Alumina aqueous dispersion for use in ceramic / refractory and its manufacturing method

Abstract

To provide an alumina aqueous dispersion useful in forming a refractory by firing ceramic or the like, without leaving residual carbon even when firing is carried out at a temperature of 600°C or below.SOLUTION: The present invention provides an alumina aqueous dispersion containing alumina particles as dispersed particles, i.e., an alumina aqueous dispersion satisfying the following characteristics: (1) an average particle size of the dispersed alumina particles measured on the basis of number of particles is in a range of 10 to 1000 nm, (2) crystal systems of the alumina particles when the alumina aqueous dispersion is dried at 100°C, are amorphous and / or x-alumina, (3) the pH of the alumina aqueous dispersion is in a range of 2.0 to 5.3, (4) the alumina aqueous dispersion contains an organic acid and an alkali, with the organic acid being formic acid or a combination of formic acid and acetic acid, and the alkali being ammonia and, (5) the concentration of alumina (Al2O3) contained in the alumina aqueous dispersion is 0.5 to 11.5 mass%, and a method of producing the same.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an alumina aqueous dispersion for ceramics and refractories and a method for producing the same.

Background Art

[0002] An alumina aqueous dispersion in which alumina particles are dispersed in water is currently used in various applications.

[0003] Patent No. 7308650 (Patent Document 1) describes a large-particle-size alumina dispersion in which alumina particles are used as dispersed particles, the average particle size of the dispersed particles is 50 to 3000 nm, the crystal form of alumina when dried at 100°C is boehmite or pseudo-boehmite, the pH is 5.5 to 9, the alumina particle dispersion contains an organic acid and an alkali, the organic acid is lactic acid and / or malic acid, and the alkali is any one or more of ammonia and alkali metals. This large-particle-size alumina dispersion has a problem that residual carbon remains when fired at a firing temperature of 600°C or lower and cannot be used for low-temperature firing applications.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] An object of the present invention is to provide an alumina aqueous dispersion that is useful for applications such as forming refractories by firing ceramics and does not leave residual carbon even when fired at 600°C or lower.

Means for Solving the Problems

[0006] That is, the present invention provides the following aspects: [1] An alumina aqueous dispersion containing alumina particles as dispersed particles, having the following characteristics: (1) The average particle diameter measured on a number basis of the alumina dispersed particles is in the range of 10 to 1000 nm, (2) The crystal system of the alumina particles when the alumina aqueous dispersion is dried at 100 °C is amorphous and / or χ-alumina, (3) The pH of the alumina aqueous dispersion is in the range of 2.0 to 5.3, (4) The alumina aqueous dispersion contains an organic acid and an alkali, the organic acid is formic acid or a combination of formic acid and acetic acid, and the alkali is ammonia, (5) The alumina (Al2O3) conversion concentration contained in the alumina aqueous dispersion is 0.5 to 11.5% by mass, An alumina aqueous dispersion satisfying the above. [2] The alumina aqueous dispersion according to [1], having a thixotropic index (TI value = rotational speed 6 rpm / rotational speed 60 rpm) of 2 to 10 measured by a B-type viscometer. [3] The alumina aqueous dispersion according to [1] or [2], containing an alkali metal or a halogen element in the range of 0 to 0.03% by mass based on the total weight of the solid components in the alumina aqueous dispersion. [4] The alumina aqueous dispersion according to [1] or [2], which is used for the formation of ceramics or refractories. [5] A first step of adding aqueous ammonia to an aqueous solution of an aluminum salt selected from either aluminum nitrate or aluminum sulfate to adjust the pH to 5 to 8, and then stirring in the range of 15 to 45 °C for 0.5 to 3 hours to form a precipitate of amorphous aluminum hydroxide, A second step of washing the formed amorphous aluminum hydroxide and drying it so that the moisture content becomes 60 to 80%, After adding water to the dried amorphous aluminum hydroxide and dispersing it, 1.8 to 10 moles of formic acid or a mixture of formic acid and acetic acid is added per 1 mole of aluminum, and the mixture is stirred at 40 to 80 °C for 1 to 3 hours to obtain an aqueous solution of aluminum formate or an aqueous solution of a mixture of aluminum formate and aluminum acetate. This is the third step, and The fourth step of concentrating the obtained aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate at a temperature of 90 to 120 °C for 1 to 24 hours, A method for producing the alumina aqueous dispersion of [1] including [6] When the volume of the aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate obtained in the third step is C, and the volume after heating and concentrating at 90 to 120 °C for 1 to 24 hours in the fourth step is D, the volume concentration ratio (D / C) is 0.3 to 0.8. The production method of [5] is characterized by concentrating in such a manner.

Effect of the Invention

[0007] The alumina aqueous dispersion according to the present invention can thermally decompose the organic components at a low temperature of 600 °C or lower and be used as alumina, and has an average particle size of 10 to 1000 nm. Therefore, it is excellent in transparency, easy sinterability, etc., and can be used as an alumina coating on glass, metal, etc., an inorganic binder for adhering inorganic powders of ceramics and refractories, surface modification of a catalyst carrier, a fine abrasive, etc. The alumina aqueous dispersion of the present invention has no residual carbon even when fired at a low temperature of 600 °C or lower, and contains almost no alkali metals or halogens that cause problems during firing. Furthermore, the alumina aqueous dispersion of the present invention has thixotropic properties for imparting shape retention when mixed with an inorganic filler.

