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

Abstract

Provided is a method for synthesizing a sol solution for forming a porous alumina film having excellent adhesiveness to various substrate surfaces, high heat resistance and a high specific surface area.　A SiO2Al2O3-containing sol solution is prepared by separately preparing an alkoxysilane solution and an aluminum solution in advance, precipitating a precipitate comprising a silicon compound adsorbed on aluminum hydroxide in a mixed solution of the alkoxysilane solution and the aluminum solution, washing the precipitate filtrated off from the mixed solution with water to produce a precipitate cake, adding water to the precipitate cake to prepare a slurry solution, and subjecting the slurry solution to a pH adjustment treatment and subsequently to an autoclave treatment. By the pH adjustment treatment of the slurry solution, the pH value of the slurry solution is controlled so as to fall within a specified pH range in which the solution state of the SiO2Al2O3-containing sol solution after the autoclave treatment becomes a sol state. The sol solution is suitable for forming a porous alumina film having excellent adhesiveness to various substrate surfaces, high heat resistance and a high specific surface area.

Description

[Technical field]

[0001] The present invention relates to a method for synthesizing a SiO2Al2O3-containing sol solution for forming silica-doped porous alumina, and a method for forming a heat-resistant porous alumina membrane. [Background technology]

[0002] Porous alumina materials having a large specific surface area, such as γ-alumina, are useful as catalyst supports for supporting catalytic substances, filters, and the like, and efforts have been made to improve their properties (see, for example, Patent Documents 1 to 5, etc.). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2004-203654 A [Patent Document 2] International Publication No. 2014 / 051091 [Patent Document 3] International Publication No. 2012 / 096386 [Patent Document 4] International Publication No. 2013 / 111457 [Patent Document 5] JP 2009-061383 A [Patent Document 6] International Publication No. 2021 / 192752 Summary of the Invention [Problem to be solved by the invention]

[0004] A catalyst carrier needs to suppress a decrease in specific surface area and a change in composition due to a hydration reaction under harsh conditions such as high temperature, high pressure, and the presence of steam. The inventors of the present application have revealed that Al2O3 with added SiO2 or Ba maintains a high specific surface area even when fired at 1200°C for several tens of hours, and does not produce α-Al2O3 due to the transformation of Al2O3 (see Patent Document 6 above). Such a highly heat-resistant alumina powder can be formed into pellets or the like and used as a catalyst carrier for reactions that require high heat resistance, such as steam reforming reactions.

[0005] However, catalyst supports molded into pellets have an increased pressure loss under high SV conditions. An example of an efficient catalyst surface layer under high SV conditions is an automobile exhaust gas purification catalyst in which alumina layers are formed by wash-coating a support component such as alumina on a cordierite honeycomb, and precious metals are supported on the alumina layers. However, the alumina layers obtained by existing technologies are prone to sintering under high temperature, high pressure, and steam atmospheres such as those used in steam reforming reactions, and catalytic activity is significantly reduced.

[0006] The present invention has been made in consideration of the above-mentioned problems, and an object of the present invention is to provide a method for forming a porous alumina film having excellent adhesion, high heat resistance, and a large specific surface area on the surface of various substrates (e.g., cordierite, quartz glass, α-Al2O3, etc.), and to provide a method for synthesizing a sol solution that serves as an alumina precursor for producing such a porous alumina film. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into the preparation conditions for the sol solution serving as the above-mentioned alumina precursor, and into methods for forming the above-mentioned alumina film on the surfaces of various substrates, and as a result have found a method for forming a highly functional catalyst support layer on the surface of a substrate in terms of adhesion, heat resistance, and specific surface area, leading to the invention described below.

[0008] The method for synthesizing a sol solution according to the present invention is a method for synthesizing a sol solution containing SiO2Al2O3 for forming porous alumina doped with silica, comprising the steps of: preparing an alkoxysilane solution containing an alkoxysilane, water, an alcohol, and an inorganic acid; preparing an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate, and water; a step of precipitating a precipitate in which a silicon compound is adsorbed on aluminum hydroxide in a mixed solution of the alkoxysilane solution and the aluminum solution; filtering the precipitate from the mixed solution and washing the filtered precipitate with water to prepare a precipitate cake; adding water to the precipitate cake to prepare a slurry solution, adjusting the pH of the slurry solution, and then autoclaving the slurry solution to prepare the SiO2Al2O3-containing sol solution; A first feature of the present invention is that 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 is in a sol state by the pH adjustment treatment of the slurry solution.

[0009] According to the above-mentioned first characteristic of the method for synthesizing a sol solution, a SiO2Al2O3-containing sol solution containing highly dispersed sol particles in which silica is bonded to boehmite particles is obtained by the autoclave treatment in the step of preparing the SiO2Al2O3-containing sol solution. Since the sol solution is in a sol state, when the sol solution is applied to a substrate surface and dried, a gel film of a homogeneous coating film in which the sol particles are uniformly dispersed is obtained, and by firing the gel film, a silica-added porous alumina film with high heat resistance and large specific surface area, excellent adhesion, can be formed on the surface of various substrates.

[0010] In a preferred embodiment of the method for synthesizing a sol solution according to the first aspect, in the step of precipitating the precipitate, When the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, the mixed solution is heated and refluxed, and then a pH adjustment treatment is performed to co-precipitate the precipitate, When the aluminum compound is sodium aluminate, the aluminum solution is heated to reflux, and then subjected to a pH adjustment treatment, and then mixed with the alkoxysilane solution to prepare the mixed solution, and a precipitate having the silicon compound adsorbed thereon is precipitated in the mixed solution on the precipitate of aluminum hydroxide that has precipitated during the pH adjustment treatment.

[0011] Furthermore, in a preferred embodiment of the method for synthesizing a sol solution according to the first aspect, the specific pH range varies depending on a SiO2 concentration, which is defined as a mass concentration of SiO2 relative to SiO2Al2O3 in the SiO2Al2O3-containing sol solution after preparation, and is within a range of 2.8 to 7.8 when the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, and is within a range of 1.0 to 6.2 when the aluminum compound is the sodium aluminate.

[0012] Furthermore, in a preferred embodiment of the method for synthesizing a sol solution according to the first aspect, in the step of preparing the SiO2Al2O3-containing sol solution, The processing temperature of the autoclave treatment is controlled to a specific processing temperature within a range of 100° C. or more and 200° C. or less, 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 varies depending on the specific treatment temperature, the SiO2Al2O3 content in the SiO2Al2O3-containing sol solution after preparation, and the SiO2 concentration, defined as the mass concentration of SiO2 relative to SiO2Al2O3 in the SiO2Al2O3-containing sol solution after preparation, and is within the range of 1 hour or more and 100 hours or less.

[0013] Further, the present invention provides a method for synthesizing a sol solution containing SiO2Al2O3 for forming a porous alumina doped with silica, comprising the steps of: preparing an alkoxysilane solution containing an alkoxysilane, water, an alcohol, and an inorganic acid; preparing an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate, and water; allowing an aluminum hydroxide precipitate to form in the aluminum solution; filtering the precipitate from the aluminum solution and washing the filtered precipitate with water to produce a precipitate cake; adding water to the precipitate cake to prepare a slurry solution, adjusting the pH of the slurry solution, and then autoclaving the slurry solution to prepare an Al2O3-containing sol solution; adding the alkoxysilane solution to the Al2O3-containing sol solution to prepare the SiO2Al2O3-containing sol solution; A second feature of the present invention is that the pH value of the slurry solution is controlled within a specific pH range in which the solution state of the Al2O3-containing sol solution after the autoclave treatment is in a sol state by the pH adjustment treatment of the slurry solution.

[0014] According to the synthesis method of the sol solution of the second feature, an Al2O3-containing sol solution containing highly dispersed boehmite sol particles is obtained by autoclaving in the step of preparing the Al2O3-containing sol solution, and after adding the alkoxysilane solution in which the alkoxysilane obtained in the step of preparing the alkoxysilane solution is uniformly dissolved to the Al2O3-containing sol solution, a hydrolysis reaction proceeds at a certain temperature and over time to generate silica particles, and a SiO2Al2O3-containing sol solution containing highly dispersed sol particles in which silica particles are adsorbed to the boehmite sol particles is obtained in the same manner as the synthesis method of the sol solution of the first feature. Since the solution state of the sol solution is a sol state, when the sol solution is applied to a substrate surface and dried, a gel film of a homogeneous coating film in which the sol particles are uniformly dispersed is obtained, and by firing the gel film, a porous alumina film containing silica with high heat resistance and high specific surface area with excellent adhesion can be formed on the surface of various substrates.

[0015] In a preferred embodiment of the method for synthesizing a sol solution according to the second aspect, in the step of precipitating the precipitate, the aluminum solution is heated under reflux, and then a pH adjustment treatment is performed to precipitate the precipitate.

[0016] In a preferred embodiment of the method for synthesizing a sol solution according to the second aspect, the specific pH range is within a range of 3.8 to 7.8 when the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, and is within a range of 2.0 to 6.2 when the aluminum compound is sodium aluminate.

[0017] In a preferred embodiment of the method for synthesizing a sol solution according to the second aspect, in the step of preparing the Al2O3-containing sol solution, The processing temperature of the autoclave treatment is controlled to a specific processing temperature within a range of 100° C. or more and 200° C. or less, 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 varies depending on the specific treatment temperature and the Al2O3 content in the Al2O3-containing sol solution after preparation, and is within the range of 1 hour to 100 hours.

[0018] Furthermore, in a preferred embodiment of the method for synthesizing a sol solution according to the first or second aspect, the alkoxysilane is tetraethoxysilane (TEOS).

[0019] Furthermore, in addition to the first or second feature, the method for synthesizing a sol solution according to the present invention has a third feature in that it 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, thereby preparing a Ba-added SiO2Al2O3-containing sol solution.

[0020] According to the above-mentioned third characteristic of the method for synthesizing a sol solution, the addition of barium can further improve the heat resistance of the porous alumina film obtained by applying the sol solution to the surface of a substrate, drying and firing the same.

[0021] Furthermore, in addition to the third feature, the method for synthesizing a sol solution according to the present invention has a fourth feature in that it further comprises a step of adding an organic solvent having a boiling point higher than that of water and a surface tension lower than that of water to the Ba-doped SiO2Al2O3-containing sol solution prepared in the step of preparing the Ba-doped SiO2Al2O3-containing sol solution.

[0022] Furthermore, in addition to the first or second feature, the method for synthesizing a sol solution according to the present invention has a fifth feature in that it further comprises a step of preparing a Ba-added SiO2Al2O3-containing sol solution by adding an organic solvent having a boiling point higher than that of water and a surface tension lower than that of water and a barium compound to the SiO2Al2O3-containing sol solution prepared in the step of preparing the SiO2Al2O3-containing sol solution.

[0023] According to the method for synthesizing a sol solution having the fourth or fifth characteristic described above, the addition of barium can further improve the heat resistance of the porous alumina film obtained by applying the sol solution to a substrate surface, drying and firing the same, and the addition of an organic solvent having a higher boiling point than water and a lower surface tension than water can suppress the reduction in the total pore volume that occurs when the sol solution is dried, thereby further improving the specific surface area of ​​the porous alumina film.

[0024] Furthermore, in addition to the first or second feature, the method for synthesizing a sol solution according to the present invention has a sixth feature in that it further comprises a step of adding an organic solvent having a boiling point higher than that of water and a surface tension lower than that of water to the SiO2Al2O3-containing sol solution prepared in the step of preparing the SiO2Al2O3-containing sol solution.

[0025] According to the method for synthesizing a sol solution having the sixth characteristic described above, the addition of an organic solvent having a higher boiling point and a lower surface tension than water suppresses the reduction in the total pore volume that occurs when the sol solution is dried, and the specific surface area of ​​the porous alumina film obtained by applying the sol solution to a substrate surface, drying and firing the same can be further improved.

[0026] In a preferred embodiment of the method for synthesizing a sol solution according to the third to fifth aspects, the barium compound is at least one selected from barium nitrate, barium hydroxide, barium chloride, and barium acetate.

[0027] In a preferred embodiment of the method for synthesizing a sol solution according to the fourth to sixth aspects, the organic solvent is ethylene glycol or N,N-dimethylformamide. blood The compound is dimethylformamide.

[0028] Furthermore, a method for forming a porous alumina film according to the present invention is a method for forming a porous alumina film, comprising the steps of: Any of the above first to sixth features preparing a sol solution containing SiO2Al2O3 or a sol solution containing Ba-added SiO2Al2O3, which is a sol solution finally synthesized by the synthesis method of the sol solution; applying the sol solution to a surface of a substrate; drying the coating film of the sol solution; and baking the dried coating film of the sol solution. Effect of the Invention

[0029] According to the method for synthesizing a sol solution of the present invention, a SiO2Al2O3-containing sol solution containing highly dispersed sol particles in which silica is bonded to boehmite particles can be obtained. By applying the sol solution to a substrate surface, drying and firing the surface, a silica-added porous alumina film with excellent adhesion, high heat resistance and large specific surface area can be formed on the surface of various substrates. [Brief description of the drawings]

[0030] [Figure 1] A process transition diagram showing an overview of a synthesis method (first synthesis method) for a SiO2Al2O3-containing sol solution in the first embodiment. [Diagram 2] TEM images of four types of SiO2Al2O3-containing sol solutions in the solution state: sol, gel, first half sol, and precipitate. [Diagram 3] A scatter diagram showing the relationship between the solution state of the SiO2Al2O3-containing sol solution synthesized by the first synthesis method, and the pH value and SiO2 concentration of the slurry solution. [Figure 4] A scatter diagram showing the relationship between the solution state, sol solution concentration, and SiO2 concentration of the SiO2Al2O3-containing sol solution synthesized using the first synthesis method. [Diagram 5] A scatter diagram showing the relationship between the solution state of the SiO2Al2O3-containing sol solution synthesized by the first synthesis method and the heating conditions (treatment temperature, treatment time) of the autoclave treatment. [Figure 6] A scatter diagram showing the relationship between the solution state of the SiO2Al2O3-containing sol solution synthesized by the first synthesis method, the sol solution concentration, and the autoclave treatment time. [Figure 7]Graph showing the measurement results of the specific surface area of ​​the powder sample S1 prepared by drying and sintering the SiO2Al2O3-containing sol solution synthesized by the first synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 8] Graph showing the measurement results of the specific surface area after the initial heat treatment, the first heat treatment, and the second heat treatment of Comparative Example C1 produced by the precipitation method. [Figure 9] XRD pattern diagrams showing the crystal structure of powder sample S1 with a SiO2 concentration of 1 mass% produced by drying and sintering the SiO2Al2O3-containing sol solution synthesized by the first synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 10] XRD pattern diagrams showing the crystal structure of Comparative Example C1 having an SiO2 concentration of 1 mass% produced by a precipitation method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 11] XRD pattern diagram showing the crystal structure of powder sample S1 (dried sample S1D) before the initial heat treatment by drying the SiO2Al2O3-containing sol solution synthesized by the first synthesis method. [Figure 12] XRD pattern diagram showing the crystal structure of Comparative Example C1 (Comparative Dry Sample C1D) before initial heat treatment [Figure 13] BJH plot showing the pore distribution of the powder sample S1 and the comparative sample C1B after the first heat treatment with an SiO2 concentration of 3 mass%. [Figure 14] BJH plot showing the pore distribution of the powder sample S1 and the comparative example C1 after the first heat treatment with an SiO2 concentration of 10 mass%. [Figure 15] A process transition diagram showing an overview of a method for synthesizing a SiO2Al2O3-containing sol solution (second synthesis method) in the second embodiment. [Figure 16] A scatter diagram showing the relationship between the solution state of the SiO2Al2O3-containing sol solution synthesized by the second synthesis method, and the pH value and SiO2 concentration of the slurry solution. [Figure 17] A scatter diagram showing the relationship between the solution state, sol solution concentration, and SiO2 concentration of the SiO2Al2O3-containing sol solution synthesized using the second synthesis method. [Figure 18]XRD pattern diagrams showing the crystal structure of powder sample S2 with a SiO2 concentration of 1 mass% produced by drying and sintering the SiO2Al2O3-containing sol solution synthesized by the second synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 19] XRD pattern diagrams showing the crystal structure of Comparative Example C2 having an SiO2 concentration of 1 mass% produced by a precipitation method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 20] Graph showing the measurement results of the specific surface area of ​​the powder sample S2 prepared by drying and sintering the SiO2Al2O3-containing sol solution synthesized by the second synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 21] Graph showing the measurement results of the specific surface area after the initial heat treatment, the first heat treatment, and the second heat treatment of Comparative Example C2 produced by the precipitation method. [Figure 22] A process transition diagram showing an overview of a method for synthesizing a SiO2Al2O3-containing sol solution (third synthesis method) in the third embodiment. [Figure 23] Graph showing the measurement results of the specific surface area after the initial heat treatment of the present powder sample S1, the present powder sample S3, and the comparative example C1, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the first synthesis method, the third synthesis method (Example 5), and the precipitation method, respectively. [Figure 24] Graph showing the measurement results of the specific surface area after the first heat treatment of the present powder sample S1, the present powder sample S3, and the comparative example C1, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the first synthesis method, the third synthesis method (Example 5), and the precipitation method, respectively. [Diagram 25] Graph showing the measurement results of the specific surface area after the second heat treatment of the present powder sample S1, the present powder sample S3, and the comparative example C1, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the first synthesis method, the third synthesis method (Example 5), and the precipitation method, respectively. [Figure 26] XRD pattern diagrams showing the crystal structure of powder sample S3 with a SiO2 concentration of 1 mass% produced by drying and sintering the SiO2Al2O3-containing sol solution synthesized by the third synthesis method (Example 5) after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 27]Graph showing the measurement results of the specific surface area after the initial heat treatment of the present powder sample S2, the present powder sample S4, and the comparative example C2, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the second synthesis method, the third synthesis method (Example 6), and the precipitation method, respectively. [Figure 28] Graph showing the measurement results of the specific surface area after the first heat treatment of powder sample S2, powder sample S4, and comparative example C2, which were prepared by drying and firing SiO2Al2O3-containing sol solutions synthesized by the second synthesis method, the third synthesis method (Example 6), and the precipitation method, respectively. [Figure 29] Graph showing the measurement results of the specific surface area after the second heat treatment of the present powder sample S2, the present powder sample S4, and the comparative example C2, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the second synthesis method, the third synthesis method (Example 6), and the precipitation method, respectively. [Diagram 30] XRD pattern diagrams showing the crystal structure of powder sample S4 with a SiO2 concentration of 1 mass% produced by drying and sintering the SiO2Al2O3-containing sol solution synthesized by the third synthesis method (Example 6) after the initial heat treatment, the first heat treatment, and the second heat treatment. [Diagram 31] A process transition diagram showing an overview of a synthesis method (fourth synthesis method) for a SiO2Al2O3-containing sol solution in the fourth embodiment. [Diagram 32] BJH plot showing the pore distribution after the first heat treatment of powder sample S5 to which specific additives EG and DMF with a SiO2 concentration of 3 mass% were added, and powder sample S1 to which no specific additives were added. [Diagram 33] BJH plot showing the pore distribution after the first heat treatment of powder sample S5 with specific additives EG and DMF added separately at a SiO2 concentration of 10 mass%, and powder sample S1 with no specific additive added. [Diagram 34] Graph showing the measurement results of the specific surface area after the initial heat treatment of the powder samples S5, S11, and C1 prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the fourth synthesis method (Example 7), the fourth synthesis method (Example 9), and the precipitation method, respectively. [Diagram 35]Graph showing the measurement results of the specific surface area after the first heat treatment of the powder sample S5, the powder sample S11, and the comparative example C1, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the fourth synthesis method (Example 7), the fourth synthesis method (Example 9), and the precipitation method, respectively. [Diagram 36] Graph showing the measurement results of the specific surface area after the second heat treatment of the powder sample S5, the powder sample S11, and the comparative example C1, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the fourth synthesis method (Example 7), the fourth synthesis method (Example 9), and the precipitation method, respectively. [Figure 37] Graph showing the measurement results of the specific surface area after the initial heat treatment of the powder samples S6, S12, and C2 prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the fourth synthesis method (Example 8), the fourth synthesis method (Example 10), and the precipitation method, respectively. [Figure 38] Graph showing the measurement results of the specific surface area after the first heat treatment of powder sample S6, powder sample S12, and comparative example C2, which were prepared by drying and firing SiO2Al2O3-containing sol solutions synthesized by the fourth synthesis method (Example 8), the fourth synthesis method (Example 10), and a precipitation method, respectively. [Figure 39] Graph showing the measurement results of the specific surface area after the second heat treatment of the powder sample S6, the powder sample S12, and the comparative example C2, which were prepared by drying and firing the SiO2Al2O3-containing sol solutions synthesized by the fourth synthesis method (Example 8), the fourth synthesis method (Example 10), and the precipitation method, respectively. [Diagram 40] A process transition diagram showing an overview of a synthesis method (fifth synthesis method) for a Ba-added SiO2Al2O3-containing sol solution in the fifth embodiment. [Diagram 41] XRD pattern diagrams showing the crystal structure of powder sample S7 with a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass% produced by drying and sintering the Ba-added SiO2Al2O3-containing sol solution synthesized by the fifth synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Diagram 42] XRD pattern diagrams showing the crystal structure of Comparative Example C7, which has a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass%, produced by a precipitation method, after the initial heat treatment, the first heat treatment, and the second heat treatment. [Diagram 43] XRD pattern diagrams showing the crystal structure of powder sample S8 with a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass% produced by drying and sintering the Ba-added SiO2Al2O3-containing sol solution synthesized by the fifth synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Diagram 44] XRD pattern diagrams showing the crystal structure of Comparative Example C8, which has a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass%, produced by a precipitation method, after the initial heat treatment, the first heat treatment, and the second heat treatment. [Diagram 45] A process transition diagram showing an overview of a synthesis method (sixth synthesis method) for a Ba-added SiO2Al2O3-containing sol solution in the sixth embodiment. [Diagram 46] XRD pattern diagrams showing the crystal structure of powder sample S9 with a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass% prepared by drying and firing the Ba-added SiO2Al2O3-containing sol solution synthesized by the sixth synthesis method (Example 13) after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 47] XRD pattern diagrams showing the crystal structure of powder sample S10 having a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass% produced by drying and sintering the Ba-added SiO2Al2O3-containing sol solution synthesized by the sixth synthesis method (Example 14) after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 48] A process transition diagram showing an overview of a method for forming a porous alumina film in the seventh embodiment (this forming method) [Figure 49] FE-SEM photograph of 6.5%BaO-1%SiO2Al2O3 porous alumina membrane formed on the surface of glass cloth and silica cloth [Figure 50] FE-SEM images of the cross section and surface of a porous alumina film of 1% SiO2Al2O3 formed on the surface of a glass plate using two types of sol solutions containing 1% SiO2Al2O3, with sol solution concentrations of 2.5 mass% and 3.75 mass%. [Figure 51] XRD pattern diagram showing the crystal structure of 6.5%BaO-1%SiO2Al2O3 formed on the surface of the silica cloth and the silica cloth alone after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 52] A process transition diagram showing an overview of a synthesis method (seventh synthesis method) for a SiO2Al2O3-containing sol solution in the eighth embodiment. [Figure 53] A process transition diagram showing an overview of an example of a method for synthesizing a Ba-added SiO2Al2O3-containing sol solution in the eighth embodiment (Example 20 of the seventh synthesis method) [Figure 54] A process transition diagram showing an overview of an example of a method for synthesizing a Ba-added SiO2Al2O3-containing sol solution in the eighth embodiment (Example 21 of the seventh synthesis method) [Figure 55] A process transition diagram showing an overview of an example of a method for synthesizing a sol solution containing SiO2Al2O3 at a high sol solution concentration in the eighth embodiment (Example 22 of the seventh synthesis method) [Figure 56] XRD pattern diagrams showing the crystal structure of the powder sample S11 having a SiO2 concentration of 1 mass% produced by drying and sintering the SiO2Al2O3-containing 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. [Figure 57] XRD pattern diagrams showing the crystal structure of the powder sample S12 having a SiO2 concentration of 1 mass% produced by drying and sintering the SiO2Al2O3-containing 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. [Figure 58] XRD pattern diagrams showing the crystal structure of the powder sample S13 having a SiO2 concentration of 1 mass% prepared by drying and sintering the Ba-added SiO2Al2O3-containing sol solution synthesized in Example 20 of the seventh synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. [Figure 59] XRD pattern diagrams showing the crystal structure of the powder sample S14 having a SiO2 concentration of 1 mass% prepared by drying and sintering the Ba-added SiO2Al2O3-containing sol solution synthesized in Example 21 of the seventh synthesis method after the initial heat treatment, the first heat treatment, and the second heat treatment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a method for synthesizing a SiO2Al2O3-containing sol solution according to the present invention (hereinafter, appropriately referred to as "the present synthesis method") and a method for forming a porous alumina film will be described in detail with reference to the drawings.

