range of 100°C to 200°C, and the autoclave treatment time is set to a specific time range corresponding to the specific treatment temperature, which allows the solution to become a sol state after the autoclave treatment. However, the specific time range is within the range of 1 hour to 100 hours.

[0139] [2] Example of the first synthesis method

[0140] The following describes an example of steps #11 to #15 for synthesizing a SiO2-containing Al2O3 sol solution having a SiO2 concentration of 1% by mass. For ease of explanation, SiO2Al2O3 having a SiO2 concentration of X% by mass is referred to as X% SiO2Al2O3.

[0141] Hereinafter, Example 1 using aluminum nitrate as the aluminum compound, Example 2 using aluminum chloride, and Example 3 using aluminum sulfate will be described in order.

[0142] [2.1] Example 1 (Aluminum compound: aluminum nitrate)

[0143] In step #11, tetraethoxysilane (TEOS) was used as the alkoxysilane, ethanol was used as the alcohol, and hydrochloric acid was used as the inorganic acid. Specifically, 7.52 g of ethanol was added to 5 g of TEOS and stirred at room temperature for 5 minutes. Then, 1.25 g of concentrated hydrochloric acid (37%) was added and stirred at room temperature for another 5 minutes. While stirring the mixed solution, 71.2 g of water was added dropwise and mixed to obtain a transparent and uniform 5.88% TEOS solution (alkoxysilane solution).

[0144] In step #12, aluminum nitrate was used as the aluminum compound, and 14.57 g of aluminum nitrate nonahydrate was dissolved in 57.10 g of water to obtain an aluminum nitrate aqueous solution (aluminum solution).

[0145] In step #13, 1.18 g of the 5.88% TEOS solution obtained in step #11 was added to the aluminum nitrate aqueous solution obtained in step #12. The resulting homogeneous mixed solution was heated under reflux at 100°C, and 28% aqueous ammonia was added dropwise, followed by stirring until the pH reached 9.0. As the aqueous ammonia was added, aluminum hydroxide and the silicon compound coprecipitated, forming a precipitate in the mixed solution.

[0146] Next, in step #14, the mixed solution containing the precipitate is suction filtered using No. 1 filter paper to separate the precipitate by filtration. The precipitate separated by filtration is washed with ion-exchanged water at room temperature to obtain a precipitate cake.

[0147] Next, in step #15, water was added to the resulting precipitate cake to a total of 80 g and stirred to prepare a slurry solution. Nitric acid (60% aqueous solution) was added to this slurry solution until the pH reached 5.0, and the solution was autoclaved at 150°C for 15 hours to obtain a sol solution containing 1% SiO₂Al₂O₃. For the autoclave treatment, an autoclave consisting of a 100 ml Teflon (registered trademark) container enclosed in a stainless steel jacket was used.

[0148] The total amount of the 1% SiO₂Al₂O₃ sol solution obtained in step #15 was 80 g, and the amount of 1% SiO₂Al₂O₃ powder obtained by drying this sol solution was 2.0 g. The sol concentration of the 80 g sol solution containing 2.0 g of 1% SiO₂Al₂O₃ powder was 2.5% by mass. Furthermore, the amount of nitric acid (60% aqueous solution) added to adjust the pH of the slurry solution was a trace amount of approximately 400 to 600 μL, so the total amount of the 1% SiO₂Al₂O₃ sol solution was approximately 80 g, the same as the total amount of the slurry solution. The autoclave volume and structure used in the main synthesis process are not limited to those used in Example 1. For example, an autoclave with a volume corresponding to the total amount of the SiO₂Al₂O₃ sol solution to be synthesized may be used.

[0149] For convenience, a SiO₂Al₂O₃-containing sol solution with an SiO₂ concentration of X mass% and a sol solution concentration of Y mass% is denoted as X%SiO₂Al₂O₃Y%sol. Therefore, the 1% SiO₂Al₂O₃-containing sol solution obtained in step #15 is denoted as 1%SiO₂Al₂O₃2.5%sol.

[0150] [2.2] Example 2 (Aluminum compound: aluminum chloride)

[0151] In Example 2, except for dissolving 9.38 g of aluminum (III) chloride hexahydrate in 83.24 g of water in step #12 to obtain an aluminum chloride aqueous solution (aluminum solution), the conditions were identical to those of Example 1, thereby synthesizing a 1% SiO₂Al₂O₃ sol solution. In other words, in Example 2, similar to Example 1, a total of 80 g of a 1% SiO₂Al₂O₃ 2.5% sol was obtained. Therefore, the description repeated in Example 1 is omitted. Furthermore, in Example 1, an aluminum nitrate aqueous solution was prepared at a concentration of approximately 20% by mass (including water of crystallization). In contrast, in Example 2, at 20% by mass, the amount of water relative to the amount of precipitate was too low to allow for sufficient stirring. Therefore, an aluminum chloride aqueous solution was prepared at a lower concentration of approximately 10% by mass (including water of crystallization).

[0152] [2.3] Example 3 (Aluminum compound: aluminum sulfate)

[0153] In Example 3, similar to Examples 1 and 2, to synthesize a total of 80 g of a 1% SiO₂Al₂O₃ 2.5% sol, in step #12, 6.64 g of anhydrous aluminum sulfate was dissolved in 58.58 g of water to obtain an aqueous aluminum sulfate solution (aluminum solution). However, in step #15, even if the pH of the slurry solution was controlled within the same specific pH range as when the aluminum compound was aluminum nitrate, under the same autoclave heating conditions as in Example 1 (150°C, 15 hours), if the sol concentration exceeded 0.63% by mass, the solution would still contain undissolved precipitate (described later as the second half sol) mixed with the sol. Therefore, by adjusting the respective raw material amounts of the alkoxysilane and aluminum compound in steps #11 and #12, and the amount of water added to the precipitate cake in step #15, a 1% SiO₂Al₂O₃ sol solution could be synthesized by controlling the sol concentration of the total 80 g to below 0.63% by mass. The conditions other than those described above were identical to those in Example 1, and any duplicate descriptions of Example 1 are omitted. Furthermore, in Example 1, the aluminum nitrate aqueous solution was prepared at a concentration of approximately 20% by mass (including water of crystallization). In contrast, in Example 3, at 20% by mass, the amount of water relative to the amount of precipitate was too small to allow for sufficient stirring. Therefore, the aluminum sulfate aqueous solution was prepared at a low concentration of approximately 10% by mass.

[0154] Furthermore, even if the sol solution concentration is higher than 0.63% by mass, as described later, by adjusting the heating conditions during the autoclave treatment to increase the amount of heating, the solution state can still be converted from the second semi-sol state to the sol state.

[0155] [3] Study on the autoclave treatment conditions of the first synthesis method

[0156] The state of the solution after the autoclave treatment in step #15 can vary depending on the SiO2 concentration and sol concentration of the synthesized SiO2Al2O3-containing sol solution, the pH of the slurry solution, and the autoclave heating conditions (treatment temperature and treatment time). These conditions can form six states: sol, first semi-sol, second semi-sol, gel, precipitate, and turbid sol. Below, the SiO2 concentration and sol concentration of the synthesized SiO2Al2O3-containing sol solution, the pH of the slurry solution, and the autoclave heating conditions (treatment temperature and treatment time) are collectively referred to as the autoclave treatment conditions.

[0157] In the research results presented below, the choice of one of the five solution states (sol, first semi-sol, second semi-sol, gel, and precipitate) is determined by the SiO₂ concentration and the pH of the slurry solution, at the sol solution concentration and heating conditions that allow the solution to become a sol. Furthermore, the choice of one of the four solution states (sol, second semi-sol, and cloudy sol-main gel) is determined by the combination of the SiO₂ concentration and the pH of the slurry solution that allows the solution to become a sol, at the sol solution concentration and heating conditions.

[0158] The sol is a transparent solution with a slightly whitish color, and exhibits a solution state in which light scattering caused by the Tyndall phenomenon can be confirmed by laser irradiation. In addition, the "transparency" of the sol is such that when the sol solution is contained in a colorless, transparent glass container with an inner diameter of about 8 cm, the text and graphics on the side of the glass container can be visually confirmed by looking through the sol solution from the opposite side. The gel is in a state where the viscosity is increased compared to the sol. If the precipitate is left to stand, it will show a state where the white precipitate is separated from the solution, and the white precipitate is opaque. The first half of the sol is in an intermediate state in the process from sol to gel, and is in a state where part of the sol solution is gelled, and the gelled part is transparent. The second half of the sol is in a state where the precipitate is not fully degelled, and a part of the solution still has precipitate remaining, and is opaque.

[0159] In step #15 of Example 1, where the SiO2 concentration was 1% by mass, the pH of the slurry solution was varied to prepare SiO2Al2O3-containing sol solutions in four different states: sol, gel, first semi-sol, and precipitate. These four sol solutions were observed using a transmission electron microscope (TEM). A JEM-2100 field emission microscope manufactured by JEOL Ltd. was used. Figure 2 TEM photos are shown in . Each sol solution was diluted with ethanol and observed on a Cu mesh. The gel in photo (a) is in a state of agglomeration of needle-shaped particles with a width of 5 nm and a length of 50 to 100 nm. The first half of the sol in photo (b) can also be observed with needle-shaped particles similar to the gel. However, thin plate-shaped particles with a side length of about 10 to 15 nm can be observed in the sol in photo (c). In addition, needle-shaped particles with a width of 2 to 3 nm and a length of 20 to 30 nm and thin plate-shaped particles with a side length of about 10 to 15 nm can be observed in the precipitate in photo (d). As Figure 2 As shown, it can be seen that the particle morphology varies greatly depending on the solution state, and in particular, the sol shows a structure that is significantly different from the highly viscous gel and precipitate.

[0160] The second half-sol is caused by insufficient heating during the autoclave treatment, resulting in a partially undissolved precipitate of boehmite adsorbed with silica (when the SiO2 concentration is 0 mass%, this is boehmite without adsorbed silica). A turbid sol is caused by excessive heating during the autoclave treatment, which leads to the formation of a precipitate caused by the growth of sol particles. The boehmite polymerization causes the sol to transition to gel formation, resulting in a turbid sol. In this embodiment, the turbid sol is distinguished as a solution state different from the first half-sol, the second half-sol, the gel, and the precipitate.

[0161] The solution state after autoclaving, regardless of the five states other than sol, has the potential to form a porous alumina film with a certain degree of heat resistance and specific surface area. However, in order to form a homogeneous porous alumina film with excellent adhesion to various substrate surfaces, as described below, the solution state is most preferably a sol. Therefore, the following autoclave treatment conditions were studied for a solution state after autoclaving that was a sol.

[0162] [3.1] Dependence of SiO2 concentration in a specific pH range

[0163] The relationship between the pH range (specific pH range) of a slurry solution in which the solution state after autoclaving is a sol and the SiO 2 concentration was investigated in the following manner.

[0164] Several sets of samples (80 g of slurry solution in total) were prepared, each with the SiO2 concentration varied between 0% and 10% by mass, and the pH value after the pH adjustment treatment of the slurry solution in step #15 varied between 1.01 and 10.68. The state of the solution after autoclaving was visually confirmed. For each sample, the sol solution concentration was set to 2.5% by mass, the same as in Example 1. The autoclave heating conditions were 150°C for 15 hours, the same as in Example 1. Aluminum nitrate, the same as in Example 1, was used as the aluminum compound.

[0165] The results of the above solution state confirmation are shown as a scatter plot in Figure 3 The vertical axis of the scatter plot represents the pH value of the slurry solution, and the horizontal axis represents the SiO2 concentration. In the figure, white circles (○) represent the sol, black squares (■) represent the gel, black triangles (▲) represent the precipitate, white squares (□) represent the first half of the sol, and white triangles (△) represent the second half of the sol.

[0166] Depend on Figure 3It can be seen that when the SiO2 concentration is in the range of 0 to 10% by mass and the specific pH range (from the lower limit to the upper limit) is between 2.8 and 7.8, the width of the specific pH range (the difference between the upper limit and the lower limit) decreases as the SiO2 concentration increases. Furthermore, it can be seen that at the same SiO2 concentration, gelation occurs when the pH value is below the specific pH range, while precipitation occurs when the pH value is above the specific pH range.

[0167] If it is a sol solution without silica added (SiO2 concentration is 0% by mass), the solution state remains in a sol state when the pH value is within a specific pH range (3.84 to 7.74), but in the region where the pH value is less than pH 3.84, a transparent gel is generated. Therefore, it can be considered that the polymerization of the sol is promoted by the acid catalyst until gelation. This means that even in the region below pH 3.84, if the heating conditions of the autoclave treatment are relaxed (shortening the treatment time and / or lowering the treatment temperature) and gelation is suppressed, there is a possibility that the solution state can be converted into a sol. Therefore, even in a SiO2Al2O3 sol solution containing silica added, by relaxing the heating conditions, it is possible to convert the solution state into a sol. Figure 3 The specific pH range shown has the possibility of being extended to the lower side.

[0168] Since the isoelectric point of silica sol is pH 1-1.5, silica is dispersed in the liquid with a negative surface charge near the neutral region where boehmite sol exists. It is believed that when the boehmite is near neutral, silica and boehmite are positively charged, and thus silica and boehmite are electrostatically bonded. Figure 3 The decrease in the upper limit of the specific pH range with increasing SiO2 concentration is believed to be due to the influence of silica sol. Considering that the surface potential of particles is zero, precipitation occurs due to particle aggregation. When silica with significantly different isoelectric points is mixed with boehmite, silica adsorbs to the boehmite near neutrality, resulting in a lower apparent isoelectric point and a decrease in the upper limit of the specific pH range.

[0169] exist Figure 3 In the equation, if the SiO2 concentration is X (mass %), the lower limit of the specific pH range is P0, and the upper limit is P1, then P0 and P1 are given as approximate values ​​by the following calculation formula. Figure 3 The dashed lines are shown in the figure for reference.

[0170] When 0<X≤3,

[0171] P0=-0.68X / 3+3.84

[0172] P1=-1.6X / 3+7.74

[0173] When 3<X≤7,

[0174] P0=3.16

[0175] P1=-0.075(X-3)+6.14

[0176] When 7<X≤8,

[0177] P0=-0.38(X-7)+3.16

[0178] P1=-1.2(X-7)+5.84

[0179] When 8<X≤10,

[0180] P0=0.255(X-8)+2.78

[0181] P1=-0.675(X-8)+4.64

[0182] From the above, it can be seen that in one embodiment of the pH adjustment treatment of the slurry solution in step #15, when the SiO2 concentration is X (mass %), the pH adjustment treatment can be performed in a manner such that the pH value of the slurry solution is within a specific pH range, and the specific pH range is determined by P0 and P1 given by the above calculation formula.

[0183] [3.2] Concentration dependence of SiO2 at a specific concentration

[0184] The relationship between the upper limit value (specific concentration) of the sol solution concentration at which the solution becomes a sol after autoclave treatment under predetermined autoclave heating conditions (treatment temperature, treatment time) and the SiO2 concentration was investigated as follows.

[0185] A plurality of samples (80 g of slurry solution in total) were prepared in which the SiO2 concentration was varied in the range of 0% to 10% by mass and the concentration (mass%) of the sol solution was varied. The state of the solution after autoclaving was visually confirmed. In each sample, when the SiO2 concentration was in the range of 0% to 7% by mass, the pH value of the slurry solution was set to pH 5.0, the same as in Example 1. When the SiO2 concentration was in the range of 8% to 10% by mass, the pH value was set to pH 5.0. Figure 3 The pH value of the solution state is within a specific pH range to form a sol. The heating conditions for the autoclave treatment were the same as in Example 1, 150° C. for 15 hours, and the same aluminum nitrate as in Example 1 was used as the aluminum compound.

[0186] The results of the above solution state confirmation are shown as a scatter diagram. Figure 4The vertical axis of the scatter plot represents the sol solution concentration (mass %), and the horizontal axis represents the SiO2 concentration. In the figure, the white circle ○ represents the sol, and the black circle ● represents the second half of the sol.

[0187] Depend on Figure 4 It can be seen that regardless of the SiO2 concentration, if the sol solution concentration is higher than a certain concentration, undegraded precipitates will remain in the sol. Figure 4 It can be seen that under the heating conditions of 150°C and 15 hours, the SiO2 concentration is in the range of 0 to 10% by mass, the specific concentration is in the range of 2.5% to 9.0% by mass, and decreases as the SiO2 concentration increases. This is believed to be because SiO2 exists in the form of adsorption on aluminum hydroxide precipitates. In other words, if the SiO2 concentration increases, the amount of SiO2 that has not been debonded by the autoclave treatment increases. In addition, since SiO2 is adsorbed on the surface of the aluminum hydroxide precipitate, it is difficult for aluminum hydroxide to debond. Figure 4 The specific concentration decreases with the increase of SiO2 concentration.

[0188] In addition, as described later, at a certain SiO2 concentration, even if the sol solution concentration is higher than a specific concentration and the solution state is the second semi-sol, if the heating conditions of the autoclave treatment are appropriately adjusted to increase the heating amount, there is also the possibility that the solution state can be the sol state.

[0189] exist Figure 4 In the formula, if the SiO2 concentration is X (mass %) and the specific concentration is Y1, then Y1 is given as an approximate value by the following calculation formula. Figure 4 The dashed line diagram is for reference.

[0190] When 0<X≤1,

[0191] Y1=9

[0192] When 1<X≤3,

[0193] Y1=-0.5(X-1)+9

[0194] When 3<X≤5,

[0195] Y1=-1.5(X-3)+8

[0196] When 5<X≤7,

[0197] Y1=-0.935(X-5)+5

[0198] When 7<X≤8.5,

[0199] Y1=3.13

[0200] When 8.5<X≤10,

[0201] Y1=-0.42(X-8.5)+3.13

[0202] As can be seen from the above, in one embodiment of controlling the sol solution concentration in step #15 to be below a specific concentration, when the autoclave heating conditions are 150°C for 15 hours, the amounts of the alkoxysilane and aluminum compound raw materials in steps #11 and #12, as well as the amount of water added to the precipitate cake in step #15, can be adjusted so that the sol solution concentration is below the specific concentration Y1 given by the above calculation formula, given a SiO2 concentration of X (mass %). Furthermore, as described in Example 3, when using aluminum sulfate as the aluminum compound under the same heating conditions of 150°C for 15 hours, it is important to note that the specific concentration Y1 is 0.63% or less.

[0203] [3.3] Heating conditions for autoclave treatment (1)

[0204] Thirteen samples (Samples 1 to 13, slurry solutions) were autoclaved under various heating conditions, corresponding to three treatment temperatures (100°C, 150°C, and 200°C) and treatment times ranging from 1 to 100 hours. The state of the solutions after autoclaving was visually confirmed. Each sample used a 1% SiO₂Al₂O₃ 3.75% sol with a SiO₂ concentration of 1% by mass and a sol solution concentration of 3.75% by mass. The pH of the slurry solution was adjusted to approximately pH 5.0 using nitric acid in step #15. The same aluminum nitrate as in Example 1 was used as the aluminum compound.

[0205] The above solution state confirmation results are shown in the following Tables 1 and Figure 5 The vertical axis of the scatter diagram represents the treatment time, and the horizontal axis represents the treatment temperature. In the figure, white circles ○ represent sols, black circles ● represent the second half of the sol, and × marks represent white turbid sols.

[0206]

Table 1

[0207]

[0208] As shown in Table 1 and Figure 5As shown, the sol formation was performed at a treatment temperature of 200°C for 1 hour, at a treatment temperature of 150°C for 15 to 48 hours, and at a treatment temperature of 100°C for 24 to 100 hours. These results show that increasing the amount of heat by increasing at least one of the treatment temperature and treatment time causes the solution state to transition from a sol to a turbid sol, while decreasing the amount of heat by decreasing at least one of the treatment temperature and treatment time causes the solution state to transition from a sol to a second semi-sol. Therefore, it can be seen that as the heating conditions for converting a solution state into a sol, for example, when the treatment temperature is set to 150°C and the treatment time is set to 15 to 48 hours, if the sol in the solution state is maintained and the treatment temperature is increased from 150°C, in order to suppress the increase in the amount of heat, the treatment time can be shortened to less than 15 to 48 hours. Conversely, if the treatment temperature is lowered from 150°C, in order to suppress the decrease in the amount of heat, the treatment time can be longer than 15 to 48 hours. In addition, it can be seen that if the treatment time is longer than 15 to 48 hours, in order to suppress the increase in the amount of heat, the treatment temperature can be lowered from 150°C. Conversely, if the treatment time is shorter than 15 to 48 hours, in order to suppress the decrease in the amount of heat, the treatment temperature can be increased from 150°C.