Brief Description of the Drawings

[0008]

Figure 1

Figure 2

Figure 3

Figure 4

Mode for Carrying Out the Invention

[0009] Hereinafter, the present invention will be described in detail based on preferred embodiments. However, the present invention is not limited to the following embodiments, and various modifications are possible within the scope shown in the claims. In this specification, the notation "numerical value 1 to numerical value 2" in a numerical range means a range having numerical value 1 as the lower limit value and numerical value 2 as the upper limit value, and includes both ends of numerical value 1 and numerical value 2, which is synonymous with "numerical value 1 or more and numerical value 2 or less".

[0010] Since aluminum has an oxidation number of 3, when forming an acid and a salt, not all bonds form bonds with acid groups, and some may form bonds. Specifically, as described later, for the salt with formic acid, the formation of three types, namely Al(OH)2(OOCH), Al(OH)(OOCH)2, and Al(OOCH)3, is conceivable. In this specification, in the case of a salt with an acid, all these three cases are included.

[0011] (Alumina aqueous dispersion) When measuring the average particle size of the alumina dispersed particles in the alumina aqueous dispersion of the present invention by number distribution, the average particle size is preferably 10 to 1000 nm, more preferably 30 to 100 nm. When the average particle size is less than 10 nm, the binding property with inorganic particles deteriorates, and there is a problem that the shape retention property during molding deteriorates. On the other hand, when it exceeds 1000 nm, the average particle size is too large, and when an inorganic powder having primary particles of several hundred nm is bound and fired, it becomes a foreign substance and may become a fracture initiation point. Here, the "average particle size" means the average particle size measured by the dynamic light scattering method in an aqueous solvent using a Zetasizer Nano ZS (manufactured by Malvern Panalytical Ltd.) and measured on a number basis.

[0012] The alumina crystal system in the alumina aqueous dispersion of the present invention is preferably amorphous and / or χ-alumina because it undergoes a phase transition to γ-alumina and α-alumina depending on the firing conditions during high-temperature sintering of ceramics or the like.

[0013] The pH of the alumina aqueous dispersion of the present invention is 2.0 to 5.3, more preferably pH 3.0 to 4.7. When the pH is less than 2.0, it becomes strongly acidic, so when mixed with inorganic particles, the inorganic particles tend to be deteriorated, and when the alumina aqueous dispersion contacts a metal, it tends to cause corrosion. On the other hand, when the pH exceeds 5.3, the alumina dispersion causes aggregation when an acidic environment is required in the molding of refractories or the production of catalyst carriers. The pH of the alumina aqueous dispersion referred to here is measured using a portable pH meter "HM-40P" manufactured by TOA DKK Corporation and a pH composite electrode "GST-2739C".

[0014] The alumina aqueous dispersion of the present invention contains a short-chain carboxylic acid such as formic acid or a mixture of formic acid and acetic acid, and is designed to have good thermal decomposability at low temperatures. Alumina aqueous dispersions containing lactic acid, malic acid, etc. as in Patent Document 1 have poor thermal decomposability and leave residual carbon, so they are considered unsuitable for thermal decomposition applications at low temperatures (for example, 500 to 600 °C).

[0015] Preferably, the alumina (Al2O3) equivalent concentration in the alumina aqueous dispersion of the present invention is 0.5 to 11.5% by mass. The alumina equivalent concentration preferably ranges from 0.8 to 10.5% by mass, more preferably 2 to 10% by mass. If it is less than 0.3% by mass, the alumina concentration in the alumina aqueous dispersion is too low, resulting in poor adhesiveness when used as a binder for inorganic particles and no thixotropic property. If it exceeds 11.5% by mass, the storage stability of aluminum formate or a mixture of aluminum formate and aluminum acetate deteriorates, and there is a problem that precipitates precipitate in the alumina aqueous dispersion over time.

[0016] The calculation of the alumina (Al2O3) equivalent concentration in the alumina aqueous dispersion of the present invention is performed as follows. Measure the aluminum concentration in the alumina aqueous dispersion with an emission spectroscopic analyzer (Agilent 5110 ICP-OCS: manufactured by Agilent Technologies), and calculate it by conversion using the following formula, assuming the atomic weight of aluminum: 27, the atomic weight of oxygen: 16, and the molecular weight of Al2O3: 102. Al2O3 equivalent concentration (% by mass) = Al concentration (% by mass) × (102 / 27)

[0017] Preferably, the alumina aqueous dispersion of the present invention has a TI value (thixotropic index value) measured with a B-type viscometer (using a TVB10M TM-3 spindle rotor manufactured by Toki Sangyo Co., Ltd.) of 2 to 10. The TI value is more preferably 2.5 to 7, and even more preferably 3 to 8. The TI value is calculated as (rotation speed 6 rpm) / (rotation speed 60 rpm). If the TI value is less than 2, the liquid property does not have structural viscosity, so it becomes difficult to maintain the shape when molding a mixture of inorganic particles and the alumina aqueous dispersion into a mold, resulting in shape collapse. If the TI value exceeds 10, the structural viscosity is too strong, making it difficult to deform without increasing the shear rate, and it becomes difficult to perform pouring etc. during molding using a mold.

