Spinel-type aluminum oxide and method for producing the same

Abstract

A method for producing spinel-type aluminum oxide using a water-in-oil Pickering emulsion is provided. [Solution] The method includes the steps of: (1) mixing an aqueous dispersion of boehmite alumina sol with an aqueous solution containing one of the metal species Ni, Co, or Mg; (2) mixing a water-insoluble organic solvent with the aqueous solution from step (1) to form a phase-separated state of aqueous phase and organic solvent phase; (3) forming a water-in-oil (W / O) Pickering emulsion by applying shear to the entire liquid in the phase-separated state from step (2) to produce a spinel precursor in the organic solvent phase; (4) allowing the sheared liquid to stand to separate into an aqueous phase and an organic solvent phase; (5) removing the organic solvent phase from the phase-separated liquid from step (4); (6) drying the organic solvent phase from step (5) to obtain a cake; (7) baking the cake from step (6) at 700 to 1200°C for 2 to 8 hours; and (8) pulverizing the baked product obtained from step (7).

Description

[Technical Field]

[0001] The present invention relates to a spinel-type aluminum oxide with a high specific surface area and a method for producing the same. [Background technology]

[0002] Spinel compounds are produced by various methods. For example, Japanese Patent Publication No. 4622010 (Patent Document 1) discloses a method in which an aluminum salt prepared by dissolving aluminum hydroxide in acid is mixed with a magnesium salt prepared by dissolving magnesium hydroxide in acid, the coprecipitation is dried, and the resulting coprecipitation is calcined to synthesize spinel powder, which is then pulverized. However, in this method, dissolving aluminum hydroxide in acid at a high concentration requires dissolution at high temperatures for a long time, and because it is produced by coprecipitation, it takes a long time for the spinel precursor to settle. When a large amount is used, this can lead to compositional variations between the upper and lower parts of the precipitate. In addition, because it contains a large amount of water, it requires a long drying time, resulting in poor productivity.

[0003] Patent document 2 (Japanese Patent No. 6976642) describes a method for synthesizing magnesium aluminate spinel by performing hot water aging on an aqueous slurry of boehmite alumina at a temperature of 100 to 210°C for 1 to 6 hours, then mixing it with a magnesium precursor-containing aqueous composition to produce an aqueous spinel precursor, removing the water to produce an anhydrous spinel precursor, and finally calcining it. However, this method requires large batch processing reaction equipment to achieve high temperature and pressure for hot water aging, resulting in poor productivity.

[0004] Patent Document 3 (Japanese Patent No. 6254150) discloses a method for obtaining magnesium aluminate spinel by performing hot water aging on an aqueous slurry of a mixture of boehmite alumina and a magnesium precursor produced by hydrolysis of aluminum alkoxide, an oxide obtained by co-hydrolysis of aluminum-magnesium mixed alkoxide, a hydroxide, and a mixture thereof, to produce a hot water-aged slurry of the spinel precursor, drying the hot water-aged slurry, and then calcining it. Similar to Patent Document 2, performing hot water aging requires a large batch processing reaction facility to achieve high temperature and pressure, resulting in poor productivity.

[0005] Patent Document 4 (Japanese Unexamined Patent Publication No. 59-232915) describes a method for synthesizing fine magnesium-aluminum spinel raw material powder by adjusting the pH of aqueous solutions of water-soluble Mg compounds and water-soluble Al compounds with an alkali in the presence of alcohol, and then calcining the resulting precipitate. In this method, an alkaline agent such as ammonia water or caustic soda is added to a mixture of aluminum compounds, magnesium compounds, water, and lower alcohols to adjust the pH to 10-13, and the mixture is co-precipitated to obtain a spinel precursor. Similar to Patent Document 1, it takes a long time for the spinel precursor to settle, and when a large amount is used, there is a problem of compositional variation between the upper and lower parts of the precipitate.

[0006] Patent Document 5 (Japanese Patent Publication No. 2019-64915) discloses a method for synthesizing magnesium aluminate spinel by performing hot water aging on an aqueous slurry of a spinel precursor consisting of a mixture of boehmite alumina and a magnesium precursor, or an oxide or hydroxide of aluminum and magnesium. This aged spinel precursor slurry is then dried and calcined. However, this method, like that described in Patent Document 2, requires large batch processing reaction equipment to achieve high temperature and pressure for hot water aging, resulting in poor productivity. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Patent No. 4622010 [Patent Document 2] Patent No. 6976642 [Patent Document 3] Patent No. 6254150 [Patent Document 4] Publication No. 59-232915 [Patent Document 5] Japanese Patent Publication No. 2019-64915 [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] In light of the above-mentioned problems, the objective of the present invention is to provide an efficient method for producing a specific spinel-type aluminum oxide with a large specific surface area by utilizing a water-in-oil (W / O) Pickering emulsion without performing hot water aging or the like, preparing a precursor, and then calcining it. [Means for solving the problem]