[0032] [First embodiment] A first embodiment of the present synthesis method (first synthesis method) will be described below.

[0033] [1] Basic structure of the first synthesis method As shown in the process transition diagram of FIG. 1, the first synthesis method is roughly divided into the following steps #11 to #15.

[0034] First, an alkoxysilane solution containing an 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 does not matter which step #11 or step #12 is 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 in which a silicon compound is adsorbed on aluminum hydroxide is precipitated (step #13). Subsequently, the precipitate obtained in step #13 is filtered out from the mixed solution, and the filtered precipitate is washed with water to prepare a precipitate cake (step #14). Subsequently, water is added to the precipitate cake obtained in step #14 to prepare a slurry solution, and the 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 sol solution containing SiO2Al2O3 is synthesized.

[0035] In step #15, as described below, aluminum hydroxide (Al(OH)3) in the slurry solution is partially dehydrated under the temperature and pressure of autoclave treatment to produce boehmite (AlOOH), and a SiO2Al2O3-containing sol solution is synthesized in which sol particles in which silica is bonded to the boehmite particles are present in a highly dispersed state.

[0036] Hereinafter, the synthesis method in which a SiO2Al2O3-containing sol solution is synthesized after autoclave treatment, like 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 in the case where the aluminum compound is selected from aluminum nitrate, aluminum chloride, and aluminum sulfate.

[0037] In step #11, the alkoxysilane is preferably a tetraalkoxysilane. Furthermore, the tetraalkoxysilane is preferably selected from tetramethoxysilane, tetraethoxysilane, tetraisopropoxysilane, and tetra-n-butoxysilane, and in the embodiment described below, tetraethoxysilane (TEOS) is preferably used. As the alcohol, methanol, ethanol, n-propanol, isopropanol, etc. are used, and in the embodiment described below, ethanol is preferably used. As the inorganic acid, hydrochloric acid, nitric acid, etc. are used, and in the embodiment described below, hydrochloric acid is preferably used.

[0038] The mass concentration of SiO2 relative to SiO2Al2O3 in the SiO2Al2O3-containing sol solution prepared in step #15 (expressed in mass%, hereinafter simply referred to as "SiO2 concentration") is determined by the amount of alkoxysilane in the alkoxysilane solution prepared in step #11, the amount of aluminum compound 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 both solutions is adjusted in step #13 for the amounts of each of steps #11 and #12.

[0039] In one embodiment of step #13, the mixed solution is heated to reflux, and then ammonia water is added dropwise to the mixed solution to adjust the pH and stir. The heating to reflux and pH adjustment promote hydrolysis of the mixed solution, and aluminum hydroxide and silicon compounds are coprecipitated.

[0040] In one embodiment of step #15, the amount of water added to the precipitate cake is adjusted to control the sol solution concentration (mass%), which is the SiO2Al2O3 content relative to the total mass of the SiO2Al2O3-containing sol solution after synthesis, to a specific concentration or less at which the solution state after autoclaving becomes a sol state, and the pH value of the slurry solution is adjusted to within a specific pH range at which the solution state after autoclaving becomes a sol state.

[0041] In this embodiment, the total mass of the SiO2Al2O3-containing sol solution after synthesis is kept constant relative to the capacity of the autoclave used for the autoclave treatment, so the concentration of the sol solution is controlled by adjusting the amounts of alkoxysilane and aluminum compound charged in steps #11 and #12 and the amount of water added to the precipitate cake in step #15.

[0042] As described below, the specific concentration varies depending on the SiO2 concentration and the heating conditions of the autoclave treatment (treatment temperature, treatment time), and the specific pH range varies depending on the SiO2 concentration within the range of 2.8 to 7.8.

[0043] 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 within a specific time range in which the solution state after autoclave treatment becomes a sol state according to the specific treatment temperature, where the specific time range is within the range of 1 hour to 100 hours.

[0044] [2] Example of the first synthesis method Hereinafter, an example of steps #11 to #15 for synthesizing a sol solution containing SiO2Al2O3 with a SiO2 concentration of 1 mass % will be described. In the following explanation, for convenience of explanation, SiO2Al2O3 with a SiO2 concentration of X mass % will be expressed as X%SiO2Al2O3.

[0045] Example 1 using aluminum nitrate as the aluminum compound, Example 2 using aluminum chloride, and Example 3 using aluminum sulfate will be described below in order.

[0046] [2.1] Example 1 (Aluminum compound: aluminum nitrate) In step #11, tetraethoxysilane (TEOS) is used as the alkoxysilane, ethanol is used as the alcohol, and hydrochloric acid is 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, after which 1.25 g of concentrated hydrochloric acid (37%) was added and stirred at room temperature for another 5 minutes. While stirring this mixed solution, 71.2 g of water was added dropwise and mixed to obtain a transparent and uniform 5.88% TEOS solution (alkoxysilane solution).

[0047] 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 aqueous aluminum nitrate solution (aluminum solution).

[0048] 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 to obtain a homogeneous mixed solution, which was heated to reflux at 100°C, and 28% ammonia water was added dropwise and stirred until the pH reached 9.0. As the ammonia water was added dropwise, aluminum hydroxide and silicon compounds co-precipitated, and a precipitate was deposited in the mixed solution.

[0049] Subsequently, in step #14, the mixed solution containing the precipitate was suction filtered using No. 1 filter paper to separate the precipitate. The separated precipitate was washed with ion-exchanged water at room temperature to obtain a precipitate cake.

[0050] Subsequently, in step #15, water was added to the obtained precipitate cake so that the total amount became 80 g, and the mixture was stirred to prepare a slurry solution. Nitric acid (60% aqueous solution) was added to this slurry solution until the pH became 5.0, and autoclaving was performed at 150°C for 15 hours to obtain a sol solution containing 1% SiO2Al2O3. For the autoclaving, an autoclave was used that was composed of a Teflon (registered trademark) container with a capacity of 100 ml enclosed in a stainless steel jacket.

[0051] The total amount of the 1% SiO2Al2O3-containing sol solution obtained in step #15 is 80 g, and the 1% SiO2Al2O3 powder obtained by drying this sol solution is 2.0 g. The sol solution concentration of the 80 g total sol solution containing 2.0 g of 1% SiO2Al2O3 powder is 2.5 mass %. The amount of nitric acid (60% aqueous solution) used to adjust the pH of the slurry solution is a small amount of about 400 to 600 μL, so the total amount of the 1% SiO2Al2O3-containing sol solution is approximately the same as the total amount of the slurry solution, 80 g. The content and structure of the autoclave used in the autoclave treatment of this synthesis method are not limited to the content and structure of the autoclave used in Example 1, and for example, an autoclave with a content corresponding to the total amount of the SiO2Al2O3-containing sol solution to be synthesized may be used.

[0052] For ease of explanation, a sol solution containing SiO2Al2O3 with an SiO2 concentration of X% by mass and a sol solution concentration of Y% by mass will be referred to as X%SiO2Al2O3Y% sol. Therefore, the sol solution containing 1% SiO2Al2O3 obtained in step #15 will be referred to as 1%SiO2Al2O32.5% sol.

[0053] [2.2] Example 2 (Aluminum compound: aluminum chloride) In Example 2, a sol solution containing 1% SiO2Al2O3 was synthesized under exactly the same conditions as in Example 1, except that in step #12, 9.38 g of aluminum chloride (III) hexahydrate was dissolved in 83.24 g of water to obtain an aluminum chloride aqueous solution (aluminum solution). That is, in Example 2, a total of 80 g of 1% SiO2Al2O3 2.5% sol was obtained, as in Example 1. Therefore, the description overlapping with Example 1 will be omitted. In Example 1, the concentration of the aluminum nitrate aqueous solution was prepared at about 20 mass% (including water of crystallization), whereas in Example 2, the concentration of the aluminum chloride aqueous solution was prepared at a low concentration of about 10 mass% (including water of crystallization) because the amount of water was too small relative to the amount of precipitation at 20 mass% and stirring was not sufficient.

[0054] [2.3] Example 3 (Aluminum compound: aluminum sulfate) In Example 3, as in Examples 1 and 2, in order to synthesize a 1% SiO2Al2O3 2.5% sol of 80 g in total, in step #12, 6.64 g of aluminum sulfate (anhydrous) must be dissolved in 58.58 g of water to obtain an aluminum sulfate aqueous solution (aluminum solution). However, even if the pH value of the slurry solution is controlled within the same specific pH range as when the aluminum compound is aluminum nitrate in step #15, under the same heating conditions of the autoclave treatment as in Example 1 (150°C, 15 hours), when the sol solution concentration exceeds 0.63 mass%, the solution state becomes a state in which undissolved precipitate is mixed in the sol (second half sol described later). Therefore, by adjusting the amount of alkoxysilane and aluminum compound charged in steps #11 and #12 and the amount of water added to the precipitate cake in step #15, the sol solution concentration of the total amount of 80 g can be controlled to 0.63 mass% or less, and a sol solution containing 1% SiO2Al2O3 can be synthesized. Other than the above, the conditions were exactly the same as in Example 1, and therefore a description that overlaps with Example 1 will be omitted. In Example 1, the aluminum nitrate aqueous solution was prepared at a concentration of about 20% by mass (including water of crystallization), whereas in Example 3, the amount of water was too small relative to the amount of precipitate at 20% by mass, preventing sufficient stirring, and therefore the aluminum sulfate aqueous solution was prepared at a low concentration of about 10% by mass.

[0055] Even if the sol solution concentration exceeds 0.63 mass%, the solution state may change from the second half sol to a sol state by adjusting the heating conditions during autoclave treatment and increasing the amount of heat, as described below.

[0056] [3] Study of autoclave treatment conditions for the first synthesis method The solution state after the autoclave treatment in step #15 can be one of six states: sol, first half sol, second half sol, gel, precipitate, and cloudy sol, depending on the SiO2 concentration and sol solution concentration of the SiO2Al2O3-containing sol solution after synthesis, the pH value of the slurry solution, and the heating conditions of the autoclave treatment (treatment temperature, treatment time). Hereinafter, the SiO2 concentration and sol solution concentration of the SiO2Al2O3-containing sol solution after synthesis, the pH value of the slurry solution, and the heating conditions of the autoclave treatment (treatment temperature, treatment time) are collectively referred to as the autoclave treatment conditions.

[0057] In the results of the study shown below, the five solution states (sol, first half sol, second half sol, gel, and precipitate) are determined by the SiO2 concentration and the pH value of the slurry solution under the sol solution concentration and heating conditions that can turn the solution into a sol. Also, the four solution states (sol, second half sol, cloudy sol, and gel) are determined by the sol solution concentration and heating conditions under the combination of the SiO2 concentration and the pH value of the slurry solution that can turn the solution into a sol.

[0058] Sol is a slightly whitish transparent solution, and indicates the state of the solution in which light scattering due to the Tyndall phenomenon is confirmed by irradiating it with laser light. The "transparent" sol has a degree of transparency such that when the sol solution is placed in a colorless, transparent glass container with an inner diameter of about 8 cm, the letters and figures on the side of the glass container can be visually confirmed through the sol solution from the other side. Gel is a state in which the viscosity is higher than that of sol. Precipitation indicates a state in which the white precipitate and the solution separate when left to stand, and the white precipitate is opaque. The first half sol is an intermediate state in the process from sol to gel, and indicates a state in which part of the sol solution has gelled, and the gelled part is transparent. The second half sol is opaque in a state in which the precipitate has not been fully peptized and some of the precipitate remains in the solution.

[0059] In step #15 of Example 1 with an SiO2 concentration of 1 mass%, the pH value of the slurry solution was changed to prepare four types of SiO2Al2O3-containing sol solutions in solution states of sol, gel, first half sol, and precipitate, and these four types of sol solutions were observed with a TEM (transmission electron microscope). The transmission electron microscope used was a field emission type JEM-2100 manufactured by JEOL Ltd. Figure 2 shows TEM images. Each sol solution was diluted with ethanol and observed on a Cu mesh. The gel in photo (a) was in a state where needle-shaped particles with a width of 5 nm and a length of 50 to 100 nm were aggregated. The first half sol in photo (b) also had needle-shaped particles similar to those in the gel. However, the sol in photo (c) was a thin plate with a side length of about 10 to 15 nm. Condition In addition, in the precipitate in photo (d), needle-like particles with a width of 2 to 3 nm and a length of 20 to 30 nm and thin plate-like particles with a side length of about 10 to 15 nm were observed. As shown in Figure 2, the particle morphology differs greatly depending on the solution state, and in particular, it was found that the sol exhibits a structure that is clearly different from the highly viscous gel and precipitate.

[0060] The second half sol indicates a state in which the heating in the autoclave treatment is insufficient, and the precipitate of silica-adsorbed boehmite (when the SiO2 concentration is 0 mass%, boehmite with no silica adsorbed) is not completely peptized and some of it remains. The cloudy sol indicates a state in which the heating in the autoclave treatment is excessive, and the sol becomes cloudy as a result of the transition to precipitation due to growth of sol particles and gel formation due to polymerization of boehmite. In this embodiment, the cloudy sol is distinguished as a solution state different from the first half sol, the second half sol, the gel, and the precipitate.

[0061] Even if the solution state after autoclaving is any of the five states other than sol, it is possible 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, it is most preferable that the solution state is a sol, as described below. Therefore, the following will consider the autoclaving conditions under which the solution state after autoclaving becomes a sol.

[0062] [3.1] SiO2 concentration dependence in a specific pH range The relationship between the pH range (specific pH range) of the slurry solution in which the solution state after autoclaving becomes a sol and the SiO2 concentration was investigated as follows.

[0063] The SiO2 concentration was varied in the range of 0% to 10% by mass, and the pH value after the pH adjustment treatment of the slurry solution in step #15 was varied in the range of 1.01 to 10.68 to prepare multiple sets of samples (80 g total amount of slurry solution), and the solution state after autoclaving was visually confirmed. In each sample, the sol solution concentration was set to 2.5% by mass, the same as in Example 1 above, the heating conditions for the autoclaving were 150°C for 15 hours, the same as in Example 1 above, and aluminum nitrate was used as the aluminum compound, the same as in Example 1 above.

[0064] The results of checking the above solution state are shown as a scatter diagram in Figure 3. The vertical axis of the scatter diagram indicates the pH value of the slurry solution, and the horizontal axis indicates the SiO2 concentration. In the diagram, sols are indicated by white circles (○), gels by black squares (■), precipitates by black triangles (▲), the first half sol by white squares (□), and the second half sol by white triangles (△).

[0065] From Fig. 3, it can be seen that the specific pH range (from the lower limit to the upper limit) is within the range of 2.8 to 7.8 inclusive when the SiO2 concentration is in the range of 0 to 10 mass%, and the width of the specific pH range (the difference between the upper limit and the lower limit) decreases with increasing SiO2 concentration. It can also be seen that, at the same SiO2 concentration, gelation occurs when the pH value is smaller than the specific pH range, and precipitation occurs when the pH value is larger than the specific pH range.

[0066] In the case of a sol solution without silica (SiO2 concentration 0 mass%), the solution state remains a sol state within a specific pH range (3.84 to 7.74), but a transparent gel is generated in a region where the pH value is less than pH 3.84, which suggests that the acid catalyst promotes polymerization of the sol, leading to gelation. In that sense, even in a region where the pH value is less than 3.84, there is a possibility that the solution state can be made into a sol by relaxing the heating conditions of the autoclave treatment (shortening the treatment time and / or lowering the treatment temperature) to suppress gelation. Therefore, even in the case of a sol solution containing silica added to SiO2Al2O3, there is a possibility that the specific pH range shown in Figure 3 can be expanded downward by relaxing the heating conditions.

[0067] Since the isoelectric point of silica sol is pH 1 to 1.5, silica disperses in the liquid with its surface negatively charged near the neutral pH range where boehmite sol exists. Boehmite is positively charged near the neutral pH range, and silica is considered to be electrostatically bonded to boehmite. Therefore, the fact that the upper limit of the specific pH range decreases with increasing SiO2 concentration in Figure 3 is considered to be due to the influence of silica sol. If it is considered that precipitation occurs when the electric potential of the particle surface becomes zero and the particles aggregate, when silica and boehmite, which have significantly different isoelectric points, are mixed, silica is adsorbed to the boehmite near the neutral pH range, so the apparent isoelectric point decreases and the upper limit of the specific pH range decreases.

[0068] In Figure 3, if the SiO2 concentration is X (mass%), the lower limit of the specific pH range is P0, and the upper limit is P1, P0 and P1 are given as approximate values ​​by the following formula. For reference, the approximate values ​​of P0 and P1 are shown in Figure 3 as broken lines.

[0069] 0 <X≦3において、 P0=-0.68X / 3+3.84 P1=-1.6X / 3+7.74 3 <X≦7において、 P0=3.16 P1=-0.075(X-3)+6.14 7 <X≦8において、 P0 = -0.38(X-7) + 3.16 P1=-1.2(X-7)+5.84 8 <X≦10において、 P0 = 0.255(X-8) + 2.78 P1=-0.675(X-8)+4.64

[0070] From the above, in one embodiment of the pH adjustment treatment for the slurry solution in step #15, when the SiO2 concentration is X (mass%), the pH value of the slurry solution can be adjusted to be within a specific pH range determined by P0 and P1 given by the above calculation formula.

[0071] [3.2] Dependence of specific concentration of SiO2 The relationship between the upper limit (specific concentration) of the sol solution concentration at which the solution state after autoclaving becomes a sol under the specified heating conditions (treatment temperature, treatment time) of the autoclaving and the SiO2 concentration was investigated as follows.

[0072] The SiO2 concentration was changed in the range of 0 mass% to 10 mass%, and a plurality of sets of samples (80 g total slurry solution) with different sol solution concentrations (mass%) were prepared, and the solution state after autoclaving was visually confirmed. In each sample, 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 0 mass% to 7 mass%, and was set to a specific pH value in which the solution state becomes a sol in Figure 3, when the SiO2 concentration was in the range of 8 mass% to 10 mass%. Furthermore, the heating conditions for the autoclaving 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.

[0073] The results of checking the above solution state are shown as a scatter diagram in Figure 4. The vertical axis of the scatter diagram indicates the sol solution concentration (mass%), and the horizontal axis indicates the SiO2 concentration. In the diagram, the sol is indicated by a white circle ○, and the second half sol is indicated by a black circle ●.

[0074] From FIG. 4, it can be seen that, regardless of the SiO2 concentration, when the sol solution concentration is higher than the specific concentration, unpeptized precipitate remains in the sol. Also, from FIG. 4, it can be seen that the specific concentration is within the range of 2.5% by mass or more and 9.0% by mass or less when the SiO2 concentration is in the range of 0 to 10% by mass under the heating condition of 150°C for 15 hours, and decreases with increasing SiO2 concentration. This is considered to be because SiO2 exists in a form adsorbed to the precipitate of aluminum hydroxide. In other words, as the SiO2 concentration increases, the amount of SiO2 that is not peptized by the autoclave treatment increases, and the aluminum hydroxide becomes difficult to peptize due to the adsorption of SiO2 to the surface of the precipitate of aluminum hydroxide, so the specific concentration decreases with increasing SiO2 concentration in FIG. 4.

[0075] As described later, even if the sol solution concentration at a certain SiO2 concentration becomes higher than a specific concentration and the solution state becomes a second half sol, the solution state may become a sol state by appropriately adjusting the heating conditions of the autoclave treatment to increase the amount of heat.

[0076] In Fig. 4, if the SiO2 concentration is X (mass%) and the specific concentration is Y1, Y1 is given as an approximate value by the following formula: The approximate value of Y1 is shown by a broken line in Fig. 4 for reference.

