JP4632022B2 - Method for producing alumina powder and alumina sol γ - Google Patents

Description

  The present invention is a method for producing an alumina powder having a γ-type crystal structure and an alumina sol in which alumina particles having a γ-type crystal structure are dispersed in water or an organic solvent.

  1 μm by dry and / or wet pulverization of alumina having crystal structure such as γ, δ, κ, θ, η, α, etc. calcined aluminum hydroxide manufactured by the buyer method, which is inexpensive and manufactured in large quantities An alumina powder made of alumina fine particles having the following average particle diameter is manufactured.

  Plate-like high-purity alumina powder having a primary particle size of 20 to 80 nm and a high-purity alumina powder having a primary particle size of 150 to 200 nm or more are commercially available. Yes.

The average particle size is 1 to 300 nm by a peptization method in which a commercially available ultrafine alumina powder is used as it is or by further contacting the baked powder with a cation exchange resin in the presence of an acid in an aqueous phase. An alumina sol composed of crystals of γ, δ, κ, θ, η, α, etc., preferably 5 to 100 nm and having a sharp particle size distribution, and a method for producing the same are disclosed (for example, see Patent Document 1). .
Japanese Patent Laid-Open No. 07-089717 (Claims, Detailed Description of the Invention)

  It is desired to provide alumina powders and alumina sols having different particle sizes (particle sizes), particle size distributions, and crystal structures according to the respective applications. The present invention intends to provide an inexpensive and simple and efficient method for producing an alumina sol having a γ-type crystal structure and an alumina sol in which alumina particles having a γ-type crystal structure are dispersed in water or an organic solvent. is there.

  According to an electron microscope observation using an aqueous alkali aluminate solution and liquid or gaseous carbon dioxide, rectangular plate-like primary particles having a side size of 10 nm to 40 nm and a thickness of 2.5 to 10 nm are faces. -Drying a stable acidic aqueous alumina sol containing columnar secondary particles having a length of 50 to 400 nm and a boehmite structure formed by condensation between planes, and firing at 450 to 950 ° C for 3 to 24 hours A method for producing an alumina powder having a γ-type crystal structure, comprising a step of mixing the alumina powder, water, an acid or an alkali and performing a mechanical dispersion treatment, Method for producing organoalumina sol including process of solvent replacement with organic solvent, and mechanical dispersion treatment by mixing the alumina powder and organic solvent To provide a manufacturing method of organo alumina sol comprising the step of.

  This will be described in detail below.

  The first aspect of the present invention is a method for producing an alumina powder having a γ-type crystal structure, including the following steps (A), (B), (C) and (D).

(A): A step of generating a reaction mixture having a pH of 10.5 to 11.5 by adding liquid or gaseous carbon dioxide to an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C.
(B): A step of producing an aqueous suspension containing an alumina hydrate having a boehmite structure by hydrothermally treating the reaction mixture obtained in the step (A) at a temperature of 110 to 250 ° C.
(C): An acidic aqueous alumina sol having a pH of 3 to 7 by subjecting the aqueous suspension obtained in the step (B) to desalination by adding water and an acid by an ultrafiltration method. And (D): The acidic aqueous alumina sol obtained in the step (C) is dried and calcined at 450 to 950 ° C. for 3 to 24 hours to obtain an alumina powder having a γ-type crystal structure. Generating step.

  A second aspect of the present invention is the γ-type crystal according to the first aspect, wherein the reaction mixture obtained in the step (A) is pretreated with stirring for 2 to 24 hours before hydrothermal treatment in the step (B). It is a manufacturing method of the alumina powder which has a structure.

  The third aspect of the present invention is a method for producing an alumina powder having a γ-type crystal structure, including the following steps (a), (b), (c) and (d).

(A): A step of generating a reaction mixture having a pH of 10.5 to 11.5 by adding liquid or gaseous carbon dioxide to an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C.
(B): a step of hydrothermally treating the reaction mixture obtained in step (a) at a temperature of 110 to 250 ° C. to produce an aqueous suspension containing an alumina hydrate having a boehmite structure;
(C): The aqueous suspension obtained in the step (b) is desalted by adding water and an acid by a cake filtration method, whereby an acidic aqueous alumina sol having a pH of 3 to 7 is obtained. And (d): the acidic aqueous alumina sol obtained in the step (c) is dried and calcined at 450 to 950 ° C. for 3 to 24 hours to produce an alumina powder having a γ-type crystal structure. Process.