[0009] In other words, the present invention provides the following aspects: [1] A spinel-type aluminum oxide mainly composed of a compound having a spinel structure with the chemical formula MAl2O4 (wherein M represents one of Ni, Co, or Mg), wherein the spinel-type aluminum oxide has a particle size D50 of 5 to 500 μm and a specific surface area of ​​10 to 120 m² as measured by a laser diffraction particle size distribution analyzer. 2 A spinel-type aluminum oxide characterized by having / g. [2] (1) A step of mixing an aqueous alumina sol whose crystalline system is boehmite with an aqueous solution containing one of the metal species Ni, Co, or Mg. (2) A step of mixing an organic solvent insoluble in water with the aqueous solution obtained in step (1) to form a phase separation state between the aqueous phase and the organic solvent phase. (3) A step to prepare a spinel precursor in the organic solvent phase by applying shear to the entire liquid in the phase-separated state obtained in step (2), thereby forming a water-in-oil (W / O) Pickering emulsion. (4) A step in which the liquid subjected to shearing in step (3) is allowed to stand to separate into an aqueous phase and an organic solvent phase. (5) A step of extracting the organic solvent phase from the phase separation liquid of step (4), (6) A step to obtain a cake by drying the organic solvent phase extracted in step (5), (7) The cake obtained in step (6) is baked at 700-1200°C for 2-8 hours. (8) The process includes crushing the calcined material obtained in step (7), The aqueous solution containing any of the metal species Ni, Co, or Mg in step (1) above is prepared by dissolving one or more of the nitrates, sulfates, acetates, or chlorides of Ni, Co, or Mg in water, and the amount of the aqueous solution added is 0.7 to 20% by mass of the total mass of the aqueous dispersion of alumina sol and the aqueous solution containing any of the metal species Ni, Co, or Mg. The water-dispersed alumina sol in step (1) above has an Al2O3 equivalent concentration of 1 to 12% by mass, and the water-dispersed alumina sol has a particle size D50 of 0.005 to 0.5 μm as measured by a dynamic light scattering particle size analyzer. The organic solvent used in the organic solvent phase to form the water-in-oil Pickering emulsion in step (3) above is a hydrocarbon solvent, a ketone solvent, an alcohol solvent, or an ester solvent, and has a boiling point of 85 to 200°C. The ratio (B) / (A) = 0.2 to 0.8 is the sum of the volume of the solution obtained by mixing an aqueous alumina sol of boehmite with an aqueous solution containing one of the metal species Ni, Co, or Mg, and the volume of the organic solvent (A). A method for producing spinel-type aluminum oxide according to [1], characterized in that the main component of the obtained pulverized material is a compound having a spinel structure with the chemical formula: MAl2O4 (wherein M represents one of Ni, Co, or Mg). [3] The method for producing spinel-type aluminum oxide according to [2], characterized in that the alumina crystal system in the aqueous dispersion of alumina sol in step (1) is boehmite, and the protective molecule is one or more selected from glycine, valine, leucine, isoleucine, betaine, NN-aminobetaine, alginic acid, glutamic acid, formic acid, and acetic acid. [4] The method for producing spinel-type aluminum oxide according to [2] or [3], characterized in that the apparatus for applying shear to form a water-in-oil Pickering emulsion in step (3) is one of a homogenizer, an ultrasonic homogenizer, a propeller mixer, a homomixer, or a discharger. [5] A method for producing spinel-type aluminum oxide according to [2] or [3], wherein the baking in step (7) is performed by placing the cake in an alumina crucible or alumina sagger and baking it at 700 to 1200°C for 2 to 8 hours, and the baking environment is in the atmosphere, nitrogen, or vacuum. [6] The method for producing spinel-type aluminum oxide according to [2] or [3], characterized in that the organic solvent used in the organic solvent phase to form the water-in-oil Pickering emulsion in step (3) is a hydrocarbon solvent, a ketone solvent, an alcohol solvent, or an ester solvent, and the number of carbon atoms in the organic solvent is in the range of 4 to 12. [Effects of the Invention]

[0010] The spinel-type aluminum oxide of the present invention and its manufacturing method can provide a manufacturing method that does not use a high-temperature and high-pressure process such as hydrothermal aging, does not require waiting for a long time for components to precipitate like the coprecipitation method, and can suppress component variations to an extremely small level. Further, it was confirmed that the spinel-type aluminum oxide mainly composed of a compound having a spinel structure with the chemical formula of the present invention: MAl2O4 (where M represents any one of Ni, Co, and Mg) has a high specific surface area. The spinel-type aluminum oxide of the present invention can be manufactured by optimizing an oil-in-water (W / O) pickering emulsion preparation step using an alumina sol, an emulsion preparation step, a drying step, a firing step, and a pulverization step.

Brief Description of Drawings

[0011] [Figure 1] It is an X-ray diffraction diagram of the spinel-type aluminum oxide obtained in Example 1. [Figure 2] It is an X-ray diffraction diagram of the spinel-type aluminum oxide obtained in Comparative Example 4. [Figure 3] It is an image (×50,000 magnification) taken with a field emission type analytical scanning electron microscope of the spinel-type aluminum oxide obtained in Example 1. [Figure 4] It is an image (×50,000 magnification) taken with a field emission type analytical scanning electron microscope of the spinel-type aluminum oxide obtained in Example 4. [Figure 5] It is an image (×50,000 magnification) taken with a field emission type analytical scanning electron microscope of the spinel-type aluminum oxide obtained in Example 8.