[0209] [3.4] Heating conditions for autoclave treatment (2)

[0210] Table 1 above predicts that under certain heating conditions, when the sol solution concentration exceeds a specific concentration and the solution state is a second semi-sol, at this sol solution concentration, increasing the amount of heating by increasing at least one of the treatment temperature and treatment time will cause the solution state to become a sol. To confirm this, three slurry solutions with different SiO2 concentrations and sol solution concentrations were autoclaved at a treatment temperature of 150°C and treatment times ranging from 2 to 100 hours. A total of 13 samples (samples 14 to 26, slurry solutions) were autoclaved, and the state of the solutions after autoclaving was visually confirmed. The details of the 13 samples are as follows: Samples 14-18 were for 1% SiO₂Al₂O₃ 3.75% sols with a SiO₂ concentration of 1% by mass and a sol solution concentration of 3.75% by mass; Samples 19-21 were for 1% SiO₂Al₂O₃ 10% sols with a SiO₂ concentration of 1% by mass and a sol solution concentration of 10% by mass; and Samples 22-26 were for 7% SiO₂Al₂O₃ 6% sols with a SiO₂ concentration of 7% by mass and a sol solution concentration of 6% by mass. As in Example 1 above, each sample was prepared using aluminum nitrate as the aluminum compound. In step #15, the pH of the slurry solution was adjusted to approximately pH 5.0 using nitric acid.

[0211] exist Figure 6The scatter plot shows the state of the solutions of Samples 14 to 21 after autoclaving. Table 2 below also shows the state of the solutions of Samples 22 to 26 after autoclaving. The vertical axis of the scatter plot represents the treatment time, and the horizontal axis represents the sol solution concentration. In the figure, white circles (○) represent the sol, black circles (●) represent the second half sol, x marks represent turbid sol, and black squares (■) represent the gel.

[0212]

Table 2

[0213]

[0214] like Figure 6 As shown, samples 14-18, with a sol concentration of 3.75% by mass, showed a second semi-sol state after autoclaving at 150°C for 2 hours, but became a sol at 15 and 48 hours, and then a turbid sol at 72 and 100 hours. On the other hand, samples 19-21, with a sol concentration of 10% by mass, showed a second semi-sol state after autoclaving at 150°C for 15 hours, a sol at 24 hours, and a gel at 48 hours. In the 1% SiO₂Al₂O₃ 10% sols of samples 19-21, delamination progressed with prolonged autoclaving, transforming the solution state into a sol. Further extension of the treatment time revealed that the solution state transformed into a gel. For the 10% by mass sol concentration, the range of treatment time in which the sol state can be maintained is narrower than for the 3.75% by mass sol concentration, necessitating appropriate control of the treatment time.

[0215] Furthermore, as shown in Table 2, in samples 22 to 26 having a SiO₂ concentration of 7% by mass and a sol solution concentration of 6% by mass, the solution state after autoclaving at 150°C was a second semi-sol at treatment times of 15 and 24 hours, but did not become a sol but a gel at treatment times of 48 to 100 hours. When both the SiO₂ concentration and the sol solution concentration are high, as the treatment time elapses, the solution state progresses from the second semi-sol without passing through the sol state and directly polymerizes until it becomes a gel, or, as in the example of Figure 6 For Samples 19 to 21 shown, it is considered that the treatment time in which the samples can be kept in a sol state is limited to a narrow range of more than 24 hours and less than 48 hours.

[0216] Above, by Figures 4 to 6The results of the solution state shown in Tables 1 and 2 show that as at least one of the SiO2 concentration and the sol solution concentration decreases or increases, the range of treatment time and treatment temperature within which the solution state can be in the sol state expands or decreases. If both the SiO2 concentration and the sol solution concentration increase, the range of treatment time and treatment temperature within which the solution state can be in the sol state no longer exists. Therefore, the SiO2 concentration and the sol solution concentration are each set to an upper limit of approximately 10% by mass. When one is set high, it is necessary to set the other lower while remaining within the range within which the solution state can be in the sol state. However, overall, it can be said that the degree of freedom in combining the SiO2 concentration within which the solution state can be in the sol state, the sol solution concentration, and the treatment time and treatment temperature of the autoclave treatment is extremely high.

[0217] [3.5] Autoclave treatment conditions of 1% SiO2Al2O3 sol solution

[0218] Based on the above results, an example of the autoclave treatment conditions for synthesizing a 1% SiO2Al2O3 sol solution by the first synthesis method is as follows.

[0219] pH value of slurry solution: pH4~pH7

[0220] Sol solution concentration: 9% by mass or less

[0221] Heating conditions: 150°C, 15 hours

[0222] Furthermore, as described above, if the SiO2 concentration in the SiO2 / Al2O3-containing sol solution increases above 1% by mass, the pH of the slurry solution and the sol solution concentration can be adjusted accordingly, as described above. Furthermore, the heating conditions are not limited to the aforementioned 150°C and 15 hours. The treatment temperature and treatment time can also be varied to suppress increases or decreases in the amount of heat applied, as described above.

[0223] [4] Evaluation of heat resistance of the first synthesis method (1)

[0224] The heat resistance of SiO₂Al₂O₃ powders (hereinafter collectively referred to as "main powder sample S1") obtained by drying and calcining a SiO₂Al₂O₃ sol solution synthesized by the first synthesis method was evaluated. Furthermore, to evaluate the effect of the step #15 of the first synthesis method, which involves the precipitate cake being solified by autoclaving, on heat resistance, the heat resistance of SiO₂Al₂O₃ powders (hereinafter collectively referred to as "comparative example C1") obtained by directly drying and calcining the precipitate cake prepared in steps #11 to #14 without solification, was evaluated. The heat resistance of main powder sample S1 and comparative example C1 was compared.

[0225] Incidentally, the synthesis method of the SiO2Al2O3 powder of Comparative Example C1 is the precipitation method disclosed in the above-mentioned Patent Document 6 as one of the synthesis methods of porous alumina to which silicon dioxide and barium oxide are added (see Patent Document 6). Figure 16 ), which corresponds to the case where porous alumina with added silicon dioxide is synthesized without adding barium oxide. Hereinafter, regardless of whether barium oxide is added, the synthesis methods of Comparative Example C1 and Comparative Examples C2 and C7 described later will be appropriately referred to as "precipitation methods."

[0226] When evaluating heat resistance, since Comparative Example C1 is a powder sample, in order to facilitate investigation of changes in heat resistance due to different SiO2 concentrations, a powder sample was used instead of a coating film.

[0227] In the synthesis method of porous alumina with added silica in Comparative Example C1, the steps up to the formation of the precipitate cake are identical to steps #11 to #14 of the first synthesis method. In Comparative Example C1, the resulting precipitate cake is dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (Comparative Sample C1A). Furthermore, as needed, Comparative Sample C1B, which undergoes a first heat treatment at 1200°C for 5 hours, and Comparative Sample C1C, which undergoes a second heat treatment at 1200°C for 30 hours, are prepared. Comparative Sample C1A undergoes only the initial heat treatment, and is similar to Comparative Example C1 in that neither the first nor the second heat treatment is performed. In the first heat treatment, the temperature is raised from room temperature to 1200°C at 10°C / min, followed by a holding temperature of 1200°C for 5 hours. In the second heat treatment, the temperature was increased from room temperature to 1200° C. at a rate of 10° C. / min, and then maintained at 1200° C. for 30 hours.

[0228] On the other hand, as main powder sample S1, following steps #11 to #14 of the first synthesis method, the SiO₂Al₂O₃ sol solution obtained in step #15 was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce SiO₂Al₂O₃ powder (main sample S1A). Furthermore, as needed, main sample S1B was prepared by subjecting main sample S1A to a primary heat treatment at 1200°C for 5 hours, and main sample S1C was prepared by subjecting main sample S1A to a secondary heat treatment at 1200°C for 30 hours. Main sample S1A was subjected only to the primary heat treatment, and neither the primary nor the secondary heat treatment was performed.

[0229] Aluminum nitrate was used as the aluminum compound in the preparation of main samples S1A to S1C and comparative samples C1A to C1C. The specific processing details of steps #11 to #15 were the same as those described in Example 1 for a SiO2 concentration of 1 mass%. For SiO2 concentrations other than 1 mass%, the mixing ratio of the aluminum nitrate aqueous solution and the 5.88% TEOS solution in step #13 was adjusted based on the set SiO2 concentration.

[0230] The drying process, initial heat treatment, first heat treatment, and second heat treatment were identical in the main powder sample S1 and the comparative example C1. Furthermore, the contents of each of these processes are also identical in the heat resistance evaluations of the second to sixth embodiments, so duplicate descriptions of the respective embodiments will be omitted.

[0231] In the heat resistance evaluation, the specific surface area, pore distribution, and total pore volume of each of the main powder sample S1 and the comparative example C1 were measured, and X-ray diffraction (XRD) analysis of the crystal structure was performed. The heat resistance evaluation of the second to seventh embodiments also involved the measurement of the above-mentioned specific surface area and other parameters, as well as XRD analysis, as needed. Furthermore, the specific surface area of ​​the sample was used as an indicator of heat resistance.

[0232] Specific surface area was measured using the nitrogen adsorption BET method using a fully automated gas adsorption measurement system (Microtrac BEL BEL BELSORP-max). Pore distribution and total pore volume were measured using the BJH method using a fully automated gas adsorption measurement system (Microtrac BEL BEL BEL BEL). XRD patterns of the crystal structure were measured using an X-ray diffractometer (Rigaku ULTIMA III) using Cukα irradiation and a two-dimensional high-speed detector.

[0233] exist Figure 7 Shown in the figure are the measurement results of the specific surface areas of the main samples S1A, S1B and S1C (a total of 21 main powder samples S1) produced by varying the SiO2 concentration in seven ways: 0 mass%, 1 mass%, 3 mass%, 5 mass%, 8 mass%, 9 mass% and 10 mass%. Figure 8 Shown in the figure are the results of measuring the specific surface areas of Comparative Samples C1A, C1B and C1C (a total of 15 Comparative Examples C1) produced by varying the SiO2 concentration to 0 mass%, 1 mass%, 3 mass%, 5 mass% and 10 mass%. Figure 7 and Figure 8 In the graph of the measurement results of specific surface areas, the vertical axis represents the specific surface area (m 2 / g), and the horizontal axis represents SiO2 concentration (mass %).

[0234] like Figure 7 and Figure 8 As shown in FIG. 1 , when the SiO2 concentration is 0% to 3% by mass, the specific surface area of ​​the main powder sample S1 and the comparative sample C1 increases with the increase of the SiO2 concentration. If the specific surface area of ​​the main sample S1A with a SiO2 concentration of 3% by mass is compared with the specific surface area of ​​the comparative sample C1A, the specific surface area of ​​the main sample S1A is 175m 2 / g, the specific surface area of ​​the comparative sample C1A is 165m 2 / g, roughly the same degree of heat resistance can be obtained.

[0235] like Figure 7 and Figure 8 As shown in the figure, when the SiO2 concentration is 3% to 10% by mass, the specific surface area of ​​the comparative sample C1A increases with the increase of the SiO2 concentration. In contrast, the specific surface area of ​​the main sample S1A hardly increases. When the specific surface areas of the main sample S1A with a SiO2 concentration of 10% by mass are compared with the specific surface areas of the comparative sample C1A, the specific surface area of ​​the main sample S1A is 201m 2 / g, the specific surface area of ​​the comparative sample C1A is 227m 2 / g, and the main sample S1A showed a slightly lower specific surface area.

[0236] Figure 9 1 and 2 show XRD patterns of the crystal structures of the main sample S1A, the main sample S1B, and the main sample S1C having a SiO 2 concentration of 1% by mass after each heat treatment. Figure 10 , which shows the XRD patterns of the crystal structures of the comparative samples C1A, C1B, and C1C having a SiO2 concentration of 1% by mass after each heat treatment. Figure 11 : Shown is an XRD pattern showing the crystal structure of the main powder sample S1 before heat treatment (main dried sample S1D) which was obtained by drying the SiO2Al2O3 sol solution at 150°C without performing the initial heat treatment. Figure 12 : Shown is an XRD pattern showing the crystal structure of the sample before heat treatment (comparative dried sample C1D) of Comparative Example C1 in which the precipitate cake was dried at 150° C. without initial heat treatment.

[0237] like Figure 9 and Figure 10 As shown, the comparative example C1 obtained by the precipitation method completely transformed into α-Al2O3 (comparative sample C1B) after the first heat treatment (1200℃ and 5 hours). In contrast, the main powder sample S1 treated with autoclave did not completely transform into the α phase even in the second heat treatment (1200℃ and 30 hours). This is considered to be Figure 11 and12 As shown in the XRD patterns of the main dried sample S1D and the comparative dried sample C1D, in the dried sample S1D, the formation of boehmite is promoted by the autoclave treatment, and small fibrous particles are developed, so that the mass transfer of Al2O3 is difficult to occur, and as a result, sintering is suppressed. Figure 11 As shown in FIG. 1 , it is considered that under the temperature and pressure of the autoclave treatment, the aluminum hydroxide in the slurry solution is partially dehydrated to generate boehmite.

[0238] Figure 13 In FIG, the pore distribution (BJH plot) of the main sample S1B and the comparative sample C1B which were subjected to the first heat treatment (1200°C and 5 hours) with SiO2 concentration of 3 mass% is shown. Figure 14 In the figure, the pore distribution (BJH plot) of the main sample S1B and the comparative sample C1B which were subjected to the first heat treatment and had a SiO2 concentration of 10% by mass is shown. Figure 13 and Figure 14 In the figure, circles (●) represent the pore distribution of the main sample S1B, triangles (▲) represent the pore distribution of the comparative sample C1B, and the vertical axis represents the differential pore volume dV p / dr p (m 3 / g / nm), the horizontal axis represents the pore diameter r p (nm). In addition, the following Table 3 shows the specific surface areas (nm) of the main sample S1B and the comparative sample C1B with SiO2 concentrations of 3% by mass and 10% by mass. 2 / g) and total pore volume (cm 3 / g).

[0239]

Table 3

[0240]

[0241] As shown in Table 3, when the SiO2 concentration is 3% by mass, there is no significant difference in pore distribution and specific surface area between the main sample S1B and the comparative sample C1B. However, when the SiO2 concentration is 10% by mass, the total pore volume of the main sample S1B is 0.1275 cm 3 / g, whereas the total pore volume of comparative sample C1B is 0.1813 cm 3 / g, the total pore volume of main sample S1B decreased. This is believed to be because main powder sample S1 is obtained by drying a SiO2-containing Al2O3 sol solution to form a transparent gel, and then calcining this transparent gel. Therefore, during the process of forming the transparent gel from the sol solution, the surface tension of the evaporated water causes the total pore volume of Al2O3 to decrease. Countermeasures for this reduction in total pore volume will be described in the fourth embodiment described below.

[0242] [5] Evaluation of heat resistance of the first synthesis method (2)

[0243] Next, the aluminum compound used in main samples S1A to S1C was changed from aluminum nitrate to aluminum chloride and aluminum sulfate, respectively, and the specific surface area in each case of the change was examined.

[0244] Table 4 below shows the specific surface areas (m2) of the main samples S1A to S1C, which are aluminum nitrate, aluminum chloride, and aluminum sulfate. 2 / g).

[0245]

Table 4

[0246]

[0247] As shown in Table 4, when the aluminum compound is aluminum chloride, the specific surface areas of main samples S1A to S1C are roughly equivalent to those of aluminum nitrate. On the other hand, when the aluminum compound is aluminum sulfate, the specific surface areas of main samples S1A to S1C are slightly lower than those of aluminum nitrate and aluminum chloride, resulting in slightly inferior heat resistance to the other two aluminum compounds.

[0248] [6] Evaluation of heat resistance of the first synthesis method (3)

[0249] As mentioned above, when comparing the specific surface areas of the main powder sample S1 and the comparative example C1, no extreme difference in the specific surface area measurement results is observed. Therefore, it is believed that even if the pH adjustment treatment of the slurry solution in step #15 of the first synthesis method is not performed to control the pH value of the slurry solution within the specific pH range that allows the solution to form a sol state after autoclaving, in other words, even if the solution state is a gel or precipitate other than a sol state, the SiO2Al2O3 powder obtained by drying and calcining the solution can still have a specific surface area comparable to that of the main powder sample S1 described above.

[0250] To verify this, six sol solutions were prepared by subjecting the slurry solution prepared in step #15 to pH adjustment in the same manner as for the main powder sample S1, varying the pH of the slurry solution in six different ways. These six sol solutions were then dried and sintered in an initial heat treatment at 1000°C for 5 hours to produce six powder samples SA. Furthermore, six powder samples SB were prepared by subjecting each of the six powder samples SA to a first heat treatment at 1200°C for 5 hours, and six powder samples SC were prepared by subjecting each of the six powder samples SA to a second heat treatment at 1200°C for 30 hours. This resulted in a total of 18 powder samples with varying slurry solution pH values ​​and heat treatment conditions.

[0251] Table 5 below shows the specific surface areas (m2) of the six powder samples SA, six powder samples SB, and six powder samples SC. 2 In addition, the following Table 6 shows the total pore volume (cm2) of three samples (pH = 2.77, 3.69, 9.57) among the six powder samples SA. 3 / g) measurement results.

[0252]

Table 5

[0253]

[0254]

Table 6

[0255]

[0256] Tables 5 and 6 show that the specific surface area and total pore volume tend to increase in the order of gel, sol, and precipitate. While the specific surface area and total pore volume when the solution is in the sol state are slightly inferior to those when the solution is in the precipitate state, as will be described later in the seventh embodiment, considering the fixation of the coating film to the substrate, solutions other than sols lack adhesion to the substrate surface and are therefore unsuitable for coating film formation.

[0257] [Second embodiment]

[0258] Hereinafter, a second embodiment of the main synthesis method (second synthesis method) will be described.

[0259] [7] Basic composition of the second synthesis method

[0260] The second synthesis method, such as Figure 15 As shown in the process conversion diagram, if roughly divided, it is composed of the following steps #21 to #25. Steps #21 to #25 are Figure 1 Steps #11 to #15 of the first synthesis method shown have basically the same processing contents, but in the second synthesis method, the aluminum compound is sodium aluminate, which is different from aluminum nitrate, aluminum chloride and aluminum sulfate used as the aluminum compound in the first synthesis method.

[0261] The second synthesis method is similar to the first synthesis method in that it is a synthesis method for synthesizing a SiO2Al2O3 sol solution after autoclave treatment, which is equivalent to the first AC method when the aluminum compound is sodium aluminate.

[0262] Due to the differences in the aluminum compound mentioned above, the processing contents of steps #22, #23, #24, and #25 differ slightly from steps #12 to #15 of the first synthesis method. Step #21 is identical to step #11 of the first synthesis method. Furthermore, step #22 differs from step #12 of the first synthesis method only in the aluminum compound used. Therefore, repeated descriptions of steps #21 and #22 will be omitted. Furthermore, the methods for adjusting the SiO2 concentration and the sol solution concentration are also identical to those of the first synthesis method, and repeated descriptions will be omitted.

[0263] In step #23, the precipitate of the silicon compound adsorbed on aluminum hydroxide is added to the mixed solution obtained by mixing the alkoxysilane solution obtained in step #21 and the aluminum solution obtained in step #22. This is the same as step #13 of the first synthesis method.