[0018] The alumina aqueous dispersion of the present invention preferably contains almost no alkali metal or halogen element. The alkali metal or halogen element is preferably contained in the alumina aqueous dispersion of the present invention in the range of 0 to 0.03% by mass, preferably 0 to 0.02% by mass. Specific examples of the alkali metal include sodium and potassium, and specific examples of the halogen element include chlorine, bromine, or iodine. When the content of the alkali metal exceeds 0.03% by mass, when used in refractories, ceramics, etc., a decrease in the sintering temperature occurs during firing, and defects in the sintered body tend to occur. When the halogen element exceeds 0.03% by mass, when used in refractories, ceramics, etc., gases derived from each element are generated during firing, and there is a problem of causing corrosion in the furnace. The content of these elements is measured by energy-dispersive fluorescent X-ray (EDX) equipped with a scanning electron microscope JCM-7000 manufactured by JEOL Ltd. for the powder obtained by drying the alumina aqueous dispersion at 80°C for 30 minutes.

[0019] The alumina aqueous dispersion of the present invention has no residual carbon at a low temperature of 600°C or lower, and no generation of halogen gas or the like during firing. Also, it is possible to provide shape retention by mixing with an inorganic filler and can be used without aggregation even in the acidic region. The alumina aqueous dispersion of the present invention can be effectively used for the molding of ceramics and refractories.

[0020] (Method for producing alumina aqueous dispersion) The alumina aqueous dispersion of the present invention is produced by the following method: A first step of adding aqueous ammonia to an aqueous solution of an aluminum salt selected from either aluminum nitrate or aluminum sulfate to adjust the pH to 5 to 8, and then stirring in the range of 15 to 45°C for 0.5 to 3 hours to form a precipitate of amorphous aluminum hydroxide. A second step of washing the generated amorphous aluminum hydroxide and then drying it so that the moisture content is 60 to 80%. After adding water to and dispersing the dried amorphous aluminum hydroxide, 1.8 to 10 moles of formic acid or a mixture of formic acid and acetic acid is added per mole of aluminum, and the mixture is stirred at 40 to 80 °C for 1 to 3 hours to obtain an aqueous solution of aluminum formate or an aqueous solution of a mixture of aluminum formate and aluminum acetate, and a fourth step of concentrating the obtained aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate at a temperature of 90 to 120 °C for 1 to 24 hours, is included.

[0021] In the first step, an aqueous ammonia solution is added to an aqueous solution of an aluminum salt (specifically, aluminum nitrate or aluminum sulfate) to form a precipitate of amorphous aluminum hydroxide. This step is carried out by stirring at a temperature in the range of 15 to 45 °C for 0.5 to 3 hours. This step is preferably carried out by stirring at 20 to 35 °C for 1 to 2 hours. When the temperature is less than 15 °C, the reactivity between aluminum nitrate or aluminum sulfate and ammonia deteriorates, and the reaction takes time. When the temperature exceeds 45 °C, the volatilization of ammonia becomes intense, and the pH tends not to be stable. Also, when the stirring time is less than 0.5 hours, the reaction time is insufficient, and amorphous aluminum hydroxide tends not to precipitate sufficiently. When it exceeds 3 hours, amorphous aluminum hydroxide can be synthesized, but the reaction time is too long and the productivity deteriorates. When adding the aqueous ammonia solution, the pH becomes 5 to 8. More preferably, the pH becomes 6 to 7. When the pH is less than 5, it takes a very long time for the precipitate of amorphous aluminum hydroxide to settle, resulting in poor productivity. When the pH exceeds 8, the dispersibility tends to deteriorate when adding water to and dispersing the amorphous aluminum hydroxide.

[0022] In the second step, the produced amorphous aluminum hydroxide is washed and then dried so that the moisture content becomes 60 to 80%. The washing is carried out by washing with water and then separating the water. The separation of water can be carried out by various methods, and it may be carried out by centrifugation or the like. The washing may be carried out once, but usually, several times, preferably about 3 times, of adding water and separation are carried out.

[0023] Drying is carried out after water separation. Drying requires a process of drying to a moisture content of 60 - 80%. A more preferable moisture content is 65 - 75%. When the moisture content is less than 60%, the dispersibility deteriorates when adding water to amorphous aluminum hydroxide for dispersion. When the moisture content exceeds 80%, the moisture content of amorphous aluminum hydroxide is too high, making it difficult to handle and resulting in poor productivity. The moisture content is measured using a heated drying type moisture meter (MX50 manufactured by A&D Company, Limited) under the conditions of 105°C for 40 minutes. Drying may be carried out using a shelf dryer.

[0024] The third step is to add water to the dried amorphous aluminum hydroxide and disperse it, and then add 1.8 - 10 moles, preferably 1.8 - 6 moles, more preferably 1.8 - 3 moles of formic acid or a mixture of formic acid and acetic acid per mole of aluminum, and stir at 40 - 80°C for 1 - 3 hours to obtain an aqueous solution of aluminum formate or an aqueous solution of a mixture of aluminum formate and aluminum acetate. When the amount of formic acid or a mixture of formic acid and acetic acid is less than 1.8 moles per mole of aluminum, formic acid or the mixture of formic acid and acetic acid is insufficient, and there is a tendency that an alumina aqueous dispersion is not formed. When the amount of formic acid or a mixture of formic acid and acetic acid exceeds 10 moles per mole of aluminum, the amount of formic acid or the mixture of formic acid and acetic acid becomes excessive, and the pH of the alumina aqueous dispersion becomes less than 2, making it unusable for metal corrosion and dissolving inorganic powders during use.