Embodiments for Carrying Out the Invention

[0012] (Definition) In this specification, a numerical range, specifically "x to y", represents x or more and y or less (both x and y represent numerical values).

[0013] (Explanation of Spinel-Type Aluminum Oxide) The present invention provides a spinel-type aluminum oxide whose main component is a compound having a spinel structure with the chemical formula MAl2O4 (wherein M represents one of Ni, Co, or Mg). The spinel-type aluminum oxide of the present invention has a specific surface area of ​​10 to 120 m². 2 It is characterized by expressing / g.

[0014] (Explanation of Pickering emulsion) Pickering emulsion refers to a method of emulsification that involves adsorbing solid microparticles, rather than surfactants, at the interface between water and oil, or to the resulting emulsion. It is characterized by its surfactant-free nature, high emulsification stability, and ability to form a variety of emulsions.

[0015] (Explanation of spinel structure) Spinel is a type of oxide mineral with the chemical composition MgAl2O4 and an isometric crystal system. This crystalline structure of spinel is called the spinel-type structure, and it is a structure commonly found in ternary materials with the composition AB2O4 (where both A and B represent metallic elements). Not only oxides, but also sulfides and nitrides can exhibit the spinel structure.

[0016] The spinel-type aluminum oxide of the present invention mainly consists of a compound having a spinel structure with the chemical formula MAl2O4 (wherein M represents one of Ni, Co, or Mg), and has a particle size D50 of 5 to 500 and a specific surface area of ​​10 to 120 m² as measured by a laser diffraction particle size analyzer. 2 It contains / g

[0017] The spinel-type aluminum oxide of the present invention has a particle size D50 of 5 to 500 μm, preferably 7 to 450 μm, and more preferably 10 to 400 μm, as measured by a laser diffraction particle size distribution analyzer. The particle size shall be measured wet in an aqueous solvent using a laser diffraction particle size distribution analyzer (Malvern Panalytical Mastersizer 3000). If the particle size D50 is less than 5 μm, the powder becomes less fluid, making it difficult to handle during processing. If the particle size D50 exceeds 500 μm, the particle size is expected to be too large to penetrate the coating film during processing such as coating, or to cause defects during sintering when used as a sintering filler in refractories, thus limiting its applications.

[0018] The specific surface area of ​​the spinel-type aluminum oxide of the present invention is 10 to 120 m². 2 / g, preferably 12-115mg 2 / g, comfortable 15~110m 2 The value is / g. In this invention, the specific surface area is the value measured with a specific surface area measuring device (GeminiVII2390a manufactured by Shimadzu Corporation). The specific surface area is 5m². 2 If the specific surface area is less than 120 m², the specific surface area is too small for use as a catalyst support, resulting in low catalyst support capacity and making it unsuitable for use as a catalyst support. On the other hand, if the specific surface area is 120 m² 2 If the value exceeds / g, the specific surface area becomes too large, causing it to destabilize the material system by adsorbing oils, water, and dyes added to the resin when used as an inorganic pigment, resulting in unstable processing.

[0019] The protective molecule for the water-dispersible alumina sol used in the synthesis of spinel-type aluminum oxide in the present invention can be one or more selected from glycine, valine, leucine, isoleucine, betaine, NN-aminobetaine, alginic acid, glutamic acid, formic acid, and acetic acid, and can be used individually or in combination.

[0020] The water-dispersed alumina sol used in the synthesis of the spinel-type aluminum oxide of this invention must be boehmite. If it is α-alumina, γ-alumina, or θ-alumina, it already possesses the alumina crystal structure, making it difficult to form spinel-type aluminum oxide.

[0021] The particle size D50 of the water-dispersed alumina sol used in the synthesis of the spinel-type aluminum oxide of the present invention is 0.005 to 0.5 μm, preferably 0.01 to 0.4 μm, and more preferably 0.015 to 0.3 μm. The particle size distribution of the alumina sol is measured using a dynamic light scattering particle size analyzer (Malvern Panalytical Zetasizer Pro). If D50 is less than 0.005 μm, the particle size is too small, making it difficult to form a Pickering emulsion. On the other hand, if D50 exceeds 0.5 μm, the particle size is too large, resulting in poor storage stability of the water-dispersed alumina sol.

[0022] The Al2O3 equivalent concentration of the water-dispersed alumina sol used in the synthesis of the spinel-type aluminum oxide of the present invention is 1 to 12% by mass, preferably 1.5 to 11% by mass, and more preferably 2 to 10.5% by mass. If the Al2O3 equivalent concentration of the water-dispersed alumina sol is less than 1% by mass, the alumina concentration in the water-dispersed alumina sol is too low, making it difficult to form a Pickering emulsion. On the other hand, if the Al2O3 equivalent concentration exceeds 12% by mass, the viscosity of the water-dispersed alumina sol becomes high, making it difficult to form a Pickering emulsion.