[0077] 0 <X≦1において、 Y1=9 1 <X≦3において、 Y1=-0.5(X-1)+9 3 <X≦5において、 Y1=-1.5(X-3)+8 5 <X≦7において、 Y1=-0.935(X-5)+5 7 <X≦8.5において、 Y1=3.13 8.5 <X≦10において、 Y1=-0.42(X-8.5)+3.13

[0078] From the above, in one embodiment of controlling the sol solution concentration in step #15 to a specific concentration or less when the heating condition of the autoclave treatment is 150°C for 15 hours, when the SiO2 concentration is X (mass%), the amount of alkoxysilane and aluminum compound charged in steps #11 and #12 and the amount of water added to the precipitate cake in step #15 can be adjusted so that the sol solution concentration is the specific concentration Y1 given by the above calculation formula or less. Note that, as explained in Example 3, when using the same heating condition of 150°C for 15 hours and using aluminum sulfate as the aluminum compound, the specific concentration Y1 is 0.63 mass% or less.

[0079] [3.3] Heating conditions for autoclave treatment (1) For each of the three treatment temperatures (100°C, 150°C, 200°C), the treatment time was changed in three or five ways within the range of 1 to 100 hours, and a total of 13 samples (samples 1 to 13, slurry solution) were autoclaved under different heating conditions, and the solution state after autoclaving was visually confirmed. Each sample was for a 1%SiO2Al2O3 3.75% sol with a SiO2 concentration of 1 mass% and a sol solution concentration of 3.75 mass%, and the pH value of the slurry solution was adjusted to about pH 5.0 using nitric acid in step #15. In addition, the aluminum compound used was the same aluminum nitrate as in Example 1 above.

[0080] The results of checking the above solution state are shown in Table 1 below and in the scatter diagram of Figure 5. The vertical axis of the scatter diagram indicates the treatment time, and the horizontal axis indicates the treatment temperature. In the diagram, sol is indicated by a white circle ○, the second half sol by a black circle ●, and the cloudy sol by a cross.

[0081] [Table 1]

[0082] 5, the solution was converted into a sol in 1 hour at a treatment temperature of 200° C., in 15 to 48 hours at a treatment temperature of 150° C., and in 24 to 100 hours at a treatment temperature of 100° C. The above results show that when the amount of heat is increased by increasing at least one of the treatment temperature and treatment time, the solution state transitions from a sol to a cloudy sol, and when the amount of heat is decreased by decreasing at least one of the treatment temperature and treatment time, the solution state transitions from a sol to a second half sol. Therefore, for example, when the heating conditions for turning the solution into a sol are set to a treatment temperature of 150°C and a treatment time of 15 to 48 hours, if the treatment temperature is increased from 150°C while maintaining the solution in a sol state, it is understood that the treatment time should be shorter than 15 to 48 hours in order to suppress an increase in the amount of heat, and conversely, if the treatment temperature is decreased from 150°C, the treatment time should be longer than 15 to 48 hours in order to suppress a decrease in the amount of heat. Furthermore, it is understood that if the treatment time is increased beyond 15 to 48 hours, the treatment temperature should be decreased from 150°C in order to suppress an increase in the amount of heat, and conversely, if the treatment time is decreased beyond 15 to 48 hours, the treatment temperature should be increased from 150°C in order to suppress a decrease in the amount of heat.

[0083] [3.4] Heating conditions for autoclaving (2) From Table 1 above, when the sol solution concentration becomes higher than a specific concentration under certain heating conditions and the solution state becomes the second half sol, it is predicted that the solution state can become a sol by increasing at least one of the treatment temperature and treatment time at the sol solution concentration to increase the amount of heat. To confirm this point, autoclaving was performed on three types of slurry solutions with different SiO2 concentrations and sol solution concentrations at a treatment temperature of 150°C for three or five treatment times within the range of 2 to 100 hours, and a total of 13 samples (samples 14 to 26, slurry solutions) were autoclaved, and the solution state after autoclaving was visually confirmed. The 13 samples are broken down as follows: Samples 14-18 are for 1%SiO2Al2O3 3.75% sol with SiO2 concentration of 1 mass% and sol solution concentration of 3.75 mass%, Samples 19-21 are for 1%SiO2Al2O3 10% sol with SiO2 concentration of 1 mass% and sol solution concentration of 10 mass%, and Samples 22-26 are for 7%SiO2Al2O3 6% sol with SiO2 concentration of 7 mass% and sol solution concentration of 6 mass%. Each sample was prepared using aluminum nitrate as the aluminum compound as in Example 1 above, and in step #15, the pH value of the slurry solution was adjusted to about pH 5.0 using nitric acid.

[0084] The solution state after autoclaving for samples 14 to 21 is shown in the scatter diagram in Figure 6. The solution state after autoclaving for samples 22 to 26 is shown in Table 2 below. The vertical axis of the scatter diagram indicates the treatment time, and the horizontal axis indicates the sol solution concentration. In the diagram, sol is indicated by a white circle ○, the second half sol by a black circle ●, the cloudy sol by an ×, and the gel by a black square ■.

[0085] [Table 2]

[0086] As shown in FIG. 6, the solution state of Samples 14-18 with a sol solution concentration of 3.75% by mass after autoclaving at 150°C was the second half sol at 2 hours, but became a sol at 15 hours and 48 hours, and further became a cloudy sol at 72 hours and 100 hours. On the other hand, the solution state of Samples 19-21 with a sol solution concentration of 10% by mass after autoclaving at 150°C was the second half sol at 15 hours, but became a sol at 24 hours, and further became a gel at 48 hours. In the 1% SiO2Al2O3 10% sol of Samples 19-21, it was found that the peptization progressed by applying autoclaving for a long time, and the solution state became a sol, and when the treatment time was further extended, the solution state transitioned to a gel. In the case of a sol solution concentration of 10% by mass, the range of treatment time in which the sol state can be maintained is narrower than that of a sol solution concentration of 3.75% by mass, and appropriate control of the treatment time is required.

[0087] In addition, as shown in Table 2, in samples 22 to 26 with SiO2 concentration of 7 mass% and sol solution concentration of 6 mass%, the solution state after autoclaving at 150°C was the second half sol for treatment times of 15 and 24 hours, but became a gel instead of a sol for treatment times of 48 to 100 hours. When the SiO2 concentration and the sol solution concentration are both high, the solution state changes from the second half sol to a gel state by polymerization immediately proceeding without passing through a sol state as the treatment time elapses, or, as in samples 19 to 21 shown in Figure 6, the treatment time during which the solution can become a sol state is limited to a narrow range of more than 24 hours and less than 48 hours.

[0088] As mentioned above, Figs. 4 to 6 and Tables 1 and 2 showFrom the results of the solution state, it can be seen that as at least one of the SiO2 concentration and the sol solution concentration becomes lower or higher, the range of the treatment time and treatment temperature in which the solution state can become a sol state expands or shrinks, and when both the SiO2 concentration and the sol solution concentration become higher, the range of the treatment time and treatment temperature in which the solution state can become a sol state does not exist. Therefore, the SiO2 concentration and the sol solution concentration should each be set to an upper limit of about 10 mass%, and when one is set higher, the other should be set lower within the range in which the solution state can become a sol state. However, looking at the whole picture, it can be said that the degree of freedom of the combination of the SiO2 concentration, the sol solution concentration, the treatment time and treatment temperature of the autoclave treatment in which the solution state can become a sol state is extremely high.

[0089] [3.5] Autoclave treatment conditions for sol solution containing 1% SiO2Al2O3 As a result of the above, an example of the autoclave treatment conditions for synthesizing a sol solution containing 1% SiO2Al2O3 by the first synthesis method is as follows. Slurry solution pH value: pH4~pH7 Sol solution concentration: 9% by mass or less Heating conditions: 150℃, 15 hours

[0090] As described above, when the SiO2 concentration of the SiO2Al2O3-containing sol solution is increased to more than 1 mass%, the pH value of the slurry solution and the sol solution concentration can be adjusted accordingly in the above-mentioned manner. In addition, the heating conditions are not limited to the above-mentioned 150°C and 15 hours, and the treatment temperature and treatment time may be changed so as to suppress the increase / decrease in the amount of heat, as described above.

[0091] [4] Heat resistance evaluation of the first synthesis method (1) The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "the powder sample S1") obtained by drying and firing the SiO2Al2O3-containing sol solution synthesized by the first synthesis method was evaluated. In order to evaluate the influence on heat resistance of the process of soling the precipitate cake by autoclaving in step #15 of the first synthesis method, the heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "comparative example C1") obtained by directly drying and firing the precipitate cake prepared through steps #11 to #14 without soling was evaluated, and the heat resistance of the powder sample S1 was compared with that of comparative example C1.

[0092] Incidentally, the synthesis method of the SiO2Al2O3 powder of Comparative Example C1 corresponds to the synthesis of silica-added porous alumina without adding barium oxide in the precipitation method (see FIG. 16 of Patent Document 6), which is one of the synthesis methods of porous alumina to which silica and barium oxide are added as disclosed in the above Patent Document 6. Hereinafter, the synthesis methods of Comparative Example C1 and Comparative Examples C2 and C7 described below will be appropriately referred to as the "precipitation method" regardless of whether barium oxide is added or not.

[0093] In evaluating the heat resistance, since Comparative Example C1 is a powder sample, a powder sample was used instead of a coating film in order to easily examine the change in heat resistance due to the difference in SiO2 concentration.

[0094] The synthesis method of silica-added porous alumina of Comparative Example C1 is the same as steps #11 to #14 of the first synthesis method in the steps until the precipitation cake is produced. In Comparative Example C1, the obtained precipitation cake was dried at 150°C, subsequently crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (Comparative Sample C1A). Furthermore, Comparative Sample C1B, which is obtained by adding a first heat treatment at 1200°C for 5 hours to Comparative Sample C1A, and Comparative Sample C1C, which is obtained by adding a second heat treatment at 1200°C for 30 hours to Comparative Sample C1A, were produced as necessary. Comparative Sample C1A is Comparative Example C1, which is only subjected to the initial heat treatment, and neither the first nor the second heat treatment was performed. In the first heat treatment, the temperature was raised from room temperature to 1200°C at 10°C / min, and then the temperature was held at 1200°C for 5 hours. In the second heat treatment, the temperature was increased from room temperature to 1200° C. at 10° C. / min, and then the temperature was maintained at 1200° C. for 30 hours.

[0095] On the other hand, as the present powder sample S1, the SiO2Al2O3-containing sol solution obtained through steps #11 to #14 of the first synthesis method followed by step #15 was dried at 150°C, crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (present sample S1A). Furthermore, present sample S1B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S1A, and present sample S1C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S1A, as necessary. Present sample S1A is present powder sample S1 that was only subjected to the initial heat treatment and did not undergo either the first or second heat treatment.

[0096] In preparing the present samples S1A to S1C and the comparative samples C1A to C1C, aluminum nitrate was used as the aluminum compound. The specific processing contents of steps #11 to #15 are as described in Example 1 when the SiO2 concentration is 1 mass%, and when the SiO2 concentration is other than 1 mass%, the mixing ratio of the aluminum nitrate aqueous solution and the 5.88% TEOS solution in step #13 was adjusted according to the set value of the SiO2 concentration.

[0097] The drying process, initial heat treatment, first heat treatment, and second heat treatment are the same for powder sample S1 and comparative example C1. Furthermore, the above-mentioned processes are the same for the evaluation of heat resistance in the second to sixth embodiments, so that the overlapping explanations in each embodiment will be omitted.

[0098] In the evaluation of heat resistance, the specific surface area, pore distribution, and total pore volume were measured, and the crystal structure was analyzed by X-ray diffraction (XRD) for each of the powder sample S1 and the comparative sample C1. In the evaluation of heat resistance in the second to seventh embodiments, the above-mentioned measurement of the specific surface area and XRD analysis were also performed as necessary. The specific surface area of ​​the sample was used as an index of heat resistance.

[0099] The specific surface area was measured by the nitrogen adsorption BET method using a fully automatic gas adsorption measurement (MicrotracBEL BELSORP-max). The pore distribution and total pore volume were measured by the BJH method using a fully automatic gas adsorption measurement (MicrotracBEL BELSORP-max). The XRD pattern of the crystal structure was measured by an X-ray diffractometer (Rigaku ULTIMA III) using Cukα and a two-dimensional high-speed detector.

[0100] FIG. 7 shows the measurement results of the specific surface area of ​​the present samples S1A, S1B, and S1C (a total of 21 present powder samples S1) prepared by changing the SiO2 concentration in seven ways, namely, 0 mass%, 1 mass%, 3 mass%, 5 mass%, 8 mass%, 9 mass%, and 10 mass%. FIG. 8 shows the measurement results of the specific surface area of ​​the comparative samples C1A, C1B, and C1C (a total of 15 comparative samples C1) prepared by changing the SiO2 concentration in five ways, namely, 0 mass%, 1 mass%, 3 mass%, 5 mass%, and 10 mass%. In the graphs showing the measurement results of the specific surface area in FIG. 7 and FIG. 8, the vertical axis indicates the specific surface area (m 2 / g), and the horizontal axis represents the SiO2 concentration (mass%).

[0101] 7 and 8, in the silica addition amount with an SiO2 concentration of 0 mass% to 3 mass%, the specific surface area increases with increasing SiO2 concentration in both the powder sample S1 and the comparative sample C1. Comparing the specific surface area of ​​the present sample S1A and the comparative sample C1A, which have an SiO2 concentration of 3 mass%, the specific surface area of ​​the present sample S1A is 175 m 2 / g, and the specific surface area of ​​the comparative sample C1A is 165 m 2 / g, and the heat resistance is almost the same.

[0102] As shown in Figures 7 and 8, when the silica concentration is 3 mass% to 10 mass%, the specific surface area of ​​the comparative sample C1A increases with an increase in the SiO2 concentration, whereas the specific surface area of ​​the present sample S1A hardly increases. Comparing the specific surface areas of the present sample S1A and the comparative sample C1A, which has an SiO2 concentration of 10 mass%, the specific surface area of ​​the present sample S1A is 201 m 2 / g, and the specific surface area of ​​the comparative sample C1A is 227 m 2 / g, and the specific surface area of ​​this sample S1A is slightly lower.

[0103] FIG. 9 shows XRD patterns of the crystal structures of the present sample S1A, the present sample S1B, and the present sample S1C after each heat treatment, each having an SiO2 concentration of 1 mass%. FIG. 10 shows XRD patterns of the crystal structures of the comparative sample C1A, the comparative sample C1B, and the comparative sample C1C after each heat treatment, each having an SiO2 concentration of 1 mass%. Furthermore, FIG. 11 shows an XRD pattern of the crystal structure of the pre-heat-treatment sample (the present dried sample S1D) of the present powder sample S1, which was not subjected to the initial heat treatment after drying the SiO2Al2O3-containing sol solution at 150°C. FIG. 12 shows an XRD pattern of the pre-heat-treatment sample (the comparative dried sample C1D) of the comparative example C1, which was not subjected to the initial heat treatment after drying the precipitate cake at 150°C.

[0104] As shown in Figures 9 and 10, Comparative Example C1 by the precipitation method completely transitioned to α-Al2O3 (Comparative Sample C1B) in the first heat treatment (1200°C for 5 hours), whereas the powder sample S1 by autoclaving did not completely transition to α-phase even in the second heat treatment (1200°C for 30 hours). This is because, as shown in the XRD patterns of the present dried sample S1D and the comparative dried sample C1D in Figures 11 and 12, the autoclaving promotes the formation of boehmite in the present dried sample S1D, and the small fibrous particles develop, making it difficult for the mass transfer of Al2O3 to occur, and as a result, sintering is suppressed. As shown in Figure 11, it is thought that the aluminum hydroxide in the slurry solution was partially dehydrated under the temperature and pressure of the autoclaving to form boehmite.

[0105] Fig. 13 shows the pore distribution (BJH plot) of the present sample S1B and the comparative sample C1B, which were subjected to the first heat treatment (1200°C for 5 hours) with an SiO2 concentration of 3 mass%. Fig. 14 shows the pore distribution (BJH plot) of the present sample S1B and the comparative sample C1B, which were subjected to the first heat treatment with an SiO2 concentration of 10 mass%. In Figs. 13 and 14, the circles (●) indicate the pore distribution of the present sample S1B, the triangles (▲) indicate the pore distribution of the comparative sample C1B, and the vertical axis is the differential pore volume dV p / dr p (m 3 / g / nm), and the horizontal axis is the pore diameter r p In addition, the specific surface area (m2) of the present sample S1B and the comparative sample C1B with SiO2 concentrations of 3 mass% and 10 mass% are shown in Table 3 below. 2 / g) and total pore volume (cm 3 / g).

[0106] [Table 3]

[0107] As shown in Table 3, at an SiO2 concentration of 3 mass%, there was no significant difference in the pore distribution or specific surface area between the present sample S1B and the comparative sample C1B. However, at an SiO2 concentration of 10 mass%, the total pore volume of the present sample S1B was 0.1275 cm 3 / g, whereas the total pore volume of comparative sample C1B is 0.1813 cm 3 / g, and the total pore volume of sample S1B was smaller. This is because the powder sample S1 is obtained by drying a sol solution containing SiO2Al2O3 to produce a transparent gel, which is then sintered, and the total pore volume of Al2O3 is thought to have decreased due to the surface tension of the evaporating water in the process of producing the transparent gel from the sol solution. Measures against the decrease in the total pore volume will be described in the fourth embodiment below.

[0108] [5] Heat resistance evaluation of the first synthesis method (2) Next, the specific surface area was examined when the aluminum compound used in the samples S1A to S1C was changed from aluminum nitrate to aluminum chloride and aluminum sulfate, respectively.

[0109] Table 4 below shows the specific surface area (m2) of the present samples S1A to S1C, in which the aluminum compounds are aluminum nitrate, aluminum chloride, and aluminum sulfate. 2 / g).

[0110] [Table 4]

[0111] As shown in Table 4, when the aluminum compound is aluminum chloride, the specific surface areas of Samples S1A to S1C are almost the same as those of aluminum nitrate. On the other hand, when the aluminum compound is aluminum sulfate, the specific surface areas of Samples S1A to S1C are smaller than those of aluminum nitrate and aluminum chloride, resulting in slightly inferior heat resistance to the other two aluminum compounds.

[0112] [6] Heat resistance evaluation of the first synthesis method (3) As described above, there is no significant difference in the specific surface area between the powder sample S1 and the comparative example C1. Therefore, even if the pH value of the slurry solution is not controlled within a specific pH range in which the solution state after autoclaving is a sol state in the pH adjustment process for the slurry solution in step #15 of the first synthesis method, that is, even if the solution state is a gel or precipitate other than a sol state, the SiO2Al2O3 powder obtained by drying and firing the solution can have a specific surface area similar to that of the powder sample S1 described above.

[0113] In order to verify this, six types of sol solutions were prepared by changing the pH value of the slurry solution in six ways in the pH adjustment process for the slurry solution in step #15 in the same manner as for the powder sample S1. The six types of sol solutions were then dried and sintered by an initial heat treatment at 1000°C for five hours to prepare six types of powder samples SA. A To the six powder samples SA, a first heat treatment at 1200°C for five hours was added to produce six types of powder samples SB, and to the six powder samples SA, a second heat treatment at 1200°C for 30 hours was added to produce six types of powder samples SC. In total, 18 types of powder samples with different slurry solution pH values ​​and heat treatment conditions were prepared.

[0114] The specific surface areas (m2) of the six types of powder samples SA, the six types of powder samples SB, and the six types of powder samples SC are shown in Table 5 below. 2 The results of the measurements of total pore volume (cm3 / g) are shown in Table 6. The total pore volume (cm3) of three of the six powder samples SA (pH values: 2.77, 3.69, and 9.57) is also shown in Table 6. 3 / g) measurement results are shown.

[0115] [Table 5]

[0116] [Table 6]

[0117] From Tables 5 and 6, it can be seen that the specific surface area and the total pore volume tend to increase in the order of the solution state: gel, sol, and precipitate. The specific surface area and the total pore volume when the solution state is sol are slightly inferior to those when the solution state is precipitate, but as will be described in the seventh embodiment later, when considering fixing of a coating film to a substrate, solution states other than sol have poor adhesion to the substrate surface and are unsuitable for forming a coating film.

[0118] [Second embodiment] A second embodiment of the present synthesis method (second synthesis method) will be described below.

[0119] [7] Basic structure of the second synthesis method The second synthesis method is roughly divided into steps #21 to #25 as shown in the process transition diagram of Fig. 15. Steps #21 to #25 have basically the same process contents as steps #11 to #15 of the first synthesis method shown in Fig. 1, but the aluminum compound in the second synthesis method is sodium aluminate, which is different from the aluminum nitrate, aluminum chloride, and aluminum sulfate used as the aluminum compound in the first synthesis method.

[0120] The second synthesis method, like the first synthesis method, is a synthesis method in which a SiO2Al2O3-containing sol solution is synthesized after autoclave treatment, and corresponds to the first AC method in the case where the aluminum compound is sodium aluminate.

[0121] Due to the difference in the aluminum compound, the processing contents of steps #22, #23, #24, and #25 differ in some details from steps #12 to #15 of the first synthesis method. Step #21 is the same as step #11 of the first synthesis method. Moreover, step #22 differs from step #12 of the first synthesis method only in the aluminum compound used. Therefore, duplicated explanations of steps #21 and #22 will be omitted. Furthermore, the method of adjusting the SiO2 concentration and the method of adjusting the sol solution concentration are also the same as the first synthesis method, and duplicated explanations will be omitted.

[0122] Step #23 is the same as step #13 in the first synthesis method in that a precipitate in which a silicon compound is adsorbed on aluminum hydroxide is deposited in a mixed solution obtained by mixing the alkoxysilane solution obtained in step #21 and the aluminum solution obtained in step #22.

[0123] However, in the second synthesis method, as one embodiment of step #23, the aluminum solution obtained in step #22 is heated to reflux, nitric acid is added dropwise to adjust the pH, and then the aluminum solution obtained in step #21 is mixed to prepare a mixed solution. In the mixed solution, a precipitate of aluminum hydroxide that precipitated during the pH adjustment of the aluminum solution is allowed to precipitate a precipitate with the silicon compound adsorbed thereon. In other words, step #23 differs from step #13 in that, while in step #13, the mixed solution is heated to reflux and the pH is adjusted, in step #23, these treatments are performed on the aluminum solution.