[0025] Stirring is carried out at 40°C - 80°C, preferably 45°C - 65°C. When the temperature is less than 40°C, the reaction between amorphous aluminum hydroxide and formic acid or a mixture of formic acid and acetic acid is insufficient, and unreacted formic acid or a mixture of formic acid and acetic acid remains in the system, resulting in poor storage stability. On the other hand, when the temperature exceeds 80°C, the evaporation of water and formic acid becomes significant, and precipitates may form on the wall surface of the reaction kettle during synthesis.

[0026] The number of moles of aluminum in the amorphous aluminum hydroxide in the above - mentioned third step is calculated from the following formula, assuming the atomic weight of aluminum: 27, the atomic weight of oxygen: 16, the atomic weight of hydrogen: 1, and the molecular weight of Al(OH)3: 78: Number of moles of aluminum = (weight of aluminum hydroxide) × (100 - moisture content) / 100 × (27 / 78) / 27

[0027] When using a combination of formic acid and acetic acid, the ratio of the number of moles of formic acid: A to the number of moles of acetic acid: B (B / A) needs to be 0 to 0.25, preferably 0 to 0.15. If B / A exceeds 0.25, the amount of acetic acid in the system increases, and precipitation may occur during storage over time.

[0028] The fourth step is a step of concentrating the obtained aqueous solution of aluminum formate or an aqueous solution of a mixture of aluminum formate and aluminum acetate at a temperature of 90 to 120°C for 1 to 24 hours. The heating method when heating and stirring aluminum formate or aluminum acetate is not particularly limited, and ordinary heating methods or the use of an autoclave, etc. are possible. Also, in terms of the stirring method, there is no problem as long as it is an ordinary stirring method. The reaction temperature is preferably 90 to 120°C, more preferably 95 to 110°C. The reaction time can be arbitrarily determined within 1 to 24 hours including productivity. If the heating temperature is less than 90°C, the reaction does not proceed sufficiently and an alumina particle dispersion liquid cannot be obtained. If it exceeds 120°C, a special reaction environment such as applying pressure to increase the temperature is required, and the productivity deteriorates.

[0029] When the volume of the aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate obtained in the third step is C, and the volume after heating and concentrating at 90 to 120°C for 1 to 24 hours in the fourth step is D, it is preferable to concentrate so that the volume concentration ratio (D / C) is 0.3 to 0.8. Usually, the alumina aqueous dispersion is often synthesized by applying heat with the reaction vessel sealed, so concentration is not performed, but in the present invention, a concentration step is positively provided. If the volume concentration ratio (D / C) is less than 0.3, it is excessive concentration, and it is difficult to maintain the form as an alumina aqueous dispersion. Conversely, if the volume concentration ratio (D / C) exceeds 0.8, the concentration is insufficient, and there is a problem that an alumina aqueous dispersion cannot be formed.

[0030] The alumina aqueous dispersion of the present invention needs to be designed by selecting materials that do not contain halogen gases such as chlorine and bromine that damage the furnace during high-temperature firing for ceramics and refractories, and alkali metals such as sodium and potassium that lower the sintering temperature of ceramics and refractories. Therefore, when producing the alumina aqueous dispersion, it is necessary to use raw materials that do not contain these elements (i.e., alkali metals and halogen elements) as the main components.

[0031] It is important that the alumina aqueous dispersion obtained in the present invention thermally decomposes at low temperature firing, and the temperature at which weight loss is completed is preferably in the range of 400 to 600 °C, more preferably 450 to 550 °C. Also, the firing time is preferably in the range of 2 to 300 minutes, more preferably 5 to 60 minutes. When the temperature at which weight loss due to firing is completed is less than 400 °C, when resin or the like is blended and molding or the like is performed at a temperature of about 300 °C, decomposition starts and there is a problem that the molded body becomes unstable. On the other hand, when the temperature at which weight loss is completed exceeds 600 °C, when coating a metal, glass, or the like, if the substrate is exposed to a high temperature, it may melt and deform, and coating may become impossible. When the firing time is less than 2 minutes, the thermal decomposition rate is too fast when firing large coatings, refractories, and ceramics at a predetermined temperature, and it is likely to cause firing variations between the ends and the center. When the firing time exceeds 300 minutes, productivity tends to deteriorate.

Examples

[0032] The present invention will be described in more detail with reference to examples, but the present invention is not limited thereto.

[0033] (Example 1) 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution was charged into a 20 L separable flask, and then 1160.6 g of 13.3 mol / l aqueous ammonia was added while stirring at 250 rpm. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a measuring cylinder, transferred to a separable flask, and heated and concentrated at 110 °C for 8 hours at 250 rpm to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a measuring cylinder, and when the volume was measured, it was 235 ml (D).

[0034] (Example 2) After adding 2250 g of an aqueous aluminum sulfate solution with a concentration of 0.17 mol / l into a 20 L separable flask, while stirring at 250 rpm, 1260.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 7.0. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water addition was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a measuring cylinder, transferred to a separable flask, and heated and concentrated at 110 °C for 8 hours at 250 rpm to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a measuring cylinder, and when the volume was measured, it was 225 ml (D).