[0023] The organic solvent used in the organic solvent phase for forming a water-in-oil (W / O) Pickering emulsion for the synthesis of the spinel-type aluminum oxide of the present invention is a solvent that is water-insoluble and capable of forming a water-in-oil (W / O) Pickering emulsion. Specifically, one or more of the following can be selected: hydrocarbon solvents, such as nonane and decane; ketone solvents, such as methyl isobutyl ketone and cyclohexanone; alcohol solvents, such as pentanol and octanol; and ester solvents, such as butyl acetate and butyl lactate.

[0024] The organic solvent used in the organic solvent phase for forming a water-in-oil (W / O) Pickering emulsion for the synthesis of spinel-type aluminum oxide in the present invention preferably has a boiling point of 85 to 200°C. If the boiling point is below 85°C, heat is generated when shear is applied to the aqueous phase and the organic solvent phase to form the Pickering emulsion, causing the organic solvent phase to volatilize and preventing the formation of the desired water-in-oil (W / O) Pickering emulsion. On the other hand, if the boiling point exceeds 200°C, productivity is reduced because the set temperature must be higher or the drying process takes a long time after separating the organic solvent phase.

[0025] The organic solvent used in the organic solvent phase for forming a water-in-oil (W / O) Pickering emulsion for the synthesis of spinel-type aluminum oxide in the present invention preferably has a carbon number in the range of 4 to 12. If the number of carbon atoms in the organic solvent is less than 4, the boiling point becomes low, and when shear is applied to the aqueous phase and the organic solvent phase to form the Pickering emulsion, heat is generated, and the volatilization of the organic solvent phase progresses, making it impossible to form the desired water-in-oil (W / O) Pickering emulsion. On the other hand, if the number of carbon atoms in the organic solvent exceeds 12, the boiling point becomes high, and after separating the organic solvent phase, the set temperature for drying must be high or the drying time must be long, which worsens productivity.

[0026] The aqueous solution of Ni, Co, or Mg used to synthesize the spinel-type aluminum oxide of the present invention is prepared by dissolving one or more of the nitrates, sulfates, acetates, or chlorides of Ni, Co, or Mg in water. The aqueous solution can be used in an amount of 0.7 to 20% by mass, preferably 1 to 19% by mass, and more preferably 2 to 18% by mass, relative to the total mass of the aqueous solution of water-dispersed alumina sol and the aqueous solution of Ni, Co, or Mg. If the amount of the aqueous solution of Ni, Co, or Mg is less than 0.7% by mass, the solution is dilute, requiring a large amount of water-dispersed alumina sol to achieve the stoichiometric ratio of MAl2O4, which leads to a decrease in productivity. On the other hand, if it exceeds 20% by mass, it is necessary to use a water-dispersed alumina sol with a high Al2O3 equivalent concentration to achieve the stoichiometric ratio of MAl2O4, and the viscosity of the water-dispersed alumina sol becomes a production issue.

[0027] The crystal system used to synthesize the spinel-type aluminum oxide of the present invention is one in which the ratio of the volume of the organic solvent to the volume of the aqueous solvent (B) is (B) / (A) = 0.2 to 0.8, preferably (B) / (A) = 0.25 to 0.75, and more preferably (B) / (A) = 0.3 to 0.7. If (B) / (A) = less than 0.3, the volume of the organic solvent phase that forms the water-in-oil Pickering emulsion is too small, and the water-in-oil Pickering emulsion cannot be sufficiently held, resulting in decreased productivity. On the other hand, if (B) / (A) = greater than 0.7, the amount of the organic solvent phase is too large, and the separation and drying of the aqueous phase and organic solvent takes time, resulting in decreased productivity.

[0028] The apparatus used to apply shear force to form a water-in-oil (W / O) Pickering emulsion for synthesizing the spinel-type aluminum oxide of the present invention can be any apparatus capable of applying shear force to an aqueous solution, and specifically, it can be selected from a homogenizer, ultrasonic homogenizer, propeller mixer, homomixer, or dispatcher.

[0029] In the process of synthesizing the spinel-type aluminum oxide of the present invention, a water-in-oil (W / O) Pickering emulsion is formed, and then the aqueous phase and organic solvent phase are separated to extract the organic solvent phase. This process can be selected from a separatory funnel, a liquid-liquid extraction apparatus, or liquid separation by draining from the bottom of the kettle.

[0030] In the calcination process carried out to synthesize the spinel-type aluminum oxide of the present invention, the dried material is placed in an alumina crucible or alumina sagger and calcined at 700 to 1200°C, preferably 750 to 1170°C, more preferably 800 to 1150°C for 2 to 8 hours, preferably 2.5 to 7.5 hours, more preferably 3 to 7 hours, and the calcination environment must be in air, nitrogen, or vacuum. If the temperature is below 700°C, the calcination temperature is insufficient, and the spinel structure of MAl2O4 will not be formed. On the other hand, if the temperature exceeds 1200°C, a special furnace is required, and the heating and cooling process takes time, resulting in decreased productivity. If the calcination time is less than 1 hour, the calcination time is insufficient, and the spinel structure of MAl2O4 will not be formed. On the other hand, if the calcination time exceeds 8 hours, the calcination time becomes very long, resulting in decreased production.