The fourth aspect of the present invention is:
In the step (b), the method for producing an alumina powder having a γ-type crystal structure according to the third aspect, wherein the reaction mixture obtained in the step (a) is pretreated by stirring for 2 to 24 hours before hydrothermal treatment. It is.

The fifth aspect of the present invention is:
A method for producing an alumina powder having a γ-type crystal structure, including the following steps (A ′), (B ′), (C ′), and (D ′).

(A ′): a step of generating a reaction mixture having a pH of 10.5 to 11.5 by adding liquid or gaseous carbon dioxide to an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C.,
(B ′): A step of producing an aqueous suspension containing an alumina hydrate having a boehmite structure by hydrothermally treating the reaction mixture obtained in the step (A ′) at a temperature of 110 to 250 ° C. And (C ′): The aqueous suspension obtained in the step (B ′) is brought into contact with a hydrogen-type acidic cation exchange resin and a hydroxyl-type strongly basic anion exchange resin to obtain 3- A step of forming an acidic aqueous alumina sol having a pH of 7, and (D ′): by drying the acidic aqueous alumina sol obtained in the step (C ′) and calcining at 450 to 950 ° C. for 3 to 24 hours. producing alumina powder having a gamma-type crystal structure;

The sixth aspect of the present invention is:
In the step (B ′), before the hydrothermal treatment, the reaction mixture obtained in the step (A ′) is pretreated by stirring for 2 to 24 hours. The alumina powder having the γ-type crystal structure according to the fifth aspect Production method.

The seventh aspect of the present invention is:
Including a step of mixing the alumina powder having the γ-type crystal structure obtained by the production method according to any one of the first aspect to the sixth aspect, water, an acid or an alkali, and performing a mechanical dispersion treatment. A method for producing an aqueous alumina sol.

The eighth aspect of the present invention is:
A method for producing an organoalumina sol, comprising a step of replacing the aqueous alumina sol obtained in the seventh aspect with an organic solvent.

The ninth aspect of the present invention is:
An organoalumina sol comprising a step of mixing alumina powder having a γ-type crystal structure obtained by the production method according to any one of the first aspect to the sixth aspect and an organic solvent, and performing a mechanical dispersion treatment Manufacturing method.

  The suspension containing an alumina powder having a γ-type crystal structure and an alumina having a γ-type crystal structure obtained by the present invention is, for example, an alumina hydrate having a commercially available boehmite structure as compared with a conventional aqueous alumina sol. Between an aqueous alumina sol containing hexagonal plate particles and / or rectangular plate particles having a high dispersibility and an aqueous alumina sol containing fibrous particles having high thixotropic properties of alumina hydrate having a boehmite structure on the market The behavior results in improvements not previously available for various applications.

  The first and subsequent aspects of the present invention relate to a method for producing an alumina sol used as a raw material. The (A) step of the first aspect of the present invention, the (a) step of the third aspect and the (A ′) step of the fifth aspect are liquid or gaseous in an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C. It is a step of producing a reaction mixture having a pH of 10.5 to 11.5 by adding carbon dioxide.

Examples of the alkali species of the raw material alkali aluminate or concentrated liquid include Na, K, Mg, Zn, Fe, Ca, Ba, and Be. These alkali aluminate salts or concentrated liquids are publicly known. It can be easily obtained by this method and can also be obtained as a commercial industrial chemical. In particular, an inexpensive sodium aluminate salt or concentrate is preferred. Usually, as commercially available sodium aluminate, there are a high-concentration powder product and an Al ₂ O ₃ concentration concentrate of 10 to 25% by mass, but considering the uniform reaction when adding carbon dioxide in the next step, the concentrate Is easy to handle and preferable.

In the present invention, at the time of addition of liquid or gaseous carbon dioxide, the Al ₂ O ₃ concentration of the aqueous alkali aluminate solution is not particularly limited, but when considering the uniform reaction and production efficiency at the time of carbon dioxide addition, Al It is preferable to use an aqueous solution diluted with 1 to 10% by mass, preferably 2 to 6% by mass as ₂ O ₃ concentration with pure water or the like.