[0035] (Example 3) 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution was charged into a 20 L separable flask, and then 1060.6 g of 13.3 mol / l aqueous ammonia was added while stirring at 250 rpm. After stirring at 30 °C for 1 hour, the pH was 6.2. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried at 100 °C for 1 hour using a shelf dryer. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a measuring cylinder, transferred to a separable flask, and heated and concentrated at 110 °C for 8 hours at 250 rpm to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a measuring cylinder, and when the volume was measured, it was 250 ml (D).

[0036] (Example 4) After adding 2250 g of a 0.5 mol / l aqueous aluminum nitrate solution to a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried at 100 °C for 1 hour using a shelf dryer. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 120 °C for 6 hours at 250 rpm to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a graduated cylinder, and when the volume was measured, it was 200 ml (D).

[0037] (Example 5) After adding 2250 g of a 0.5 mol / l aqueous aluminum nitrate solution to a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of a 13.3 mol / l aqueous ammonia solution was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried at 100 °C for 1 hour using a shelf dryer. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 100 °C and 250 rpm for 20 hours to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a graduated cylinder, and when the volume was measured, it was 235 ml (D).

[0038] (Example 6) 2250 g of a 0.5 mol / l aqueous aluminum nitrate solution was placed into a 20 L separable flask. Then, while stirring at 250 rpm, 1160.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added. This process was repeated three times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 72%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 1431.9 g of 23.1 mol / l formic acid was added and stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a measuring cylinder, transferred to a separable flask, and heated and concentrated at 100 °C and 250 rpm for 20 hours to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a measuring cylinder, and when the volume was measured, it was 225 ml (D).

[0039] (Example 7) 2250 g of a 0.5 mol / l aqueous aluminum nitrate solution was put into a 20 L separable flask, and then 1160.6 g of 13.3 mol / l aqueous ammonia was added while stirring at 250 rpm. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 60 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 110 °C for 8 hours at 250 rpm to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a graduated cylinder, and when the volume was measured, it was 225 ml (D).

[0040] (Example 8) After adding 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution to a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of a 13.3 mol / l aqueous ammonia solution was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel, stirring and dispersing, 2000 g of 23.1 mol / l formic acid and 386.6 g of 17.4 mol / l acetic acid were added, and it was stirred at 60 °C and 250 rpm for 1 hour to synthesize a mixture of a basic aluminum formate aqueous solution and a basic aluminum acetate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a measuring cylinder, transferred to a separable flask, and heated and concentrated at 110 °C and 250 rpm for 8 hours to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a measuring cylinder, and when the volume was measured, it was 225 ml (D).

[0041] (Comparative Example 1) After adding 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution to a 20 L separable flask, while stirring at 250 rpm, 1960.6 g of a 13.3 mol / l aqueous ammonia solution was added. After stirring at 30 °C for 1 hour, the pH was 8.9. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel, stirring and dispersing, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution.

[0042] (Comparative Example 2) After charging 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution into a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of a 13.3 mol / l aqueous ammonia solution was charged. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 8 hours. The moisture content was 45%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution.

[0043] (Comparative Example 3) After charging 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution into a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of a 13.3 mol / l aqueous ammonia solution was charged. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 10 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 110 °C for 8 hours at 250 rpm to obtain an alumina aqueous dispersion.

[0044] (Comparative Example 4) After adding 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution to a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2000 rpm for 1 minute using a centrifuge (KBS-10 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried at 100 °C for 1 hour using a shelf dryer. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 50 °C and 250 rpm for 24 hours to obtain an alumina aqueous dispersion.

[0045] (Comparative Example 5) After adding 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution to a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2000 rpm for 1 minute using a centrifuge (KBS-12 commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried at 100 °C for 1 hour using a shelf dryer. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 315.0 g of 23.1 mol / l formic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum formate aqueous solution. 500 ml (C) of the obtained basic aluminum formate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 110 °C and 250 rpm for 8 hours to obtain an alumina aqueous dispersion.

[0046] (Comparative Example 6) After charging 2250 g of an aqueous aluminum nitrate solution with a concentration of 0.5 mol / l into a 20 L separable flask, while stirring at 250 rpm, 386.9 g of an aqueous sodium hydroxide solution with a concentration of 8.0 mol / l was added, and after stirring at a temperature of 30 °C for 1 hour, the pH was 6.9. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried at 100 °C for 1 hour using a shelf dryer. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of formic acid with a concentration of 23.1 mol / l was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize an aqueous basic aluminum formate solution. 500 ml (C) of the obtained aqueous basic aluminum formate solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 110 °C for 8 hours at 250 rpm to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a graduated cylinder, and when the volume was measured, it was 225 ml (D).

[0047] (Comparative Example 7) 2250 g of a 0.5 mol / l aluminum nitrate aqueous solution was put into a 20 L separable flask. Then, while stirring at 250 rpm, 1160.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l lactic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize a basic aluminum lactate aqueous solution. 500 ml (C) of the obtained basic aluminum lactate aqueous solution was collected with a graduated cylinder, transferred to a separable flask, and heated and concentrated at 110 °C and 250 rpm for 8 hours to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a graduated cylinder, and when the volume was measured, it was 210 ml (D).