[0031] In the method for producing spinel-type aluminum oxide of the present invention, the drying step only needs to completely dry the organic solvent, and drying may be performed using a hot air circulation dryer, a shelf dryer, a vibrating dryer, or a vacuum dryer.

[0032] For synthesizing the spinel-type aluminum oxide of the present invention, the furnace used is preferably selected from batch furnaces, elevator furnaces, pusher furnaces, and conveyor furnaces.

[0033] In the method for producing spinel-type aluminum oxide according to the present invention, grinding is preferably carried out using various grinding machines, specifically mortars, automatic mortars, pot mills, ball mills, stone mill grinders, pin mills, or hammer mills. In the present invention, in order to prevent contamination (impurity metal elements) such as metals during grinding, it is desirable that the powder contact parts of the grinder be made of materials such as SUS, resin, alumina, or alumina coated by alumina thermal spraying. [Examples]

[0034] The present invention will be described in more detail by reference to examples. The present invention should not be construed as being limited to these examples. In the examples, parts and percentages are all based on mass unless otherwise indicated.

[0035] (Example 1) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0036] Table 1, described later, shows the crystalline system, particle size D50 (μm), type of organic solvent, and boiling point (°C) of the alumina sol in Example 1.

[0037] Furthermore, Table 1 shows the D50 values ​​for the spinel-type aluminum oxide obtained in Example 1, measured as follows. The D50 values ​​are those measured wet in an aqueous solvent using a laser diffraction particle size analyzer (Mastersizer 3000; Malvern Panalytical).

[0038] Furthermore, the specific surface area of ​​the spinel-type aluminum oxide obtained in Example 1 was measured as follows, and D50 is listed in Table 1. The specific surface area was measured using a specific surface area measuring device (GeminiVII2360a; manufactured by Shimadzu Corporation) with N2.

[0039] For the spinel-type aluminum oxide obtained in Example 1, the crystalline phase was measured using an X-ray diffractometer, and the crystalline system is shown in Table 1. The X-ray diffractometer used was a desktop X-ray diffractometer (Miniflex; manufactured by Rigaku Corporation).

[0040] (Example 2) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 9.1% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0041] Similar to Example 1, Table 1 lists the crystalline system of the alumina sol in Example 2, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0042] (Example 3) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 9.1% by mass cobalt nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0043] Similar to Example 1, Table 1 lists the crystalline system of the alumina sol in Example 3, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0044] (Example 4) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a 4% Al2O3 equivalent concentration of glycine as a protective molecule is mixed with 30 ml of 3.0% magnesium nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0045] Similar to Example 1, Table 1 lists the crystalline system of the alumina sol in Example 4, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0046] (Example 5) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 6% by mass is mixed with 30 ml of 9.1% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0047] Similar to Example 1, Table 1 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0048] (Example 6) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of butyl lactate is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper butyl lactate phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0049] Similar to Example 1, Table 2 lists the crystalline system of the alumina sol in Example 6, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0050] (Example 7) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) containing valine as a protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of butyl lactate is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0051] Similar to Example 1, Table 2 lists the crystalline system of the alumina sol in Example 7, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0052] (Example 8) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of butyl lactate is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 800 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0053] Similar to Example 1, Table 2 lists the crystalline system of the alumina sol in Example 8, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0054] (Example 9) In a 300 ml separable flask, 20 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 20 ml of 7.3% by mass nickel nitrate aqueous solution, and 60 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio (B) / (A) = 0.6 was obtained by mixing the volume of the aqueous solution containing one of the metal species Ni, Co, or Mg with the volume of the organic solvent (A).

[0055] Similar to Example 1, Table 2 lists the crystalline system of the alumina sol in Example 9, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0056] (Example 10) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of an 8.8% by mass nickel acetate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0057] Similar to Example 1, Table 2 lists the crystalline system of the alumina sol in Example 10, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0058] (Comparative Example 1) In a 300 ml separable flask, 45 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 45 ml of 7.3% by mass nickel nitrate aqueous solution, and 10 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio (B) / (A) = 0.1 was obtained by mixing the volume of the aqueous solution containing one of the metal species Ni, Co, or Mg (A) with the volume of the organic solvent (A) to the volume of the organic solvent (B).

[0059] Similar to Example 1, Table 3 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0060] (Comparative Example 2) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 0.5 mass% is mixed with 30 ml of 7.3 mass% nickel nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0061] Similar to Example 1, Table 3 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0062] (Comparative Example 3) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 0.07% by mass magnesium nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0063] Similar to Example 1, Table 3 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0064] (Comparative Example 4) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 0.5% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0065] Similar to Example 1, Table 3 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0066] (Comparative Example 5) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.4% by mass nickel nitrate aqueous solution, and 40 ml of hexane is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. In synthesizing this product, the ratio (B) / (A) = 0.4 is the ratio of the sum of the volume of the aqueous solution (A) and the volume of the organic solvent to the volume of the organic solvent (B).