[0264] However, in the second synthesis method, one embodiment of step #23 involves heating and refluxing the aluminum solution obtained in step #22, then adding nitric acid to adjust the pH, and then mixing it with the alkoxysilane solution obtained in step #21 to prepare a mixed solution. In the mixed solution, a precipitate of silicon compound adsorbed on the aluminum hydroxide precipitate formed during the pH adjustment of the aluminum solution is deposited. In other words, whereas step #13 involves heating and refluxing the mixed solution and adjusting the pH, step #23 differs from step #13 in that these treatments are performed on the aluminum solution.

[0265] In step #24, the precipitate obtained in step #23 is separated from the mixed solution by filtration and then washed with water to form a precipitate cake, which is similar to step #14 of the first synthesis method. However, when washing the precipitate, the first synthesis method embodiment uses ion-exchanged water at room temperature, while the second synthesis method embodiment uses ion-exchanged water at, for example, 60°C. This differs from step #14 in that, if sodium contained in the aluminum compound is present in the SiO₂Al₂O₃ sol solution synthesized in step #25, the sintering of aluminum oxide is accelerated during drying and calcining of the sol solution. Therefore, in step #24, the precipitate is washed with warm water at 60°C to improve washability and remove the sodium from the precipitate.

[0266] In step #25, water is added to the precipitate cake obtained in step #24 to prepare a slurry solution. This slurry solution is then subjected to pH adjustment and then autoclaved to prepare a SiO₂Al₂O₃-containing sol solution, similar to step #15 of the first synthesis method. Furthermore, in the prepared SiO₂Al₂O₃-containing sol solution, sol particles containing silica bound to boehmite particles are present in a highly dispersed state, similar to step #15 of the first synthesis method.

[0267] In addition, as an embodiment of step #25, the concentration (mass %) of the sol solution is controlled to be below a specific concentration at which the solution state after autoclaving becomes a sol state, and the pH adjustment treatment is performed on the slurry solution to control the pH value of the slurry solution within a specific pH range at which the solution state after autoclaving becomes a sol state. This is also the same as step #15 of the first synthesis method.

[0268] In addition, as an embodiment of step #25, the treatment temperature of the autoclave treatment is set to a specific treatment temperature in the range of not less than 100°C and not more than 200°C, and the treatment time of the autoclave treatment is set to a specific time range corresponding to the specific treatment temperature so that the solution state after the autoclave treatment becomes a sol state, and the specific time range is within the range of not less than 1 hour and not more than 100 hours, which is also the same as step #15 of the first synthesis method.

[0269] As described later, the specific concentration varies depending on the SiO2 concentration and the heating conditions (treatment temperature and treatment time) of the autoclave treatment, and the specific pH range varies depending on the SiO2 concentration within a range of 1.0 to 6.2. The specific concentration and specific pH range in step #25 differ from those in step #15 of the first synthesis method.

[0270] [8] Example of the Second Synthesis Method

[0271] Hereinafter, Example 4 of steps #21 to #25 for synthesizing a SiO2-containing Al2O3 sol solution having a SiO2 concentration of 1% by mass will be described. Sodium aluminate was used as the aluminum compound.

[0272] In step #21, a transparent and uniform 5.88% TEOS solution (alkoxysilane solution) was obtained by following the same procedure as step #11 of Example 1.

[0273] In step #22, 3.57 g of sodium aluminate was dissolved in 66.56 g of water to obtain a sodium aluminate aqueous solution (aluminum solution).

[0274] In step #23, the sodium aluminate aqueous solution obtained in step #22 was heated to reflux, and nitric acid was added dropwise with stirring until the pH reached 8.0. A precipitate of aluminum hydroxide precipitated with the addition of nitric acid. Next, 1.18 g of the 5.88% TEOS solution obtained in step #21 was added dropwise to the sodium aluminate aqueous solution containing the aluminum hydroxide precipitate, and the mixture was stirred at room temperature for 30 minutes. As a result, a precipitate containing a silicon compound adsorbed on the aluminum hydroxide was obtained in the mixed solution of the sodium aluminate aqueous solution and the TEOS solution.

[0275] Next, in step #24, the mixed solution containing the precipitate obtained in step #23 was suction filtered using No. 1 filter paper to separate the precipitate by filtration. The separated precipitate was washed with ion-exchanged water at 60°C to obtain a precipitate cake.

[0276] Next, in step #25, water was added to the resulting precipitate cake to a total of 80 g, and the mixture was stirred to prepare a slurry solution. Nitric acid (60% aqueous solution) was added to the slurry solution until the pH reached 3.0, and the solution was autoclaved at 150°C for 15 hours to obtain a 1% SiO₂Al₂O₃-containing sol solution. For the autoclave treatment, a 100 ml autoclave was used, similar to Examples 1-3.

[0277] The total amount of the 1% SiO₂Al₂O₃ sol solution obtained in step #25 was 80 g, and the 1% SiO₂Al₂O₃ powder obtained by drying this sol solution was 2.0 g. The sol concentration of the 80 g sol solution containing 2.0 g of 1% SiO₂Al₂O₃ powder was 2.5% by mass. Therefore, the 1% SiO₂Al₂O₃ sol solution obtained in step #25 was a 1% SiO₂Al₂O₃ 2.5% sol. Furthermore, the amount of nitric acid (60% aqueous solution) added to adjust the pH of the slurry solution was the same small amount as in the first synthesis method. Therefore, the total amount of the 1% SiO₂Al₂O₃ sol solution was approximately the same as the total amount of the slurry solution, 80 g.

[0278] [9] Study on the autoclave treatment conditions of the second synthesis method

[0279] The state of the solution after the autoclave treatment in step #25 depends on the SiO2 concentration of the synthesized SiO2Al2O3-containing sol solution, the sol solution concentration, the pH value of the slurry solution, and the heating conditions of the autoclave treatment (treatment temperature, treatment time). It can form six states: sol, first semi-sol, second semi-sol, gel, precipitate, and turbid sol. This is the same as the first synthesis method. The above six solution states have been explained in the above-mentioned "[3] Study of Autoclave Treatment Conditions for the First Synthesis Method", so repeated explanation is omitted.

[0280] Next, the autoclave treatment conditions for converting the solution state into a sol after the autoclave treatment in the second synthesis method were examined.

[0281] [9.1] Dependence of SiO2 concentration in a specific pH range

[0282] The relationship between the pH range (specific pH range) of a slurry solution in which the solution state after autoclaving is a sol and the SiO 2 concentration was investigated according to the following procedure.

[0283] Several sets of samples (80 g total) were prepared, each with the SiO2 concentration varying from 0% to 5% by mass, and the pH of the slurry solution after pH adjustment in step #25 varying from 0.22 to 7.65. The state of the solution after autoclaving was visually confirmed. For each sample, the sol solution concentration was set to 2.5% by mass, the same as in Example 4, and the autoclave heating conditions were 150°C for 15 hours, the same as in Example 4.

[0284] The results of the above solution state confirmation are shown as a scatter plot in Figure 16 The vertical axis of the scatter plot represents the pH value of the slurry solution, and the horizontal axis represents the SiO2 concentration. In the figure, white circles (○) represent the sol, black squares (■) represent the gel, black triangles (▲) represent the precipitate, and white squares (□) represent the first half of the sol. Figure 16 In the measurement results shown, no second semi-sol was confirmed.

[0285] Depend on Figure 16 It can be seen that when the SiO2 concentration is in the range of 0 to 5 mass%, the specific pH range (from the lower limit to the upper limit) is within the range of 1.0 to 6.2, and decreases with increasing SiO2 concentration. Furthermore, similarly to the first synthesis method, at the same SiO2 concentration, gelation occurs when the pH value is below the specific pH range, and precipitation occurs when the pH value is above the specific pH range.

[0286] If it is a sol solution without silica added (SiO2 concentration is 0% by mass), the solution state remains in a sol state when the pH value is within a specific pH range (2.07 to 6.15), but in the region where the pH value is less than pH 2.07, a transparent gel is generated. Therefore, it is believed that the polymerization of the sol is promoted by the acid catalyst until gelation. This means that even in the region below pH 2.07, if the heating conditions of the autoclave treatment are relaxed (shortening the treatment time and / or lowering the treatment temperature) to suppress gelation, there is a possibility that the solution state can be turned into a sol. Therefore, even in a SiO2Al2O3 sol solution containing silica added, by relaxing the heating conditions, it is possible to turn the solution into a sol. Figure 16 The specific pH range shown is extended toward the lower side.

[0287] Since the isoelectric point of silica sol is pH 1-1.5, the silica sol is dispersed in the liquid with a negative surface charge near the neutral region where the boehmite sol exists. It is believed that when the boehmite is near neutral, the silica and boehmite are electrostatically bonded. Therefore, similar to the case of the first synthesis method, the reason Figure 16 The upper limit of the specific pH range decreases with increasing SiO2 concentration, presumably due to the influence of silica sol. Considering that the surface potential of particles is zero, precipitation occurs due to particle aggregation. When silica with widely different isoelectric points is mixed with boehmite, silica adsorbs on the boehmite near neutrality, lowering the apparent isoelectric point and reducing the upper limit of the specific pH range.

[0288] exist Figure 16 In the equation, if the SiO2 concentration is X (mass %), the lower limit of the specific pH range is P0, and the upper limit is P1, then P0 and P1 are given as approximate values ​​by the following calculation formula. Figure 16 The dashed lines are shown in the figure for reference.

[0289] When 0<X≤1,

[0290] P0=2.07

[0291] P1=-2.71X+6.15

[0292] When 1<X≤3,

[0293] P0=-0.48(X-1)+2.07

[0294] P1=-0.615(X-1)+3.44

[0295] When 3<X≤5,

[0296] P0=-0.02(X-3)+1.11

[0297] P1=-0.57(X-3)+2.21

[0298] From the above, it can be seen that in one embodiment of the pH adjustment treatment of the slurry solution in step #25, when the SiO2 concentration is X (mass %), the pH adjustment treatment can be performed in a manner such that the pH value of the slurry solution is within a specific pH range determined by P0 and P1 given by the above calculation formula.

[0299] [9.2] Concentration dependence of SiO2 at a specific concentration

[0300] The relationship between the upper limit value (specific concentration) of the sol solution concentration at which the solution becomes a sol after autoclave treatment under predetermined autoclave heating conditions (treatment temperature, treatment time) and the SiO2 concentration was investigated as follows.

[0301] Prepare a plurality of samples (80 g of slurry solution in total) with SiO2 concentration varying in the range of 0% to 5% by mass and sol solution concentration (mass %), and visually check the state of the solution after autoclaving. Figure 16 The solution state becomes a pH value within a specific pH range of the sol. The heating conditions for the autoclave treatment were the same as those in Example 4 above, 150° C. and 15 hours.

[0302] The results of the above solution state confirmation are shown as a scatter plot in Figure 17 The vertical axis of the scatter plot represents the sol solution concentration (mass %), and the horizontal axis represents the SiO2 concentration. In the figure, the white circle ○ represents the sol, and the black circle ● represents the second half of the sol.

[0303] Depend on Figure 17 It can be seen that regardless of the SiO2 concentration, if the sol solution concentration is higher than a certain concentration, undegraded precipitates will remain in the sol. Figure 17 It can be seen that under the heating conditions of 150°C for 15 hours, the SiO2 concentration ranges from 0 to 5% by mass, with a specific concentration between 2.5% and 6.0% by mass, decreasing as the SiO2 concentration increases. As can be seen from the above, the relationship between the sol solution concentration and the SiO2 concentration in the second synthesis method shows a trend similar to that in the first synthesis method. Furthermore, as in the case of the first synthesis method, at a certain SiO2 concentration, even if the sol solution concentration exceeds the specific concentration and the solution state is the second semi-sol, there is a possibility that the solution state will transition to a sol state by appropriately adjusting the heating conditions of the autoclave treatment and increasing the heating amount.

[0304] exist Figure 17 In the formula, if the SiO2 concentration is X (mass %) and the specific concentration is Y1, then Y1 is given as an approximate value by the following calculation formula. Figure 17 The dashed line is shown in the figure for reference.

[0305] When 0<X≤1,

[0306] Y1=6

[0307] When 1<X≤3,

[0308] Y1=-1.5(X-1)+6

[0309] When 3<X≤5,

[0310] Y1=-0.25(X-3)+3

[0311] According to the above, when the heating conditions of the autoclave treatment are 150°C and 15 hours, in one embodiment, the concentration of the sol solution in step #25 is controlled to be below a specific concentration. When the SiO2 concentration is X (mass %), the amounts of the respective raw materials of alkoxysilane and sodium aluminate in steps #21 and #22, and the amount of water added to the precipitate cake in step #25 can be adjusted in such a way that the concentration of the sol solution is below the specific concentration Y1 given by the above calculation formula.

[0312] [9.3] Autoclave treatment conditions of 1% SiO2Al2O3 sol solution

[0313] Based on the above results, an example of the autoclave treatment conditions for synthesizing a 1% SiO2Al2O3 sol solution by the second synthesis method is as follows.

[0314] pH value of slurry solution: pH2.1~pH3.4

[0315] Sol solution concentration: 6% by mass or less

[0316] Heating conditions: 150°C, 15 hours

[0317] Furthermore, as described above, if the SiO2 concentration in the SiO2 / Al2O3-containing sol solution increases above 1% by mass, the pH of the slurry solution and the sol solution concentration can be adjusted accordingly, as described above. Furthermore, the heating conditions are not limited to the aforementioned 150°C and 15 hours. The treatment temperature and treatment time can be varied to suppress increases or decreases in the amount of heating, as described in the first synthesis method.

[0318]

[10] Heat resistance evaluation of the second synthesis method

[0319] The heat resistance of SiO2Al2O3 powders (hereinafter collectively referred to as "main powder sample S2") obtained by drying and calcining a SiO2Al2O3 sol solution synthesized by the second synthesis method was evaluated. Furthermore, to evaluate the effect of the step of solification of the precipitate cake by autoclaving in step #25 of the second synthesis method on heat resistance, the heat resistance of SiO2Al2O3 powders (hereinafter collectively referred to as "Comparative Example C2") obtained by directly drying and calcining the precipitate cake prepared in steps #21 to #24 without solification was evaluated. The heat resistance of main powder sample S2 was compared with that of Comparative Example C2. Hereinafter, the synthesis method of Comparative Example C2 will be appropriately referred to as the "precipitation method," similar to the synthesis method of Comparative Example C1.

[0320] When evaluating heat resistance, since Comparative Example C2 is a powder sample, in order to facilitate investigation of changes in heat resistance due to different SiO2 concentrations, a powder sample was used instead of a coating film.

[0321] In the synthesis method of silica-added porous alumina of Comparative Example C2, the steps up to the formation of the precipitate cake are identical to steps #21 to #24 of the second synthesis method. In Comparative Example C2, the resulting precipitate cake is dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (Comparative Sample C2A). Furthermore, as needed, Comparative Sample C2B, which undergoes a first heat treatment at 1200°C for 5 hours, and Comparative Sample C2C, which undergoes a second heat treatment at 1200°C for 30 hours, were prepared.

[0322] On the other hand, as main powder sample S2, following steps #21 to #24 of the second synthesis method, the SiO₂Al₂O₃ sol solution obtained in step #25 was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce SiO₂Al₂O₃ powder (main sample S2A). Furthermore, as needed, main sample S2B was produced by subjecting main sample S2A to a first heat treatment at 1200°C for 5 hours, and main sample S2C was produced by subjecting main sample S2A to a second heat treatment at 1200°C for 30 hours.

[0323] In the main powder sample S2 and the comparative example C2, the specific processing contents of steps #21 to #25 are as described in Example 4 when the SiO2 concentration is 1 mass%. When the SiO2 concentration is other than 1 mass%, the mixing ratio of the sodium aluminate aqueous solution and the 5.88% TEOS solution in step #23 is adjusted according to the set value of the SiO2 concentration.

[0324] Figure 18 1 and 2 show XRD patterns of the crystal structures of the main sample S2A, the main sample S2B, and the main sample S2C having a SiO2 concentration of 1% by mass after each heat treatment. Figure 19 1 and 2 show XRD patterns of the crystal structures of comparative samples C2A, C2B, and C2C having a SiO2 concentration of 1% by mass after heat treatment.

[0325] Depend on Figure 18 and Figure 19 It is known that even when the aluminum compound is sodium aluminate, the aluminum compound is different from the case where the aluminum compound is aluminum nitrate (refer to Figure 9 and 10) Similarly, SiO2Al2O3 can be obtained. In addition, after the second heat treatment at 1200°C and 30 hours, the comparative sample C2C obtained by the precipitation method completely transformed into the α phase, but the main sample S2C treated in the autoclave did not completely transform into the α phase.

[0326] exist Figure 20 Shown are the measurement results of the specific surface areas of main sample S2A, main sample S2B and main sample S2C (a total of 12 main powder samples S2) made by changing the SiO2 concentration in four ways: 0 mass%, 1 mass%, 3 mass% and 5 mass%. Figure 21 Shown in the figure are the measurement results of the specific surface areas of the comparative samples C2A, C2B and C2C (a total of 12 comparative examples C2) prepared by changing the SiO2 concentration to 0 mass%, 1 mass%, 3 mass% and 5 mass%. Figure 20 and Figure 21 In each figure, the vertical axis represents the specific surface area (m 2 / g), and the horizontal axis represents SiO2 concentration (mass %).

[0327] like Figure 21 As shown, the specific surface areas of the comparative samples C2A, C2B and C2C after the initial and first and second heat treatments are similar to those when the aluminum compound is aluminum nitrate (reference Figure 8 ) The specific surface areas of the comparative samples C1A, C1B and C1C at the initial stage and after the first and second heat treatments are substantially the same.

[0328] like Figure 20 As shown, the specific surface areas of the main samples S2B and S2C after the first and second heat treatments are similar to those when the aluminum compound is aluminum nitrate (refer to Figure 7 ) showed that the specific surface areas of main sample S1B and main sample S1C after the first and second heat treatments were approximately equal. However, main sample S2A, after the initial heat treatment at 1000°C for 5 hours, had a SiO2 concentration of 1% by mass or higher and a roughly constant specific surface area. This is similar to the case where the aluminum compound is aluminum nitrate, and is believed to be due to a decrease in the total pore volume during drying of the sol solution.

[0329] [Third embodiment]

[0330] Hereinafter, a third embodiment of the main synthesis method (third synthesis method) will be described.

[0331]

[11] Basic composition of the third synthesis method

[0332] The third synthesis method, such as Figure 22As shown in the process transition diagram, the process is broadly divided into the following steps #31 to #36. In step #36, the third synthesis method directly adds the alkoxysilane solution prepared in step #31 to the Al2O3 sol solution containing no silicon dioxide (SiO2 concentration of 0 mass%) synthesized in steps #32 to #35, thereby synthesizing a SiO2-containing Al2O3 sol solution.

[0333] The third synthesis method is different from the first and second synthesis methods as the first AC method, which synthesize the SiO2Al2O3 sol solution after autoclave treatment. It synthesizes the Al2O3 sol solution without adding silica after the autoclave treatment in step #35.

[0334] Hereinafter, as in the third synthesis method, the synthesis method of synthesizing a SiO2-containing Al2O3 sol solution after preparing an Al2O3-containing sol solution without adding silica by autoclave treatment is referred to as the second AC (autoclave) method.

[0335] In step #31, an alkoxysilane solution containing alkoxysilane, water, alcohol, and an inorganic acid is prepared. In step #32, an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate, and water is prepared. The alkoxysilane solution obtained in step #31 is used in step #36, so steps #31 to #36 are sufficient.

[0336] In step #33, a mixed solution of an alkoxysilane solution and an aluminum solution is not prepared, and a precipitate of aluminum hydroxide, free of adsorbed silicon compounds, is precipitated from the aluminum solution. Therefore, step #33 differs significantly from steps #13 and #23 of the first and second synthesis methods, which involve precipitating a precipitate of aluminum hydroxide with adsorbed silicon compounds.

[0337] Next, in step #34, the precipitate obtained in step #33 is separated from the aluminum solution by filtration, and the precipitate separated by filtration is washed with water to prepare a precipitate cake.