[0048] (Comparative Example 8) After adding 2250 g of an aqueous aluminum chloride solution with a concentration of 0.5 mol / l to a 20 L separable flask, while stirring at 250 rpm, 1160.6 g of 13.3 mol / l aqueous ammonia was added. After stirring at 30 °C for 1 hour, the pH was 6.6. The precipitated amorphous aluminum hydroxide gel was centrifuged at 2,000 rpm for 1 minute using a centrifuge (KBS-12, commercially available from Kansai Centrifuge Manufacturing Co., Ltd.) and 4 L of water was added, and this process was repeated 3 times to wash the amorphous aluminum hydroxide gel. Then, it was dried in a shelf dryer at a set temperature of 100 °C for 1 hour. The moisture content was 65%. After adding 6695 g of water to 1137.5 g of the dried amorphous aluminum hydroxide gel and stirring to disperse it, 2386.6 g of 23.1 mol / l acetic acid was added, and it was stirred at 45 °C and 250 rpm for 1 hour to synthesize an aqueous basic aluminum acetate solution. 500 ml (C) of the obtained aqueous basic aluminum acetate solution was collected with a measuring cylinder and transferred to a separable flask, and heated and concentrated at 110 °C and 250 rpm for 8 hours to obtain an alumina aqueous dispersion. The obtained alumina aqueous dispersion was put into a measuring cylinder, and when the volume was measured, it was 250 ml (D).

[0049] Regarding the alumina aqueous dispersions of Examples 1 to 8 and Comparative Examples 1 to 8, the average particle diameter (nm) of the alumina particles, the crystal system at 100 °C drying, the pH of the alumina aqueous dispersion, and the concentration in terms of Al2O3 (mass%) were measured as follows, and the results are shown in Tables 1 to 4. In Comparative Examples 1 to 5, the formation state of the alumina aqueous dispersion was insufficient, and the final state is described in Table 3.

[0050] (Average particle diameter (nm) of alumina particles) The average particle diameters of Examples 1 to 8 and Comparative Examples 6 to 8 were measured by the dynamic light scattering method in an aqueous solvent using a Zetasizer Nano ZS (manufactured by Spectris Co., Ltd.), and the average particle diameters measured based on the number are shown in Tables 1 to 2 and Table 4.

[0051] (Crystal system at 100 °C drying) The crystal systems at 100 °C drying of Examples 1 to 8 and Comparative Examples 6 to 8 were measured using an X-ray diffractometer (Smartlab 9kw: manufactured by Rigaku Corporation), and the results are shown in Tables 1 to 2 and Table 3.

[0052] (pH) Measurement was performed using the portable pH meter "HM-40P" manufactured by Toa DKK Corporation and the pH composite electrode "GST-2739C", and the results are shown in Tables 1 to 2 and Table 3.

[0053] (Al2O3 equivalent concentration) For the Al2O3 equivalent concentrations of Examples 1 to 8 and Comparative Examples 6 to 8, first, the aluminum concentration was measured using an emission spectroscopic analyzer (Agilent 5110 ICP-OCS: manufactured by Agilent Technologies), and the aluminum concentration was converted to the Al2O3 concentration using the following formula and is shown in Tables 1 to 2 and Table 4. Al2O3 equivalent concentration (mass%) = Al concentration (mass%) × (102 / 27)

[0054] (Thixotropic index (TI value)) The TI value (thixotropic index) measured with a B-type viscometer (using the TVB10M TM-3 spindle rotor manufactured by Toki Sangyo Co., Ltd.) was calculated as (rotation speed 6 rpm) / (rotation speed 60 rpm).

[0055] (D / C) The volume of the aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate was set to 500 ml (C), and then the volume of the finally obtained alumina aqueous dispersion was set to (D). The values of the volume concentration ratio (D / C) are shown in Tables 1 to 2 and Table 4.

[0056] (Concentrations of chlorine, bromine, iodine, sodium, and potassium) For the concentrations of chlorine, bromine, iodine, sodium, and potassium in Examples 1 to 8 and Comparative Examples 6 to 8, measurement was carried out using SEM (JCM-7000, manufactured by JEOL Ltd.) and EDS (energy-dispersive fluorescent X-ray), and the results are shown in Tables 1 to 2 and Table 4. Those not detected were indicated as n.d.

[0057] (Thermal decomposability evaluation) The alumina aqueous dispersions of Examples 1 to 8 and Comparative Examples 6 to 8 were each dropped in an amount of 1 g onto the surface of a glass plate measuring 30 mm × 50 mm × 2 mm, and then dried at 100°C for 5 minutes using a hot air circulation dryer. Subsequently, firing was performed at 600°C for 5 minutes in an electric furnace (FO200, manufactured by Yamato Scientific Co., Ltd.), and the appearance of the residue on the glass was visually confirmed and the color thereof was described in Tables 1 to 2 and Table 4.

[0058]

Table 1

[0059]

Table 2

[0060]

Table 3

[0061]

Table 4

[0062] The result of observing, at a magnification of 100,000 times using a FE-SEM (JSM-7001F, manufactured by JEOL Ltd.), the alumina aqueous dispersion of Example 1 after drying at 100°C for 10 minutes in a glass evaporating dish is shown in FIG. 1.