[0067] Similar to Example 1, Table 3 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0068] (Comparative Example 6) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass was mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone was added. The resulting solution was not subjected to shearing. In synthesizing this product, the ratio (B) / (A) = 0.4 was obtained between the sum of the volume of the aqueous solution (A) and the volume of the organic solvent (B) of the aqueous solution containing one of the metal species Ni, Co, or Mg.

[0069] Similar to Example 1, Table 4 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0070] (Comparative Example 7) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper cyclohexanone phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 600 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0071] Similar to Example 1, Table 4 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0072] (Comparative Example 8) In a 300 ml separable flask, 30 ml of aqueous alumina sol (manufactured by Asada Chemical Industries, Ltd.) with a glycine protective molecule at an Al2O3 equivalent concentration of 4% by mass is mixed with 30 ml of 7.3% by mass nickel nitrate aqueous solution, and 40 ml of liquid paraffin is added. A homogenizer T10 (manufactured by IKA) is then placed in the mixture and sheared at 18000 rpm for 1 minute to form a water-in-oil (W / O) Pickering emulsion. The liquid in the 300 ml separable flask is transferred to a 200 ml separatory funnel, the lower aqueous phase is removed, and the upper liquid paraffin phase is transferred to a 100 ml alumina crucible and dried in a hot air circulating dryer set to 150 °C for 30 minutes. The dried alumina crucible is then calcined in a batch-type calcination furnace at 1000 °C in air for 5 hours. The sintered powder was ground in an alumina mortar for 10 minutes to obtain the oxide. In synthesizing this product, the ratio of the volume of the aqueous solution (A) to the volume of the organic solvent (B) is (B) = 0.4.

[0073] Similar to Example 1, Table 4 lists the crystalline system of the alumina sol, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point of the organic solvent (°C), the crystalline system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of ​​the obtained spinel-type aluminum oxide.

[0074] (Comparative Example 9) In a 300 ml separable flask, 30 ml of aluminum sulfate with an Al2O3 equivalent concentration of 8.1% by mass was mixed with 30 ml of a 7.3% by mass nickel nitrate aqueous solution, and 40 ml of cyclohexanone was added. A homogenizer T10 (manufactured by IKA) was then placed in the flask and sheared at 18,000 rpm for 1 minute. In synthesizing this product, the ratio (B) / (A) = 0.4 was obtained between the sum of the volume of the aqueous solution (A) and the volume of the organic solvent (B) of the aqueous solution containing one of the metal species Ni, Co, or Mg.

[0075] Similar to Example 1, the crystal system of the alumina sol of Comparative Example 9, the particle size D50 (μm) of the alumina sol, the type of organic solvent, the boiling point (°C) of the organic solvent, the crystal system of the obtained spinel-type aluminum oxide, the particle size D50 (μm) of the obtained spinel-type aluminum oxide, and the specific surface area of the obtained spinel-type aluminum oxide were described in Table 4.

[0076]

Table 1

[0077]

Table 2

[0078]

Table 3

[0079]

Table 4

[0080] As shown in Tables 1 and 2, it was confirmed that spinel-type aluminum oxides of nickel aluminate, cobalt aluminate, and magnesium aluminate could all be synthesized in Examples 1 to 10. Examples 1 to 10 were all measured with a laser diffraction particle size distribution analyzer.

[0081] The alumina sols obtained in Examples 1 to 10 had a D50 of the particle size measured with a laser diffraction particle size distribution analyzer in the range of 5 to 500 μm and a specific surface area in the range of 10 to 120 m 2 / g, and it was confirmed that the desired spinel-type aluminum oxide could be easily produced with good productivity by the method via the water-in-oil (W / O) Pickering emulsion.

[0082] As shown in Table 3, in Comparative Example 1, the amount of cyclohexanone in the organic solvent phase was too low, resulting in insufficient formation of a water-in-oil (W / O) Pickering emulsion. Sintering progressed during firing, and the specific surface area became smaller than intended. In Comparative Example 2, the concentration of alumina sol was too low, and the water-in-oil (W / O) Pickering emulsion could not be formed.

[0083] As shown in Table 3, in Comparative Examples 3 and 4, the concentrations of magnesium nitrate and nickel nitrate were too low, respectively. Although a water-in-oil (W / O) Pickering emulsion could be formed and the process could proceed to calcination after drying, the large amount of alumina sol resulted in the formation of an α-alumina phase in addition to the spinel-type aluminum oxide.

[0084] As shown in Table 3, Comparative Example 5 used hexane as the organic solvent phase. As a result, when shearing was applied to form a water-in-oil (W / O) Pickering emulsion, the hexane evaporated, and a sufficient water-in-oil (W / O) Pickering emulsion could not be obtained.