[0124] Step #24 is the same as step #14 in the first synthesis method in that the precipitate obtained in step #23 is filtered out from the mixed solution and the filtered precipitate is washed with water to produce a precipitate cake. However, step #24 differs from step #14 in that, when washing the filtered precipitate, in the example of the first synthesis method, the filtered precipitate is washed with ion-exchanged water at room temperature, whereas in the example of the second synthesis method, the filtered precipitate is washed with ion-exchanged water at, for example, 60°C. If sodium contained in the aluminum compound is present in the SiO2Al2O3-containing sol solution synthesized in step #25, the sol solution is dried and calcined to remove sodium. Growth When this process is performed, sintering of alumina is promoted, so in step #24, hot water at 60°C is used to wash the filtered precipitate to improve washability and remove the sodium from the precipitate.

[0125] In step #25, water is added to the precipitate cake obtained in step #24 to prepare a slurry solution, and the slurry solution is subjected to pH adjustment and then autoclaved to prepare a SiO2Al2O3-containing sol solution, which is the same as step #15 in the first synthesis method. Furthermore, the sol particles in which silica is bonded to boehmite particles are present in a highly dispersed state in the prepared SiO2Al2O3-containing sol solution, which is the same as step #15 in the first synthesis method.

[0126] Furthermore, as one embodiment of step #25, the sol solution concentration (mass %) is controlled to a specific concentration or less at which the solution state after autoclaving is in a sol state, and a pH adjustment process 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 is in a sol state, which is the same as step #15 of the first synthesis method.

[0127] Furthermore, as one embodiment of step #25, the processing temperature of the autoclave treatment is set to a specific processing temperature within the range of 100°C or more and 200°C or less, the processing time of the autoclave treatment is set within a specific time range in which the solution state after the autoclave treatment becomes a sol state according to the specific processing temperature, and the specific time range is within the range of 1 hour or more and 100 hours or less, which is the same as step #15 of the first synthesis method.

[0128] As described later, the specific concentration varies depending on the SiO2 concentration and the heating conditions of the autoclave treatment (treatment temperature, treatment time), and the specific pH range varies depending on the SiO2 concentration within the range of 1.0 to 6.2. The specific concentration and specific pH range in step #25 are different from those in step #15 of the first synthesis method.

[0129] [8] Example of the second synthesis method Hereinafter, steps #21 to #25 of Example 4 in the case of synthesizing a sol solution containing SiO2Al2O3 with a SiO2 concentration of 1 mass % will be described. Sodium aluminate is used as the aluminum compound.

[0130] In step #21, a transparent and uniform 5.88% TEOS solution (alkoxysilane solution) was obtained by following the same procedure as in step #11 of Example 1.

[0131] In step #22, 3.57 g of sodium aluminate was dissolved in 66.56 g of water to obtain an aqueous sodium aluminate solution (aluminum solution).

[0132] In step #23, the aqueous sodium aluminate solution obtained in step #22 was heated to reflux, and nitric acid was added dropwise and stirred until the pH reached 8.0. As the nitric acid was added dropwise, a precipitate of aluminum hydroxide was deposited. Subsequently, 1.18 g of the 5.88% TEOS solution obtained in step #21 was added dropwise to the aqueous sodium aluminate solution in which the aluminum hydroxide precipitate had been deposited, and the solution was stirred at room temperature for 30 minutes. As a result, a precipitate in which silicon compounds were adsorbed to the aluminum hydroxide was obtained in the mixed solution of the aqueous sodium aluminate solution and the TEOS solution.

[0133] Subsequently, 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. The separated precipitate was washed with ion-exchanged water at 60°C to obtain a precipitate cake.

[0134] Subsequently, in step #25, water was added to the obtained precipitate cake so that the total amount became 80 g, and the mixture was stirred to prepare a slurry solution. Nitric acid (60% aqueous solution) was added to this slurry solution until the pH became 3.0, and autoclaving was performed at 150°C for 15 hours to obtain a sol solution containing 1% SiO2Al2O3. For the autoclaving, an autoclave with a capacity of 100 ml was used as in Examples 1 to 3.

[0135] The total amount of the sol solution containing 1% SiO2Al2O3 obtained in step #25 is 80 g, and the 1% SiO2Al2O3 powder obtained by drying this sol solution is 2.0 g. The sol solution concentration of the 80 g total sol solution containing 2.0 g of 1% SiO2Al2O3 powder is 2.5 mass %. Therefore, the sol solution containing 1% SiO2Al2O3 obtained in step #25 is a 1% SiO2Al2O3 2.5% sol. Note that the amount of nitric acid (60% aqueous solution) used to adjust the pH of the slurry solution is very small, as in the first synthesis method, so the total amount of the sol solution containing 1% SiO2Al2O3 is approximately the same as the total amount of the slurry solution, 80 g.

[0136] [9] Study of autoclave treatment conditions for the second synthesis method The solution state after the autoclave treatment in step #25 can be one of six states: sol, first half sol, second half sol, gel, precipitate, and cloudy sol, depending on the SiO2 concentration and sol solution concentration of the SiO2Al2O3-containing sol solution after synthesis, the pH value of the slurry solution, and the heating conditions of the autoclave treatment (treatment temperature, treatment time). This is the same as in the first synthesis method. The above six solution states have already been explained in the above ``[3] Consideration of autoclave treatment conditions for the first synthesis method'', so repeated explanations will be omitted.

[0137] In the following, the autoclave treatment conditions under which the solution state after autoclave treatment in the second synthesis method becomes a sol will be considered.

[0138] [9.1] SiO2 concentration dependence in a specific pH range The relationship between the pH range (specific pH range) of the slurry solution in which the solution state after autoclaving becomes a sol and the SiO2 concentration was investigated as follows.

[0139] The SiO2 concentration was varied in the range of 0% to 5% by mass, and the pH value after the pH adjustment treatment of the slurry solution in step #25 was varied in the range of 0.22 to 7.65 to prepare multiple sets of samples (80 g total slurry solution), and the solution state after autoclaving was visually confirmed. In each sample, the sol solution concentration was set to 2.5% by mass, the same as in Example 4, and the heating conditions for the autoclaving were the same as in Example 4, 150°C for 15 hours.

[0140] The results of checking the above solution state are shown as a scatter diagram in Figure 16. The vertical axis of the scatter diagram indicates the pH value of the slurry solution, and the horizontal axis indicates the SiO2 concentration. In the diagram, sol is indicated by a white circle ○, gel by a black square ■, precipitate by a black triangle ▲, and the first half sol by a white square □. In the measurement results shown in Figure 16, the second half sol was not confirmed.

[0141] 16, it can be seen that the specific pH range (from the lower limit to the upper limit) is within the range of 1.0 to 6.2 when the SiO2 concentration is in the range of 0 to 5 mass%, and decreases with increasing SiO2 concentration. Also, as in the first synthesis method, it can be seen that at the same SiO2 concentration, gelation occurs when the pH value is lower than the specific pH range, and precipitation occurs when the pH value is higher than the specific pH range.

[0142] In the case of a sol solution without silica (SiO2 concentration 0 mass%), the solution state remains a sol state within a specific pH range (2.07 to 6.15), but a transparent gel is generated in a region where the pH value is less than pH 2.07, which suggests that the acid catalyst promotes polymerization of the sol, leading to gelation. In that sense, even in a region where the pH value is less than pH 2.07, there is a possibility that the solution state can be made into a sol by relaxing the heating conditions of the autoclave treatment (shortening the treatment time and / or lowering the treatment temperature) to suppress gelation. Therefore, even in the case of a sol solution containing silica added to SiO2Al2O3, there is a possibility that the specific pH range shown in FIG. 16 can be expanded downward by relaxing the heating conditions.

[0143] Since the isoelectric point of silica sol is pH 1 to 1.5, in the vicinity of neutrality in the region where boehmite sol exists, the silica sol is dispersed in the liquid with its surface negatively charged. In the vicinity of neutrality, boehmite is positively charged, and it is considered that silica is electrostatically bonded to boehmite. Therefore, as in the case of the first synthesis method, the upper limit value of the specific pH range decreases with increasing SiO2 concentration in Figure 16, which is considered to be due to the influence of silica sol. If it is considered that precipitation occurs when the electric potential of the particle surface becomes zero and the particles aggregate, when silica and boehmite, which have significantly different isoelectric points, are mixed, silica is adsorbed to boehmite in the vicinity of neutrality, so that the apparent isoelectric point decreases and the upper limit value of the specific pH range decreases.

[0144] In Fig. 16, if the SiO2 concentration is X (mass%), the lower limit of the specific pH range is P0, and the upper limit is P1, P0 and P1 are given as approximate values ​​by the following formula. For reference, the approximate values ​​of P0 and P1 are shown as broken lines in Fig. 16.

[0145] 0 <X≦1において、 P0=2.07 P1=-2.71X+6.15 1 <X≦3において、 P0 = -0.48(X-1) + 2.07 P1=-0.615(X-1)+3.44 3 <X≦5において、 P0 = -0.02(X-3) + 1.11 P1=-0.57(X-3)+2.21

[0146] From the above, in one embodiment of the pH adjustment treatment for the slurry solution in step #25, when the SiO2 concentration is X (mass%), the pH adjustment treatment can be performed so that the pH value of the slurry solution falls within a specific pH range determined by P0 and P1 given by the above calculation formula.

[0147] [9.2] Dependence of specific concentration of SiO2 The relationship between the upper limit (specific concentration) of the sol solution concentration at which the solution state after autoclaving becomes a sol under the specified heating conditions (treatment temperature, treatment time) of the autoclaving and the SiO2 concentration was investigated as follows.

[0148] The SiO2 concentration was changed in the range of 0 mass% to 5 mass%, and multiple sets of samples (80 g total slurry solution) with different sol solution concentrations (mass%) were prepared, and the solution state after autoclaving was visually confirmed. In each sample, the pH value of the slurry solution was set to a specific pH range where the solution state becomes a sol in Figure 16. Furthermore, the heating conditions for the autoclaving were the same as those in Example 4, 150 °C for 15 hours.

[0149] The results of checking the above solution state are shown as a scatter diagram in Figure 17. The vertical axis of the scatter diagram indicates the sol solution concentration (mass%), and the horizontal axis indicates the SiO2 concentration. In the diagram, the sol is indicated by a white circle ○, and the second half sol is indicated by a black circle ●.

[0150] From FIG. 17, it can be seen that, regardless of the SiO2 concentration, when the sol solution concentration is higher than the specific concentration, undissolved precipitate remains in the sol. Also, from FIG. 17, it can be seen that the specific concentration is within the range of 2.5 mass% to 6.0 mass% when the SiO2 concentration is in the range of 0 to 5 mass% under the heating condition of 150°C for 15 hours, and decreases with the increase in the SiO2 concentration. From the above, it can be seen that the relationship between the sol solution concentration and the SiO2 concentration in the second synthesis method shows a similar tendency to the relationship between the sol solution concentration and the SiO2 concentration in the first synthesis method. Furthermore, as in the case of the first synthesis method, even if the sol solution concentration becomes higher than the specific concentration at a certain SiO2 concentration and the solution state becomes the second half sol, the solution state may become a sol state by appropriately adjusting the heating conditions of the autoclave treatment to increase the heating amount.

[0151] In Fig. 17, if the SiO2 concentration is X (mass%) and the specific concentration is Y1, Y1 is given as an approximate value by the following calculation formula. For reference, the approximate value of Y1 is shown by a broken line in Fig. 17.

[0152] 0 <X≦1において、 Y1=6 1 <X≦3において、 Y1=-1.5(X-1)+6 3 <X≦5において、 Y1=-0.25(X-3)+3

[0153] From the above, in one embodiment for controlling the sol solution concentration in step #25 to a specific concentration or less when the heating conditions for the autoclave treatment are 150°C for 15 hours, when the SiO2 concentration is X (mass%), the amounts of alkoxysilane and sodium aluminate charged in steps #21 and #22 and the amount of water added to the precipitate cake in step #25 can be adjusted so that the sol solution concentration is equal to or less than the specific concentration Y1 given by the above calculation formula.

[0154] [9.3] Autoclave treatment conditions for sol solution containing 1% SiO2Al2O3 As a result of the above, an example of the autoclave treatment conditions for synthesizing a sol solution containing 1% SiO2Al2O3 by the second synthesis method is as follows. Slurry solution pH value: pH2.1~pH3.4 Sol solution concentration: 6% by mass or less Heating conditions: 150℃, 15 hours

[0155] As described above, when the SiO2 concentration of the SiO2Al2O3-containing sol solution is increased to more than 1 mass%, the pH value of the slurry solution and the sol solution concentration can be adjusted accordingly in the above-mentioned manner. In addition, the heating conditions are not limited to the above-mentioned 150°C and 15 hours, and the treatment temperature and treatment time may be changed to suppress an increase / decrease in the amount of heat, as explained in the first synthesis method.

[0156]

[10] Heat resistance evaluation of the second synthesis method The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "the powder sample S2") obtained by drying and firing the SiO2Al2O3-containing sol solution synthesized by the second synthesis method was evaluated. In addition, in order to evaluate the influence on heat resistance of the process of soling the precipitate cake by autoclaving in step #25 of the second synthesis method, the heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "comparative example C2") obtained by directly drying and firing the precipitate cake prepared through steps #21 to #24 without soling was evaluated, and the heat resistance of the powder sample S2 and comparative example C2 were compared. Hereinafter, the synthesis method of comparative example C2 will be appropriately referred to as the "precipitation method" as in the synthesis method of comparative example C1.

[0157] In evaluating the heat resistance, since Comparative Example C2 is a powder sample, and further, in order to easily examine the change in heat resistance due to the difference in SiO2 concentration, a powder sample is used instead of a coating film.

[0158] The synthesis method of silica-added porous alumina of Comparative Example C2 is the same as steps #21 to #24 of the second synthesis method in the steps up to the preparation of the precipitated cake. In Comparative Example C2, the obtained precipitated cake was dried at 150°C, subsequently crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to prepare SiO2Al2O3 powder (Comparative Sample C2A). Furthermore, Comparative Sample C2B, which is obtained by adding a first heat treatment at 1200°C for 5 hours to Comparative Sample C2A, and Comparative Sample C2C, which is obtained by adding a second heat treatment at 1200°C for 30 hours to Comparative Sample C2A, were prepared as necessary.

[0159] On the other hand, the SiO2Al2O3-containing sol solution obtained through steps #21 to #24 of the second synthesis method followed by step #25 was dried at 150°C, crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (Sample S2A). Furthermore, Sample S2B was prepared by adding a first heat treatment of 1200°C for 5 hours to Sample S2A, and Sample S2C was prepared by adding a second heat treatment of 1200°C for 30 hours to Sample S2A, as necessary.

[0160] In this powder sample S2 and 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%, and 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 was adjusted according to the set value of the SiO2 concentration.

[0161] Fig. 18 shows XRD patterns indicating the crystal structures of the present samples S2A, S2B, and S2C after each heat treatment, each having an SiO2 concentration of 1 mass%, and Fig. 19 shows XRD patterns indicating the crystal structures of the comparative samples C2A, C2B, and C2C after each heat treatment, each having an SiO2 concentration of 1 mass%.

[0162] 18 and 19, it was found that even when the aluminum compound is sodium aluminate, SiO2Al2O3 can be obtained, as in the case where the aluminum compound is aluminum nitrate (see Figs. 9 and 10). Furthermore, it was found that after the second heat treatment at 1200°C for 30 hours, the comparative sample C2C obtained by the precipitation method had completely transitioned to the α phase, but the present sample S2C, which had been subjected to autoclave treatment, had not completely transitioned to the α phase.

[0163] Fig. 20 shows the measurement results of the specific surface area of ​​present sample S2A, present sample S2B, and present sample S2C (a total of 12 present powder samples S2) prepared by changing the SiO2 concentration in four ways, namely, 0 mass%, 1 mass%, 3 mass%, and 5 mass%. Fig. 21 shows the measurement results of the specific surface area of ​​comparative samples C2A, comparative samples C2B, and comparative samples C2C (a total of 12 comparative samples C2) prepared by changing the SiO2 concentration in four ways, namely, 0 mass%, 1 mass%, 3 mass%, and 5 mass%. In Figs. 20 and 21, the vertical axis of each graph represents the specific surface area (m 2 / g), and the horizontal axis represents the SiO2 concentration (mass%).

[0164] As shown in Figure 21, the specific surface areas of comparative samples C2A, C2B, and C2C at the initial stage and after the first and second heat treatments are approximately the same as the specific surface areas of comparative samples C1A, C1B, and C1C at the initial stage and after the first and second heat treatments when the aluminum compound is aluminum nitrate (see Figure 8).

[0165] As shown in Fig. 20, the specific surface areas of the present samples S2B and S2C after the first and second heat treatments are almost the same as those of the present samples S1B and S1C after the first and second heat treatments when the aluminum compound is aluminum nitrate (see Fig. 7). However, the present sample S2A after the initial heat treatment at 1000°C for 5 hours has a nearly constant specific surface area at a SiO2 concentration of 1 mass% or more. This is thought to be due to a decrease in the total pore volume accompanying the drying treatment of the sol solution, as in the case when the aluminum compound is aluminum nitrate.

[0166] [Third embodiment] A third embodiment of the present synthesis method (third synthesis method) will be described below.

[0167]

[11] Basic structure of the third synthesis method The third synthesis method is roughly divided into the following steps #31 to #36, as shown in the process transition diagram of Figure 22. In the third synthesis method, in step #36, the alkoxysilane solution prepared in step #31 is directly added to the Al2O3-containing sol solution to which no silica has been added (SiO2 concentration 0 mass%) synthesized through steps #32 to #35, to synthesize a SiO2Al2O3-containing sol solution.

[0168] The third synthesis method is different from the first and second synthesis methods, which are the first AC methods, in that a SiO2Al2O3-containing sol solution is synthesized after the autoclave treatment, in that a silica-free Al2O3-containing sol solution is synthesized after the autoclave treatment in step #35.

[0169] Hereinafter, the synthesis method in which a silica-free Al2O3-containing sol solution is prepared by autoclave treatment and then a SiO2Al2O3-containing sol solution is synthesized, as in the third synthesis method, will be referred to as a second AC (autoclave) method.

[0170] In step #31, an alkoxysilane solution containing an alkoxysilane, water, alcohol, and an inorganic acid is prepared, and 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 step #31 may be performed before step #36.

[0171] In step #33, a precipitate of aluminum hydroxide not adsorbing silicon compounds is precipitated from the aluminum solution without preparing a mixed solution of an alkoxysilane solution and an aluminum solution. Therefore, step #33 is significantly different from steps #13 and #23 in the first and second synthesis methods in which a precipitate of aluminum hydroxide adsorbing silicon compounds is precipitated.

[0172] Subsequently, in step #34, the precipitate obtained in step #33 is filtered off from the aluminum solution, and the filtered off precipitate is washed with water to produce a precipitate cake.

[0173] Subsequently, in step #35, water is added to the precipitate cake obtained in step #34 to prepare a slurry solution, which is then pH-adjusted and autoclaved to prepare an Al2O3-containing sol solution to which no silica has been added. The autoclaving process partially dehydrates the aluminum hydroxide in the slurry solution to produce boehmite, and an Al2O3-containing sol solution is prepared in which the boehmite particles are present as sol particles in a highly dispersed state.

[0174] Subsequently, 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 in which silica particles are adsorbed on boehmite particles exist in a highly dispersed state.

[0175] Step #31 is the same as steps #11 and #21 of the first and second synthesis methods, and step #32 is the same as step #1 2 and #2 2 Step #34 is the same as steps #14 and #24 in the first and second synthesis methods, except that no silica is present in the precipitated cake. Therefore, a description that overlaps with the first and second synthesis methods will be omitted.

[0176] In step #35, water is added to the precipitate cake obtained in step #34 to prepare a slurry solution, and the slurry solution is subjected to pH adjustment and then autoclaved to prepare an Al2O3-containing sol solution, which is the same as steps #15 and #25 in the first and second synthesis methods, except that no silica is present in the prepared sol solution. Furthermore, the boehmite particles are present in a highly dispersed state as sol particles in the prepared Al2O3-containing sol solution, which is the same as steps #15 and #25 in the first and second synthesis methods, except that silica is not bonded to the boehmite particles.

[0177] In one embodiment of step #33, the aluminum solution is heated to reflux, and then nitric acid is added dropwise to adjust the pH and the solution is stirred. The heating to reflux and pH adjustment promote hydrolysis of the aluminum solution, resulting in the deposition of aluminum hydroxide precipitate.

[0178] In one embodiment of step #35, the amount of water added to the precipitate cake is adjusted to control the sol solution concentration (mass%), which is the Al2O3 content relative to the total mass of the synthesized Al2O3-containing sol solution, to a specific concentration or less at which the solution state after autoclaving becomes a sol state, and the pH value of the slurry solution is adjusted to within a specific pH range at which the solution state after autoclaving becomes a sol state.

[0179] In this embodiment, the total mass of the silica-free Al2O3-containing sol solution is kept constant relative to the capacity of the autoclave used in the autoclave treatment, so the concentration of the sol solution is controlled by adjusting the amount of aluminum compound charged in step #32 and the amount of water added to the precipitate cake in step #35.

[0180] The specific concentration in step #35 is the specific concentration of SiO2 concentration 0 mass% (silica not added) in step #15 of the first synthesis method, or the specific concentration of SiO2 concentration 0 mass% in step #25 of the second synthesis method, depending on the aluminum compound used. The specific pH range in step #35 is the specific pH range of SiO2 concentration 0 mass% in step #15 of the first synthesis method, or the specific pH range of SiO2 concentration 0 mass% in step #25 of the second synthesis method, depending on the aluminum compound used. Therefore, in the third synthesis method, unlike the first and second synthesis methods, in step #35, 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, autoclave treatment can be performed under the condition of a SiO2 concentration of 0 mass%, which has the highest specific concentration and the widest specific pH range (see Figures 3, 4, 16, and 17), making it easier to prepare a SiO2Al2O3-containing sol solution in a sol state compared to the first AC method, and further enabling the preparation of a SiO2Al2O3-containing sol solution with a high solution concentration.

[0181] The first AC method is divided into the first and second synthesis methods according to the aluminum compound, and there are slight differences between step #13 of the first synthesis method and step #23 of the second synthesis method in some treatments (heating under reflux and pH adjustment). On the other hand, in the second AC method, there is no process of preparing a mixed solution of an alkoxysilane solution and an aluminum solution in step #33, which corresponds to steps #13 and #23, so the treatment content of step #33 is the same regardless of whether the aluminum compound is aluminum nitrate, aluminum chloride, aluminum sulfate, or sodium aluminate.