[0338] Next, in step #35, water is added to the precipitate cake obtained in step #34 to prepare a slurry solution. This slurry solution is then pH-adjusted and then autoclaved to prepare an Al2O3-containing sol solution to which no silica is added. The autoclave treatment partially dehydrates the aluminum hydroxide in the slurry solution to produce boehmite, producing an Al2O3-containing sol solution in which the boehmite particles are highly dispersed as sol particles.

[0339] Next, in step #36, the alkoxysilane solution prepared in step #31 is mixed with the Al2O3-containing sol solution prepared in step #35 and stirred to prepare a SiO2Al2O3-containing sol solution. As a result, a SiO2Al2O3-containing sol solution is synthesized in which sol particles containing silica particles adsorbed on boehmite particles are highly dispersed.

[0340] Step #31 is identical to Steps #11 and #21 of the first and second synthesis methods, and Step #32 is identical to Steps #12 and #22 of the first and second synthesis methods. Step #34 is identical to Steps #14 and #24 of the first and second synthesis methods, except that silica is absent from the precipitate cake. Therefore, any overlapping descriptions of the first and second synthesis methods will be omitted.

[0341] In step #35, water is added to the precipitate cake obtained in step #34 to prepare a slurry solution, which is then subjected to pH adjustment and then autoclaved to produce an Al2O3-containing sol solution. This process is similar to steps #15 and #25 of the first and second synthesis methods, except that silica is not present in the prepared sol solution. Furthermore, boehmite particles are present in a highly dispersed state as sol particles in the prepared Al2O3-containing sol solution, and this process is similar to steps #15 and #25 of the first and second synthesis methods, except that silica is not bonded to the boehmite particles.

[0342] As one embodiment of step #33, after heating the aluminum solution under reflux, nitric acid is added dropwise and stirred to adjust the pH. The heating under reflux and pH adjustment cause hydrolysis of the aluminum solution to proceed, resulting in precipitation of aluminum hydroxide.

[0343] As an embodiment of step #35, the amount of water added to the precipitate cake is adjusted, and the sol solution concentration (mass %) represented by the Al2O3 content relative to the total mass of the synthesized Al2O3-containing sol solution is controlled to be below a specific concentration at which the solution state after autoclaving becomes a sol state, and the slurry solution is subjected to pH adjustment treatment to control the pH value of the slurry solution to be within a specific pH range at which the solution state after autoclaving becomes a sol state.

[0344] In addition, in this embodiment, in order to make the total mass of the Al2O3 sol solution containing no silicon dioxide added to a certain value relative to the content of the autoclave used for the autoclave treatment, the concentration of the sol solution is controlled by adjusting the amount of the raw material of the aluminum compound in step #32 and the amount of water added to the precipitate cake in step #35.

[0345] The specific concentration of step #35 is, depending on the aluminum compound used, the specific concentration of 0 mass% SiO2 concentration (no silica added) in step #15 of the first synthesis method, or the specific concentration of 0 mass% SiO2 concentration in step #25 of the second synthesis method. The specific pH range in step #35 is, depending on the aluminum compound used, the specific pH range of 0 mass% SiO2 concentration in step #15 of the first synthesis method, or the specific pH range of 0 mass% SiO2 concentration in step #25 of the second synthesis method. Therefore, in step #35 of the third synthesis method, unlike the first and second synthesis methods, it is possible to easily set the sol solution concentration and adjust the pH of the slurry solution without being restricted by the SiO2 concentration. In other words, in the second AC method, regardless of the aluminum compound used, it is possible to carry out autoclave treatment under the conditions of 0 mass% SiO2 concentration, which has the highest specific concentration and the widest specific pH range (see Figure 3 、 Figure 4 、 Figure 16 、 Figure 17 ), therefore, compared with the first AC method, the preparation of the SiO2Al2O3-containing sol solution in which the solution state becomes a sol is easier, and in addition, the SiO2Al2O3-containing sol solution with a high solution concentration can be produced.

[0346] The first AC method is divided into a first synthesis method and a second synthesis method based on the aluminum compound. Step #13 of the first synthesis method and step #23 of the second synthesis method differ slightly in some of the processes (heating under reflux and pH adjustment). Meanwhile, in step #33 of the second AC method, which corresponds to steps #13 and #23, there is no step for preparing a mixed solution of an alkoxysilane solution and an aluminum solution. Therefore, regardless of whether the aluminum compound is aluminum nitrate, aluminum chloride, aluminum sulfate, or sodium aluminate, step #33 follows the same process.

[0347]

[12] Example of the third synthesis method

[0348] Hereinafter, an example of steps #31 to #35 for synthesizing a SiO2-containing Al2O3 sol solution having a SiO2 concentration of 1% by mass will be described. However, descriptions overlapping with those of the first and second synthesis methods will be omitted.

[0349] Hereinafter, Example 5 in which aluminum nitrate was used as the aluminum compound will be described.

[0350] In step #31, a transparent and uniform 5.88% TEOS solution (alkoxysilane solution) is obtained by the same procedure as in step #11 of Example 1. In step #32, an aqueous aluminum nitrate solution (aluminum solution) is obtained by the same procedure as in step #12 of Example 1. However, in step #32, the amount of water added to the aluminum solution is preferably increased by the same amount as the TEOS solution added in step #13 of Example 1 compared to the amount of water in step #12 of Example 1. This ensures that the total amount of aluminum solution at the time of precipitation in step #33 will be the same as the total amount of the mixed solution at the time of precipitation in step #13 of Example 1.

[0351] In step #33, instead of adding 5.88% TEOS solution to the aluminum nitrate aqueous solution obtained in step #32, heating reflux and pH adjustment are performed in the same manner as in step #13 of Example 1, and aluminum hydroxide precipitates in the aluminum nitrate aqueous solution.

[0352] In step #34, a precipitate cake was obtained by the same procedure as in step #14 of Example 1. Next, in step #35, a 0% SiO2- and Al2O3-containing sol solution (Al2O3-containing sol solution) without the addition of silica was obtained by the same procedure as in step #15 of Example 1.

[0353] The total amount of Al2O3-containing sol solution obtained in step #35 was 80 g, and the Al2O3 powder obtained by drying the sol solution was 1.98 g. The sol solution concentration of 80 g of the sol solution containing 1.98 g of Al2O3 powder was 2.475 mass %.

[0354] Next, in step #36, 1.18 g of the 5.88% TEOS solution prepared in step #31 was mixed with the Al2O3-containing sol solution obtained in step #35, and then stirred at room temperature for 5 minutes to synthesize a SiO2-containing Al2O3 sol solution having a SiO2 concentration of 1% by mass and a sol solution concentration of 2.46% by mass (1% SiO2Al2O32.46% sol). The SiO2 concentration can be adjusted by adjusting the amount of TEOS solution added. Even after adding the TEOS solution to the Al2O3-containing sol solution, the solution remained in a sol state, and no precipitation or gelation was observed.

[0355] In the above, Example 5, in which aluminum nitrate was used as the aluminum compound, was described with reference to Example 1 of the first synthesis method. In Example 6, in which sodium aluminate was used as the aluminum compound, in step #33, instead of adding a 5.88% TEOS solution to the sodium aluminate aqueous solution obtained in step #32, heating under reflux and pH adjustment were performed in the same manner as in step #23 of Example 4 to precipitate aluminum hydroxide in the sodium aluminate aqueous solution. Based on Example 4 of the second synthesis method and following the same procedures, a 1% SiO₂Al₂O₃-containing sol solution was synthesized.

[0356] In addition, the situation of Example 6 is the same as that of Example 5, and in a manner that makes the total amount of aluminum solution when the precipitate is precipitated in step #33 the same as the total amount of the mixed solution when the precipitate is precipitated in step #23 of Example 2, it is preferred that in step #32, the amount of water added to the aluminum solution is increased by the same amount as the TEOS solution added in step #23 of Example 2 compared to the amount of water in step #22 of Example 2.

[0357] Furthermore, in Example 6, the pH adjustment treatment of the sodium aluminate aqueous solution in step #33 differs from that in Example 5 in that the pH is adjusted from the alkaline side to the acidic side using nitric acid. Therefore, the target pH value for pH adjustment is set to pH 7.5, which is lower than the target pH 8.0 in step #23 of Example 4 of the second synthesis method (first AC method), based on the amount of alkoxysilane solution added. This is because, whereas in the second synthesis method (first AC method), the pH decreases with the addition of the alkoxysilane solution in step #23, in the second synthesis method (first AC method), this pH decrease does not occur because no alkoxysilane solution is added in step #33.

[0358]

[13] Autoclave treatment conditions for the third synthesis method

[0359] The autoclave treatment conditions of the third synthesis method can be the autoclave treatment conditions of the first synthesis method or the second synthesis method with a SiO2 concentration of 0 mass%, depending on the aluminum compound used.

[0360]

[14] Heat resistance evaluation of the third synthesis method (1)

[0361] The heat resistance of SiO₂Al₂O₃ powder (hereinafter collectively referred to as "main powder sample S3") obtained by drying and calcining a SiO₂Al₂O₃ sol solution synthesized using the third synthesis method instead of the first synthesis method was evaluated. In the following heat resistance evaluation, aluminum nitrate was used as the aluminum compound, and the SiO₂ concentration was set to 1 mass%.

[0362] As main powder sample S3, a 1% SiO₂Al₂O₃ sol solution obtained through steps #31 to #36 of the third synthesis method described in Example 5 was dried at 150°C, then pulverized into a powder, and sintered in air at 1000°C for 5 hours (initial heat treatment) to produce SiO₂Al₂O₃ powder (main sample S3A). Furthermore, main sample S3B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S3C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0363] The specific surface areas (m2) of the main samples S3A, S3B, and S3C prepared with a SiO2 concentration of 1% by mass are shown in Table 7 below. 2 For comparison and control, the measurement results of the specific surface areas of the main samples S1A, S1B, and S1C with a SiO2 concentration of 1% by mass produced by the first synthesis method are also recorded in Table 7.

[0364]

Table 7

[0365]

[0366] As shown in Table 7, the SiO2Al2O3 powder (main samples S3A~S3C) produced by the SiO2Al2O3 sol solution synthesized by the third synthesis method (second AC method) shows, under various heat treatment conditions, the same specific surface area as the SiO2Al2O3 powder (main samples S1A~S1C) produced by the SiO2Al2O3 sol solution synthesized by the first synthesis method (first AC method). Sufficient heat resistance can also be obtained when using the third synthesis method.

[0367] Based on the above, it can be confirmed that by adding TEOS to the Al2O3 sol solution containing no silicon dioxide, the SiO2Al2O3 sol solution can be easily synthesized without precipitation and gelation.

[0368] Next, as the main powder sample S3, in addition to the above-mentioned main samples S3A to S3C in which aluminum nitrate was used as the aluminum compound and the SiO2 concentration was 1% by mass, main samples S3A to S3C (initial heat treatment, first heat treatment, second heat treatment) prepared by changing the SiO2 concentration to 0% by mass, 3% by mass, 5% by mass and 10% by mass were added. The specific surface areas (m 2 / g) are displayed according to the heat treatment Figures 23 to 25For comparison and control, the measurement results of the specific surface areas of the main samples S1A, S1B and S1C, which were prepared by the first synthesis method using aluminum nitrate as the aluminum compound and had SiO2 concentrations of 0 mass%, 1 mass%, 3 mass%, 5 mass%, 8 mass%, 9 mass% and 10 mass%, and the measurement results of the specific surface areas of the comparative samples C1A, C1B and C1C, which were prepared by the precipitation method using aluminum nitrate as the aluminum compound and had SiO2 concentrations of 0 mass%, 1 mass%, 3 mass%, 5 mass% and 10 mass%, are recorded together according to the heat treatment. Figures 23 to 25 middle.

[0369] In addition, Figure 26 Shown in FIG are XRD patterns showing the crystal structures of the main sample S3A, main sample S3B, and main sample S3C having a SiO2 concentration of 1% by mass after each heat treatment. In addition, XRD patterns showing the crystal structures of the main sample S1A, main sample S1B, and main sample S1C having a SiO2 concentration of 1% by mass produced by the first synthesis method, and the comparative sample C1A, comparative sample C1B, and comparative sample C1C having a SiO2 concentration of 1% by mass produced by the precipitation method after each heat treatment, are shown in FIG. Figure 9 and Figure 10 .

[0370] like Figures 23 to 25 As shown, the SiO₂Al₂O₃ powders (main samples S3A to S3C) produced from the SiO₂Al₂O₃-containing sol solution synthesized by the third synthesis method (second AC method) showed, under various heat treatment conditions, little increase in specific surface area even when the SiO₂ concentration was increased to 10% by mass, similar to the SiO₂Al₂O₃ powders (main samples S1A to S1C) produced from the SiO₂Al₂O₃-containing sol solution synthesized by the first synthesis method (first AC method). This is presumably because, as described above in the explanation of the measurement results in Table 3, the total pore volume of Al₂O₃ decreases due to the surface tension of water during the gel formation process by drying the sol solution.

[0371] like Figure 26 As shown, the SiO₂Al₂O₃ powder (main sample S3C) produced by the third synthesis method (second AC method) still contains θ-Al₂O₃ even during the second heat treatment (1200°C for 30 hours), and has not completely transformed into the α phase. This confirms that the third synthesis method (second AC method) can achieve the same heat resistance as the first synthesis method (first AC method).

[0372]

[15] Heat resistance evaluation of the third synthesis method (2)

[0373] The heat resistance of SiO₂Al₂O₃ powder (hereinafter collectively referred to as "main powder sample S4") obtained by drying and calcining a SiO₂Al₂O₃ sol solution synthesized using sodium aluminate as the aluminum compound using the third synthesis method instead of the second synthesis method was evaluated. In the following heat resistance evaluation, the SiO₂ concentration was set at 5% and 10% by mass.

[0374] As the main powder sample S4, a SiO2Al2O3 sol solution containing 5% and 10% SiO2 concentrations, obtained in steps #31 to #36 of Example 6 of the third synthesis method, was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (main sample S4A). Furthermore, main sample S4B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S4C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0375] Table 8 below shows the specific surface areas (m2) of the main samples S4A to S4C prepared with SiO2 concentrations of 5% by mass and 10% by mass. 2 For comparison and control, the measurement results of the specific surface areas of main samples S2A to S2C with a SiO2 concentration of 5% by mass, produced by the second synthesis method (first AC method), and the measurement results of the specific surface areas of comparative samples C2A to C2C with SiO2 concentrations of 5% and 10% by mass, produced by the precipitation method, are also recorded in Table 8.

[0376]

Table 8

[0377]

[0378] First, as shown in Table 8, when the SiO2 concentration was 5% by mass, the main samples S4A to S4C synthesized by the third synthesis method exhibited a specific surface area comparable to that of the main samples S2A to S2C synthesized by the second synthesis method and the comparative samples C2A to C2C synthesized by the precipitation method. Furthermore, when the SiO2 concentration was 10% by mass, the main samples S4A to S4C synthesized by the third synthesis method exhibited a specific surface area comparable to that of the comparative samples C2A to C2C synthesized by the precipitation method. This demonstrates that, when the third synthesis method is used, sufficient heat resistance can be achieved even when sodium aluminate is used as the aluminum compound.

[0379] Furthermore, as shown in the measurement results in Table 8, when sodium aluminate is used as the aluminum compound, in the second synthesis method of the main samples S2A to S2C, as shown in FIG. Figure 16As shown, the upper limit of the SiO2 concentration is 5 mass %, but by using the third synthesis method, the SiO2 concentration can be increased to 10 mass % as in the main samples S4A to S4C.

[0380] Next, as the main powder sample S4, in addition to the above-mentioned main samples S4A to S4C in which the aluminum compound is sodium aluminate and the SiO2 concentration is 1% by mass, main samples S4A to S4C (initial heat treatment, first heat treatment, second heat treatment) prepared by changing the SiO2 concentration to 0% by mass, 3% by mass, 5% by mass and 10% by mass were added. The specific surface areas (m 2 / g) are displayed according to the heat treatment Figures 27 to 29 For comparison and control, the measurement results of the specific surface areas of the main samples S2A, S2B and S2C, which were prepared by the second synthesis method using sodium aluminate as the aluminum compound and had SiO2 concentrations of 0 mass%, 1 mass%, 3 mass% and 5 mass%, and the measurement results of the specific surface areas of the comparative samples C2A, C2B and C2C, which were prepared by the precipitation method using sodium aluminate as the aluminum compound and had SiO2 concentrations of 0 mass%, 1 mass%, 3 mass%, 5 mass% and 10 mass%, are recorded together according to the heat treatment. Figures 27 to 29 .

[0381] In addition, Figure 30 Shown in FIG are XRD patterns of the crystal structures of the main sample S4A, main sample S4B and main sample S4C having a SiO2 concentration of 1% by mass after each heat treatment. In addition, XRD patterns of the crystal structures of the main sample S2A, main sample S2B and main sample S2C having a SiO2 concentration of 1% by mass produced by the second synthesis method, and the comparative sample C2A, comparative sample C2B and comparative sample C2C having a SiO2 concentration of 1% by mass produced by the precipitation method after each heat treatment are shown in FIG. Figure 18 and Figure 19 middle.

[0382] like Figures 27 to 29 As shown, the SiO2Al2O3 powder produced by the SiO2Al2O3 sol solution synthesized by the third synthesis method (second AC method) also shows roughly the same heat resistance when sodium aluminate is used as the aluminum compound as when aluminum nitrate is used as the aluminum compound.

[0383] In addition, if Figure 30As shown, the XRD patterns of the SiO₂Al₂O₃ powders (S₄A to S₄C) produced by the third synthesis method (second AC method) exhibit peaks similar to those observed in the XRD patterns of the comparative samples (C₂A to C₂C) produced by the precipitation method. This confirms that the third synthesis method (second AC method) can also achieve heat resistance comparable to that achieved by the precipitation method and the first synthesis method (first AC method).

[0384] [Fourth embodiment]

[0385] Hereinafter, a fourth embodiment of the main synthesis method (fourth synthesis method) will be described.

[0386]

[16] Basic composition and examples of the fourth synthesis method

[0387] The fourth synthesis method, such as Figure 31 As shown in the process conversion diagram, the method comprises a step #41 of adding an organic solvent (hereinafter appropriately referred to as a "specific additive") having a higher boiling point than water and a lower surface tension than water to the SiO2Al2O3 sol solution synthesized by any of the first, second and third synthesis methods (step #40) as a post-treatment.

[0388] As described in the above-mentioned "[4] Evaluation of Heat Resistance of the First Synthesis Method (1)", during the process of drying the SiO2Al2O3 sol solution synthesized by any of the first to third synthesis methods in step #40 to generate a transparent gel, the total pore volume of Al2O3 decreases due to the surface tension of the evaporated water. Step #41 of the fourth synthesis method is designed as a countermeasure to this problem.

[0389] In one embodiment of step #41, ethylene glycol (EG) or N,N-dimethylformamide (DMF) is preferably used as a specific additive. EG has a surface tension of 48.4 dyne / cm, and DMF has a surface tension of 36.8 dyne / cm, both lower than the surface tension of water (72.8 dyne / cm).

[0390] In addition, as a preferred embodiment of the fourth synthesis method, in step #41, a specific additive (EG or DMF) is added to the SiO2Al2O3-containing sol solution synthesized by any one of the above-mentioned first, second and third synthesis methods (step #40), so that the specific additive is 3 mass% relative to the total amount of the sol solution after addition and stirred to prepare a SiO2Al2O3-containing sol solution added with the specific additive.

[0391] As an example of the preferred embodiment of the fourth synthesis method (Example 7), EG and DMF were added to SiO₂ and Al₂O₃ sol solutions with SiO₂ concentrations of 3% and 10% by mass, respectively, synthesized by the first synthesis method using aluminum nitrate as the aluminum compound in step #40. Four SiO₂ and Al₂O₃ sol solutions containing the specific additive were prepared by adding EG and DMF, respectively, and stirring in step #41. The sol solution concentration in Example 7 was set to, for example, 2.5% by mass, similar to Example 1 of the first synthesis method. Furthermore, as another example of the preferred embodiment of the fourth synthesis method (Example 8), DMF was added to SiO₂ and Al₂O₃ sol solutions with SiO₂ concentrations of 5% and 10% by mass, synthesized by the third synthesis method instead of the second synthesis method using sodium aluminate as the aluminum compound. Two SiO₂ and Al₂O₃ sol solutions containing the specific additive were prepared by adding DMF as the specific additive in step #41. The sol solution concentration in Example 8 was set to, for example, 2.5% by mass, similar to Example 7.