[0085] As shown in Table 4, Comparative Example 6 could not form a water-in-oil (W / O) Pickering emulsion because no shearing was applied. Comparative Example 7 did not reach the temperature required to form spinel-type aluminum oxide due to its low firing temperature, resulting in only alumina sintering and exhibiting only a γ-alumina phase. Comparative Example 8 used liquid paraffin as the organic solvent phase, so it did not dry at 150°C and could not proceed to the firing process.

[0086] As shown in Table 4, Comparative Example 9 used an aqueous solution of aluminum sulfate instead of alumina sol, and therefore could not form a Pickering emulsion even when sheared, and could not proceed to the drying and calcination process.

[0087] Figures 1 and 2 show the results of X-ray diffraction measurements performed on Example 1 and Comparative Example 4. Figures 3-5 show scanning electron microscope (SEM) images (50,000x magnification) of Example 1, Example 4, and Example 5. X-ray diffraction measurements were mainly performed using an X-ray diffractometer (specifically, a MiniFlex manufactured by Rigaku Corporation) with a Cu target using the θ / 2θ method. The scanning electron microscope images in Figures 3-5 were observed using a field emission analytical scanning electron microscope (JSM-7610F; manufactured by JEOL Ltd.).

[0088] As can be seen in Figures 1 and 2, Example 1 shows the X-ray diffraction pattern of nickel aluminate, while Comparative Example 4 shows a peak of α-alumina along with the nickel aluminate peak, as indicated by the arrow. It is predicted that in Comparative Example 4, the alumina sol was in excess within the Pickering emulsion, causing crystallization of α-alumina alone without forming spinel-type aluminum oxide.

[0089] As shown in Figures 3 and 5, the SEM images (550,000x magnification) of nickel aluminate in Examples 1 and 8 confirm that it is an aggregate of elongated nickel aluminate crystals with a length of 0.1 to 0.3 μm. Figure 4 shows the SEM image (50,000x magnification) of magnesium aluminate in Example 4, confirming that the magnesium aluminate is formed as an aggregate of crystals smaller than 0.1 μm. We believe that this shape is a factor contributing to the large specific surface area.

[0090] According to the present invention, (1) A step of mixing an aqueous alumina sol whose crystalline system is boehmite with an aqueous solution containing one of the metal species Ni, Co, or Mg. (2) A step of mixing an organic solvent insoluble in water with the aqueous solution obtained in step (1) to form a phase separation state between the aqueous phase and the organic solvent phase. (3) A step to prepare a spinel precursor in the organic solvent phase by applying shear to the entire liquid in the phase-separated state obtained in step (2), thereby forming a water-in-oil (W / O) Pickering emulsion. (4) A step in which the liquid subjected to shearing in step (3) is allowed to stand to separate into an aqueous phase and an organic solvent phase. (5) A step of extracting the organic solvent phase from the phase separation liquid of step (4), (6) A step to obtain a cake by drying the organic solvent phase extracted in step (5), (7) The cake obtained in step (6) is baked at 700-1200°C for 2-8 hours. (8) The process includes crushing the calcined material obtained in step (7), The aqueous solution containing any of the metal species Ni, Co, or Mg in step (1) above is prepared by dissolving one or more of the nitrates, sulfates, acetates, or chlorides of Ni, Co, or Mg in water, and the amount of the aqueous solution added is 0.7 to 20% by mass of the total mass of the aqueous dispersion of alumina sol and the aqueous solution containing any of the metal species Ni, Co, or Mg. The water-dispersed alumina sol in step (1) above has an Al2O3 equivalent concentration of 1 to 12% by mass, and the water-dispersed alumina sol has a particle size D50 of 0.005 to 0.5 μm as measured by a dynamic light scattering particle size analyzer. The organic solvent used in the organic solvent phase to form the water-in-oil Pickering emulsion in step (3) above is a hydrocarbon solvent, a ketone solvent, an alcohol solvent, or an ester solvent, and has a boiling point of 85 to 200°C. The ratio (B) / (A) = 0.2 to 0.8 is the sum of the volume of the solution obtained by mixing an aqueous alumina sol of boehmite with an aqueous solution containing one of the metal species Ni, Co, or Mg, and the volume of the organic solvent (A). It was confirmed that the main component of the obtained pulverized material is a spinel-type aluminum oxide, which is a compound having a spinel structure with the chemical formula MAl2O4 (wherein M represents one of Ni, Co, or Mg).

[0091] Furthermore, the spinel-type aluminum oxide has a particle size D50 of 5-500 μm and a specific surface area of ​​10-120 m², as measured by a laser diffraction particle size distribution analyzer. 2 It was confirmed that it possesses the characteristics of / g.

[0092] The present invention also includes the following embodiments: The method for producing the spinel-type aluminum oxide described above, characterized in that the alumina crystal system in the aqueous-dispersed alumina sol in step (1) is boehmite, and the protective molecule is one or more selected from glycine, valine, leucine, isoleucine, betaine, NN-aminobetaine, alginic acid, glutamic acid, formic acid, and acetic acid.

[0093] The method for producing spinel-type aluminum oxide, characterized in that the apparatus used to apply shear in step (3) to form a water-in-oil Pickering emulsion is a homogenizer, an ultrasonic homogenizer, a propeller mixer, a homomixer, or a discharger.