[0182]

[12] Example of the third synthesis method Hereinafter, an example of steps #31 to #35 for synthesizing a sol solution containing SiO2Al2O3 with a SiO2 concentration of 1 mass % will be described. However, explanations that overlap with the examples of the first and second synthesis methods will be omitted as appropriate.

[0183] Hereinafter, Example 5 will be described, in which aluminum nitrate is used as the aluminum compound.

[0184] In step #31, a transparent and uniform 5.88% TEOS solution (alkoxysilane solution) was obtained in the same manner as in step #11 of Example 1. In step #32, an aluminum nitrate aqueous solution (aluminum solution) was obtained in the same manner as in step #12 of Example 1. However, in step #32, it is preferable to increase the amount of water added to the aluminum solution by the same amount as the TEOS solution added in step #13 of Example 1, rather than the amount of water in step #12 of Example 1. This makes the total amount of aluminum solution at the time of precipitation of the precipitate in step #33 the same as the total amount of the mixed solution at the time of precipitation of the precipitate in step #13 of Example 1.

[0185] In step #33, the aluminum nitrate aqueous solution obtained in step #32 was heated to reflux and the pH was adjusted in the same manner as in step #13 of Example 1, without adding the 5.88% TEOS solution, and a precipitate of aluminum hydroxide was deposited in the aluminum nitrate aqueous solution.

[0186] In step #34, a precipitated cake was obtained in exactly the same manner as in step #14 of Example 1. Subsequently, in step #35, a 0% SiO2Al2O3-containing sol solution (Al2O3-containing sol solution) without added silica was obtained in exactly the same manner as in step #15 of Example 1.

[0187] The total amount of the Al2O3-containing sol solution obtained in step #35 was 80 g, and the amount of Al2O3 powder obtained by drying this sol solution was 1.98 g. The sol solution concentration of the 80 g total sol solution containing 1.98 g of Al2O3 powder was 2.475 mass%.

[0188] Subsequently, 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 SiO2Al2O3-containing sol solution (1%SiO2Al2O3 2.46% sol) with a SiO2 concentration of 1 mass% and a sol solution concentration of 2.46 mass%. The SiO2 concentration can be adjusted by the amount of TEOS solution added. Even when the TEOS solution was added to the Al2O3-containing sol solution, the solution maintained a sol state, and no precipitation or gelation was observed.

[0189] Above, Example 5, which uses aluminum nitrate as the aluminum compound, has been described with reference to Example 1 of the first synthesis method. In the case of Example 6, which uses sodium aluminate as the aluminum compound, in step #33, the sodium aluminate aqueous solution obtained in step #32 is heated under reflux and pH adjusted in the same manner as in step #23 of Example 4 without adding 5.88% TEOS solution, and aluminum hydroxide precipitate is precipitated in the sodium aluminate aqueous solution, and a 1% SiO2Al2O3-containing sol solution can be synthesized in the same manner based on Example 4 of the second synthesis method.

[0190] In the case of Example 6, similarly to Example 5, it is preferable to increase the amount of water added to the aluminum solution in step #32 from the amount of water in step #22 of Example 2 by the same amount as the TEOS solution added in step #23 of Example 2 so that the total amount of aluminum solution during precipitation of the precipitate in step #33 is the same as the total amount of the mixed solution during precipitation of the precipitate in step #23 of Example 2.

[0191] Furthermore, in the case of Example 6, the pH adjustment treatment for the sodium aluminate aqueous solution in step #33 is different from that in Example 5 in that the pH is adjusted from the basic side to the acidic side using nitric acid, and therefore the target value for the pH adjustment is set to pH 7.5, which is lower than the target value pH 8.0 in step #23 of Example 4 of the second synthesis method (first AC method), depending on the amount of alkoxysilane solution added. This is because, in the second synthesis method (first AC method), a decrease in pH value occurs due to the addition of an alkoxysilane solution in step #23, but in the second synthesis method (first AC method), no decrease in pH value occurs because no alkoxysilane solution is added in step #33.

[0192]

[13] Autoclave treatment conditions for the third synthesis method As the autoclave treatment conditions in the third synthesis method, the autoclave treatment conditions in the first synthesis method or the second synthesis method in which the SiO2 concentration is 0 mass % can be used depending on the aluminum compound used.

[0193]

[14] Heat resistance evaluation of the third synthesis method (1) The heat resistance of the SiO2Al2O3 powder (hereinafter collectively referred to as "powder sample S3") obtained by drying and firing the SiO2Al2O3-containing sol solution synthesized by 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%.

[0194] As the present powder sample S3, the 1% SiO2Al2O3-containing sol solution obtained through steps #31 to #36 of the third synthesis method described in Example 5 was dried at 150°C, subsequently pulverized into powder form, and sintered in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (present sample S3A). Furthermore, present sample S3B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S3A, and present sample S3C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S3A.

[0195] Table 7 below shows the specific surface area (m2) of the present sample S3A, the present sample S3B, and the present sample S3C, which were prepared with an SiO2 concentration of 1 mass%. 2 For comparison, Table 7 also shows the measurement results of the specific surface area of ​​the present sample S1A, the present sample S1B, and the present sample S1C, which were prepared by the first synthesis method and had an SiO2 concentration of 1 mass %, respectively.

[0196] [Table 7]

[0197] As shown in Table 7, the SiO2Al2O3 powder (present samples S3A to S3C) made from the SiO2Al2O3-containing sol solution synthesized by the third synthesis method (Method 2 AC) showed a specific surface area equivalent to that of the SiO2Al2O3 powder (present samples S1A to S1C) made from the SiO2Al2O3-containing sol solution synthesized by the first synthesis method (Method 1 AC) under each heat treatment condition, indicating that sufficient heat resistance can be obtained even when the third synthesis method is used.

[0198] From the above, it was confirmed that by adding TEOS to an Al2O3-containing sol solution without added silica, phenomena such as precipitation and gelation do not occur, and it is possible to easily synthesize a SiO2Al2O3-containing sol solution.

[0199] Next, as the present powder sample S3, aluminum nitrate was used as the aluminum compound, and in addition to the above-mentioned present samples S3A to S3C with an SiO2 concentration of 1 mass%, five present samples S3A to S3C (initial heat treatment, first heat treatment, second heat treatment) were prepared by changing the SiO2 concentration in five ways, namely, 0 mass%, 3 mass%, 5 mass%, and 10 mass%, and the specific surface area (m 2 23 to 25 show the results of measuring the specific surface area of ​​each of the 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%, respectively, and the results of measuring the specific surface area of ​​each of the 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%, respectively, are shown in Figs. 23 to 25 for each heat treatment.

[0200] Furthermore, Fig. 26 shows XRD patterns showing the crystal structures after each heat treatment in the present sample S3A, the present sample S3B, and the present sample S3C, each having an SiO2 concentration of 1 mass%, respectively. Note that Figs. 9 and 10 show XRD patterns showing the crystal structures after each heat treatment in the present sample S1A, the present sample S1B, and the present sample S1C, each having an SiO2 concentration of 1 mass%, respectively, produced by the first synthesis method, and the comparative sample C1A, the comparative sample C1B, and the comparative sample C1C, each having an SiO2 concentration of 1 mass%, respectively, produced by the precipitation method.

[0201] 23 to 25, the SiO2Al2O3 powder (Samples S3A to S3C) made from the SiO2Al2O3-containing sol solution synthesized by the third synthesis method (Method 2AC) showed almost no increase in specific surface area even when the SiO2 concentration increased to 10 mass%, similar to the SiO2Al2O3 powder (Samples S1A to S1C) made from the SiO2Al2O3-containing sol solution synthesized by the first synthesis method (Method 1AC) under each heat treatment condition. This is considered to be because, as described above in the explanation of the measurement results in Table 3, the total pore volume of Al2O3 decreased due to the surface tension of water during the process of gel formation by drying the sol solution.

[0202] As shown in Figure 26, the SiO2Al2O3 powder (this sample S3C) produced by the third synthesis method (second AC method) retains θ-Al2O3 even after the second heat treatment (1200℃ 30 hours), and does not completely transition to the α phase. This confirms that the same heat resistance as the first synthesis method (first AC method) can be obtained when using the third synthesis method (second AC method).

[0203]

[15] Heat resistance evaluation of the third synthesis method (2) The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "powder sample S4") obtained by drying and firing the SiO2Al2O3-containing sol solution synthesized by the third synthesis method instead of the second synthesis method using sodium aluminate as the aluminum compound was evaluated. In the following heat resistance evaluation, the SiO2 concentration was set to 5 mass% and 10 mass%.

[0204] As the present powder sample S4, the SiO2Al2O3-containing sol solutions with SiO2 concentrations of 5% and 10% by mass obtained through steps #31 to #36 of Example 6 of the third synthesis method were dried at 150°C, crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (present sample S4A). Furthermore, present sample S4B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S4A, and present sample S4C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S4A.

[0205] Table 8 below shows the specific surface area (m 2 The measurement results of the specific surface area of ​​each of the samples S2A to S2C with an SiO2 concentration of 5 mass% produced by the second synthesis method (method 1AC) and the specific surface area of ​​each of the comparative samples C2A to C2C with SiO2 concentrations of 5 mass% and 10 mass% produced by the precipitation method are also shown in Table 8 for comparison.

[0206] [Table 8]

[0207] First, as shown in Table 8, at an SiO2 concentration of 5 mass%, the present samples S4A to S4C synthesized by the third synthesis method exhibit a specific surface area equivalent to that of the present samples S2A to S2C synthesized by the second synthesis method and the comparative samples C2A to C2C synthesized by the precipitation method, and further, at an SiO2 concentration of 10 mass%, the present samples S4A to S4C synthesized by the third synthesis method exhibit a specific surface area equivalent to that of the comparative samples C2A to C2C synthesized by the precipitation method. This shows that when the third synthesis method is used, sufficient heat resistance can be obtained even if sodium aluminate is used as the aluminum compound.

[0208] Furthermore, from the measurement results shown in Table 8, it was found that when sodium aluminate was used as the aluminum compound, the upper limit of the SiO2 concentration was 5 mass% in the second synthesis method of the present samples S2A to S2C, as shown in FIG. 16, but by using the third synthesis method, the SiO2 concentration could be increased to 10 mass%, as in the present samples S4A to S4C.

[0209] Next, as the present powder sample S4, sodium aluminate was used as the aluminum compound, and in addition to the above-mentioned present samples S4A to S4C with an SiO2 concentration of 1 mass%, five present samples S4A to S4C (initial heat treatment, first heat treatment, second heat treatment) were prepared by changing the SiO2 concentration to 0 mass%, 3 mass%, 5 mass%, and 10 mass%, and the specific surface area (m 2 27 to 29 show the results of measuring the specific surface area of ​​each of the 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%, respectively, and the results of measuring the specific surface area of ​​each of the 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%, respectively, are shown in Figs. 27 to 29 for each heat treatment.

[0210] Furthermore, Fig. 30 shows XRD patterns showing the crystal structures after each heat treatment in the present sample S4A, the present sample S4B, and the present sample S4C, each having an SiO2 concentration of 1 mass%. Note that Figs. 18 and 19 show XRD patterns showing the crystal structures after each heat treatment in the present sample S2A, the present sample S2B, and the present sample S2C, each having an SiO2 concentration of 1 mass% and prepared by the second synthesis method, and the comparative sample C2A, the comparative sample C2B, and the comparative sample C2C, each having an SiO2 concentration of 1 mass% and prepared by the precipitation method.

[0211] As shown in Figures 27 to 29, the SiO2Al2O3 powder produced from the SiO2Al2O3-containing sol solution synthesized by the third synthesis method (second AC method) shows roughly the same heat resistance both when sodium aluminate is used as the aluminum compound and when aluminum nitrate is used as the aluminum compound.

[0212] Furthermore, as shown in Figure 30, the XRD patterns of the SiO2Al2O3 powders (S4A-S4C) produced by the third synthesis method (second AC method) show peaks similar to those of the comparative samples (C2A-C2C) produced by the precipitation method. This confirms that the third synthesis method (second AC method) also provides heat resistance similar to that of the precipitation method and the first synthesis method (first AC method).

[0213] [Fourth embodiment] A fourth embodiment of the present synthesis method (fourth synthesis method) will be described below.

[0214]

[16] Basic structure and examples of the fourth synthesis method As shown in the process transition diagram of FIG. 31, the fourth synthesis method is configured by adding, as a post-treatment to any one of the first, second, and third synthesis methods (step #40), step #41 in which an organic solvent having a boiling point higher than that of water and a surface tension lower than that of water (hereinafter, appropriately referred to as a “specific additive”) is added to the SiO2Al2O3-containing sol solution synthesized by any one of the synthesis methods.

[0215] As explained in the above “[4] Evaluation of heat resistance of the first synthesis method (1)”, step #41 of the fourth synthesis method is provided as a measure against the reduction in the total pore volume of Al2O3 due to the surface tension of evaporating water in the process of drying the SiO2Al2O3-containing sol solution synthesized by any one of the first to third synthesis methods in step #40 to produce a transparent gel.

[0216] In one embodiment of step #41, ethylene glycol (EG) or N,N-dimethylformamide (DMF) is preferably used as the specific additive. The surface tension of EG is 48.4 dyne / cm, and the surface tension of DMF is 36.8 dyne / cm, both of which are lower than the surface tension of water (72.8 dyne / cm).

[0217] Furthermore, 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, or third synthesis methods (step #40) in an amount of 3 mass% based on the total amount of the sol solution after the addition of the specific additive, and the mixture is stirred to prepare a SiO2Al2O3-containing sol solution to which the specific additive has been added.

[0218] As an example (Example 7) of the above-mentioned preferred embodiment of the fourth synthesis method, in step #40, EG and DMF were added to SiO2Al2O3-containing sol solutions with SiO2 concentrations of 3 mass% and 10 mass% synthesized by the first synthesis method using aluminum nitrate as an aluminum compound, and stirred in step #41 to prepare four types of SiO2Al2O3-containing sol solutions with specific additives added. The sol solution concentration in Example 7 was set to, for example, 2.5 mass%, the same as in Example 1 of the first synthesis method. Furthermore, as another example (Example 8) of the above-mentioned preferred embodiment of the fourth synthesis method, sodium aluminate was used as an aluminum compound, and DMF was added as a specific additive in step #41 to SiO2Al2O3-containing sol solutions with SiO2 concentrations of 5 mass% and 10 mass% synthesized by the third synthesis method instead of the second synthesis method, and stirred to prepare two types of SiO2Al2O3-containing sol solutions with specific additives added. The sol solution concentration in Example 8 was set to, for example, 2.5 mass%, the same as in Example 7 above.

[0219] Furthermore, as another example (Example 9) of the above-mentioned preferred embodiment of the fourth synthesis method, in step #40, aluminum nitrate was used as the aluminum compound, and a 0% SiO2Al2O3-containing sol solution with a sol solution concentration of 9 mass% was prepared using the third synthesis method instead of the first synthesis method, and then 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%, and DMF was added as a specific additive to obtain sufficient heat resistance, and the mixture was stirred at room temperature to prepare a SiO2Al2O3-containing sol solution with the specific additive added. It was confirmed that by using the third synthesis method in step #40, a SiO2Al2O3-containing sol solution with a high sol solution concentration can be prepared without phenomena such as precipitation and gelation.

[0220]

[17] Heat resistance evaluation of the fourth synthesis method (1) The four types of SiO2Al2O3-containing sol solutions of Example 7 were dried at 150°C to form dry gels, which were then fired in a first heat treatment at 1200°C for 5 hours to prepare four types of SiO2Al2O3 powders (hereinafter collectively referred to as "Sample S5B"). The specific surface area and total pore volume of the four types of Sample S5B were measured to evaluate their heat resistance.

[0221] The specific surface area (m2) of the above four types of sample S5B is shown in Table 9 below. 2 / g) and total pore volume (cm 3 The specific surface area (m2) of the present sample S1B and the comparative sample C1B, which were prepared with SiO2 concentrations of 3 mass% and 10 mass%, respectively, shown in Table 3 of “[4] Evaluation of heat resistance of the first synthesis method (1)” above, is shown in Table 3. 2 / g) and total pore volume (cm 3 / g) are also shown in Table 9 for comparison. Sample S1B is a SiO2Al2O3 powder obtained by drying and pulverizing a SiO2Al2O3-containing sol solution with SiO2 concentrations of 3 mass% and 10 mass% synthesized by the first synthesis method using aluminum nitrate as an aluminum compound at 150°C without adding any specific additives, forming a powdered dry gel, and then firing it in a first heat treatment at 1200°C for 5 hours. Comparative sample C1B is a SiO2Al2O3 powder obtained by drying and pulverizing a precipitation cake with SiO2 concentrations of 3 mass% and 10 mass% obtained by a precipitation method using aluminum nitrate as an aluminum compound at 150°C, forming a powdered dry gel, and then firing it in a first heat treatment at 1200°C for 5 hours.

[0222] [Table 9]

[0223] As shown in Table 9, in both cases of SiO2 concentration of 3 mass% and 10 mass%, by adding the specific additives EG and DMF in step #41, the specific surface area and total pore volume of the present sample S5B are increased compared to the specific surface area and total pore volume of the present sample S1B synthesized without adding the specific additives. Moreover, the increase is larger as the SiO2 concentration is higher.

[0224] Figure 32 shows the pore distribution (BJH plot) of two types of samples, S5B and S1B, with an SiO2 concentration of 3 mass% and specific additives of EG and DMF, and Figure 33 shows the pore distribution (BJH plot) of two types of samples, S5B and S1B, with an SiO2 concentration of 10 mass% and specific additives of EG and DMF. In Figures 32 and 33, the circle (●) indicates the pore distribution of sample S1B (no specific additive), the triangle (▲) indicates the pore distribution of sample S5B (EG added), and the square (■) indicates the pore distribution of sample S5B (DMF added), respectively. The vertical axis is the differential pore volume dV p / dr p (m 3 / g / nm), and the horizontal axis is the pore diameter r p (nm) are shown.

[0225] As shown in Figures 32 and 33, in both cases of SiO2 concentrations of 3 mass% and 10 mass%, by adding the specific additives EG and DMF in step #41, the total pore volume and most frequent pore size of the present sample S5B were larger than those of the present sample S1B synthesized without adding the specific additives. Total Pore Volume and Most common pore size When the SiO2 concentration was 10 mass%, the most frequent pore size for sample S1B, which had no specific additives, was 4.17 nm, whereas the most frequent pore size for sample S5B, which had EG and DMF added, expanded to 5.45 nm. From the above, it was found that adding an organic solvent with a higher boiling point and lower surface tension than water suppresses the decrease in the pore volume of SiO2Al2O3 and is effective in improving the specific surface area.

[0226] Next, as Example 7 of the fourth synthesis method in which an SiO2Al2O3-containing sol solution is synthesized by the first synthesis method using aluminum nitrate as the aluminum compound in step #40, in addition to the above four types of present sample S5B (SiO2 concentration: 3 mass%, 10 mass%), present samples S5A to S5C (initial heat treatment, first heat treatment, second heat treatment) were prepared in which the SiO2 concentration was changed to 0 mass%, 1 mass%, and 5 mass%, and the specific additive was DMF. Figures 34 to 36 show the specific surface area (m 2 The measurement results of (g) are shown for each heat treatment. Furthermore, as Example 9 of the fourth synthesis method in which an SiO2Al2O3-containing sol solution is synthesized by the third synthesis method using aluminum nitrate as the aluminum compound in step #40, an SiO2Al2O3-containing sol solution was prepared by changing the SiO2 concentration to 0 mass%, 3 mass%, 5 mass%, and 10 mass%, in addition to 1 mass% SiO2 concentration, and DMF was added as a specific additive. The SiO2Al2O3-containing sol solution to which the specific additive was added was stirred at room temperature and then calcined at 1000°C for 5 hours (initial heat treatment) to obtain SiO2Al2O3 powder (this sample S 5a A) was prepared. Furthermore, this sample S 5a This sample S was made by adding the first heat treatment at 1200℃ for 5 hours to A. 5a B and this sample S 5aThis sample S was made by adding a second heat treatment at 1200℃ for 30 hours to A. 5a Figures 34 to 36 show the results of the samples S and C with different SiO2 concentrations. 5a A, this sample S 5a B and this sample S 5a C's specific surface area (m 2 34 to 36 show, for comparison purposes, the measurement results of the specific surface area of ​​each of comparative samples C1A, C1B, and C1C, which were prepared by a 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%, respectively, and are shown for each heat treatment.

[0227] As shown in Figures 34 to 36, regardless of whether the first or third synthesis method is used in step #40 of the fourth synthesis method, a specific surface area equivalent to that of the precipitation method can be obtained by adding a specific additive in step #41 to the SiO2Al2O3-containing sol solution synthesized in step #40.

[0228]

[18] Heat resistance evaluation of the fourth synthesis method (2) The two types of SiO2Al2O3-containing sol solutions of Example 8 were dried and fired in the same manner as in

[17] Evaluation of heat resistance of the fourth synthesis method (1) above to prepare two types of SiO2Al2O3 powders (hereinafter collectively referred to as "present powder sample S6"). The heat resistance of the two types of present powder sample S6 was evaluated.

[0229] As the present powder sample S6, two kinds of SiO2Al2O3-containing sol solutions with SiO2 concentrations of 5 mass% and 10 mass% obtained through step #40 (step #31 to step #36 of Example 6 of the third synthesis method) and step #41 of the fourth synthesis method were dried at 150°C, crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (present sample S6A). Furthermore, present sample S6B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S6A, and present sample S6C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S6A.

[0230] Table 10 below shows the specific surface area (m2) of samples S6A, S6B, and S6C, which were prepared with SiO2 concentrations of 5% and 10% by mass. 2 For comparison, the specific surface areas (m 2 Table 10 also shows the measurement results of the specific surface area of ​​each of the present samples S2A to S2C with an SiO2 concentration of 5 mass% prepared by the second synthesis method, and the measurement results of the specific surface area of ​​each of the comparative samples C2A to C2C with SiO2 concentrations of 5 mass% and 10 mass% prepared by the precipitation method.