[0392] In another example (Example 9) of the preferred embodiment of the fourth synthesis method, in step #40, aluminum nitrate was used as the aluminum compound, and the third synthesis method was used instead of the first synthesis method. After preparing a 0% SiO2Al2O3-containing sol solution with a sol solution concentration of 9 mass%, 4.25 g of a 5.88% TEOS solution was added to prepare a SiO2Al2O3-containing sol solution with a SiO2 concentration of 1 mass%. To achieve more sufficient heat resistance, DMF was added as a specific additive, and the mixture was stirred at room temperature to prepare a SiO2Al2O3-containing sol solution containing the specific additive. It was confirmed that by using the third synthesis method in step #40, a SiO2Al2O3-containing sol solution with a high sol solution concentration could be prepared without precipitation or gelation.

[0393]

[17] Heat resistance evaluation of the fourth synthesis method (1)

[0394] The four SiO₂Al₂O₃ sol solutions of Example 7 were dried at 150°C to form dried gels, and then sintered at 1200°C for 5 hours in a first heat treatment to produce four types of SiO₂Al₂O₃ powders (hereinafter collectively referred to as "main sample S5B"). The specific surface area and total pore volume of the four main samples S5B were measured to evaluate their heat resistance.

[0395] The specific surface areas (m 2 / g) and total pore volume (cm 3 / g) of the measurement results. In addition, the specific surface areas (m2) of the main sample S1B and the comparative sample C1B prepared with SiO2 concentrations of 3% by mass and 10% by mass shown in Table 3 of the above-mentioned "[4] Evaluation of heat resistance of the first synthesis method (1)" are as follows: 2 / g) and total pore volume (cm 3 / g), which are also recorded in Table 9 for comparison. Main sample S1B was prepared by drying and pulverizing a SiO2-containing Al2O3 sol solution with SiO2 concentrations of 3% and 10% by mass, synthesized by the first synthesis method using aluminum nitrate as the aluminum compound, without adding any specific additives, to obtain a powdered dry gel, which was then calcined by a first heat treatment at 1200°C for 5 hours. Comparative sample C1B was prepared by drying and pulverizing a precipitate cake with SiO2 concentrations of 3% and 10% by mass, obtained by a precipitation method using aluminum nitrate as the aluminum compound, to obtain a powdered dry gel, which was then calcined by a first heat treatment at 1200°C for 5 hours.

[0396]

Table 9

[0397]

[0398] As shown in Table 9, at both SiO2 concentrations of 3% and 10% by mass, the addition of the specific additives EG and DMF in step #41 increased the specific surface area and total pore volume of Master Sample S5B compared to those of Master Sample S1B synthesized without the specific additives. Furthermore, the magnitude of this increase was greater with increasing SiO2 concentration.

[0399] exist Figure 32 In the figure, the pore distribution (BJH plot) of two main samples S5B and S1B containing EG and DMF as specific additives at a SiO2 concentration of 3 mass% is shown. Figure 33 In the figure, the pore distribution (BJH plot) of two main samples S5B and S1B containing EG and DMF as specific additives at a SiO2 concentration of 10 mass% is shown. Figure 32 and Figure 33 In the figure, circles (●) represent the pore distribution of the main sample S1B (without specific additives), triangles (▲) represent the pore distribution of the main sample S5B (with EG added), and squares (■) represent the pore distribution of the main sample S5B (with DMF added). The vertical axis represents the differential pore volume dV p / dr p (m 3 / g / nm), the horizontal axis represents the pore diameter r p (nm).

[0400] like Figure 32 and Figure 33 As shown, in both cases where the SiO2 concentration was 3% and 10% by mass, the addition of EG and DMF as specific additives in step #41 increased the total pore volume and mode pore diameter of master sample S5B compared to the total pore volume and mode pore diameter of master sample S1B synthesized without the specific additives. At a SiO2 concentration of 10% by mass, the mode pore diameter of master sample S1B without the specific additives was 4.17 nm, whereas the mode pore diameter of master sample S5B with the addition of EG and DMF increased to 5.45 nm. This demonstrates that the addition of an organic solvent with a higher boiling point and lower surface tension than water is effective in suppressing the reduction in pore volume of SiO2 and Al2O3 and increasing the specific surface area.

[0401] Next, as Example 7 of the fourth synthesis method for synthesizing a SiO2Al2O3 sol solution using aluminum nitrate as the aluminum compound in step #40 by the first synthesis method, in addition to the above-mentioned four main samples S5B (SiO2 concentration: 3 mass %, 10 mass %), main samples S5A to S5C (initial heat treatment, first heat treatment, second heat treatment) in which the SiO2 concentration is changed to 0 mass %, 1 mass % and 5 mass % and the specific additive is DMF are also prepared. Figures 34 to 36 In the figure, the specific surface areas (m2) of the main sample S5A, main sample S5B and main sample S5C of each SiO2 concentration are shown according to the heat treatment. 2 / g) of the measurement results. In addition, as Example 9 of the fourth synthesis method of synthesizing a SiO2Al2O3 sol solution by the third synthesis method using aluminum nitrate as the aluminum compound in step #40, in addition to the SiO2 concentration of 1 mass%, a SiO2Al2O3 sol solution synthesized by changing the SiO2 concentration to 0 mass%, 3 mass%, 5 mass% and 10 mass% was prepared, DMF was added as a specific additive, and stirred at room temperature to obtain a SiO2Al2O3 sol solution to which a specific additive was added, which was calcined at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (main sample S5aA). In addition, main sample S5aB was subjected to a first heat treatment of 1200°C for 5 hours with respect to main sample S5aA, and main sample S5aC was subjected to a second heat treatment of 1200°C for 30 hours with respect to main sample S5a A. In the Figures 34 to 36 The specific surface areas (m2) of the main sample S5aA, main sample S5aB and main sample S5aC of each SiO2 concentration were recorded by heat treatment. 2 / g) of the measurement results. In addition, Figures 34 to 36In the present invention, for the purpose of comparison and control, the measurement results of the specific surface areas of the comparative samples C1A, C1B and C1C, which were prepared by precipitation method using aluminum nitrate as the aluminum compound and with SiO2 concentrations of 0 mass%, 1 mass%, 3 mass%, 5 mass% and 10 mass%, are recorded together according to the heat treatment.

[0402] like Figures 34 to 36 As shown, when any one of the first synthesis method and the third synthesis method is used in step #40 of the fourth synthesis method, by adding specific additives to the SiO2Al2O3 sol solution synthesized in step #40 in step #41, the same specific surface area as the precipitation method can be obtained.

[0403]

[18] Heat resistance evaluation of the fourth synthesis method (2)

[0404] Similar to the heat resistance evaluation (1) of the fourth synthesis method

[17] above, the two SiO2Al2O3 sol solutions of the above-mentioned Example 8 were dried and sintered to prepare two SiO2Al2O3 powders (hereinafter collectively referred to as "main powder samples S6"), and the heat resistance of the two main powder samples S6 was evaluated.

[0405] As main powder sample S6, two SiO₂Al₂O₃ sol solutions with SiO₂ concentrations of 5% and 10% by mass, obtained through step #40 of the fourth synthesis method (steps #31 to #36 of Example 6 of the third synthesis method) and step #41, were dried at 150°C, pulverized into powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce SiO₂Al₂O₃ powder (main sample S6A). Furthermore, main sample S6B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S6C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0406] Table 10 below shows the specific surface areas (m2) of the main samples S6A, S6B, and S6C prepared with SiO2 concentrations of 5% by mass and 10% by mass. 2 For comparison, the specific surface areas (m2 / g) of the main samples S4A to S4C with SiO2 concentrations of 5% by mass and 10% by mass as shown in Table 8 above were obtained. 2 / g), the measurement results of the specific surface areas of the main samples S2A~S2C with a SiO2 concentration of 5 mass% produced by the second synthesis method, and the measurement results of the specific surface areas of the comparative samples C2A~C2C with SiO2 concentrations of 5 mass% and 10 mass% produced by the precipitation method are also recorded in Table 10.

[0407]

Table 10

[0408]

[0409] As shown in Table 10, with the exception of sample S6B with a SiO2 concentration of 5 mass%, the specific surface area of ​​samples S6A-S6C synthesized by the third synthesis method (second AC method) increased compared to the specific surface area of ​​samples S4A-S4C synthesized by the third synthesis method (second AC method) without the specific additive, regardless of whether the SiO2 concentration was 5 mass% or 10 mass%. The specific surface area of ​​sample S6B with a SiO2 concentration of 5 mass% was slightly lower than that of sample S4B synthesized by the third synthesis method without the specific additive, but the specific surface area was approximately the same. This demonstrates that, even for SiO2-Al2O3-containing sol solutions synthesized by the third synthesis method, the addition of an organic solvent with a higher boiling point and lower surface tension than water is effective in suppressing the reduction in SiO2-Al2O3 pore volume and increasing the specific surface area.

[0410] Secondly, as Example 8 of the fourth synthesis method for synthesizing a SiO2Al2O3 sol solution using sodium aluminate as the aluminum compound in step #40 and replacing the second synthesis method with the third synthesis method, in addition to the above-mentioned two main samples S6A~S6C (SiO2 concentration: 5 mass% and 10 mass%), main samples S6A~S6C (initial heat treatment, first heat treatment, second heat treatment) were also prepared in which the SiO2 concentration was changed to 0 mass%, 1 mass% and 3 mass% and the specific additive was DMF. Figures 37 to 39 In the figure, the specific surface areas (m2) of the main sample S6A, main sample S6B and main sample S6C of each SiO2 concentration are shown according to the heat treatment. 2 / g) of the measurement result. In addition, as Example 10 of the fourth synthesis method using sodium aluminate as the aluminum compound in step #40 and synthesizing the SiO2Al2O3-containing sol solution by the second synthesis method, a SiO2Al2O3-containing sol solution synthesized by changing the SiO2 concentration in five ways of 0 mass%, 1 mass%, 3 mass%, 5 mass% and 10 mass% is prepared, and DMF is added as a specific additive, and stirred at room temperature to obtain a SiO2Al2O3-containing sol solution added with the specific additive, and the SiO2Al2O3 powder (main sample S6aA) is prepared by calcining it at 1000°C for 5 hours (initial heat treatment). In addition, main sample S6aB, which is subjected to a first heat treatment of 1200°C for 5 hours with respect to main sample S6aA, and main sample S6aC, which is subjected to a second heat treatment of 1200°C for 30 hours with respect to main sample S6aA, are prepared. In Figures 37 to 39In the experiment, the specific surface areas (m2) of the main sample S6aA, main sample S6aB and main sample S6aC of each SiO2 concentration were recorded according to the heat treatment. 2 / g) of the measurement results. In addition, Figures 37 to 39 In the present invention, for the purpose of comparison and control, the measurement results of the specific surface areas of comparison samples C2A, comparison sample C2B and comparison sample C2C, which are prepared by precipitation method using sodium aluminate as the aluminum compound and have SiO2 concentrations of 0 mass%, 1 mass%, 3 mass%, 5 mass% and 10 mass%, are recorded together according to the heat treatment.

[0411] like Figures 37 to 39 As shown, even if the aluminum compound is sodium aluminate, when any one of the second synthesis method and the third synthesis method is used in step #40 of the fourth synthesis method, in step #41, by adding specific additives to the SiO2Al2O3 sol solution synthesized in step #40, a specific surface area equivalent to that of the precipitation method can be obtained.

[0412] [Fifth embodiment]

[0413] Hereinafter, a fifth embodiment of the main synthesis method (fifth synthesis method) will be described.

[0414] The inventors of the present application have previously reported on the effect of improving heat resistance due to the addition of barium to SiO₂Al₂O₃ synthesized by a precipitation method (see Patent Document 6 above). In the fifth embodiment, the goal was to investigate whether the same effect of improving heat resistance due to the addition of barium could be achieved in SiO₂Al₂O₃-containing sol solutions synthesized by the first to third synthesis methods described above.

[0415]

[19] Basic composition and examples of the fifth synthesis method

[0416] The fifth synthesis method, such as Figure 40 As shown in the process conversion diagram, the process comprises a step #51 of adding powder of a barium compound and stirring the SiO2Al2O3 sol solution synthesized by any one of the first, second and third synthesis methods (step #50) as a post-treatment.

[0417] In one embodiment of step #51, the barium compound is preferably any one of barium nitrate, barium hydroxide, barium chloride, and barium acetate. Furthermore, the barium hydroxide is barium hydroxide octahydrate, and the barium chloride is barium chloride dihydrate.

[0418] In the following description, the Ba-added SiO2Al2O3 obtained by drying and calcining the Ba-added SiO2Al2O3 sol solution synthesized in step #51 is appropriately expressed as Z%BaO-X%SiO2Al2O3, assuming that the SiO2 concentration (the mass concentration of SiO2 relative to SiO2Al2O3) is X mass% and the BaO concentration (the mass concentration of BaO relative to SiO2Al2O3) is Z mass%.

[0419] If the SiO2Al2O3 sol solution containing Ba added synthesized in step #51 is dried, a boehmite gel to which a barium compound (e.g., barium nitrate) and silicon dioxide are added is generated. Since the barium compound is added to the sol solution and stirred, it is dispersed in the gel after drying. Therefore, it can be considered that according to the fifth synthesis method, by adding a barium compound (barium nitrate) to the precipitate disclosed in the above-mentioned patent document 6, the barium compound is present in a highly dispersed state in the dried gel. In addition, if this boehmite gel is calcined at 1000°C, SiO2Al2O3 and BaO can be generated. These points can be explained later. Figure 41 The XRD patterns shown show that.

[0420] As an example of the fifth synthesis method (Example 11), the preparation of a 6.5% BaO-1% SiO2Al2O3 sol solution, which is used as a precursor for synthesizing the 6.5% BaO-1% SiO2Al2O3 sol solution exhibiting high heat resistance and having a SiO2 concentration of 1% by mass and a BaO concentration of 6.5% by mass, as described in Patent Document 6, will be described. In Example 11, in step #50, aluminum nitrate is used as the aluminum compound. A total of 80 g of a 1% SiO2Al2O3 2.5% sol is obtained through steps #11 to #15 of Example 1 of the first synthesis method. In step #51, 0.2386 g of barium nitrate is added to the obtained 1% SiO2Al2O3 2.5% sol, and the mixture is stirred at room temperature to prepare a 6.5% BaO-1% SiO2Al2O3 2.5% sol.

[0421] In Example 11, when barium hydroxide, barium chloride or barium acetate is added as a barium compound instead of barium nitrate, 0.2880 g of barium hydroxide octahydrate, 0.2230 g of barium chloride dihydrate or 0.2332 g of barium acetate is added to a total of 80 g of 1%SiO2Al2O32.5% sol, and the mixture is stirred at room temperature to prepare a 6.5%BaO-1%SiO2Al2O32.5% sol in the same manner.

[0422] As another example (Example 12) of the fifth synthesis method, the preparation of a 6.5% BaO-1% SiO₂Al₂O₃ sol solution similar to that of Example 11 will be described. In Example 12, sodium aluminate was used as the aluminum compound in step #50. A total of 80 g of a 1% SiO₂Al₂O₃ 2.5% sol was obtained through steps #21 to #25 of Example 4 of the second synthesis method. In step #51, 0.2386 g of barium nitrate was added to the obtained 1% SiO₂Al₂O₃ 2.5% sol, and the mixture was stirred at room temperature to prepare a 6.5% BaO-1% SiO₂Al₂O₃ 2.5% sol. In Example 12, as in Example 11, barium hydroxide, barium chloride, or barium acetate can be used as the barium compound instead of barium nitrate.

[0423]

[20] Heat resistance evaluation of the fifth synthesis method (1)

[0424] The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "main powder sample S7") obtained by drying and calcining 6.5% BaO-1% SiO2Al2O32.5% sol synthesized by Example 11 of the fifth synthesis method using aluminum nitrate as the aluminum compound and barium nitrate as the barium compound was evaluated.

[0425] As the main powder sample S7, the 6.5% BaO-1% SiO2Al2O3 2.5% sol obtained through step #50 of Example 11 of the fifth synthesis method (step #11 to step #15 of Example 1 of the first synthesis method) and step #51 was dried at 150°C, then pulverized into a powder, and sintered in air at 1000°C for 5 hours (initial heat treatment) to produce a 6.5% BaO-1% SiO2Al2O3 powder (main sample S7A). In addition, main sample S7B was produced by adding a first heat treatment of 1200°C for 5 hours to main sample S7A, and main sample S7C was produced by adding a second heat treatment of 1200°C for 30 hours to main sample S7A. In addition, the main powder sample S7 after drying at 150°C but before the initial heat treatment is referred to as main dried sample S7D (see below). Figure 41 ).

[0426] In Comparative Example C7, corresponding to Main Powder Sample S7, a 6.5% BaO-1% SiO₂Al₂O₃ 2.5% sol prepared by a precipitation method using aluminum nitrate as the aluminum compound instead of the fifth synthesis method was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce a 6.5% BaO-1% SiO₂Al₂O₃ powder (Comparative Sample C7A). Furthermore, Comparative Sample C7B, which was subjected to a first heat treatment at 1200°C for 5 hours, and Comparative Sample C7C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also prepared.

[0427] Table 11 below shows the specific surface areas (m 2 / g) and the specific surface areas (m 2 / g) were measured. In addition, for comparison and control, the specific surface areas (m2 / g) of the main samples S1A, S1B and S1C obtained by drying and calcining the SiO2 concentration of 1% by mass and the non-Ba-added SiO2Al2O3 sol solution synthesized by Example 1 of the first synthesis method described in "[4] Evaluation of heat resistance of the first synthesis method (1)" were obtained. 2 / g) (refer to Figure 7 ), and the specific surface areas (m 2 / g) (refer to Figure 8 ), which are also recorded in Table 11.

[0428]

Table 11

[0429]

[0430] As shown in Table 11, no significant difference in specific surface area was observed for the samples (main sample S7A, main sample S1A, comparative sample C7A, and comparative sample C1A) sintered at 1000°C for 5 hours (initial heat treatment), regardless of the synthesis method or the presence or absence of barium addition. However, for the samples (main samples S7B and S7C, main samples S1B and S1C, comparative samples C7B and C7C, and comparative samples C1B and C1C) subjected to the first and second heat treatments at 1200°C for 5 and 30 hours, an increase in specific surface area was observed with the addition of barium, regardless of the synthesis method. Furthermore, for the samples with barium added after the first and second heat treatments, main samples S7B and S7C, derived from the fifth synthesis method, exhibited higher specific surface areas than comparative samples C7B and C7C in each heat treatment.

[0431] exist Figure 41 , which are XRD patterns showing the crystal structures of the main sample S7A, the main sample S7B, the main sample S7C and the main drying sample S7D after and before the heat treatment. Figure 42 ] Shown in FIG are XRD patterns showing the crystal structures of comparative samples C7A, C7B, and C7C after each heat treatment.

[0432] First, in Figure 41 In the XRD pattern of the main dried sample S7D, the peak of barium nitrate appeared together with boehmite. As described above, it was confirmed that boehmite gel to which barium nitrate and silica were added was generated during the drying stage.

[0433] Depend on Figure 41 and Figure 42 In the barium-added main sample S7C and comparative sample C7C, which underwent a second heat treatment at 1200°C for 30 hours, the peak in the diffraction pattern for α-Al₂O₃ was significantly lower in the main sample S7C synthesized by the fifth synthesis method than in the comparative sample C7C synthesized by the precipitation method, indicating that the phase transition to the α phase was suppressed. Furthermore, in the barium-added main sample S7B and comparative sample C7B, which underwent a first heat treatment at 1200°C for 5 hours, no α phase formation was observed in the main sample S7B, but the formation of barium aluminate (monoaluminate: BaO·Al₂O₃, hexaaluminate: BaO·6Al₂O₃) was confirmed. This suggests that barium aluminate hinders the mass transfer of aluminum at high temperatures, thereby suppressing the phase transition to the α phase. In the fifth synthesis method, the addition of barium nitrate powder to the sol solution results in higher dispersibility of barium than in the precipitation method. As a result, it is believed that the formation of barium aluminate is faster than that of the α phase, effectively enhancing heat resistance.