  Since this diluted aqueous alkali aluminate solution is susceptible to hydrolysis, it is necessary to react quickly after dilution. In particular, when an aqueous solution obtained by diluting an alkali aluminate held at a high temperature of 50 ° C. or higher before addition of carbon dioxide is used, it is difficult to obtain the intended primary particles.

  The diluted aqueous alkali aluminate solution is agitated by a mechanical method known to those skilled in the art for homogenization. Partial stirring is performed at the time of addition of alkali aluminate salt or pure water used for dilution of the concentrated solution, but unless mechanical stirring is performed, the diluted solution of the alkali aluminate aqueous solution becomes non-uniform. This is not preferable because the reaction with carbon dioxide becomes non-uniform.

The alkali aluminate salt or concentrate used as the raw material contains a basic aluminum salt and / or an aluminum normal salt having an Al ₂ O ₃ content of 5 to 200 parts per 100 parts of the Al ₂ O ₃ content of the alkali aluminate. Also included are dissolved alkali aluminates. The object of the present invention is also achieved with this mixed solution.

  The basic aluminum salt and / or normal aluminum salt used can be easily obtained by a known production method, and can also be obtained as a commercial industrial chemical. Examples of basic aluminum salts include water-soluble basic aluminum salts such as basic aluminum chloride, basic aluminum nitrate, basic aluminum acetate, and basic aluminum lactate. Examples of the aluminum normal salt used include aluminum chloride, aluminum nitrate, and aluminum acetate.

  By using an aqueous alumina sol in which the mixing amount ratio of basic aluminum salt and / or aluminum positive salt is increased, the primary particle diameter of alumina hydrate having a boehmite structure obtained by hydrothermal treatment can be increased. it can. Similarly, as long as the object of the present invention is achieved, any component such as a cation maintaining the stability of alkali aluminate can be contained.

  Carbon dioxide is used for the aqueous alkali aluminate solution of the present invention. Gaseous carbon dioxide is preferably used in consideration of the working environment such as corrosion and odor of the apparatus and the price. Liquid or gaseous carbon dioxide should be added at a concentration that does not cause large lumps when added to the aqueous alkali aluminate solution. The concentration of the acid added and the rate of addition are determined by the strength of stirring during the addition. Determined by.

  When carbon dioxide is added to an alkali aluminate aqueous solution to carry out the reaction, heat is generated due to heat of neutralization. Due to this heat generation, the produced aluminum reaction product is aged, and becomes crystalline aluminum hydroxide. Since the crystalline aluminum hydroxide produced by this exotherm remains after the hydrothermal treatment which is the subsequent step, only the aqueous suspension of alumina hydrate having the boehmite structure which is the main object of the present invention is used. Can't get. In addition, the particle form of the alumina hydrate having the boehmite structure of the present invention is a secondary particle in which rectangular plate-like primary particles are connected, as will be described later. It becomes easy to produce monodisperse particles. Therefore, it is possible to suppress the formation of crystalline aluminum hydroxide by keeping the temperature at the time of addition of carbon dioxide to the alkali aluminate aqueous solution low, and the alumina hydrate (colloid) having the desired particle shape and crystal structure. Shaped particles). Here, crystalline aluminum hydroxide refers to a substance in which a peak clearly exists by analysis by X-ray diffraction.

  As a method of lowering the temperature at the time of addition of carbon dioxide, a method of adding an acid after cooling the temperature of an alkali aluminate aqueous solution in advance, a method of adding a solution in which the temperature of carbon dioxide to be added is lowered in advance, Examples thereof include a method of cooling the reaction mixture using an external cooling device or the like.

  The most preferable method is a method in which all of the above temperature control methods are performed, but one or two of these methods can be selected for reasons such as increased capital investment costs.

  In the present invention, the reaction temperature of the alkali aluminate aqueous solution is 5 to 35 ° C, preferably 10 to 25 ° C. When the temperature is 5 ° C. or lower, the amount of carbon dioxide used in the reaction increases and the viscosity of the reaction mixture (slurry) increases, which is not preferable. Moreover, since the primary particle | grains of an alumina hydrate will become larger than desired size when it exceeds 35 degreeC, it is unpreferable.

  The time required for the reaction of the alkali aluminate aqueous solution with carbon dioxide is effective within 3 hours in order to prevent crystallization of the produced aluminum hydroxide, and preferably within 1.5 hours.