[0231] [Table 10]

[0232] As shown in Table 10, except for the present sample S6B with a SiO2 concentration of 5 mass%, in both cases of SiO2 concentrations of 5 mass% and 10 mass%, by adding the specific additive DMF in step #41, the specific surface area of ​​the present samples S6A to S6C synthesized by the third synthesis method (second AC method) is increased compared to the specific surface area of ​​the present samples S4A to S4C synthesized by the same third synthesis method (second AC method) without adding the specific additive. The specific surface area of ​​the present sample S6B with a SiO2 concentration of 5 mass% is slightly lower than that of the present sample S4B synthesized by the same third synthesis method without adding the specific additive, but the specific surface area is almost the same. From the above, it was found that adding an organic solvent with a higher boiling point and lower surface tension than water to the SiO2Al2O3-containing sol solution synthesized by the third synthesis method is effective in suppressing the decrease in the pore volume of SiO2Al2O3 and improving the specific surface area.

[0233] Next, in step #40, sodium aluminate was used as the aluminum compound, and the SiO2Al2O3-containing sol solution was synthesized by the third synthesis method instead of the second synthesis method, as Example 8 of the fourth synthesis method. In addition to the above two types of present samples S6A to S6C (SiO2 concentration: 5 mass%, 10 mass%), present samples S6A to S6C (initial heat treatment, first heat treatment, second heat treatment) were prepared with the SiO2 concentration changed to 0 mass%, 1 mass%, and 3 mass% and the specific additive was DMF. To , the specific surface area (m 2 The measurement results of the amount of SiO2Al2O3 per unit mass / g are shown for each heat treatment. Furthermore, as Example 10 of the fourth synthesis method in which a SiO2Al2O3-containing sol solution is synthesized by the second synthesis method using sodium aluminate as the aluminum compound in step #40, SiO2Al2O3-containing sol solutions were prepared by changing the SiO2 concentration in five ways, 0 mass%, 1 mass%, 3 mass%, 5 mass%, and 10 mass%, and DMF was added as a specific additive. The SiO2Al2O3-containing sol solution to which the specific additive was added was stirred at room temperature and then calcined at 1000°C for 5 hours (initial heat treatment) to obtain SiO2Al2O3 powder (this sample S). 6a A) was prepared. Furthermore, this sample S 6a This sample S was made by adding the first heat treatment at 1200℃ for 5 hours to A. 6a B and this sample S 6a This sample S was made by adding a second heat treatment at 1200℃ for 30 hours to A. 6a Figures 37 to 39 show the results of the present sample S with each SiO2 concentration. 6a A, this sample S 6a B and this sample S 6a C's specific surface area (m 2 37 to 39 show the measurement results of the specific surface area of ​​each of the comparative samples C2A, C2B, and C2C, which were prepared by a 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%, for each heat treatment.

[0234] As shown in Figures 37 to 39, when the aluminum compound is sodium aluminate and either the second or third synthesis method is used in step #40 of the fourth synthesis method, a specific additive is added in step #41 to the SiO2Al2O3-containing sol solution synthesized in step #40, thereby making it possible to obtain a specific surface area equivalent to that obtained by the precipitation method.

[0235] [Fifth embodiment] A fifth embodiment of the present synthesis method (fifth synthesis method) will be described below.

[0236] The present inventors have already reported the effect of improving heat resistance by adding barium to SiO2Al2O3 synthesized by a precipitation method (see Patent Document 6 above). In the fifth embodiment, we investigated whether the effect of improving heat resistance by adding barium, similar to that by the precipitation method, can be obtained in the SiO2Al2O3-containing sol solution synthesized by the above-mentioned first to third synthesis methods.

[0237]

[19] Basic structure and examples of the fifth synthesis method As shown in the process transition diagram of FIG. 40, the fifth synthesis method is configured by adding, as a post-treatment to any one of the first, second, and third synthesis methods (step #50), step #51 in which a barium compound powder is added to and stirred in the SiO2Al2O3-containing sol solution synthesized by any one of the first, second, and third synthesis methods.

[0238] In one embodiment of step #51, the barium compound is preferably any one of barium nitrate, barium hydroxide, barium chloride, and barium acetate. Note that, as the barium hydroxide, barium hydroxide octahydrate is used, and as the barium chloride, barium chloride dihydrate is used.

[0239] In the following description, the Ba-doped SiO2Al2O3 obtained by drying and firing the Ba-doped SiO2Al2O3-containing sol solution synthesized in step #51 is appropriately expressed as Z%BaO-X%SiO2Al2O3, where the SiO2 concentration (mass concentration of SiO2 relative to SiO2Al2O3) is X mass% and the BaO concentration (mass concentration of BaO relative to SiO2Al2O3) is Z mass%.

[0240] When the Ba-added SiO2Al2O3-containing sol solution synthesized in step #51 is dried, a boehmite gel to which a barium compound (e.g., barium nitrate) and silica are added is produced. The barium compound is added to the sol solution and stirred, so that it is dispersed in the gel after drying. Therefore, according to the fifth synthesis method, the barium compound is considered to be present in a highly dispersed state in the dried gel, compared to the case in which a barium compound (barium nitrate) is added to the precipitate disclosed in the above Patent Document 6. Furthermore, when this boehmite gel is fired at 1000°C, SiO2Al2O3 and BaO are produced. These points are clear from the XRD pattern shown in FIG. 41, which will be described later.

[0241] As an example (Example 11) of the fifth synthesis method, a case of preparing a 6.5%BaO-1%SiO2Al2O3-containing sol solution, which is a precursor for synthesizing 6.5%BaO-1%SiO2Al2O3 with a SiO2 concentration of 1 mass% and a BaO concentration of 6.5 mass%, which showed high heat resistance in the above Patent Document 6, will be described. In Example 11, in step #50, aluminum nitrate is used as an aluminum compound to obtain a total amount of 80 g of 1%SiO2Al2O3 2.5% sol obtained through steps #11 to #15 of Example 1 of the first synthesis method, and in step #51, 0.2386 g of barium nitrate is added and stirred at room temperature to prepare a 6.5%BaO-1%SiO2Al2O3 2.5% sol.

[0242] In Example 11, when barium hydroxide, barium chloride or barium acetate is used as the barium compound instead of barium nitrate, 6.5%BaO-1%SiO2Al2O3 2.5% sol can be similarly prepared by adding 0.2880g of barium hydroxide octahydrate, 0.2230g of barium chloride dihydrate or 0.2332g of barium acetate to a total of 80g of 1%SiO2Al2O3 2.5% sol and stirring at room temperature.

[0243] As another example (Example 12) of the fifth synthesis method, a case of preparing a 6.5%BaO-1%SiO2Al2O3-containing sol solution as in Example 11 will be described. In Example 12, in step #50, sodium aluminate is used as an aluminum compound, and 80 g of 1%SiO2Al2O3 2.5% sol is obtained through steps #21 to #25 of Example 4 of the second synthesis method. In step #51, 0.2386 g of barium nitrate is added to the 1%SiO2Al2O3 2.5% sol, and the mixture is 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 instead of barium nitrate as a barium compound.

[0244]

[20] Heat resistance evaluation of the fifth synthesis method (1) The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "this powder sample S7") obtained by drying and firing a 6.5%BaO-1%SiO2Al2O3 2.5% sol synthesized in Example 11 of the fifth synthesis method using aluminum nitrate as the aluminum compound and barium nitrate as the barium compound was evaluated.

[0245] As the present powder sample S7, the 6.5%BaO-1%SiO2Al2O3 2.5% sol obtained through step #50 (step #11 to step #15 of Example 1 of the first synthesis method) and step #51 of the fifth synthesis method example 11 was dried at 150°C, subsequently pulverized into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce 6.5%BaO-1%SiO2Al2O3 powder (present sample S7A). Furthermore, the present sample S7B was produced by adding a first heat treatment at 1200°C for 5 hours to the present sample S7A, and the present sample S7C was produced by adding a second heat treatment at 1200°C for 30 hours to the present sample S7A. The present powder sample S7 before the initial heat treatment after drying at 150°C is referred to as the present dried sample S7D (see FIG. 41 described later).

[0246] As a comparative example C7 for the powder sample S7, instead of the fifth synthesis method, a 6.5%BaO-1%SiO2Al2O3 2.5% sol was prepared by the precipitation method using aluminum nitrate as the aluminum compound, dried at 150°C, crushed into powder, and fired 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 was prepared by adding a first heat treatment of 1200°C for 5 hours to comparative sample C7A, and comparative sample C7C was prepared by adding a second heat treatment of 1200°C for 30 hours to comparative sample C7A.

[0247] Table 11 below shows the specific surface area (m2) of the prepared samples S7A, S7B, and S7C. 2 / g) Measurement results , and Comparative Sample C7A, Comparative Sample C7B, and Comparative Sample C7C Each specific surface area (m 2 / g) The measurement results are shown below. Furthermore, for comparison, the specific surface area (m2) of each of the present samples S1A, S1B, and S1C obtained by drying and firing the Ba-free SiO2Al2O3-containing sol solution with an SiO2 concentration of 1 mass% synthesized in Example 1 of the first synthesis method described above in "[4] Evaluation of heat resistance of the first synthesis method (1)" is also shown. 2The results of the measurement of the specific surface area (m2 / g) of Comparative Samples C1A, C1B, and C1C, which were synthesized by the precipitation method with a SiO2 concentration of 1 mass% and no barium added (see FIG. 7), are shown in Table 7. 2 The measurement results of the total molecular weight (Mg) (see FIG. 8) are also shown in Table 11.

[0248] [Table 11]

[0249] As shown in Table 11, in the samples (Sample S7A, Sample S1A, Comparative Sample C7A, Comparative Sample C1A) after sintering (initial heat treatment) at 1000°C for 5 hours, no significant difference in specific surface area was observed regardless of whether barium was added or not in any synthesis method. However, in the samples (Sample S7B and S7C, Sample S1B and S1C, Comparative Sample C7B and C7C, Comparative Sample 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 confirmed by adding barium in any synthesis method. In addition, in the barium-added samples subjected to the first and second heat treatments, the samples S7B and S7C of the fifth synthesis method showed a higher specific surface area than the comparative samples C7B and C7C in each heat treatment.

[0250] Figure 41 shows XRD patterns indicating the crystal structures of Samples S7A, S7B, S7C, and S7D before and after each heat treatment, and Figure 42 shows XRD patterns indicating the crystal structures of Comparative Samples C7A, C7B, and C7C after each heat treatment.

[0251] First, in the XRD pattern of the dried sample S7D in FIG. 41, peaks of boehmite and barium nitrate appear, and as described above, it was confirmed that a boehmite gel with added barium nitrate and silica was formed at the drying stage.

[0252] As shown in Figures 41 and 42, the peak of the diffraction pattern of α-Al2O3 in the present sample S7C and comparative sample C7C, which were subjected to the second heat treatment at 1200℃ for 30 hours, is significantly lower in the present sample S7C, which was synthesized by the fifth synthesis method, than in the comparative sample C7C, which was synthesized by the precipitation method, and it was confirmed that the phase transition to the α phase was suppressed. In addition, in the present sample S7B and comparative sample C7B, which were subjected to the first heat treatment at 1200℃ for 5 hours, the formation of the α phase was not observed in the present sample S7B, but the formation of barium aluminate (barium monoaluminate: BaO·Al2O3, barium hexaaluminate: BaO·6Al2O3) was confirmed. Barium aluminate is known to inhibit the mass transfer of Al at high temperatures, thereby suppressing the phase transition to the α phase. In the fifth synthesis method, barium nitrate powder is added to the sol solution, which results in higher dispersibility of barium compared to the precipitation method. As a result, barium aluminate is produced faster than the α phase, which is thought to be effective in improving heat resistance.

[0253] From the above, it was confirmed that the fifth synthesis method, in which barium is added to a sol solution containing SiO2Al2O3, can provide a higher heat resistance than the precipitation method.

[0254] Next, in Table 12 below, the present powder sample S7 (present sample S7A, present sample S7B, present sample S7C) was prepared using barium nitrate, barium hydroxide, barium chloride, and barium acetate as the barium compound in Example 11, and the specific surface area (m 2 The results of measuring the specific surface area (g) of each barium compound are shown in Table 12. As shown in Table 12, whichever of these four barium compounds was used, a high specific surface area was shown after the second heat treatment at 1200°C for 30 hours, and furthermore, the specific surface area was higher than that of the comparative sample C7C produced by the precipitation method shown in Table 11. As a result, it was confirmed that barium nitrate, barium hydroxide, barium chloride, and barium acetate can be suitably used as the barium compound to be added to the SiO2Al2O3-containing sol solution.

[0255] [Table 12]

[0256]

[21] Heat resistance evaluation of the fifth synthesis method (2) The heat resistance of the SiO2Al2O3 powder (hereinafter collectively referred to as "this powder sample S8") obtained by drying and firing the 6.5%BaO-1%SiO2Al2O3 2.5% sol synthesized in Example 12 of the fifth synthesis method using sodium aluminate as the aluminum compound was evaluated.

[0257] As the present powder sample S8, the 6.5%BaO-1%SiO2Al2O3 2.5% sol obtained through step #50 (step #21 to step #25 of Example 4 of the second synthesis method) and step #51 of Example 12 of the fifth synthesis method was dried at 150°C, subsequently crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce 6.5%BaO-1%SiO2Al2O3 powder (present sample S8A). Furthermore, present sample S8B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S8A, and present sample S8C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S8A.

[0258] As a comparative example C8 for the powder sample S8, instead of the fifth synthesis method, a 6.5%BaO-1%SiO2Al2O3 2.5% sol was prepared by the precipitation method using sodium aluminate as the aluminum compound, dried at 150°C, crushed into powder, and fired 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 was prepared by adding a first heat treatment of 1200°C for 5 hours to comparative sample C8A, and comparative sample C8C was prepared by adding a second heat treatment of 1200°C for 30 hours to comparative sample C8A.

[0259] Table 13 below shows the specific surface area (m2) of the samples S8A, S8B, and S8C. 2 / g) Measurement results , and Comparative Sample C8A, Comparative Sample C8B, and Comparative Sample C8 Each specific surface area (m2 / g) Furthermore, for comparison, the specific surface area (m2) of each of the present samples S2A, S2B, and S2C obtained by drying and firing a Ba-free SiO2Al2O3-containing sol solution with an SiO2 concentration of 1 mass% synthesized in Example 4 of the second synthesis method described above in “

[10] Evaluation of heat resistance of the second synthesis method” is also shown. 2 The results of the measurement of the specific surface area (m2 / g) of Comparative Samples C2A, C2B, and C2C, which were synthesized by the precipitation method with an SiO2 concentration of 1 mass% and no barium added (see FIG. 18). 2 The measurement results of the total molecular weight (Mg) and the total molecular weight (g) are also shown in Table 13 (see FIG. 19).

[0260] [Table 13]

[0261] As shown in Table 13, in the samples (Sample S8A, Sample S2A, Comparative Sample C8A, Comparative Sample C2A) after sintering (initial heat treatment) at 1000°C for 5 hours, the specific surface area was slightly decreased by the addition of barium in all synthesis methods. However, in the samples (Sample S7B and S7C, Sample S1B and S1C, Comparative Sample C7B and C7C, Comparative Sample C1B and C1C) subjected to the first and second heat treatments at 1200°C for 5 and 30 hours, the specific surface area was confirmed to increase by the addition of barium in all synthesis methods. In addition, in the barium-added samples subjected to the second heat treatment, Sample S8C of the fifth synthesis method showed a higher specific surface area than Comparative Sample C8C in each heat treatment.

[0262] Figure 43 shows XRD patterns indicating the crystal structures of present sample S8A, present sample S8B, and present sample S8C after each heat treatment, and Figure 44 shows XRD patterns indicating the crystal structures of comparative sample C8A, comparative sample C8B, and comparative sample C8C after each heat treatment.

[0263] 43 and 44, in the case of the present sample S8C and the comparative sample C8C, which were added with barium and were subjected to the second heat treatment at 1200℃ for 30 hours, the peak of the diffraction pattern of α-Al2O3 is significantly lower in the present sample S8C, which was synthesized by the fifth synthesis method, than in the comparative sample C8C, which was synthesized by the precipitation method, and it was confirmed that the phase transition to the α phase was suppressed. This is the same as in the case of the present sample S7C and the comparative sample C7C, which used aluminum nitrate as the aluminum compound (see Figures 41 and 42).

[0264] From the above, it was confirmed that even when sodium aluminate is used as the aluminum compound, the fifth synthesis method, in which barium is added to the SiO2Al2O3-containing sol solution, can provide higher heat resistance than the precipitation method.

[0265]

[22] Heat resistance evaluation of the fifth synthesis method (3) In the heat resistance evaluations (1) and (2) of the fifth synthesis method described above, the heat resistance of the SiO2Al2O3 powder (powder samples S7 and S8) obtained by drying and firing 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) respectively in step #50 was evaluated, and the heat resistance improvement effect of adding barium to the SiO2Al2O3-containing sol solution was confirmed.

[0266] In this embodiment, the heat resistance evaluation was not performed on the SiO2Al2O3 powder obtained by drying and firing the Ba-added SiO2Al2O3-containing sol solution synthesized by the fifth synthesis method using the third synthesis method (second AC method) in step #50. However, in the heat resistance evaluations (1) and (2) of the third synthesis method described above, it was confirmed that the present powder samples S3 and S4 obtained via the third synthesis method (second AC method) have sufficient heat resistance equivalent to that of the present powder samples S1 and S2 obtained via the first and second synthesis methods (first AC method), and in the heat resistance evaluations (1) and (2) of the fourth synthesis method described above, it was confirmed that the present powder samples S5 and S6 obtained via the fourth synthesis method using the first and third synthesis methods (first and second AC methods) respectively in step #40 have sufficient heat resistance. Considering that the effect of improving the specific surface area (improving heat resistance) by adding a specific additive (DMF) has been confirmed for all of S6, it is believed that the SiO2Al2O3 obtained by drying and firing the Ba-added SiO2Al2O3-containing sol solution synthesized by the fifth synthesis method using the third synthesis method (second AC method) in step #50 will also have the effect of improving heat resistance by adding barium, similar to the fifth synthesis method using the first and second synthesis methods (first AC method) in step #50.

[0267] [Sixth embodiment] A sixth embodiment of the present synthesis method (sixth synthesis method) will be described below.

[0268]

[23] Basic structure and examples of the sixth synthesis method The sixth synthesis method corresponds to a synthesis method that combines the fourth and fifth synthesis methods described above, and as shown in the process transition diagram of FIG. 45, it is configured by adding, as a post-treatment to any one of the first, second, or third synthesis methods (step #60), step #61 in which a specific additive and a barium compound are added to and stirred in the SiO2Al2O3-containing sol solution synthesized by any one of the first, second, or third synthesis methods.

[0269] Step #61 of the sixth synthesis method is provided, firstly, as in step #41 of the fourth synthesis method, as a measure against the reduction in the total pore volume of Al2O3 due to the surface tension of evaporating water in the process of drying the SiO2Al2O3-containing sol solution synthesized by any one of the first to third synthesis methods in step #60 to produce a transparent gel, and secondly, as in step #51 of the fifth synthesis method, to obtain the effect of improving heat resistance by adding barium. In other words, the sixth synthesis method is intended to simultaneously obtain two effects of improving heat resistance by adding a specific additive (EG or DMF) and a barium compound.

[0270] 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 further, 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.

[0271] In the above step #61, a specific additive and a barium compound are added to the SiO2Al2O3-containing sol solution synthesized in step #60 and stirred to synthesize a SiO2Al2O3-containing sol solution to which a specific additive and barium are added. In step #61, a barium compound is first added to the SiO2Al2O3-containing sol solution synthesized in step #60 and stirred to synthesize a Ba-added SiO2Al2O3-containing sol solution in the same manner as the fifth synthesis method, and then a specific additive is added to the Ba-added SiO2Al2O3-containing sol solution in the same manner as the fourth synthesis method and stirred to synthesize a similar SiO2Al2O3-containing sol solution to which a specific additive and barium are added. That is, as described in the fourth embodiment, in the process of drying the SiO2Al2O3-containing sol solution synthesized in step #60 to generate a transparent gel, the specific additive is added as a measure against the decrease in the total pore volume of Al2O3 caused by the surface tension of evaporating water, and the timing of the addition may be after the Ba-added SiO2Al2O3-containing sol solution is synthesized.

[0272] As an example (Example 13) of the sixth synthesis method, in the same manner as in Example 11 of the fifth synthesis method, in step #60, aluminum nitrate is used as the aluminum compound to obtain a total amount of 80 g of 1%SiO2Al2O3 2.5% sol obtained through steps #11 to #15 of Example 1 of the first synthesis method, and in step #61, 0.2386 g of barium nitrate is added, and further, 3 mass % of a specific additive (EG or DMF) is added with respect 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%SiO2Al2O3 2.5% sol to which the specific additive has been added.

[0273] As another example (Example 14) of the sixth synthesis method, in the same manner as in Example 12 of the fifth synthesis method, in step #60, sodium aluminate is used as the aluminum compound to obtain a total amount of 80 g of 1%SiO2Al2O3 2.5% sol obtained through steps #21 to #25 of Example 4 of the second synthesis method, and in step #61, 0.2386 g of barium nitrate is added, and further, 3 mass % of a specific additive (EG or DMF) is added with respect 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%SiO2Al2O3 2.5% sol to which the specific additive has been added.

[0274]

[24] Heat resistance evaluation of the sixth synthesis method The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "Powder Sample S9") obtained by drying and firing a 6.5%BaO-1%SiO2Al2O3 2.5% sol with DMF added, which was synthesized in Example 13 of the Sixth Synthesis Method using aluminum nitrate as the aluminum compound, and the heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "Powder Sample S10") obtained by drying and firing a 6.5%BaO-1%SiO2Al2O3 2.5% sol with DMF added, which was synthesized in Example 14 of the Sixth Synthesis Method using sodium aluminate as the aluminum compound, were evaluated.

[0275] As present powder sample S9, a 6.5%BaO-1%SiO2Al2O3 2.5% sol to which DMF had been added, obtained through step #60 (steps #11 to #15 of Example 1 of the first synthesis method) and step #61 of Example 13 of the sixth synthesis method, was dried at 150°C, subsequently pulverized into powder, and calcined in air at 1000°C for 5 hours (initial heat treatment) to produce 6.5%BaO-1%SiO2Al2O3 powder (present sample S9A).

[0276] As present powder sample S10, a 6.5%BaO-1%SiO2Al2O3 2.5% sol to which DMF had been added, obtained through step #60 (steps #21 to #25 of Example 4 of the second synthesis method) and step #61 of Example 14 of the sixth synthesis method, was dried at 150°C, subsequently pulverized into powder, and calcined at 1000°C for 5 hours in air (initial heat treatment) to produce 6.5%BaO-1%SiO2Al2O3 powder (present sample S10A).