[0063] The result of measuring and evaluating, using an X-ray diffractometer (Smartlab 9kw, manufactured by Rigaku Corporation), the powder obtained by drying the alumina aqueous dispersion of Example 1 at 100°C for 20 minutes in a glass evaporating dish using a hot air circulation dryer is shown in FIG. 2.

[0064] The powder obtained by drying the alumina aqueous dispersion of Example 1 at 100°C for 20 minutes in a glass evaporating dish using a hot air circulation dryer was placed in an alumina crucible, and the powder obtained by firing at 700°C for 2 hours in an electric furnace (FO200, manufactured by Yamato Scientific Co., Ltd.) was measured and evaluated using an X-ray diffractometer (Smartlab 9kw, manufactured by Rigaku Corporation), and the result is shown in FIG. 3.

[0065] Regarding the alumina aqueous dispersion of Example 1, measurements were carried out by the dynamic light scattering method in an aqueous solvent using a Zetasizer Nano ZS (manufactured by Malvern Panalytical Ltd.), and the results measured on a number basis are shown in Fig. 4.

[0066] As shown in Table 1 and Table 2, in Examples 1 to 3 and Examples 5 to 8, amorphous alumina aqueous dispersions were all formed, and the average particle diameter, pH, Al2O3 value, and TI value satisfied the scope of the present invention. When calcined at 600 °C for 5 minutes, white substances were confirmed, no calcination residue of the organic matter was confirmed, and it was confirmed that the thermal decomposition of the organic matter was completed. As shown in Table 1, in Example 4, an alumina aqueous dispersion of amorphous + χ alumina was formed, and the average particle diameter, pH, Al2O3 value, and TI value satisfied the scope of the present invention. When calcined at 600 °C for 5 minutes, white substances were confirmed, no calcination residue of the organic matter was confirmed, and it was confirmed that the thermal decomposition of the organic matter was completed.

[0067] As shown in Table 3, in Comparative Example 1, the pH of amorphous aluminum hydroxide was too high, and amorphous aluminum hydroxide could not be dispersed in water in the next step. In Comparative Example 2, the moisture content during drying was too low, and amorphous aluminum hydroxide could not be dispersed in water in the next step. In Comparative Example 3, after dispersing amorphous aluminum hydroxide gel in water and then adding formic acid, the temperature was too low, and aluminum formate containing basicity was not synthesized, and no alumina aqueous dispersion was formed even when heated at a high temperature.

[0068] As shown in Table 3, in Comparative Example 4, after dispersing amorphous aluminum hydroxide gel in water and then adding formic acid, the temperature during stirring was too low, resulting in a large number of formations of aluminum formate, and no alumina aqueous dispersion could be formed. As shown in Table 3, in Comparative Example 5, the addition amount of formic acid to amorphous aluminum hydroxide gel was too small, the production amount of aluminum formate was small, and although an alumina aqueous dispersion was formed when further heated, its concentration was low.

[0069] As shown in Table 4, in Comparative Example 6, since sodium hydroxide was used for neutralization instead of ammonia during the neutralization of amorphous aluminum hydroxide gel, there is a possibility that a large amount of sodium remains when synthesizing the alumina aqueous dispersion. As shown in Table 4, in Comparative Example 7, basic aluminum lactate was synthesized using lactic acid instead of formic acid for amorphous aluminum hydroxide gel, and an alumina aqueous dispersion was synthesized. Although the alumina aqueous dispersion could be synthesized, when performing the thermal decomposability evaluation, it was confirmed that the glass surface turned black, residual carbon generated from un-decomposed organic matter remained, and it was not alumina, indicating that there is a problem with low-temperature thermal decomposability. In Comparative Example 8, aluminum chloride was used and acetic acid aluminum was synthesized without using formic acid in an attempt to synthesize an alumina aqueous dispersion. However, the product contains a large amount of chlorine and at the same time the water solubility of acetic acid aluminum containing basicity is low, and precipitation preferentially occurs during additional heating, so that the alumina aqueous dispersion cannot be synthesized.

[0070] As shown in Fig. 1, the alumina aqueous dispersion of Example 1 dried at 100 °C for 10 minutes was observed by FE-SEM. It was confirmed that a large number of particles had a primary particle size of 100 nm or less, indicating that the target alumina aqueous dispersion was successfully synthesized.

[0071] As shown in Fig. 2, the X-ray diffraction of the alumina aqueous dispersion of Example 1 dried at 100 °C for 20 minutes is shown. No distinct peak was confirmed, indicating that an amorphous alumina particle dispersion was formed.

[0072] As shown in Fig. 3, the X-ray diffraction of the alumina aqueous dispersion of Example 1 dried at 100 °C for 20 minutes and calcined at 700 °C for 2 hours is shown. It shows a γ-alumina peak pattern, indicating that by raising the calcination temperature from the amorphous alumina particle dispersion, it can be phase-transformed into γ-alumina.

[0073] As shown in Fig. 4, from the result of measuring the particle size distribution of the alumina aqueous dispersion of Example 1 based on the number, it was confirmed that an alumina aqueous dispersion with an average particle size of 55 nm and no coarse particles exceeding 100 nm was obtained.