[0434] From the above, it can be confirmed that according to the fifth synthesis method of adding barium to the SiO2Al2O3 sol solution, high heat resistance exceeding that of the precipitation method can be obtained.

[0435] Next, in Example 11, barium nitrate, barium hydroxide, barium chloride, and barium acetate were used as barium compounds to prepare main powder samples S7 (main sample S7A, main sample S7B, and main sample S7C). The specific surface area (m 2 As shown in Table 12, all four barium compounds exhibited high specific surface areas after the second heat treatment at 1200°C for 30 hours. Furthermore, they exhibited a higher specific surface area than the comparative sample C7C prepared by the precipitation method shown in Table 11. These results confirm that barium nitrate, barium hydroxide, barium chloride, and barium acetate are preferably used as barium compounds to be added to the SiO₂Al₂O₃-containing sol solution.

[0436]

Table 12

[0437]

[0438]

[21] Heat resistance evaluation of the fifth synthesis method (2)

[0439] The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "main powder sample S8") obtained by drying and calcining 6.5% BaO-1% SiO2Al2O3 2.5% sol synthesized by Example 12 of the fifth synthesis method using sodium aluminate as the aluminum compound was evaluated.

[0440] As main powder sample S8, a 6.5% BaO-1% SiO₂Al₂O₃ 2.5% sol obtained through step #50 of Example 12 of the fifth synthesis method (steps #21 to #25 of Example 4 of the second synthesis method) and step #51 was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce a 6.5% BaO-1% SiO₂Al₂O₃ powder (main sample S8A). Furthermore, main sample S8B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S8C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0441] In Comparative Example C8, corresponding to Main Powder Sample S8, a 2.5% sol containing 6.5% BaO and 1% SiO₂Al₂O₃ was prepared by a precipitation method using sodium aluminate as the aluminum compound, instead of the fifth synthesis method, and dried at 150°C. The sol was then pulverized into a powder form and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce a 6.5% BaO-1% SiO₂Al₂O₃ powder (Comparative Sample C8A). Furthermore, Comparative Sample C8B, which was subjected to a first heat treatment at 1200°C for 5 hours, and Comparative Sample C8C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also prepared.

[0442] Table 13 below shows the specific surface areas (m 2 / g) and the specific surface areas (m 2 / g) were measured. In addition, for comparison and control, the specific surface areas (m2) of the main samples S2A, S2B and S2C obtained by drying and calcining the SiO2 concentration 1 mass % non-Ba-added SiO2Al2O3 sol solution synthesized by Example 4 of the second synthesis method described in the above-mentioned "

[10] Evaluation of heat resistance of the second synthesis method" were obtained. 2 / g) measurement results ( Figure 18 Reference), and the specific surface areas (m 2 / g) (refer to Figure 19 ), which are also recorded in Table 13.

[0443]

Table 13

[0444]

[0445] As shown in Table 13, the samples (main sample S8A, main sample S2A, comparative sample C8A, and comparative sample C2A) sintered at 1000°C for 5 hours (initial heat treatment) showed a slight decrease in specific surface area due to the addition of barium, regardless of the synthesis method. However, the samples (main samples S7B and S7C, main samples S1B and S1C, comparative samples C7B and C7C, and comparative samples C1B and C1C) that underwent the first and second heat treatments at 1200°C for 5 and 30 hours, respectively, showed an increase in specific surface area due to the addition of barium, regardless of the synthesis method. Furthermore, for the samples with the addition of barium that underwent the second heat treatment, main sample S8C from the fifth synthesis method exhibited a higher specific surface area than comparative sample C8C in each heat treatment.

[0446] exist Figure 43 ] Shown in FIG are XRD patterns showing the crystal structures of the main sample S8A, the main sample S8B, and the main sample S8C after each heat treatment. Figure 44 ] Shown in FIG are XRD patterns showing the crystal structures of comparative samples C8A, C8B, and C8C after each heat treatment.

[0447] Depend on Figure 43 and Figure 44 It was confirmed that in the main sample S8C and comparative sample C8C with added barium, which were subjected to the second heat treatment at 1200°C for 30 hours, the peak of the diffraction pattern of α-Al2O3 in the main sample S8C synthesized by the fifth synthesis method was significantly lower than that in the comparative sample C8C synthesized by the precipitation method, and the phase transition to the α phase was suppressed. This is the same as the case of the main sample S7C and comparative sample C7C using aluminum nitrate as the aluminum compound (refer to Figure 41 and Figure 42 ).

[0448] From the above, it was confirmed that even when sodium aluminate was used as the aluminum compound, high heat resistance exceeding that of the precipitation method could be obtained according to the fifth synthesis method of adding barium to the SiO2Al2O3-containing sol solution.

[0449]

[22] Heat resistance evaluation of the fifth synthesis method (3)

[0450] In the heat resistance evaluations (1) and (2) of the fifth synthesis method described above, the heat resistance of the SiO2Al2O3 powders (main powder samples S7 and S8) obtained by drying and calcining the 6.5% BaO-1% SiO2Al2O3 2.5% sol synthesized by the fifth synthesis method using the first and second synthesis methods (first AC method) in step #50 were evaluated, and the effect of improving the heat resistance by adding barium to the SiO2Al2O3 sol solution was confirmed.

[0451] In this embodiment, the heat resistance evaluation of the SiO2Al2O3 powder obtained by drying and calcining the SiO2Al2O3 sol solution containing Ba added synthesized by the fifth synthesis method using the third synthesis method (second AC method) in step #50 was not performed. However, considering that in the heat resistance evaluation (1) and (2) of the third synthesis method mentioned above, it was confirmed that the main powder samples S3 and S4 obtained by the third synthesis method (second AC method) can obtain sufficient heat resistance equivalent to that of the main powder samples S1 and S2 obtained by the first and second synthesis methods (first AC method), and in the heat resistance evaluation (1) and (2) of the fourth synthesis method mentioned above, it was confirmed that the main powder samples S3 and S4 obtained by the fourth synthesis method using the first and third synthesis methods (first and second AC methods) in step #40 can obtain sufficient heat resistance. As for the effect of increasing the specific surface area (improving heat resistance) brought about by adding a specific additive (DMF) to any of the main powder samples S5 and S6, it can be considered that the SiO2Al2O3 obtained by drying and calcining the Ba-added SiO2Al2O3 sol solution synthesized by the fifth synthesis method using the third synthesis method (second AC method) in step #50 can achieve the effect of improving heat resistance by adding barium, just like the fifth synthesis method using the first and second synthesis methods (first AC method) in step #50 respectively.

[0452] [Sixth embodiment]

[0453] Hereinafter, a sixth embodiment of the main synthesis method (sixth synthesis method) will be described.

[0454]

[23] Basic composition and examples of the sixth synthesis method

[0455] The sixth synthesis method is equivalent to a synthesis method combining the fourth synthesis method and the fifth synthesis method, such as Figure 45 As shown in the process conversion diagram, for any one of the above-mentioned first, second and third synthesis methods (step #60), a step #61 is provided in which a specific additive and a barium compound are added to the SiO2Al2O3 sol solution synthesized by any one of the synthesis methods and the stirring is performed as a post-treatment.

[0456] Step #61 of the sixth synthesis method, like step #41 of the fourth synthesis method, serves as a countermeasure to the reduction in the total pore volume of the Al2O3 due to the surface tension of evaporating water during the drying process of the SiO2-Al2O3-containing sol solution synthesized by any of the first through third synthesis methods in step #60 to form a transparent gel. Second, like step #51 of the fifth synthesis method, it is designed to maximize the heat resistance-enhancing effect of adding barium. In other words, the sixth synthesis method aims to simultaneously achieve the two heat resistance-enhancing effects of adding a specific additive (EG or DMF) and a barium compound.

[0457] Therefore, in one embodiment of step #61, as in step #41 of the fourth synthesis method, ethylene glycol (EG) or N,N-dimethylformamide (DMF) is preferably used as the specific additive, and as in step #51 of the fifth synthesis method, any one of barium nitrate, barium hydroxide, barium chloride and barium acetate is preferably used as the barium compound.

[0458] In step #61, a specific additive and a barium compound are added to the SiO₂Al₂O₃-containing sol solution synthesized in step #60, followed by stirring, thereby synthesizing a SiO₂Al₂O₃-containing sol solution doped with the specific additive and barium. In step #61, the barium compound is first added to the SiO₂Al₂O₃-containing sol solution synthesized in step #60, followed by stirring, and then, in the same manner as the fifth synthesis method, a SiO₂Al₂O₃-containing sol solution doped with Ba is synthesized. Subsequently, the specific additive is added to the Ba-doped SiO₂Al₂O₃-containing sol solution, followed by stirring, in the same manner as the fourth synthesis method, thereby synthesizing a similar SiO₂Al₂O₃-containing sol solution doped with the specific additive and barium. In other words, as described in the fourth embodiment, a specific additive is added as a countermeasure against the reduction in the total pore volume of Al2O3 due to the surface tension of evaporated water during the process of drying the SiO2Al2O3-containing sol solution synthesized in step #60 to generate a transparent gel. Therefore, the timing of its addition can also be after the synthesis of the SiO2Al2O3-containing sol solution to which Ba is added.

[0459] As an embodiment of the sixth synthesis method (Example 13), according to the same procedure as Example 11 of the fifth synthesis method, in step #60, aluminum nitrate is used as the aluminum compound and steps #11 to #15 of Example 1 of the first synthesis method are carried out to obtain a total amount of 80 g of 1%SiO2Al2O32.5% sol. In step #61, 0.2386 g of barium nitrate is added to the obtained 1%SiO2Al2O32.5% sol. In addition, 3 mass% of the specific additive (EG or DMF) is added relative to the total amount of the sol solution after the addition of the specific additive, and the mixture is stirred at room temperature to prepare a 6.5%BaO-1%SiO2Al2O32.5% sol to which the specific additive is added.

[0460] As another embodiment of the sixth synthesis method (Example 14), according to the same procedure as Example 12 of the fifth synthesis method, in step #60, sodium aluminate is used as the aluminum compound, and a total of 80 g of 1%SiO2Al2O32.5% sol is obtained through steps #21 to #25 of Example 4 of the second synthesis method. In step #61, 0.2386 g of barium nitrate is added to the obtained 1%SiO2Al2O32.5% sol. In addition, 3 mass% of the specific additive (EG or DMF) is added relative to the total amount of the sol solution after adding the specific additive, and the mixture is stirred at room temperature to prepare a 6.5%BaO-1%SiO2Al2O32.5% sol to which the specific additive is added.

[0461]

[24] Heat resistance evaluation of the sixth synthesis method

[0462] The heat resistance of the SiO2Al2O3 powder obtained by drying and calcining a 6.5% BaO-1% SiO2Al2O3 2.5% sol added with DMF synthesized by Example 13 of the sixth synthesis method using aluminum nitrate as the aluminum compound (hereinafter collectively referred to as "main powder sample S9") and the heat resistance of the SiO2Al2O3 powder obtained by drying and calcining a 6.5% BaO-1% SiO2Al2O3 2.5% sol added with DMF synthesized by Example 14 of the sixth synthesis method using sodium aluminate as the aluminum compound (hereinafter collectively referred to as "main powder sample S10") were evaluated respectively.

[0463] As the main powder sample S9, the 6.5% BaO-1% SiO2Al2O32.5% sol added with DMF obtained through step #60 of Example 13 of the sixth synthesis method (step #11 to step #15 of Example 1 of the first synthesis method) and step #61 was dried at 150°C, then crushed into powder, and sintered (initial heat treatment) at 1000°C for 5 hours in air to produce 6.5% BaO-1% SiO2Al2O3 powder (main sample S9A).

[0464] As the main powder sample S10, the 6.5% BaO-1% SiO2Al2O32.5% sol added with DMF obtained through step #60 of Example 14 of the sixth synthesis method (step #21 to step #25 of Example 4 of the second synthesis method) and step #61 was dried at 150°C, then crushed into powder, and sintered (initial heat treatment) at 1000°C for 5 hours in air to produce 6.5% BaO-1% SiO2Al2O3 powder (main sample S10A).

[0465] Furthermore, Master Samples S9B and S10B were prepared by subjecting Master Samples S9A and S10A, respectively, to a first heat treatment at 1200°C for 5 hours. Master Samples S9C and S10C were also prepared by subjecting Master Samples S9A and S10A, respectively, to a second heat treatment at 1200°C for 30 hours. Furthermore, the DMF added to the 6.5% BaO-1% SiO₂Al₂O₃2.5% sol combusted during the initial heat treatment and was absent from Master Samples S9A-S9C and S10A-S10C after calcination.

[0466] Table 14 below shows the specific surface areas (m 2 / g) and the total pore volume of the main sample S9B (cm 3 / g) of the measurement results. In addition, for comparison and control, the specific surface areas (m2 / g) of the main samples S1A to S1C obtained by drying and calcining the SiO2 concentration 1 mass % non-Ba-added SiO2Al2O3 sol solution synthesized by Example 1 of the first synthesis method described in "[4] Evaluation of heat resistance of the first synthesis method (1)" were obtained. 2 / g) and the total pore volume of the main sample S1B (cm 3 / g) measurement results ( Figure 7and Table 3), and the specific surface areas (m2) of the main samples S7A to S7C obtained by drying and calcining the 6.5% BaO-1% SiO2Al2O32.5% sol synthesized by Example 11 of the fifth synthesis method as described in the above-mentioned "

[20] Evaluation of heat resistance of the fifth synthesis method (1)". 2 / g) and the total pore volume of the main sample S7B (cm 3 The measurement results of 100 g / kg (see Table 11) are also recorded in Table 14.

[0467]

Table 14

[0468]

[0469] Table 15 below shows the specific surface areas (m 2 / g) and the total pore volume of the main sample S10B (cm 3 / g) of the measurement results. In addition, for comparison and control, the specific surface areas (m2) of the main samples S2A to S2C obtained by drying and calcining the SiO2 concentration 1 mass % non-Ba-added SiO2Al2O3 sol solution synthesized by Example 4 of the second synthesis method described in the above "

[10] Evaluation of heat resistance of the second synthesis method" were 2 / g) and the total pore volume of the main sample S2B (cm 3 / g) (refer to Figure 20 ), and the specific surface areas (m 2 / g) and the total pore volume of the main sample S8B (cm 3 The measurement results of 3 (3 / g) are also recorded in Table 15.

[0470]

Table 15

[0471]

[0472] As shown in Table 14, regardless of the heat treatment, Master Samples S9A to S9C, which had both the specific additive and the barium compound added, exhibited higher specific surface areas than Master Samples S7A to S7C, which had only the barium compound added. Master Sample S9B, after the first heat treatment, showed an increase in the total pore volume ratio compared to Master Sample S7B. Furthermore, as shown in Table 15, Master Samples S10B and S10C, which had both the specific additive and the barium compound added after the first and second heat treatments, exhibited higher specific surface areas than Master Samples S8B and S8C, which had only the barium compound added. Master Sample S10B, after the first heat treatment, showed an increase in the total pore volume ratio compared to Master Sample S8B. These results confirm that, regardless of the aluminum compound used in preparing the aluminum solution, the addition of both the specific additive and the barium compound improves heat resistance compared to the addition of the barium compound alone.

[0473] Figure 46 Shown are XRD patterns showing the crystal structures of main samples S9A to S9C after each heat treatment. Figure 47 The XRD patterns of the crystal structures of the main samples S10A to S10C after each heat treatment are shown in FIG. Figure 46 and Figure 47 The XRD patterns of the main samples S9A to S9C and the main samples S10A to S10C are shown in FIG. Figure 41 and Figure 43 The XRD patterns of samples S7A-S7C and S8A-S8C, which were prepared with the addition of a barium compound alone, show some phase transition to the α-Al₂O₃ phase in samples S7C and S8C after a second heat treatment at 1200°C for 30 hours. However, no α-phase formation was observed in samples S9C and S10C, which were prepared with both the specific additive and the barium compound. In addition to the improved heat resistance achieved by the formation of Ba aluminate, the addition of the specific additive also suppresses the reduction in SiO₂Al₂O₃ pore volume, resulting in a high specific surface area and suppressed phase transition to the α-Al₂O₃ phase.

[0474] [Seventh embodiment]

[0475] The following describes an embodiment of a method for forming a porous alumina film using a SiO2Al2O3 sol solution synthesized by the first to sixth synthesis methods or a SiO2Al2O3 sol solution with added Ba (hereinafter appropriately referred to as the "main formation method").

[0476]

[25] Basic structure of the main forming method

[0477] Main forming method, such as Figure 48As shown in the process transition diagram, if roughly divided, it is composed of the following steps #71 to #74. First, in step #71, using any of the above-mentioned first to sixth synthesis methods, a SiO2Al2O3 sol solution (when any of the first to fourth synthesis methods are used) or a SiO2Al2O3 sol solution with added Ba (when the fifth or sixth synthesis method is used) is prepared (sol solution preparation step). Then, in step #72, the sol solution prepared in step #71 is applied to the surface of a predetermined substrate to form a coating film (coating step). Then, in step #73, the coating film formed in step #72 is dried (drying step), and in step #74, the coating film dried in step #73 is fired (firing step). As a result, a porous alumina film of SiO2Al2O3 film or SiO2Al2O3 film with added Ba is formed on the surface of the substrate.

[0478] The substrate used in step #72 can be made of a variety of materials and shapes, as long as it can maintain the coating film formed on the surface in step #72 through steps #72 to #74. In other words, any material or shape can serve as a support for the coating film. Therefore, since the SiO₂Al₂O₃ film or Ba-doped SiO₂Al₂O₃ film formed on the substrate surface has a high specific surface area, the substrate itself does not need to be porous. An example of a substrate used in the following examples is shown below.

[0479] 1) Granular alumina (activated): manufactured by Kanto Chemical (alpha-alkalinized by calcination at 1200°C for 5 hours. hereinafter referred to as "cicaAl").

[0480] 2) Diesel particulate filter made of silicon carbide (hereinafter referred to as "SiC-DPF").

[0481] 3) Silica filter: QR-100 manufactured by ADVANTEC

[0482] 4) Glass cloth: Nitto Bosho #2116

[0483] 5) Silica cloth: Made by NICHIAS (fired at 1000°C for 5 hours)

[0484] 6) Glass Plate

[0485]

[26] First embodiment of the main forming method (Example 15)

[0486] Following the same procedures as in Example 1 of the first synthesis method, two sol solutions, a 1% SiO₂Al₂O₃ 3.75% sol and a 3% SiO₂Al₂O₃ 3.75% sol, with SiO₂ concentrations of 1% and 3% by mass, were prepared. The five substrates described in 1) to 5) above were immersed in each sol solution for 10 minutes and then removed. After the substrates were impregnated with the sol solution, they were dried at 150°C for 30 minutes, resulting in a total of 10 dried samples. Each sol solution was used in an amount sufficient to completely immerse the substrate in the sol solution. In this Example 15, in the coating step #72, the coating film was formed by immersing the substrate in the sol solution. Furthermore, increasing the amount of SiO₂ loaded on each substrate surface can be achieved by repeating the aforementioned coating and drying steps. The substrate and coating film, which had undergone at least one coating and drying step, were fired at 1000°C for 5 hours to form porous alumina films with 1% SiO₂Al₂O₃ and 3% SiO₂Al₂O₃, respectively, on the surfaces of the respective substrates. However, if the substrate is glass cloth, firing at 1000°C for 5 hours would cause the substrate to melt, so firing at 500°C for 5 hours was used. This firing at 1000°C for 5 hours or 500°C for 5 hours corresponds to the initial heat treatment of the powder sample described in the heat resistance evaluation of the first to sixth synthesis methods, and is also referred to as the "initial heat treatment" in the main formation method.