[0094] The above method for producing spinel-type aluminum oxide, wherein step (7) involves baking the cake in an alumina crucible or alumina sagger at 700-1200°C for 2-8 hours, and the baking environment is carried out in air, nitrogen, or vacuum.

[0095] The method for producing spinel-type aluminum oxide described above, characterized in that the organic solvent used in the organic solvent phase to form the water-in-oil Pickering emulsion in step (3) is a hydrocarbon solvent, a ketone solvent, an alcohol solvent, or an ester solvent, and the number of carbon atoms in the organic solvent is in the range of 4 to 12. [Industrial applicability]

[0096] Nickel aluminate, cobalt aluminate, and magnesium aluminate, which are spinel-type aluminum oxides obtained by the spinel-type aluminum oxide synthesis method according to the present invention, have durability, heat resistance, and high specific surface area. Nickel aluminate and cobalt aluminate exhibit a blue-green to blue color, making them promising for use as heat-resistant inorganic pigments, while magnesium aluminate is expected to be used as a compounding material for ceramics and refractories. Furthermore, they are important materials for catalyst supports and sensors that require various heat resistances, and can be specifically used as glazes, refractories, ceramics, and catalyst supports for chemical plants and exhaust gases.

Claims

1. (1) A step of mixing an aqueous alumina sol whose crystalline system is boehmite with an aqueous solution containing one of the metal species Ni, Co, or Mg. (2) A step of mixing an organic solvent insoluble in water with the aqueous solution obtained in step (1) to form a phase separation state between the aqueous phase and the organic solvent phase. (3) A step to prepare a spinel precursor in the organic solvent phase by applying shear to the entire liquid in the phase-separated state obtained in step (2), thereby forming a water-in-oil (W / O) Pickering emulsion. (4) A step in which the liquid subjected to shearing in step (3) is allowed to stand to separate into an aqueous phase and an organic solvent phase. (5) A step of extracting the organic solvent phase from the phase separation liquid of step (4), (6) A step to obtain a cake by drying the organic solvent phase extracted in step (5), (7) A step in which the cake obtained in step (6) is baked at 700 to 1200°C for 2 to 8 hours. (8) The process includes a step of crushing the calcined material obtained in step (7), The aqueous solution containing any of the metal species Ni, Co, or Mg in step (1) above is prepared by dissolving one or more of the nitrates, sulfates, acetates, or chlorides of Ni, Co, or Mg in water, and the amount of the aqueous solution added is 0.7 to 20% by mass of the total mass of the aqueous dispersion of alumina sol and the aqueous solution containing any of the metal species Ni, Co, or Mg. The Al of the aqueous alumina sol in step (1) ２ O ３ The converted concentration is 1 to 12% by mass, and the particle size D50 measured by a dynamic light scattering particle size analyzer for water-dispersed alumina sols is 0.005 to 0.5 μm. The organic solvent used in the organic solvent phase to form the water-in-oil Pickering emulsion in step (3) above is a hydrocarbon solvent, a ketone solvent, an alcohol solvent, or an ester solvent, and has a boiling point of 85 to 200°C. The ratio (B) / (A) = 0.2 to 0.8 is the sum of the volume of the solution obtained by mixing an aqueous alumina sol of boehmite with an aqueous solution containing one of the metal species Ni, Co, or Mg, and the volume of the organic solvent (A), and the volume of the organic solvent (B). The main component of the resulting pulverized material is, chemical formula: MAl 2 O 4 A spinel-type aluminum oxide having (wherein M represents one of Ni, Co, or Mg), wherein the spinel-type aluminum oxide has a particle size D50 of 5 to 500 μm and a specific surface area of ​​10 to 120 m² / g as measured by a laser diffraction particle size distribution analyzer. A method for producing spinel-type aluminum oxide, characterized by the following features.

2. The method for producing spinel-type aluminum oxide according to claim 1, characterized in that the alumina crystal system in the aqueous dispersion of alumina sol in step (1) is boehmite, and the protective molecule is one or more selected from glycine, valine, leucine, isoleucine, betaine, NN aminobetaine, alginic acid, glutamic acid, formic acid, and acetic acid.

3. The method for producing spinel-type aluminum oxide according to claim 1 or 2, characterized in that the apparatus used to apply shear in step (3) to form a water-in-oil Pickering emulsion is a homogenizer, an ultrasonic homogenizer, a propeller mixer, a homomixer, or a discharger.

4. The method for producing spinel-type aluminum oxide according to claim 1 or 2, wherein step (7) involves baking the cake in an alumina crucible or alumina sagger at 700 to 1200°C for 2 to 8 hours, and the baking environment is carried out in air, nitrogen, or vacuum.

5. The method for producing spinel-type aluminum oxide according to claim 1 or 2, characterized in that the organic solvent used in the organic solvent phase to form the water-in-oil type Pickering emulsion in step (3) is a hydrocarbon solvent, a ketone solvent, an alcohol solvent, or an ester solvent, and the number of carbon atoms in the organic solvent is in the range of 4 to 12.

Images