[0277] Furthermore, samples S9B and S10B were prepared by adding a first heat treatment at 1200°C for 5 hours to samples S9A and S10A, respectively, and samples S9C and S10C were prepared by adding a second heat treatment at 1200°C for 30 hours to samples S9A and S10A, respectively. Note that the DMF added to the 6.5%BaO-1%SiO2Al2O3 2.5% sol was heat It was burned during the treatment and was not present in the present samples S9A to S9C and the present samples S10A to S10C after firing.

[0278] The specific surface area (m2) of each of the samples S9A to S9C is shown in Table 14 below. 2 / g) and the total pore volume of this sample S9B (cm 3 Further, for comparison, the specific surface area (m 2 / g and the total pore volume of sample S1B (cm 3The specific surface area (m2) of each of the samples S7A to S7C obtained by drying and firing the 6.5%BaO-1%SiO2Al2O3 2.5% sol synthesized in Example 11 of the fifth synthesis method described above in “

[20] Evaluation of heat resistance of the fifth synthesis method (1)” was also measured (see FIG. 7 and Table 3). 2 / g and the total pore volume of this sample S7B (cm 3 The measurement results of the total molecular weight of the polymer (mg / g) (see Table 11) are also shown in Table 14.

[0279] [Table 14]

[0280] The specific surface area (m 2 / g) and the total pore volume of this sample S10B (cm 3 Further, for comparison, the specific surface area (m 2 / g and the total pore volume of this sample S2B (cm 3 The specific surface area (m2) of each of the present samples S8A to S8C obtained by drying and firing the 6.5%BaO-1%SiO2Al2O3 2.5% sol synthesized in Example 12 of the fifth synthesis method described above in “

[21] Evaluation of heat resistance of the fifth synthesis method (2)” was also measured (see FIG. 20). 2 / g and the total pore volume of this sample S8B (cm 3 The measurement results of the total molecular weight of the polymer (mg / g) (see Table 13) are also shown in Table 15.

[0281] [Table 15]

[0282] As shown in Table 14, in any heat treatment, the present samples S9A to S9C to which both the specific additive and the barium compound were added showed a higher specific surface area than the present samples S7A to S7C to which the barium compound was added alone, and it was confirmed that the present sample S9B after the first heat treatment had a larger total pore volume than the present sample S7B. Furthermore, as shown in Table 15, the present samples S10B and S10C to which both the specific additive and the barium compound were added after the first and second heat treatments showed a higher specific surface area than the present samples S8B and S8C to which the barium compound was added alone, and it was confirmed that the present sample S10B after the first heat treatment had a larger total pore volume than the present sample S8B. From the above, it was confirmed that regardless of the aluminum compound used to prepare the aluminum solution, the heat resistance was improved by adding both the specific additive and the barium compound compared to the case of adding the barium compound alone.

[0283] Fig. 46 shows XRD patterns showing the crystal structures of the present samples S9A to S9C after each heat treatment. Fig. 47 shows XRD patterns showing the crystal structures of the present samples S10A to S10C after each heat treatment. Comparing the XRD patterns of the present samples S9A to S9C and S10A to S10C shown in Fig. 46 and Fig. 47 with the XRD patterns of the present samples S7A to S7C and S8A to S8C shown in Fig. 41 and Fig. 43 to which a barium compound was added alone, some phase transition to the α-Al2O3 phase was confirmed in the present samples S7C and S8C after the second heat treatment at 1200°C for 30 hours, but no generation of the α phase was confirmed in the present samples S9C and S10C after the second heat treatment to which both the specific additive and the barium compound were added. In addition to the improved heat resistance achieved by the formation of Ba aluminate, the addition of specific additives has the effect of suppressing the decrease in the pore volume of SiO2Al2O3, making it possible to achieve a high specific surface area and suppress the phase transition to the α-Al2O3 phase.

[0284] [Seventh embodiment] Hereinafter, an embodiment of a method for forming a porous alumina film using the SiO2Al2O3-containing sol solution or the Ba-added SiO2Al2O3-containing sol solution synthesized by the above-mentioned first to sixth synthesis methods will be described (hereinafter, appropriately referred to as "this formation method").

[0285]

[25] Basic configuration of this formation method As shown in the process transition diagram of FIG. 48, this forming method is roughly divided into the following steps #71 to #74. First, in step #71, a SiO2Al2O3-containing sol solution (when using any of the first to fourth synthesis methods) or a Ba-added SiO2Al2O3-containing sol solution (when using the fifth or sixth synthesis method) is prepared using any of the first to sixth synthesis methods described above (sol solution preparation step). Subsequently, 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). Subsequently, 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 a SiO2Al2O3 film or a Ba-added SiO2Al2O3 film is formed on the substrate surface.

[0286] The substrate used in step #72 can be of various materials and shapes as long as it can hold the coating film formed on the surface in step #72 from step #72 to step #74, that is, can be used as a carrier for the coating film. Therefore, since the SiO2Al2O3 film or Ba-added 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 the substrate used in the examples described later is shown below.

[0287] 1) Granular aluminum oxide (activated): manufactured by Kanto Chemical (gelatinized by calcination at 1200°C for 5 hours. Hereinafter referred to as "cicaAl") 2) Silicon carbide diesel particulate filter (hereinafter referred to as "SiC-DPF") 3) Silica filter: ADVANTEC QR-100 4) Glass cloth: Nittobo #2116 5) Silica cloth: Nichias (baked at 1000°C for 5 hours) 6) Glass plate

[0288]

[26] First Example of the Forming Method (Example 15) In the same manner as in Example 1 of the first synthesis method described above, two types of sol solutions, 1%SiO2Al2O3 3.75% sol and 3%SiO2Al2O3 3.75% sol, with SiO2 concentrations of 1% and 3% by mass, were prepared. The five types of substrates described above in 1) to 5) were immersed in each sol solution for 10 minutes and then pulled out. The substrates were impregnated with the sol solution, and then dried at 150°C for 30 minutes to prepare a total of 10 types of dried samples. Each sol solution was used in an amount that allowed the substrate to be completely immersed in the sol solution. In this Example 15, in the coating process of step #72, the substrate is immersed in the sol solution to form a coating film. Furthermore, if the amount of support on each substrate surface is to be increased, this can be achieved by repeating the above-mentioned coating and drying processes. The substrate and coating film that had been subjected to one or more coating and drying processes were fired at 1000°C for 5 hours, and a porous alumina film of 1%SiO2Al2O3 and 3%SiO2Al2O3 was formed on each substrate surface, respectively. However, when the substrate is a glass cloth, the substrate is melted when fired at 1000° C. for 5 hours, so the firing is performed at 500° C. for 5 hours. These firings at 1000° C. for 5 hours or 500° C. for 5 hours correspond to the initial heat treatment of the powder sample explained in the heat resistance evaluation of the first to sixth synthesis methods, and are also referred to as the "initial heat treatment" in this formation method.

[0289] Table 16 below shows the relationship between the number of coatings and the amount of 1% SiO2Al2O3 supported on the substrate surface after firing at 1000°C for 5 hours for two examples of substrates in Example 15 described above, 1) cicaAl and 5) silica cloth. The amount of support x (mass%) in Table 16 is given by the following formula (1). In formula (1), Wb is the mass (g) of the substrate, and Wt is the total mass (g) of the substrate and coating film. x = (Wt - Wb) / Wt (1)

[0290] [Table 16]

[0291] From Table 16, it can be seen that the amount of 1%SiO2Al2O3 supported on the substrate surface increases with the number of coatings. However, for cicaAl, whose substrate is made of α-Al2O3, the increase in the amount supported was slight after the third coating.

[0292]

[27] Second Example of the Forming Method (Example 16) A 6.5%BaO-1%SiO2Al2O3 2.5% sol was prepared in the same manner as in Example 11 of the fifth synthesis method described above, and the three types of substrates (cicaAl, glass cloth, silica cloth) 1), 4) and 5) were immersed in the sol solution for 10 minutes each in the same manner as in Example 15 above, and then pulled out. The substrates were impregnated with the sol solution, and then dried at 150°C for 30 minutes. The substrates and coating film that had undergone one or more coating and drying steps were fired at 1000°C for 5 hours, and a porous alumina film of 6.5%BaO-1%SiO2Al2O3 was formed on the substrate surface. The above-mentioned coating, drying and firing steps were the same as in Example 15, so duplicated explanations will be omitted.

[0293] Fig. 49 shows SEM photographs taken by a field emission scanning microscope (FE-SEM) of the porous alumina film of 6.5%BaO-1%SiO2Al2O3 formed on each surface of the glass cloth and silica cloth of Example 16. In this embodiment, the FE-SEM used was a JSM-7001F manufactured by JEOL Ltd. As shown in Fig. 49, it was possible to observe that the porous alumina film was uniformly applied to each surface of the glass cloth and silica cloth.

[0294]

[28] Third Example of the Forming Method (Example 17) In the same manner as in Example 1 of the first synthesis method described above, a 1% SiO2Al2O3 2.5% sol and a 1% SiO2Al2O3 3.75% sol with different sol solution concentrations were prepared, and the substrate (glass plate) of 6) above, which had been washed with aqua regia, was immersed in each sol solution for 10 minutes, then removed and dried for 30 minutes at 150° C. The substrate and coating film after drying were fired at 500° C. for 5 hours, and a porous alumina film of 1% SiO2Al2O3 was formed on the substrate surface.

[0295] FIG. 50 shows two types of 1% SiO2Al2O3 with different sol solution concentrations in Example 17. Contains The cross-sectional and surface SEM photographs of a porous alumina film of 1% SiO2Al2O3 formed using a sol solution are shown by the above FE-SEM. From the cross-sectional photograph in FIG. 50, it can be seen that a porous alumina film is formed in close contact with the glass plate in both of the two types of sol solutions with different sol solution concentrations applied. The thickness of the porous alumina film was 0.65 μm when the sol solution concentration was 2.5 mass %, and 1.2 μm when the sol solution concentration was 3.75 mass %. As a result, it can be seen that the thickness of the porous alumina film can be adjusted by the sol solution concentration. In addition, from the surface photograph in FIG. 50, it was confirmed that the porous alumina film uniformly covers the glass plate surface in all sol solution concentrations. From this result, it can be seen that the porous alumina film of SiO2Al2O3 synthesized by the above first to sixth synthesis methods is formed in a uniform thickness. Contains Sol solution or Ba-doped SiO2Al2O3 Contains It is clear that by using a sol solution, a porous alumina film that is uniform and has excellent adhesion can be easily formed on the surface of a substrate, even if the surface is flat.

[0296] Next, the results of verifying the state of the sol solution prepared in step #71 of this forming method and the adhesion of the coating film to the substrate surface will be described. In step #71, the following steps are performed in the same manner as in Example 1 of the first synthesis method: #The pH value of the slurry solution was changed in three ways by the pH adjustment process for the 15 slurry solution, and three types of solutions were prepared in which the solution state was gel, sol, and precipitate. The gel and precipitate solutions were also thoroughly stirred to make a homogeneous solution. A glass plate washed with aqua regia was then immersed in the three types of solutions for 10 minutes, removed, and dried at 150°C for 30 minutes. The dried substrate and coating were fired at 500°C for 5 hours, and a porous alumina film of SiO2Al2O3 was formed on the substrate surface.

[0297] When the solution state is a sol, the porous alumina film formed is transparent, and the pattern of the base can be visually confirmed, just like a glass plate, and the formation of a homogeneous porous alumina film with excellent adhesion was confirmed. However, when the solution state is a gel, the formed porous alumina film was confirmed to have a thin film peeled off, and a homogeneous porous alumina film with excellent adhesion could not be formed. Also, when the solution state is a precipitate, the surface of the porous alumina film becomes cloudy, and a uniform porous alumina film could not be 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 a sol state.

[0298]

[29] Heat resistance evaluation of this forming method (1) In Example 15 of this formation method, the heat resistance of the 1% SiO2Al2O3 and 3% SiO2Al2O3 porous alumina films formed on the surfaces of the five types of substrates 1) to 5) above was evaluated as follows. Since it is difficult to separate the specific surface area of ​​the formed porous alumina film from the substrate and measure it separately, the specific surface area Sa (m 2 / g) was calculated from the relational expression shown in the following mathematical formula (2). St=Sa×x / 100+Sb×(1-x / 100) ···(2)

[0299] In formula (2), Sb is the specific surface area (m 2 / g), and St is the specific surface area (m 2 / g), where x is the number above. Formula (1)The specific surface areas Sb and St are values ​​actually measured by the nitrogen adsorption BET method, similar to the method for measuring the specific surface area described in the heat resistance evaluation (1) of the first synthesis method above.

[0300] Table 17 below shows the amount x (mass%) of 1% SiO2Al2O3 formed on the surface of the five types of substrates 1) to 5) above after the initial heat treatment and the three specific surface areas St, Sa, and Sb (m 2 / g), and the specific surface area Sc1 (m 2 Further, in Table 18 below, the amount x (mass%) of 3% SiO2Al2O3 supported on the surface of the five types of substrates 1) to 5) above after the initial heat treatment and the specific surface areas St, Sa, and Sb (m 2 / g), and the specific surface area Sc2 (m 2 In Tables 17 and 18, the specific surface area Sb of the glass cloth and silica cloth substrates was not measurable by the nitrogen adsorption BET method, and was therefore set to 0 (m 2 / g).

[0301] [Table 17]

[0302] [Table 18]

[0303] As shown in Tables 17 and 18, when the specific surface area Sa of the porous alumina film calculated by formula (2) is compared with the specific surface areas Sc1 and Sc2 of the SiO2Al2O3 powder of the comparative example, the specific surface areas are roughly the same. Therefore, the results of the heat resistance evaluation of the above-mentioned first to sixth synthesis methods are considered to be valid for the heat resistance evaluation of the porous alumina film formed on the surface of various substrates. Therefore, the SiO2Al2O3 synthesized by the first to sixth synthesis methods Contains Sol solution or Ba-doped SiO2Al2O3 Contains It was confirmed that a SiO2Al2O3 film or Ba-doped SiO2Al2O3 film with a high specific surface area could be formed by applying the sol solution to the surface of various substrates.

[0304]

[30] Heat resistance evaluation of this formation method (2) In Example 16 of this formation method, a porous alumina membrane of 6.5%BaO-1%SiO2Al2O3 was formed on the surface of the two types of substrates (cicaAl, silica cloth) in 1) and 5) above (hereinafter referred to as "this membrane sample S"). f The heat resistance of the above-mentioned materials was evaluated as follows.

[0305] Main membrane sample S f The above two types of substrates were subjected to initial heat treatment (1000°C for 5 hours) in Example 16 of the present formation method, and then a porous alumina film of 6.5%BaO-1%SiO2Al2O3 (sample S f A) were prepared. In addition, two types of this sample S f This sample S was made by adding the first heat treatment at 1200℃ for 5 hours to A. f B and this sample S f This sample S was made by adding a second heat treatment at 1200℃ for 30 hours to A. f C was prepared respectively.

[0306] Table 19 below shows the results of the sample S prepared on the surfaces of the two types of substrates mentioned above (cicaAl and silica cloth). f A~S f The specific surface area St and specific surface area Sa of C are shown for each substrate.

[0307] [Table 19]

[0308] As shown in Table 19, this sample S f A~S f The specific surface area Sa of sample C is close to that of samples S7A to S7C (powder sample S7 obtained by drying and sintering the 6.5%BaO-1%SiO2Al2O3 2.5% sol synthesized by the fifth synthesis method) shown in Table 11. Contains It was confirmed that a Ba-doped SiO2Al2O3 film with a high specific surface area could be formed by applying the sol solution to the surface of various substrates.

[0309] Figure 51 shows the sample S, whose base material is silica cloth. f A~S f 51 shows XRD patterns indicating the crystal structure after each heat treatment in Sample S. The loading amount x is 6.2 mass %. For reference, FIG. 51 also shows the XRD pattern of a substrate without a Ba-added SiO2Al2O3 film. As shown in FIG. 51, a γ-Al2O3 peak was detected in the firing at 1000°C for 5 hours (initial heat treatment), and a cristobalite peak was detected due to the crystallization of SiO2 in the substrate in the firing at 1200°C for 5 hours and 30 hours (first and second heat treatments). However, in the present sample S fired at 1200°C for 30 hours, f No α-Al2O3 peak was detected in C, confirming that the heat resistance of Al2O3 was maintained even at high temperatures due to the effect of adding barium.

[0310] [Eighth embodiment] An eighth embodiment (seventh synthesis method) of the present synthesis method will be described below.

[0311]

[31] Basic structure of the seventh synthesis method As shown in the process transition diagram of Figure 52, the seventh synthesis method is roughly divided into a step (step #80) of preparing a SiO2Al2O3-containing sol solution by any one of the above-mentioned first, second, and third synthesis methods, a step (step #81) of drying the SiO2Al2O3-containing sol solution prepared in step #80 to prepare SiO2Al2O3 powder, and a step (step #82) of adding water to the SiO2Al2O3 powder and stirring the mixture to reprepare a SiO2Al2O3-containing sol solution having a desired sol solution concentration. As an embodiment, the drying process 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".

[0312] The seventh synthesis method has the advantage that the sol solution concentration of the reprepared SiO2Al2O3-containing sol solution can be easily controlled by adjusting the amount of water added in step #82 relative to the mass of SiO2Al2O3 powder obtained in step #81.

[0313] Step #80 is the same as steps #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, to be added to the SiO2Al2O3-containing sol solution prepared in steps #40, #50, or #60 can be added to the SiO2Al2O3-containing sol solution (first sol) prepared in step #80 in step #83 before the drying process in step #81 in the seventh synthesis method, as shown in FIG. 53. Furthermore, as shown in FIG. 54, the specific additive and / or the barium compound can also be added to the SiO2Al2O3-containing sol solution (second sol) reprepared in step #81 in step #84.

[0314]

[32] Example of the seventh synthesis method [32.1] Examples 18 and 19 Hereinafter, an example (Example 18) of steps #80 to #82 in the case where aluminum nitrate is used as the aluminum compound and a SiO2Al2O3-containing sol solution with an SiO2 concentration of 1 mass % is synthesized will be described.

[0315] In Example 18, as an example, in step #80, a SiO2Al2O3-containing sol solution with a SiO2 concentration of 1 mass% is synthesized using the first synthesis method. In step #80 of Example 18, the TEOS solution and aluminum nitrate solution with the same solution concentration as those used in steps #12 and #13 of Example 1 of the first synthesis method are each 1.5 times larger in amount, and autoclaved in the same manner as in Example 1 to obtain a SiO2Al2O3-containing sol solution (first sol) with a total amount of 80 g, a SiO2 concentration of 1 mass%, and a sol solution concentration of 3.75 mass%. The sol solution concentration is 1.5 times the 2.5 mass% of Example 1 above, and the 1% SiO2Al2O3 powder obtained by drying the sol solution at 150 °C in step #81 is 3.0 g. Subsequently, in step #82, 3.0 g of the 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-containing sol solution (second sol). The sol solution concentration was 3.61%.

[0316] 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 above in [1] Basic configuration of the first synthesis method.

[0317] Furthermore, in an embodiment (embodiment 19) in which sodium aluminate is used as the aluminum compound instead of aluminum nitrate, in step #80, a sol solution containing SiO2Al2O3 with a desired SiO2 concentration is synthesized using the second or third synthesis method described above. By carrying out steps #81 and #82 in the same manner as in embodiment 18, a sol solution containing SiO2Al2O3 (second sol) with a desired sol solution concentration and SiO2 concentration can be obtained.

[0318] The solution state of the 1% SiO2Al2O3-containing sol solution (second sol) obtained in Example 18 was in a sol state similar to the solution state of the 1% SiO2Al2O3-containing sol solutions synthesized in Example 1 of the first synthesis method and Example 5 of the third synthesis method.

[0319] [32.2] Examples 20 and 21 (Addition of specific additives and barium compounds) Next, two examples (Example 20 and Example 21) of synthesizing a SiO2Al2O3-containing sol solution with a SiO2 concentration of 1 mass% to which a specific additive and a barium compound were added will be described. As in Example 18, aluminum nitrate was used as the aluminum compound.

[0320] In Example 20, as shown in Fig. 53, in step #80, a sol solution containing 1% SiO2Al2O3 (first sol) with a sol solution concentration of 3.75 mass% was prepared in the same manner as in Example 18, and in step #83, 0.3579 g of barium nitrate as a barium compound and 3 mass% of DMF as a specific additive with respect to the total amount of the sol solution after addition were added to the first sol and stirred to obtain a 6.5%BaO-1%SiO2Al2O3 3.75% sol solution with DMF added. Subsequently, in step #81, the sol solution prepared in step #83 was dried at 150 °C in the same manner as in Example 18 to obtain a 6.5%BaO-1%SiO2Al2O3 powder with DMF added. Subsequently, in step #82, in the same manner as in Example 18, the 6.5%BaO-1%SiO2Al2O3 powder with added DMF obtained in step #81 was added to 80 g of water and stirred at room temperature for 30 minutes to obtain a sol solution containing 6.5%BaO-1%SiO2Al2O3 with added DMF (second sol).

[0321] In Example 21, as shown in Fig. 54, in steps #80 to #82, the same processes as in Example 18 were performed to obtain a 1% SiO2Al2O3-containing sol solution (second sol) with a total amount of 83 g. Subsequently, in step #84, 0.3579 g of barium nitrate as a barium compound and 3 mass % of DMF as a specific additive with respect to the total amount of the sol solution after the addition were added to the second sol and stirred to obtain a 6.5%BaO-1%SiO2Al2O3-containing sol solution with DMF added.

[0322] In Examples 20 and 21, the timing of adding the specific additive and the barium compound is different from that in Example 18, when steps #80 to #82 are carried out. 20 In the example, after step #80, a specific additive and a barium compound are added to the first sol, and the result is shown in FIG. 1 In the embodiment, after step #82, a specific additive and a barium compound are added to the second sol. 20 and Example 2 1 In all cases, the powder of the specific additive and barium compound was completely dissolved in the second sol, making it possible to prepare a homogeneous sol solution containing 6.5%BaO-1%SiO2Al2O3 and doped with DMF.

[0323] [32.3] Example 22 (Preparation of High Concentration Sol Solution) In order to increase the amount of support on the carrier, we investigated increasing the concentration of the sol solution by the seventh synthesis method. Below, we will explain an example (Example 22) of steps #80 to #82 when using aluminum nitrate as the aluminum compound to synthesize a SiO2Al2O3-containing sol solution with a SiO2 concentration of 1 mass% and a sol solution concentration of 10.31 mass%.