[0487] Table 16 below shows the relationship between the number of coatings and the amount of 1% SiO₂Al₂O₃ loaded on the substrate surface after calcination at 1000°C for 5 hours for two examples of Example 15, where the substrates were cicaAl (1) above and silica cloth (5) above. The loading amount x (mass %) in Table 16 is given by the following formula (1). In formula (1), Wb represents the mass of the substrate (g), and Wt represents the total mass of the substrate and the coating film (g).

[0488] x=(Wt-Wb) / Wt…(1)

[0489] Table 16

[0490]

[0491] As shown in Table 16, the amount of 1% SiO2Al2O3 loaded on the substrate surface increases with the number of coatings. However, for cicaAl, where the substrate is composed of α-Al2O3, the increase in loading is minimal after the third coating.

[0492]

[27] Second embodiment of the main forming method (Example 16)

[0493] Following the same procedures as in Example 11 of the fifth synthesis method, a 2.5% 6.5% BaO-1% SiO₂Al₂O₃ sol was prepared. The three substrates (cicaAl, glass cloth, and silica cloth) described in 1), 4), and 5) were immersed in this sol solution for 10 minutes and then removed, following the same procedures as in Example 15. After the substrates were impregnated with the sol solution, they were dried at 150°C for 30 minutes. The substrates and the coated film, having undergone one or more coating and drying steps, were calcined at 1000°C for 5 hours, forming a porous alumina film composed of 6.5% BaO-1% SiO₂Al₂O₃ on the substrate surface. Since the coating, drying, and calcining steps are identical to those in Example 15, repeated descriptions are omitted.

[0494] exist Figure 49 In the figure, a field emission scanning microscope (FE-SEM) photograph of a porous alumina film of 6.5% BaO-1% SiO2Al2O3 formed on each surface of the glass cloth and silica cloth in Example 16 is shown. In this embodiment, the FE-SEM used is JSM-7001F manufactured by JEOL Ltd. Figure 49 As shown, it can be observed that the surfaces of the glass cloth and the silica cloth are uniformly coated with a porous alumina film.

[0495]

[28] Third embodiment of the main forming method (Example 17)

[0496] Following the same procedures as in Example 1 of the first synthesis method, a 1% SiO₂Al₂O₃ 2.5% sol and a 1% SiO₂Al₂O₃ 3.75% sol with different sol concentrations were prepared. The substrate (glass plate) described in step 6) above, cleaned with aqua regia, was immersed in each sol solution for 10 minutes, then removed and dried at 150°C for 30 minutes. The dried substrate and coating film were then calcined at 500°C for 5 hours to form a porous alumina film containing 1% SiO₂Al₂O₃ on the substrate surface.

[0497] exist Figure 50 In the figure, SEM photographs of the cross section and surface of the porous alumina film containing 1% SiO2Al2O3 formed by using two sol solutions containing 1% SiO2Al2O3 with different sol solution concentrations of Example 17 are shown. Figure 50 From the cross-sectional photographs, it can be seen that in any of the two sol solutions with different sol solution concentrations, the porous alumina film is formed in close contact with the glass plate. The thickness of the porous alumina film is 0.65 μm when the sol solution concentration is 2.5 mass %, and 1.2 μm when the sol solution concentration is 3.75 mass %. The results show that the thickness of the porous alumina film can be adjusted by the sol solution concentration. In addition, Figure 50The surface photographs confirm that a porous alumina film uniformly coats the glass plate surface regardless of the sol solution concentration. These results demonstrate that by using SiO₂Al₂O₃-containing sol solutions synthesized using the first to sixth synthesis methods or Ba-added SiO₂Al₂O₃-containing sol solutions, even flat surfaces can easily form a uniform, highly adherent porous alumina film.

[0498] Next, the verification results of the solution state of the sol solution prepared in step #71 of the main formation method and the adhesion of the coating film to the substrate surface are described. In step #71, according to the principles of Example 1 of the first synthesis method, the pH value of the slurry solution in step #15 was changed in three ways by pH adjustment treatment, and three solutions with the solution states of gel, sol, and precipitate were prepared. The gel and precipitate solutions were also thoroughly stirred to form a uniform solution. Then, a glass plate cleaned with aqua regia was immersed in these three solutions for 10 minutes, then removed and dried at 150°C for 30 minutes. The dried substrate and coating film were calcined at 500°C for 5 hours to form a porous alumina film of SiO2Al2O3 on the substrate surface.

[0499] When the solution is in a sol state, the porous alumina film formed is transparent. Similar to a glass plate, the pattern of the substrate can be visually confirmed, and the formation of a homogeneous porous alumina film with excellent adhesion can be confirmed. However, when the solution is in a gel state, the porous alumina film formed shows film peeling, and a homogeneous porous alumina film with excellent adhesion cannot be formed. In addition, when the solution is in a precipitate state, the surface of the porous alumina film becomes turbid, and the porous alumina film cannot be uniformly formed on the substrate surface. Therefore, it can be said that the optimal solution state for forming a homogeneous porous alumina film with excellent adhesion is the sol state.

[0500]

[29] Heat resistance evaluation of main forming method (1)

[0501] The heat resistance of the porous alumina films of 1% SiO2Al2O3 and 3% SiO2Al2O3 formed on the surfaces of the five substrates 1) to 5) above was evaluated in Example 15 of the main formation method according to the following method. Since it is difficult to separate the formed porous alumina film from the substrate and measure the specific surface area alone, the specific surface area Sa (m2) of the porous alumina film was calculated using the relationship shown in the following formula (2). 2 / g).

[0502] St=Sa×x / 100+Sb×(1-x / 100)…(2)

[0503] In formula (2), Sb is the specific surface area (m 2 / g), St is the specific surface area of ​​the entire sample of the substrate and the porous alumina membrane (m 2 / g), and x is the loading amount given by the above formula (1). The specific surface areas Sb and St are values ​​measured by the nitrogen adsorption BET method, similar to the specific surface area measurement method described in the heat resistance evaluation (1) of the first synthesis method.

[0504] Table 17 below shows the loading amount x (mass %) of 1% SiO2Al2O3 formed on the surfaces of the five substrates 1) to 5) after the initial heat treatment and the three specific surface areas St, Sa and Sb (m 2 / g), and the specific surface area Sc1 (m2) of the 1% SiO2Al2O3 powder obtained by drying and calcining (initial heat treatment) as a comparative example without coating the 1% SiO2Al2O3 3.75% sol prepared for each substrate in Example 15 on the substrate. 2 / g). In addition, the following Table 18 shows the loading amount x (mass %) of 3% SiO2Al2O3 formed on the surfaces of the five substrates after the initial heat treatment and the three specific surface areas St, Sa and Sb (m 2 / g), and the specific surface area Sc2 (m2) of the 3% SiO2Al2O3 powder obtained by drying and calcining (initial heat treatment) as a comparative example without applying the 3% SiO2Al2O3 3.75% sol prepared for each substrate in Example 15 to the substrate. 2 / g). In addition, since the specific surface area Sb of glass cloth and silica cloth cannot be measured by nitrogen adsorption BET method, it is 0 (m 2 / g).

[0505] Table 17

[0506]

[0507]

Table 18

[0508]

[0509] As shown in Tables 17 and 18, when the specific surface area Sa of the porous alumina film calculated by equation (2) is compared with the specific surface areas Sc1 and Sc2 of the SiO2Al2O3 powder of the comparative example, the specific surface areas are approximately the same. Therefore, it can be considered that the results of the heat resistance evaluation of the first to sixth synthesis methods described above are also applicable to the heat resistance evaluation of porous alumina films formed on the surfaces of various substrates. Therefore, it can be confirmed that by applying the SiO2Al2O3-containing sol solution or the Ba-added SiO2Al2O3-containing sol solution synthesized by the first to sixth synthesis methods to the surfaces of various substrates, a SiO2Al2O3 film or a Ba-added SiO2Al2O3 film with a high specific surface area can be formed.

[0510]

[30] Heat resistance evaluation of main forming method (2)

[0511] According to the following procedures, the heat resistance of the 6.5% BaO-1% SiO2Al2O3 porous alumina film (hereinafter collectively referred to as "main film sample Sf") formed on the surface of the two substrates (cicaAl, silica cloth) mentioned above 1) and 5) in Example 16 of the main formation method was evaluated.

[0512] As the main film samples Sf, the two substrates described above were subjected to an initial heat treatment (1000°C for 5 hours) using the main formation method of Example 16 to produce porous alumina films (main samples SfA) composed of 6.5% BaO and 1% SiO₂Al₂O₃. Furthermore, master samples SfB and SfC were prepared by subjecting the two main sample SfA samples to a first heat treatment at 1200°C for 5 hours and a second heat treatment at 1200°C for 30 hours.

[0513] Table 19 below shows the specific surface area St and specific surface area Sa of the main samples SfA to SfC prepared on the surfaces of the above two types of substrates (cicaAl and silica cloth) for each substrate.

[0514]

Table 19

[0515]

[0516] As shown in Table 19, the specific surface areas Sa of main samples SfA to SfC are close to the specific surface areas of main samples S7A to S7C (main powder sample S7, obtained by drying and calcining a 6.5% BaO-1% SiO₂Al₂O₃ 2.5% sol synthesized by the fifth synthesis method) shown in Table 11 above. These results confirm that Ba-doped SiO₂Al₂O₃ films with high specific surface areas can be formed by applying Ba-doped SiO₂Al₂O₃ sol solutions synthesized by the fifth or sixth synthesis methods to the surfaces of various substrates.

[0517] Figure 51 The figure shows the XRD patterns of the crystal structures of the main samples SfA to SfC after each heat treatment, the substrate being silica cloth. The loading amount x is 6.2 mass%. Figure 51 The XRD pattern of the substrate without Ba-added SiO2Al2O3 film is also shown for reference. Figure 51 As shown, a γ-Al2O3 peak was detected during sintering at 1000°C for 5 hours (initial heat treatment), while a cristobalite peak was detected during sintering at 1200°C for 5 and 30 hours (first and second heat treatments) as the SiO2 in the substrate crystallized. However, no α-Al2O3 peak was detected in the main sample SfC sintered at 1200°C for 30 hours, confirming that the addition of barium maintains the heat resistance of Al2O3 even at high temperatures.

[0518] [Eighth Embodiment]

[0519] Hereinafter, an eighth embodiment (seventh synthesis method) of the main synthesis method will be described.

[0520]

[31] Basic composition of the seventh synthesis method

[0521] The seventh synthesis method, such as Figure 52 As shown in the process transition diagram, the process generally comprises the following steps: a step of preparing a SiO2Al2O3-containing sol solution by any of the first, second, and third synthesis methods (step #80); a step of drying the SiO2Al2O3-containing sol solution prepared in step #80 to prepare SiO2Al2O3 powder (step #81); and a step of adding water to the SiO2Al2O3 powder and stirring to prepare a SiO2Al2O3-containing sol solution having a desired sol concentration (step #82). In one embodiment, the drying treatment in step #81 is preferably performed at, for example, 150°C. Hereinafter, the sol solution obtained in step #80 will be referred to as the "first sol," and the sol solution obtained in step #82 will be referred to as the "second sol."

[0522] The seventh synthesis method has the following advantage: by adjusting the amount of water added in step #82 relative to the mass of the SiO2Al2O3 powder obtained in step #81, the sol solution concentration of the re-prepared SiO2Al2O3 sol solution can be easily controlled.

[0523] Step #80 is the same as Step #40, #50, and #60 in the fourth, fifth, and sixth synthesis methods. Therefore, in the fourth, fifth, and sixth synthesis methods, the specific additive (EG or DMF) or the barium compound or both added to the SiO2Al2O3 sol solution prepared in Step #40, #50, or #60, in the seventh synthesis method, as Figure 53 As shown, the SiO2Al2O3 sol solution (first sol) prepared in step #80 can be added in step #83 before the drying process in step #81. Figure 54 As shown, the addition of the specific additive and / or barium compound can also be carried out in step #84 to the SiO2Al2O3 sol solution (second sol) prepared again in step #81.

[0524]

[32] Example of the seventh synthesis method

[0525] [32.1] Examples 18 and 19

[0526] Hereinafter, an example (Example 18) of steps #80 to #82 will be described in which a SiO2Al2O3 sol solution containing SiO2 at a SiO2 concentration of 1% by mass is synthesized using aluminum nitrate as the aluminum compound.

[0527] In Example 18, as an example, a SiO₂Al₂O₃ sol solution with a SiO₂ concentration of 1% by mass was synthesized using the first synthesis method in step #80. In step #80 of Example 18, the TEOS solution and aluminum nitrate solution, each with the same concentration as used in steps #12 and #13 of Example 1 of the first synthesis method, were increased to 1.5 times their respective amounts and then autoclaved in the same manner as in Example 1. This yielded a total of 80 g of a SiO₂Al₂O₃ sol solution (first sol) with a SiO₂ concentration of 1% by mass and a sol solution concentration of 3.75% by mass. This sol solution concentration was 1.5 times the 2.5% by mass in Example 1. In step #81, this sol solution was dried at 150°C to obtain 3.0 g of 1% SiO₂Al₂O₃ powder. Next, in step #82, 3.0 g of 1% SiO2Al2O3 powder obtained in step #81 was added to 80 g of water and stirred at room temperature for 30 minutes to obtain a total of 83 g of a 1% SiO2Al2O3 sol solution (second sol). The sol solution concentration was 3.61%.

[0528] In step #80 of Example 18, the SiO2 concentration can be adjusted by changing the mixing ratio of the TEOS solution and the aluminum nitrate solution, as described in the basic composition of the first synthesis method [1] above.

[0529] In an example (Example 19) in which sodium aluminate is used as the aluminum compound instead of aluminum nitrate, a SiO₂Al₂O₃ sol solution having a desired SiO₂ concentration is synthesized in step #80 using the second or third synthesis method described above. By carrying out steps #81 and #82 in the same manner as in Example 18, a SiO₂Al₂O₃ sol solution (second sol) having the desired sol solution concentration and SiO₂ concentration can be obtained.

[0530] The solution state of the 1% SiO2Al2O3 sol solution (second sol) obtained in Example 18 is the same as the solution state of the 1% SiO2Al2O3 sol solution synthesized in Example 1 of the first synthesis method and Example 5 of the third synthesis method.

[0531] [32.2] Examples 20 and 21 (Addition of specific additives and barium compounds)

[0532] Next, two examples (Examples 20 and 21) of synthesizing SiO2Al2O3 sol solutions with a SiO2 concentration of 1% by mass, to which specific additives and barium compounds were added, are described. As in Example 18, aluminum nitrate was used as the aluminum compound.

[0533] In Example 20, Figure 53 As shown, in step #80, a 1% SiO₂Al₂O₃ sol solution (first sol) having a sol concentration of 3.75% by mass was prepared in the same manner as in Example 18. In step #83, 0.3579 g of barium nitrate as a barium compound and 3% by mass of DMF as a specific additive relative to the total amount of the sol solution after addition were added to the first sol and stirred, thereby obtaining a 6.5% BaO-1% SiO₂Al₂O₃ 3.75% sol solution containing DMF. Subsequently, in step #81, the sol solution prepared in step #83 was dried at 150°C in the same manner as in Example 18, obtaining a 6.5% BaO-1% SiO₂Al₂O₃ powder containing DMF. Next, in step #82, according to the same procedure as in Example 18, the 6.5% BaO-1% SiO2Al2O3 powder added with DMF obtained in step #81 is added to 80 g of water and stirred at room temperature for 30 minutes to obtain a 6.5% BaO-1% SiO2Al2O3 sol solution added with DMF (second sol).

[0534] In Example 21, Figure 54As shown, in steps #80 to #82, the same treatment as in Example 18 was performed to obtain a total of 83 g of a 1% SiO₂Al₂O₃-containing sol solution (second sol). Next, in step #84, 0.3579 g of barium nitrate as a barium compound and 3% by mass of DMF as a specific additive relative to the total amount of the sol solution after addition were added to the second sol, and the mixture was stirred to obtain a 6.5% BaO-1% SiO₂Al₂O₃-containing sol solution containing DMF.

[0535] In Examples 20 and 21, the timing of adding the specific additive and barium compound differed from that of Example 18 during steps #80-#82. In Example 20, the specific additive and barium compound were added to the first sol after step #80, while in Example 21, the specific additive and barium compound were added to the second sol after step #82. In both Examples 20 and 21, the added specific additive and barium compound powders completely dissolved in the second sol, resulting in a uniform 6.5% BaO-1% SiO₂Al₂O₃ sol solution containing DMF.

[0536] [32.3] Example 22 (Preparation of High Concentration Sol Solution)

[0537] To increase the amount of material loaded onto the support, the seventh synthesis method was investigated for increasing the concentration of the sol solution. The following describes an example (Example 22) of steps #80 to #82, using aluminum nitrate as the aluminum compound to synthesize a SiO₂Al₂O₃-containing sol solution with a SiO₂ concentration of 1% by mass and a sol solution concentration of 10.31% by mass.

[0538] In Example 22, Figure 55 As shown, there are two steps #80 (step #80A and step #80B). In Example 22, the two steps #80 correspond to steps #11 to #15 of Example 1 of the first synthesis method. Furthermore, the SiO2 concentration of the SiO2Al2O3-containing sol solutions synthesized in both steps #80 is the same 1% by mass, and therefore the mixing ratio of the TEOS solution to the aluminum nitrate solution is the same. However, because the sol solution concentrations of the synthesized SiO2Al2O3-containing sol solutions are different, the amounts of TEOS solution and aluminum nitrate solution used in steps #80A and #80B are different.

[0539] In step #80A, the same treatment as in Example 18 was performed to obtain a total of 80 g of a 1% SiO₂Al₂O₃ 3.75% sol (first sol). Subsequently, in step #81, the sol solution was dried at 150°C to obtain 3.0 g of a 1% SiO₂Al₂O₃ powder. Separately, in step #80B, the TEOS solution and aluminum nitrate solution, each with the same concentration as used in steps #12 and #13 of Example 1 of the first synthesis method, were autoclaved in the same manner as in Example 1 to obtain a total of 80 g of a SiO₂Al₂O₃-containing sol solution (first sol) with a SiO₂ concentration of 1% by mass and a sol solution concentration of 8% by mass. Step #80A and step #80B can be performed in either order, or simultaneously. Next, in step #82, 2.47 g of the 1% SiO₂Al₂O₃ powder obtained in step #81 was weighed and added to 80 g of the 1% SiO₂Al₂O₃ 8% sol (first sol) obtained in step #80B, followed by stirring. This yielded a SiO₂Al₂O₃-containing sol solution (second sol) with a SiO₂ concentration of 1% by mass and a sol solution concentration of 10.31% by mass. The amount (mixing ratio) of the 1% SiO₂Al₂O₃ powder added in step #82 was set to 3% by mass relative to the sol solution after addition. From the 2.47 g of 1% SiO₂Al₂O₃ powder (boehmite), 2.10 g of 1% SiO₂Al₂O₃ (alumina) was obtained. Therefore, the sol solution concentration obtained in step #82 was 10.31% by mass (= (80 g × 8% by mass + 2.1 g) / 82.47 g).

[0540] As described above, in step #82 of Example 18, the 1% SiO2Al2O3 powder obtained in step #81 was added to 80g of water. In contrast, in step #82 of Example 22, the 1% SiO2Al2O3 powder obtained in step #81 was added to 80g of the 1% SiO2Al2O3 8% sol obtained in step #80B. This allows the SiO2Al2O3-containing sol solution (second sol) obtained in step #82 to be highly concentrated. When aluminum nitrate is used as the aluminum compound, as in the case of Figure 4 As shown in Figures 1 and 2, it is difficult to achieve a sol solution concentration of 10 mass % or more in the first or third synthesis method. However, it was confirmed that the sol solution concentration can be increased to 10 mass % or more by applying the seventh synthesis method.

[0541]

[33] Heat resistance evaluation of the seventh synthesis method (1)

[0542] The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "main powder sample S11") obtained by drying and calcining a SiO2Al2O3 sol solution (second sol) with SiO2 concentrations of 1 mass% and 3 mass% synthesized by Example 18 of the seventh synthesis method using aluminum nitrate as the aluminum compound (was evaluated).