[0074] Furthermore, the following aspects can also be proposed. [1] An alumina aqueous dispersion containing alumina particles as dispersed particles, having the following properties: (1) The average particle diameter measured on a number basis of the alumina dispersed particles is in the range of 10 to 1000 nm, (2) The crystal system of the alumina particles when the alumina aqueous dispersion is dried at 100 °C is amorphous and / or χ-alumina, (3) The pH of the alumina aqueous dispersion is in the range of 2.0 to 5.3, (4) The alumina aqueous dispersion contains an organic acid and an alkali, the organic acid is formic acid or a combination of formic acid and acetic acid, and the alkali is ammonia, (5) The concentration of alumina (Al2O3) in terms of the alumina aqueous dispersion is 0.5 to 11.5% by mass. An alumina aqueous dispersion satisfying the above. [2] The alumina aqueous dispersion according to [1], having a thixotropic index (TI value = rotational speed 6 rpm / rotational speed 60 rpm) of 2 to 10 measured by a B-type viscometer. [3] The alumina aqueous dispersion according to [1] or [2], containing an alkali metal or a halogen element in the range of 0 to 0.03% by mass based on the total weight of the solid components in the alumina aqueous dispersion. [4] The alumina aqueous dispersion according to any one of [1] to [3], which is used for forming ceramics or refractories. [5] A first step of adding aqueous ammonia to an aqueous solution of an aluminum salt selected from either aluminum nitrate or aluminum sulfate to adjust the pH to 5 to 8, and then stirring in the range of 15 to 45 °C for 0.5 to 3 hours to form a precipitate of amorphous aluminum hydroxide. A second step of washing the formed amorphous aluminum hydroxide and drying it so that the moisture content becomes 60 to 80%. After adding water to the dried amorphous aluminum hydroxide and dispersing it, 1.8 to 10 moles of formic acid or a mixture of formic acid and acetic acid is added per 1 mole of aluminum, and the mixture is stirred at 40 to 80 °C for 1 to 3 hours to obtain an aqueous solution of aluminum formate or an aqueous solution of a mixture of aluminum formate and aluminum acetate. The third step, and A fourth step of concentrating the obtained aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate at a temperature of 90 to 120 °C for 1 to 24 hours, A method for producing an alumina aqueous dispersion according to any one of [1] to [5], which includes [6] When the volume of the aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate obtained in the third step is C, and the volume after heating and concentrating at 90 to 120 °C for 1 to 24 hours in the fourth step is D, the volume concentration ratio (D / C) is 0.3 to 0.8. The production method according to [5], characterized by concentrating so that

Claims

1. An alumina aqueous dispersion containing alumina particles as dispersed particles, having the following properties: (1) The average particle diameter measured on a number basis of the alumina dispersed particles is in the range of 10 to 1000 nm, (2) The crystal system of the alumina particles when the alumina aqueous dispersion is dried at 100 °C is amorphous and / or χ-alumina, (3) The pH of the alumina aqueous dispersion is in the range of 2.0 to 5.3, (4) The alumina aqueous dispersion contains an organic acid and an alkali, the organic acid is formic acid or a combination of formic acid and acetic acid, and the alkali is ammonia, (5) The alumina (Al ２ O ３ ) conversion concentration in the alumina aqueous dispersion is 0.5 to 11.5% by mass, An alumina aqueous dispersion satisfying the above.

2. The alumina aqueous dispersion according to claim 1, having a thixotropic index (TI value = rotational speed 6 rpm / rotational speed 60 rpm) of 2 to 10 measured by a B-type viscometer.

3. The alumina aqueous dispersion according to claim 1 or 2, containing an alkali metal or a halogen element in the range of 0 to 0.03% by mass based on the total weight of the solid components in the alumina aqueous dispersion.

4. The alumina aqueous dispersion according to claim 1 or 2, which is used for the formation of ceramics or refractories.

5. A first step of adding aqueous ammonia to an aqueous solution of an aluminum salt selected from either aluminum nitrate or aluminum sulfate to adjust the pH to 5 to 8, and then stirring in the range of 15 to 45 °C for 0.5 to 3 hours to form a precipitate of amorphous aluminum hydroxide, A second step of washing the formed amorphous aluminum hydroxide and drying it so that the moisture content becomes 60 to 80%, A third step of adding water to the dried amorphous aluminum hydroxide, dispersing it, and then adding 1.8 to 10 moles of formic acid or a mixture of formic acid and acetic acid per mole of aluminum, and stirring at 40 to 80 °C for 1 to 3 hours to obtain an aqueous solution of aluminum formate or an aqueous solution of a mixture of aluminum formate and aluminum acetate, and A fourth step of concentrating the obtained aqueous solution of aluminum formate or the aqueous solution of the mixture of aluminum formate and aluminum acetate at a temperature of 90 to 120 °C for 1 to 24 hours, A method for producing the alumina aqueous dispersion according to claim 1, comprising the above steps.

6. Let the volume of the aqueous solution of aluminum formate or the aqueous solution of a mixture of aluminum formate and aluminum acetate obtained in the third step be C, and then when the volume after heating and concentrating at 90 to 120 ° C for 1 to 24 hours in the fourth step is D, the volume concentration ratio (D / C) is 0.3 to 0.

8. The manufacturing method according to claim 5, characterized in that it is concentrated so that it is.

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