[0324] In Example 22, there are two steps #80 (step #80A, step #80B) as shown in Fig. 55. In Example 22, the two steps #80 correspond to steps #11 to #15 of Example 1 of the first synthesis method. In addition, since the SiO2 concentrations of the SiO2Al2O3-containing sol solutions synthesized in the two steps #80 are both the same, 1 mass %, the mixing ratios of the TEOS solution and the aluminum nitrate solution are the same, but since the sol solution concentrations of the SiO2Al2O3-containing sol solutions synthesized are different, the amounts of the TEOS solution and the aluminum nitrate solution used are different in step #80A and step #80B.

[0325] In step #80A, the same treatment as in Example 18 was performed to obtain a 1% SiO2Al2O3 3.75% sol (first sol) with a total amount of 80 g. Subsequently, in step #81, the sol solution was dried at 150 °C to obtain 3.0 g of 1% SiO2Al2O3 powder. Meanwhile, in step #80B, the TEOS solution and aluminum nitrate solution with the same solution concentration as those used in steps #12 and #13 of Example 1 of the first synthesis method were used in 3.2 times the amount of each solution, and autoclaved in the same manner as in Example 1 to obtain a SiO2Al2O3-containing sol solution (first sol) with a total amount of 80 g, SiO2 concentration of 1 mass%, and sol solution concentration of 8 mass%. Note that the order of performing steps #80A and #80B may be either first or simultaneously. Next, in step #82, 2.47 g of the 1% SiO2Al2O3 powder obtained in step #81 was weighed out and added to the 1% SiO2Al2O3 8% sol (first sol) obtained in step #80B, totaling 80 g, and stirred to obtain a SiO2Al2O3-containing sol solution (second sol) with a SiO2 concentration of 1 mass% and a sol solution concentration of 10.31 mass%. The amount (mixing ratio) of the 1% SiO2Al2O3 powder added in step #82 was set to 3 mass% with respect to the sol solution after addition. 2.47 g of 1% SiO2Al2O3 powder (boehmite) gives 2.10 g of 1% SiO2Al2O3 (alumina). Therefore, the sol solution concentration obtained in step #82 is 10.31 mass% (= (80 g × 8 mass% + 2.1 g) / 82.47 g).

[0326] From the above, in step #82 of Example 18, the 1% SiO2Al2O3 powder obtained in step #81 was added to 80g of water, whereas in step #82 of Example 22, the 1% SiO2Al2O3 powder obtained in step #81 was added to 80g of 1% SiO2Al2O3 8% sol obtained in step #80B, thereby increasing the concentration of the SiO2Al2O3-containing sol solution (second sol) obtained in step #82. When aluminum nitrate is used as the aluminum compound, it is difficult to achieve a sol solution concentration of 10% by mass or more in the first or third synthesis methods, as shown in Figure 4, but it was confirmed that the seventh synthesis method can be used to increase the concentration of the sol solution to 10% by mass or more.

[0327]

[33] Heat resistance evaluation of the seventh synthesis method (1) The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "this powder sample S11") obtained by drying and firing the SiO2Al2O3-containing sol solutions (second sol) with SiO2 concentrations of 1 mass % and 3 mass % synthesized in Example 18 of the seventh synthesis method using aluminum nitrate as the aluminum compound was evaluated.

[0328] As the present powder sample S11, the SiO2Al2O3-containing sol solutions with SiO2 concentrations of 1 mass% and 3 mass% obtained through steps #80 to #82 of Example 18 were dried at 150°C, subsequently pulverized into powder form, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (present sample S11A). Furthermore, present sample S11B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S11A, and present sample S11C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S11A.

[0329] Table 20 below shows the specific surface area (m 2The results of measuring the specific surface area of ​​each of the present samples S1A to S1C having SiO2 concentrations of 1 mass % and 3 mass % produced by the first synthesis method (Example 1) and the specific surface area of ​​each of the present samples S3A to S3C having SiO2 concentrations of 1 mass % and 3 mass % produced by the third synthesis method (Example 5) are also shown in Table 20 for comparison.

[0330] [Table 20]

[0331] Furthermore, Fig. 56 shows XRD patterns showing the crystal structures after each heat treatment in the present samples S11A, S11B, and S11C with an SiO2 concentration of 1 mass%. Note that the XRD patterns showing the crystal structures after each heat treatment in the present samples S1A, S1B, and S1C with an SiO2 concentration of 1 mass% prepared by the first synthesis method, and the present samples S3A, S3B, and S3C with an SiO2 concentration of 1 mass% prepared by the third synthesis method are shown in Figs. 9 and 26.

[0332] From the measurement results shown in Table 20, it can be seen that the seventh synthesis method also exhibits a specific surface area equivalent to that of the samples produced by the first and third synthesis methods. Furthermore, when the XRD pattern of the sample produced by the seventh synthesis method shown in Figure 56 is compared with the XRD patterns of the samples produced by the first and third synthesis methods shown in Figures 9 and 26, similar peaks are observed, and taking into consideration the measurement results shown in Table 20, it can be confirmed that the samples produced by the first, third, and seventh synthesis methods have similar physical properties.

[0333]

[34] Heat resistance evaluation of the 7th synthesis method (2) Sodium aluminate was used as the aluminum compound, and the heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "this powder sample S12") obtained by drying and firing the SiO2Al2O3-containing sol solutions (second sol) with SiO2 concentrations of 1 mass % and 3 mass % synthesized in Example 19 of the seventh synthesis method was evaluated.

[0334] As the present powder sample S12, the SiO2Al2O3-containing sol solutions with SiO2 concentrations of 1 mass% and 3 mass% obtained through steps #80 to #82 of Example 19 were dried at 150°C, subsequently pulverized into powder form, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (present sample S12A). Furthermore, present sample S12B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S12A, and present sample S12C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S12A.

[0335] Table 21 below shows the specific surface area (m 2 The results of measuring the specific surface area of ​​each of the present samples S2A to S2C having SiO2 concentrations of 1 mass % and 3 mass % produced by the second synthesis method (Example 4) and the specific surface area of ​​each of the present samples S4A to S4C having SiO2 concentrations of 1 mass % and 3 mass % produced by the third synthesis method (Example 6) are also shown in Table 21 for comparison.

[0336] [Table 21]

[0337] Furthermore, Fig. 57 shows XRD patterns showing the crystal structures after each heat treatment in Samples S12A, S12B, and S12C with an SiO2 concentration of 1 mass%. Note that Figs. 18 and 30 show XRD patterns showing the crystal structures after each heat treatment in Samples S2A, S2B, and S2C with an SiO2 concentration of 1 mass% produced by the second synthesis method, and Samples S4A, S4B, and S4C with an SiO2 concentration of 1 mass% produced by the third synthesis method.

[0338] From the measurement results shown in Table 21, it can be seen that the seventh synthesis method also exhibits a specific surface area equal to or greater than those of the samples produced by the second and third synthesis methods. Furthermore, the XRD pattern of the sample produced by the seventh synthesis method shown in FIG. 57 and the XRD pattern of the sample produced by the third synthesis method shown in FIG. 18 and FIG. 2Comparing the XRD patterns of the samples prepared by the synthesis method 2 and the third synthesis method, similar peaks are observed. Taking into consideration the measurement results shown in Table 21, it can be confirmed that the samples prepared by the second, third, and seventh synthesis methods have similar physical properties.

[0339]

[35] Heat resistance evaluation of the 7th synthesis method (3) Aluminum nitrate was used as the aluminum compound, and the heat resistance of two types of 6.5%BaO-1%SiO2Al2O3 powders containing a specific additive (DMF) (hereinafter collectively referred to as "present powder sample S13" and "present powder sample S14") was evaluated by drying and firing the 6.5%BaO-1%SiO2Al2O3-containing sol solutions containing DMF, which were separately synthesized in Example 20 and Example 21 of the seventh synthesis method.

[0340] As the present powder sample S13, the 6.5%BaO-1%SiO2Al2O3-containing sol solution (second sol) containing DMF added, obtained through steps #80, #83, #81, and #82 of Example 20, was dried at 150°C, subsequently crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce DMF-added BaO-SiO2Al2O3 powder (present sample S13A). Furthermore, present sample S13B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S13A, and present sample S13C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S13A.

[0341] As the present powder sample S14, the 6.5%BaO-1%SiO2Al2O3-containing sol solution (second sol) containing DMF added obtained through steps #80 to #82 and #84 of Example 21 was dried at 150°C, subsequently crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce DMF-added BaO-SiO2Al2O3 powder (present sample S14A). Furthermore, present sample S14B was produced by adding a first heat treatment of 1200°C for 5 hours to present sample S14A, and present sample S14C was produced by adding a second heat treatment of 1200°C for 30 hours to present sample S14A.

[0342] Table 22 below shows the specific surface area (m 2 / g), and the total pore volume (cm 3 The results of the measurement of the amount of cellulose acetate per gram (g) are shown in the table. Special Table 22 also shows the measurement results of the specific surface area of ​​each of the present samples S11A to S11C (see Table 20) and the total pore volume of the present sample S11B, which has an SiO2 concentration of 1 mass% to which a specific additive (DMF) and a barium compound have not been added, as well as the measurement results of the specific surface area of ​​each of the present samples S9A to S9C (see Table 14) and the total pore volume of the present sample S9B, which has an SiO2 concentration of 1 mass% to which a specific additive (DMF) and a barium compound have been added and which were prepared by the sixth synthesis method (Example 13).

[0343] [Table 22]

[0344] Furthermore, Fig. 58 shows XRD patterns showing the crystal structures of the present samples S13A, S13B, and S13C after each heat treatment, each having an SiO2 concentration of 1 mass%, and Fig. 59 shows XRD patterns showing the crystal structures of the present samples S14A, S14B, and S14C after each heat treatment, each having an SiO2 concentration of 1 mass%. Note that the XRD patterns showing the crystal structures of the present samples S11A, S11B, and S11C after each heat treatment, each having an SiO2 concentration of 1 mass% and prepared in Example 18 of the 7th synthesis method, and the XRD patterns showing the crystal structures of the present samples S9A, S9B, and S9C after each heat treatment, each having an SiO2 concentration of 1 mass% and prepared in the 6th synthesis method (Example 13), are shown in Figs. 56 and 46.

[0345] As shown in Table 22, the specific surface area of ​​the powder sample S11 to which no DMF or barium compound was added, which was prepared in Example 18 of the seventh synthesis method, was reduced after the first and second heat treatments at 1200° C. This coincides with the fact that the alumina in the powder sample S11 to which no DMF or barium compound was added was completely α-converted after the first and second heat treatments at 1200° C. in the XRD pattern of FIG. If In contrast, in the present powder samples S13 and S14 prepared in Examples 20 and 21 of the seventh synthesis method, the decrease in specific surface area after the first and second heat treatments at 1200°C is significantly suppressed, and compared with the present powder sample S11 to which DMF and a barium compound are not added, it is found that the specific surface area and total pore volume after the first and second heat treatments are increased by the addition of DMF and a barium compound. This is also consistent with the fact that the alpha phase is suppressed after the first and second heat treatments at 1200°C in the XRD patterns of the present powder samples S13 and S14 shown in Figures 58 and 59. If is doing.

[0346] Furthermore, as shown in Table 22, powder samples S13 and S14 prepared in Examples 20 and 21 of the seventh synthesis method exhibited specific surface areas and total pore volumes comparable to those of powder sample S9 prepared by the sixth synthesis method (Example 13), confirming that the addition of DMF and a barium compound was effective.

[0347]

[36] Heat resistance evaluation of the seventh synthesis method (4) The heat resistance of SiO2Al2O3 powder (hereinafter collectively referred to as "this powder sample S15") obtained by drying and firing a SiO2Al2O3-containing sol solution (second sol) having an SiO2 concentration of 1 mass% and a sol solution concentration of 10.31 mass%, synthesized in Example 22 of the seventh synthesis method, using aluminum nitrate as the aluminum compound, was evaluated.

[0348] This powder sample S1 5As a result, the SiO2Al2O3-containing sol solution with an SiO2 concentration of 1 mass% and a sol solution concentration of 10.31 mass% obtained through steps #80 (#80A, #80B) to #82 of Example 22 was dried at 150°C, crushed into powder, and fired in air at 1000°C for 5 hours (initial heat treatment) to produce SiO2Al2O3 powder (Sample S15A). Furthermore, Sample S15B was produced by adding a first heat treatment of 1200°C for 5 hours to Sample S15A, and Sample S15C was produced by adding a second heat treatment of 1200°C for 30 hours to Sample S15A.

[0349] Table 23 below shows the specific surface area (m 2 For comparison, Table 23 also shows the measurement results of the specific surface area of ​​each of Samples S1A to S1C obtained from a sol solution containing SiO2Al2O3 with a sol solution concentration of 2.5 mass % synthesized by the first synthesis method (Example 1).

[0350] [Table 23]

[0351] As shown in Table 23, even when the sol solution concentration was increased to 10 mass% or more by Example 22 of the seventh synthesis method, the heat resistance was equivalent to that of a SiO2Al2O3-containing sol solution synthesized by the first synthesis method. This confirmed that the seventh synthesis method is an effective means for preparing a high-concentration sol.

[0352] Furthermore, as a preferred embodiment, in the sol solution preparation step (step #71) of the present formation method described in the seventh embodiment above, the seventh synthesis method may be used instead of any of the first to sixth synthesis methods to prepare a sol solution containing SiO2Al2O3 or a sol solution containing Ba-added SiO2Al2O3.

[0353] [Modifications of the First to Eighth Embodiments] The present synthesis method and the present formation method have been described in detail above using examples through the first to eighth embodiments. However, the SiO2 concentration, sol solution concentration, amount of specific additive, amount of barium compound, etc. used in the examples (Examples 1 to 22) of each of the above embodiments are merely examples, and can be appropriately changed within the limits of the present synthesis method and the present formation method to achieve the desired effects. [Industrial Applicability]

[0354] The present invention is suitable for use in the synthesis of SiO2Al2O3-containing sol solutions for forming porous alumina doped with silica on the surfaces of various substrates, and in the formation of heat-resistant porous alumina membranes.

Claims

1. SiO to form porous alumina doped with silica ２ A ２ O ３ A method for synthesizing a containing sol solution, comprising the steps of: preparing an alkoxysilane solution containing an alkoxysilane, water, an alcohol, and an inorganic acid; preparing an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate, and water; a step of precipitating a precipitate in which a silicon compound is adsorbed on aluminum hydroxide in a mixed solution of the alkoxysilane solution and the aluminum solution; filtering the precipitate from the mixed solution and washing the filtered precipitate with water to prepare a precipitate cake; Water is added to the precipitate cake to prepare a slurry solution, and the slurry solution is subjected to a pH adjustment treatment and then an autoclave treatment to obtain the SiO sol particles in which silica is bonded to boehmite particles and are dispersed. ２ A ２ O ３ and preparing a containing sol solution, The pH value of the slurry solution is adjusted to the pH value of the SiO after the autoclave treatment by the pH adjustment treatment of the slurry solution. ２ A ２ O ３ The method for synthesizing a sol solution is characterized in that the solution state of the containing sol solution is controlled within a specific pH range in which the solution is in a sol state.

2. In the step of precipitating a precipitate, When the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, the mixed solution is heated and refluxed, and then a pH adjustment treatment is performed to co-precipitate the precipitate, The method for synthesizing a sol solution according to claim 1, characterized in that, when the aluminum compound is sodium aluminate, the aluminum solution is heated to reflux, and then subjected to a pH adjustment treatment, and then mixed with the alkoxysilane solution to prepare the mixed solution, and a precipitate having the silicon compound adsorbed thereon is precipitated in the mixed solution by a precipitate of aluminum hydroxide precipitated during the pH adjustment treatment.

3. The specific pH range is the pH of the SiO ２ A ２ O ３ SiO in the sol solution ２ A ２ O ３ SiO ２ is defined as the mass concentration of ２ 3. The method for synthesizing a sol solution according to claim 1, wherein the coefficient of reactivity varies depending on the concentration, and is within a range of 2.8 to 7.8 when the aluminum compound is any one of the aluminum nitrate, the aluminum chloride, and the aluminum sulfate, and is within a range of 1.0 to 6.2 when the aluminum compound is the sodium aluminate.

4. The SiO ２ A ２ O ３ In the step of preparing a containing sol solution, The processing temperature of the autoclave treatment is controlled to a specific processing temperature within a range of 100° C. or more and 200° C. or less; 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 the specific treatment temperature, the SiO ２ A ２ O ３ SiO in the sol solution ２ A ２ O ３ The content and the SiO after preparation ２ A ２ O ３ SiO in the sol solution ２ A ２ O ３ SiO ２ is defined as the mass concentration of ２ 3. The method for synthesizing a sol solution according to claim 1, wherein the time varies depending on the concentration and is within a range of 1 hour to 100 hours.

5. SiO to form porous alumina doped with silica ２ A ２ O ３ A method for synthesizing a containing sol solution, comprising the steps of: preparing an alkoxysilane solution containing an alkoxysilane, water, an alcohol, and an inorganic acid; preparing an aluminum solution containing an aluminum compound selected from aluminum nitrate, sodium aluminate, aluminum chloride, and aluminum sulfate, and water; allowing an aluminum hydroxide precipitate to form in the aluminum solution; filtering the precipitate from the aluminum solution and washing the filtered precipitate with water to produce a precipitate cake; Water is added to the precipitate cake to prepare a slurry solution, and the slurry solution is subjected to a pH adjustment treatment and then an autoclave treatment to remove Al in which boehmite particles are dispersed as sol particles. ２ O ３ preparing a containing sol solution; The Al ２ O ３ The alkoxysilane solution is added to the sol solution containing boehmite to obtain the SiO sol having dispersed therein sol particles in which silica is bonded to boehmite particles. ２ A ２ O ３ and preparing a containing sol solution, The pH value of the slurry solution is adjusted to the pH value of the Al solution after the autoclave treatment. ２ O ３ The method for synthesizing a sol solution is characterized in that the solution state of the containing sol solution is controlled within a specific pH range in which the solution is in a sol state.

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

7. 7. The method for synthesizing a sol solution according to claim 5, wherein the specific pH range is within a range of 3.8 to 7.8 when the aluminum compound is any one of aluminum nitrate, aluminum chloride, and aluminum sulfate, and within a range of 2.0 to 6.2 when the aluminum compound is sodium aluminate.

8. The Al ２ O ３ In the step of preparing a containing sol solution, The processing temperature of the autoclave treatment is controlled to a specific processing temperature within a range of 100° C. or more and 200° C. or less; 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 the specific treatment temperature and the Al after preparation. ２ O ３ Al in the sol solution ２ O ３ 7. The method for synthesizing a sol solution according to claim 5 or 6, characterized in that the time varies depending on the content and is within the range of 1 hour to 100 hours.

9. 7. The method for synthesizing a sol solution according to claim 1, 2, 5, or 6, wherein the alkoxysilane is tetraethoxysilane (TEOS).

10. The SiO ２ A ２ O ３ The SiO prepared in the step of preparing a sol solution containing the SiO ２ A ２ O ３ A barium compound is added to the sol solution to form Ba-doped SiO ２ A ２ O ３ 7. The method for synthesizing a sol solution according to claim 1, further comprising the step of preparing a containing sol solution.

11. The Ba-doped SiO ２ A ２ O ３ The Ba-doped SiO prepared in the step of preparing the Ba-containing sol solution ２ A ２ O ３ 11. The method for synthesizing a sol solution according to claim 10, further comprising the step of adding an organic solvent having a boiling point higher than that of water and a surface tension lower than that of water to the containing sol solution.

12. The SiO ２ A ２ O ３ The SiO prepared in the step of preparing a sol solution containing the SiO ２ A ２ O ３ An organic solvent having a higher boiling point than water and a lower surface tension than water and a barium compound are added to the sol solution to obtain Ba-doped SiO ２ A ２ O ３ 7. The method for synthesizing a sol solution according to claim 1, further comprising the step of preparing a containing sol solution.

13. The SiO ２ A ２ O ３ The SiO prepared in the step of preparing a sol solution containing the SiO ２ A ２ O ３ 7. The method for synthesizing a sol solution according to claim 1, further comprising the step of adding an organic solvent having a boiling point higher than that of water and a surface tension lower than that of water to the containing sol solution.

14. 11. 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, 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.

17. 12. 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, characterized in that the organic solvent is ethylene glycol or N,N-dimethylformamide.

19. The method for synthesizing a sol solution according to claim 13, characterized in that the organic solvent is ethylene glycol or N,N-dimethylformamide.

20. 1. A method for forming a porous alumina membrane, comprising: The method for synthesizing a sol solution according to any one of claims 1, 2, 5 and 6 is used to synthesize a sol solution, which is SiO ２ A ２ O ３ preparing a containing sol solution; applying the sol solution to a surface of a substrate; drying the coating film of the sol solution; and baking the dried coating film of the sol solution.

21. A method for forming a porous alumina membrane, comprising the steps of: A process for preparing a Ba-added SiO 2 Al 2 O 3 -containing sol solution, which is a sol solution synthesized by the synthesis method of a sol solution according to claim 10 ; applying the sol solution to a surface of a substrate; drying the coating film of the sol solution; and baking the dried coating film of the sol solution.

22. A method for forming a porous alumina membrane, comprising the steps of: A process for preparing a Ba-added SiO 2 Al 2 O 3 -containing sol solution, which is a sol solution synthesized by the synthesis method of a sol solution according to claim 11 ; applying the sol solution to a surface of a substrate; drying the coating film of the sol solution; and baking the dried coating film of the sol solution.

23. A method for forming a porous alumina membrane, comprising the steps of: A process for preparing a Ba-added SiO 2 Al 2 O 3 -containing sol solution, which is a sol solution synthesized by the synthesis method of a sol solution according to claim 12 ; applying the sol solution to a surface of a substrate; drying the coating film of the sol solution; and baking the dried coating film of the sol solution.

24. A method for forming a porous alumina membrane, comprising the steps of: A process for preparing a sol solution containing SiO 2 Al 2 O 3 , which is a sol solution synthesized by the synthesis method of a sol solution according to claim 13 ; applying the sol solution to a surface of a substrate; drying the coating film of the sol solution; and baking the dried coating film of the sol solution.

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