[0543] As the main powder sample S11, a SiO₂Al₂O₃ sol solution having a SiO₂ concentration of 1% by mass and 3% by mass, obtained through steps #80 to #82 of Example 18, was dried at 150°C, then pulverized into a powder, and sintered in air at 1000°C for 5 hours (initial heat treatment) to produce SiO₂Al₂O₃ powder (main sample S11A). Furthermore, main sample S11B was produced by subjecting main sample S11A to a first heat treatment at 1200°C for 5 hours, and main sample S11C was produced by subjecting main sample S11A to a second heat treatment at 1200°C for 30 hours.

[0544] Table 20 below shows the specific surface areas (m2) of the main samples S11A to S11C prepared with SiO2 concentrations of 1% by mass and 3% by mass. 2 For comparison and control, the measurement results of the specific surface areas of the main samples S1A to S1C with SiO2 concentrations of 1% by mass and 3% by mass produced by the first synthesis method (Example 1) and the measurement results of the specific surface areas of the main samples S3A to S3C with SiO2 concentrations of 1% by mass and 3% by mass produced by the third synthesis method (Example 5) are also recorded in Table 20.

[0545] Table 20

[0546]

[0547] In addition, Figure 56 The XRD patterns of the crystal structures of the main samples S11A, S11B and S11C with a SiO2 concentration of 1% by mass after heat treatment are shown. In addition, the XRD patterns of the crystal structures of the main samples S1A, S1B and S1C with a SiO2 concentration of 1% by mass produced by the first synthesis method, and the main samples S3A, S3B and S3C with a SiO2 concentration of 1% by mass produced by the third synthesis method after heat treatment are shown. Figure 9 and Figure 26 middle.

[0548] From the measurement results shown in Table 20, it can be seen that the sample produced by the seventh synthesis method has the same specific surface area as the samples produced by the first synthesis method and the third synthesis method. Figure 56The XRD pattern of the sample prepared by the seventh synthesis method shown in FIG. Figure 9 and Figure 26 The XRD patterns of the samples produced by the first synthesis method and the third synthesis method shown in FIG20 show the same peaks. If the measurement results shown in Table 20 are also considered, it can be confirmed that the samples produced by the first, third and seventh synthesis methods have the same physical properties.

[0549]

[34] Heat resistance evaluation of the seventh synthesis method (2)

[0550] The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "main powder sample S12") obtained by drying and calcining a SiO2Al2O3 sol solution (second sol) with SiO2 concentrations of 1 mass% and 3 mass% synthesized by Example 19 of the seventh synthesis method using sodium aluminate as the aluminum compound was evaluated.

[0551] As the main powder sample S12, a SiO2Al2O3 sol solution containing 1% and 3% SiO2 concentrations, obtained through steps #80 to #82 of Example 19, was dried at 150°C, then pulverized into a powder, and sintered in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (main sample S12A). Furthermore, main sample S12B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S12C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0552] Table 21 below shows the specific surface areas (m2) of the main samples S12A to S12C prepared with SiO2 concentrations of 1% by mass and 3% by mass. 2 For comparison and control, the measurement results of the specific surface areas of the main samples S2A to S2C with SiO2 concentrations of 1% by mass and 3% by mass produced by the second synthesis method (Example 4) and the measurement results of the specific surface areas of the main samples S4A to S4C with SiO2 concentrations of 1% by mass and 3% by mass produced by the third synthesis method (Example 6) are also recorded in Table 21.

[0553] Table 21

[0554]

[0555] In addition, Figure 57Shown in FIG are XRD patterns of the crystal structures of the main samples S12A, S12B, and S12C having a SiO2 concentration of 1% by mass after each heat treatment. In addition, XRD patterns of the crystal structures of the main samples S2A, S2B, and S2C having a SiO2 concentration of 1% by mass produced by the second synthesis method, and the main samples S4A, S4B, and S4C having a SiO2 concentration of 1% by mass produced by the third synthesis method after each heat treatment are shown in FIG. Figure 18 and Figure 30 middle.

[0556] From the measurement results shown in Table 21, it can be seen that the sample produced by the seventh synthesis method has a specific surface area that is equal to or greater than that of the sample produced by the second synthesis method and the third synthesis method. Figure 57 The XRD pattern of the sample prepared by the seventh synthesis method shown in FIG. Figure 18 and Figure 30 The XRD patterns of the samples produced by the second and third synthesis methods shown in FIG21 show the same peaks. If the measurement results shown in Table 21 are also considered, it can be confirmed that the samples produced by the second, third and seventh synthesis methods have the same physical properties.

[0557]

[35] Heat resistance evaluation of the seventh synthesis method (3)

[0558] The heat resistance of two types of 6.5% BaO-1% SiO2Al2O3 powders added with DMF (hereinafter collectively referred to as "main powder sample S13" and "main powder sample S14") obtained by drying and calcining 6.5% BaO-1% SiO2Al2O3 sol solutions added with a specific additive (DMF) synthesized by Examples 20 and 21 of the seventh synthesis method using aluminum nitrate as the aluminum compound (hereinafter collectively referred to as "main powder sample S13" and "main powder sample S14") were evaluated.

[0559] As main powder sample S13, a 6.5% BaO-1% SiO₂Al₂O₃ sol solution (second sol) containing DMF and obtained through steps #80, #83, #81, and #82 of Example 20 was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce DMF-added BaO-SiO₂Al₂O₃ powder (main sample S13A). Furthermore, main sample S13B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S13C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0560] As main powder sample S14, a 6.5% BaO-1% SiO₂Al₂O₃ sol solution (second sol) containing DMF added thereto, obtained through steps #80 to #82 and #84 of Example 21, was dried at 150°C, then pulverized into a powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce DMF-added BaO-SiO₂Al₂O₃ powder (main sample S14A). Furthermore, main sample S14B, which was subjected to a first heat treatment at 1200°C for 5 hours, and main sample S14C, which was subjected to a second heat treatment at 1200°C for 30 hours, were also produced.

[0561] Table 22 below shows the specific surface areas (m2) of the main samples S13A to S13C and the main samples S14A to S14C having a SiO2 concentration of 1% by mass. 2 / g), and the total pore volume (cm2) of the main samples S13B and S14B with a SiO2 concentration of 1% by mass 3 For comparison and control, the measurement results of the specific surface areas of the main samples S11A to S11C (see Table 20) and the total pore volume of the main sample S11B produced by Example 18 of the seventh synthesis method without the addition of the specific additive (DMF) and the barium compound and having a SiO2 concentration of 1% by mass, and the measurement results of the specific surface areas of the main samples S9A to S9C and the total pore volume of the main sample S9B (see Table 14) produced by the sixth synthesis method (Example 13) with the addition of the specific additive (DMF) and the barium compound and having a SiO2 concentration of 1% by mass are also recorded in Table 22.

[0562] Table 22

[0563]

[0564] In addition, Figure 58 Shown in FIG are XRD patterns of the crystal structures of the main sample S13A, main sample S13B and main sample S13C after each heat treatment, each of which has a SiO2 concentration of 1% by mass. Figure 59 Shown in the figure are XRD patterns of the crystal structures of the main sample S14A, main sample S14B and main sample S14C after heat treatment, each of which has a SiO2 concentration of 1% by mass. In addition, XRD patterns of the crystal structures of the main sample S11A, main sample S11B and main sample S11C after heat treatment, each of which has a SiO2 concentration of 1% by mass, produced by Example 18 of the seventh synthesis method, and XRD patterns of the crystal structures of the main sample S9A, main sample S9B and main sample S9C after heat treatment, each of which has a SiO2 concentration of 1% by mass, produced by the sixth synthesis method (Example 13), are shown in FIG. Figure 56 and Figure 46 middle.

[0565] As shown in Table 22, the main powder sample S11 prepared in Example 18 of the seventh synthesis method without adding DMF and barium compound has a reduced specific surface area after the first and second heat treatments at 1200°C. This indicates that Figure 56 In the XRD spectrum of the main powder sample S11 to which DMF and barium compounds were not added, the aluminum oxide was completely alpha-ized after the first and second heat treatments at 1200°C. In contrast, the main powder samples S13 and S14 produced by Examples 20 and 21 of the seventh synthesis method had a significantly suppressed decrease in specific surface area after the first and second heat treatments at 1200°C. Compared with the main powder sample S11 to which DMF and barium compounds were not added, it can be seen that the specific surface area and total pore volume after the first and second heat treatments increased due to the addition of DMF and barium compounds. In addition, this is also consistent with the fact that Figure 58 and Figure 59 In the XRD patterns of the main powder samples S13 and S14 shown, alpha formation was suppressed after the first and second heat treatments at 1200°C.

[0566] In addition, as shown in Table 22, the main powder samples S13 and main powder samples S14 produced by Examples 20 and 21 of the seventh synthesis method showed the same specific surface area and total pore volume as the main powder sample S9 produced by the sixth synthesis method (Example 13), confirming that the addition of DMF and barium compounds played an effective role.

[0567]

[36] Heat resistance evaluation of the seventh synthesis method (4)

[0568] The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "main powder sample S15") obtained by drying and calcining a SiO2Al2O3 sol solution (second sol) synthesized by Example 22 of the seventh synthesis method using aluminum nitrate as the aluminum compound and having a SiO2 concentration of 1 mass% and a sol solution concentration of 10.31 mass% was evaluated.

[0569] As the main powder sample S15, a SiO₂Al₂O₃ sol solution containing 1% by mass of SiO₂ and 10.31% by mass of sol solution concentration, obtained through steps #80 (#80A, #80B) to #82 of Example 22, was dried at 150°C, then pulverized into a powder, and sintered in air at 1000°C for 5 hours (initial heat treatment) to produce SiO₂Al₂O₃ powder (main sample S15A). Furthermore, main sample S15B was produced by subjecting main sample S15A to a first heat treatment at 1200°C for 5 hours, and main sample S15C was produced by subjecting main sample S15A to a second heat treatment at 1200°C for 30 hours.

[0570] Table 23 below shows the specific surface areas (m2) of the main samples S15A to S15C obtained using the SiO2Al2O3 sol solution with a concentration of 10.31% by mass synthesized in Example 22 of the seventh synthesis method. 2 For comparison, the specific surface area measurements of the main samples S1A to S1C obtained using a sol solution containing SiO₂Al₂O₃ at a concentration of 2.5% by mass synthesized by the first synthesis method (Example 1) are also recorded in Table 23.

[0571] Table 23

[0572]

[0573] As shown in Table 23, even with the sol solution concentration of 10% by mass or higher achieved using Example 22 of the seventh synthesis method, the sol solution still exhibited heat resistance comparable to that achieved when synthesizing the SiO₂Al₂O₃-containing sol solution using the first synthesis method. This confirms that the seventh synthesis method is an effective means for producing high-concentration sols.

[0574] In addition, as a preferred embodiment, in the sol solution preparation process (step #71) of the main formation method described in the above-mentioned seventh embodiment, the seventh synthesis method can also be used instead of any one of the first to sixth synthesis methods to prepare a SiO2Al2O3 sol solution or a SiO2Al2O3 sol solution with added Ba.

[0575] [Modifications of the First to Eighth Embodiments]

[0576] The main synthesis method and the main formation method have been described in detail above through the first to eighth embodiments and examples. However, the SiO2 concentration, sol solution concentration, amount of specific additives, and amount of barium compound used in the examples (Examples 1 to 22) of the above embodiments are merely examples, and the main synthesis method and the main formation method may be modified as appropriate to achieve the desired effect.

[0577] Industrial applicability

[0578] The present invention is applicable to the synthesis of SiO2Al2O3-containing sol solutions, which are used to form porous alumina with added silicon dioxide on the surfaces of various substrates, and is also applicable to the formation of heat-resistant porous alumina films.

Claims

1. A method for synthesizing a sol solution, characterized in that A method for synthesizing a SiO2Al2O3 sol solution for forming porous alumina to which silicon dioxide is added, comprising the following steps: A process for preparing an alkoxysilane solution containing alkoxysilane, water, alcohol and inorganic acid; A process for preparing an aluminum solution by dissolving an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate in water; A step of precipitating a precipitate having a silicon compound adsorbed on aluminum hydroxide in a mixed solution of the alkoxysilane solution and the aluminum solution; The process of filtering and separating the precipitate from the mixed solution, and washing the filtered and separated precipitate with water to prepare a precipitate cake; The process of adding water to the precipitated cake to prepare a slurry solution, adjusting the pH of the slurry solution, and then subjecting the slurry solution to an autoclave treatment to prepare the SiO2Al2O3-containing sol solution in which sol particles having silica bound to boehmite particles are dispersed. By the pH adjustment treatment of the slurry solution, the pH value of the slurry solution is controlled within a specific pH range in which the solution state of the SiO2Al2O3-containing sol solution after the autoclave treatment becomes a sol state. By adjusting the amounts of the alkoxysilane and the aluminum compound and the amount of water added to the precipitate cake, the concentration of the prepared sol solution represented by the SiO2Al2O3 content relative to the total mass of the SiO2Al2O3-containing sol solution is controlled to a concentration below a specific concentration at which the SiO2Al2O3-containing sol solution after the autoclave treatment becomes a sol state. The specific concentration and the specific pH range vary according to the SiO 2 concentration defined as the mass concentration of SiO 2 relative to SiO 2 Al 2 O 3 in the prepared SiO 2 Al 2 O 3 -containing sol solution.

2. The method for synthesizing the sol solution according to claim 1, wherein In the step of separating the precipitate, When the aluminum compound is any one of aluminum nitrate, aluminum chloride, and aluminum sulfate, the mixed solution is heated under reflux and then subjected to pH adjustment to coprecipitate the precipitate. When the aluminum compound is sodium aluminate, the aluminum solution is heated to reflux, subjected to pH adjustment treatment, and then mixed with the alkoxysilane solution to prepare the mixed solution, in which the precipitate of the silicon compound adsorbed on the precipitate of aluminum hydroxide precipitated during the pH adjustment treatment is precipitated.

3. The method for synthesizing the sol solution according to claim 1 or 2, wherein: When the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, the specific pH range is within the range of 2.8 to 7.8, and when the aluminum compound is sodium aluminate, the specific pH range is within the range of 1.0 to 6.

2.

4. The method for synthesizing the sol solution according to claim 1 or 2, wherein: In the process of preparing the SiO2Al2O3 sol solution, The treatment temperature of the autoclave treatment is controlled to a specific treatment temperature within a range of 100° C. to 200° C., The treatment time of the autoclave treatment is controlled within a specific time range in which the solution state after the autoclave treatment becomes a sol state, The specific time range is within the range of more than 1 hour and less than 100 hours based on the specific processing temperature, the SiO2Al2O3 content in the prepared SiO2Al2O3-containing sol solution, and the SiO2 concentration change defined as the mass concentration of SiO2 relative to SiO2Al2O3 in the prepared SiO2Al2O3-containing sol solution.

5. A method for synthesizing a sol solution, characterized in that A method for synthesizing a SiO2Al2O3 sol solution for forming porous alumina to which silicon dioxide is added, comprising the following steps: A process for preparing an alkoxysilane solution containing alkoxysilane, water, alcohol and inorganic acid; A process for preparing an aluminum solution by dissolving an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate in water; A step of precipitating aluminum hydroxide in the aluminum solution; The step of filtering and separating the precipitate from the aluminum solution, and washing the filtered and separated precipitate with water to prepare a precipitate cake; A step of adding water to the precipitated cake to prepare a slurry solution, adjusting the pH of the slurry solution, and then subjecting the slurry solution to an autoclave treatment to prepare an Al2O3-containing sol solution in which boehmite particles are dispersed as sol particles; The step of adding the alkoxysilane solution to the Al2O3-containing sol solution to prepare the SiO2Al2O3-containing sol solution in which sol particles having silicon dioxide bonded to boehmite particles are dispersed. By the pH adjustment treatment of the slurry solution, the pH value of the slurry solution is controlled within a specific pH range so that the solution state of the Al2O3-containing sol solution after the autoclave treatment becomes a sol state. By adjusting the amount of the raw material of the aluminum compound and the amount of water added to the precipitate cake, the concentration of the sol solution represented by the Al2O3 content after preparation relative to the total mass of the Al2O3-containing sol solution is controlled to be below a specific concentration at which the solution state of the Al2O3-containing sol solution after the autoclave treatment becomes a sol state.

6. The method for synthesizing the sol solution according to claim 5, wherein: In the step of precipitating the precipitate, the aluminum solution is heated under reflux and then subjected to pH adjustment treatment to precipitate the precipitate.

7. The method for synthesizing the sol solution according to claim 5 or 6, characterized in that: When the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, the specific pH range is within the range of 3.8 to 7.8, and when the aluminum compound is sodium aluminate, the specific pH range is within the range of 2.0 to 6.

2.

8. The method for synthesizing the sol solution according to claim 5 or 6, characterized in that: In the process of preparing the Al2O3 sol solution, The treatment temperature of the autoclave treatment is controlled to a specific treatment temperature within a range of 100° C. to 200° C., The treatment time of the autoclave treatment is controlled within a specific time range in which the solution state after the autoclave treatment becomes a sol state, The specific time range is within a range of 1 hour to 100 hours, depending on the specific treatment temperature and the Al 2 O 3 content in the prepared Al 2 O 3 -containing sol solution.

9. The method for synthesizing a sol solution according to any one of claims 1, 2, 5 or 6, characterized in that: The alkoxysilane is tetraethoxysilane (TEOS).

10. The method for synthesizing a sol solution according to any one of claims 1, 2, 5 or 6, characterized in that: The method further comprises the step of adding a barium compound to the SiO2Al2O3-containing sol solution prepared in the step of preparing the SiO2Al2O3-containing sol solution to prepare a Ba-added SiO2Al2O3-containing sol solution.

11. The method for synthesizing a sol solution according to claim 10, wherein: The method further comprises the step of adding an organic solvent having a higher boiling point than water and a lower surface tension than water to the Ba-added SiO2Al2O3 sol solution prepared in the step of preparing the Ba-added SiO2Al2O3 sol solution.

12. The method for synthesizing a sol solution according to any one of claims 1, 2, 5 or 6, characterized in that: There is also a process for preparing a Ba-added SiO2Al2O3 sol solution by adding an organic solvent having a higher boiling point than water and a lower surface tension than water and a barium compound to the SiO2Al2O3 sol solution prepared in the process of manufacturing the SiO2Al2O3 sol solution.

13. The method for synthesizing a sol solution according to any one of claims 1, 2, 5 or 6, characterized in that: The method further comprises the step of adding an organic solvent having a higher boiling point than water and a lower surface tension than water to the SiO2Al2O3-containing sol solution prepared in the step of preparing the SiO2Al2O3-containing sol solution.

14. The method for synthesizing a sol solution according to claim 10, wherein: The barium compound is at least one selected from the group consisting of barium nitrate, barium hydroxide, barium chloride, and barium acetate.

15. The method for synthesizing a sol solution according to claim 11, characterized in that: The barium compound is at least one selected from the group consisting of barium nitrate, barium hydroxide, barium chloride, and barium acetate.

16. The method for synthesizing a sol solution according to claim 12, wherein: The barium compound is at least one selected from the group consisting of barium nitrate, barium hydroxide, barium chloride, and barium acetate.

17. The method for synthesizing a sol solution according to claim 11, wherein: The organic solvent is ethylene glycol or N,N-dimethylformamide.

18. The method for synthesizing a sol solution according to claim 12, wherein: The organic solvent is ethylene glycol or N,N-dimethylformamide.

19. The method for synthesizing a sol solution according to claim 13, wherein: The organic solvent is ethylene glycol or N,N-dimethylformamide.

20. A method for forming a porous alumina film, characterized in that: The process is as follows: A step of preparing a SiO2Al2O3-containing sol solution or a Ba-added SiO2Al2O3-containing sol solution as a final sol solution synthesized by the sol solution synthesis method according to any one of claims 1 to 19; The process of coating the sol solution on the surface of the substrate; a step of drying the coating film of the sol solution; The dried sol solution coating film is then fired.

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