  The pH of the reaction mixture (slurry) is preferably between 10 and 11.2. In a reaction mixture having a pH of 10 or less, even if a hydrothermal treatment of the next step is performed, an aqueous alumina sol containing an alumina hydrate having a target boehmite structure cannot be obtained. Moreover, when neutralizing using carbonate or carbon dioxide and adjusting the pH to 10 or less, a large amount of needle-like dawsonite is produced after the subsequent hydrothermal synthesis, and the production efficiency of alumina hydrate having a boehmite structure is deteriorated. Therefore, it is not preferable. On the other hand, when the pH is 11.2 or more, crystalline aluminum hydroxide such as gypsite is generated by later hydrothermal synthesis, which is not preferable. The pH of the reaction mixture immediately after the reaction at which alumina hydrate having a boehmite structure is most efficiently obtained after hydrothermal synthesis is in the range of 10.6 to 10.8.

  The reaction mixture obtained after the reaction was dried at 50 ° C. under reduced pressure, and the dried product was analyzed by X-ray diffraction. As a result, it was amorphous that did not show a specific peak. Then, aluminum hydroxide remains even after the hydrothermal synthesis reaction to be performed later.

  In the reaction mixture after the reaction, coarse particles are confused depending on the stirring method and the stirring intensity when carbon dioxide is added. If coarse particles are present, a non-uniform reaction occurs during the subsequent hydrothermal treatment, so that more uniform fine particles are required. Here, the finer particles are particles that cannot be visually observed as granular particles, and are not particularly limited by numerical values. To obtain these fine particles, stirring and dispersion are performed. There is no particular limitation on the stirring and dispersion method performed to obtain more uniform fine particles. For example, medium mill treatment, colloid mill treatment, high-speed shear stirring treatment, high-pressure impact dispersion treatment, and the like are used. Stirring and dispersion vary depending on the capacity of the apparatus used, but may be performed until there are no large lumps. The longer the stirring and dispersion time, the finer and more uniform the solid matter in the reaction mixture, but from the viewpoint of production efficiency, it is preferably within 2 to 24 hours. Although it does not specifically limit about the temperature at the time of stirring, Usually, it is 5-40 degreeC and normal temperature may be sufficient.

  Next, the (B) process of the 1st viewpoint of this invention, the (b) process of the 3rd viewpoint, and the (B ') process of the 5th viewpoint, the said reaction mixture obtained at the previous process is 110-250 degreeC. This is a step of producing an aqueous suspension containing an alumina hydrate having a boehmite structure by hydrothermal treatment at a temperature.

  By carrying out hydrothermal treatment of the reaction mixture after the homogenized reaction, rectangular plate-like primary particles having a side length of 10 to 40 nm and a thickness of 2.5 to 10 nm are observed in a plane in observation with a transmission electron microscope. An aqueous suspension of alumina hydrate (secondary particles) having a columnar structure formed by condensation between planes or an inclined columnar structure and a boehmite structure is obtained.

  The morphology of the secondary particles is similar to a columnar structure (rouleax: French, long cylindrical and branched structures: English) formed by the aggregation of red blood cells in the blood.

  The temperature of the hydrothermal treatment can be performed at 110 to 250 ° C. When the reaction mixture is hydrothermally treated at a temperature of less than 110 ° C., it takes a long time to produce a crystal structure from amorphous alumina hydrate to rectangular plate-like primary particles of alumina hydrate having a boehmite structure in an aqueous suspension. Therefore, it is not preferable. On the other hand, hydrothermal treatment exceeding 250 ° C. is not preferable because a rapid cooling facility, an ultrahigh pressure vessel, and the like are required for the apparatus. Considering the equipment cost due to the corrosion of the equipment and the pressure-resistant structure, it is preferable to carry out at 120 to 160 ° C. By selecting a higher temperature in the hydrothermal treatment, the primary particle diameter and particle thickness of the colloid obtained by the hydrothermal treatment can be further increased.

  As the hydrothermal treatment apparatus, a known apparatus such as an autoclave with a stirrer or a high-pressure equipment such as a flow-through tubular reactor is used. The hydrothermal synthesis time varies depending on the temperature, but is 5 to 24 hours, preferably 8 to 20 hours.

  The aqueous suspension obtained by the hydrothermal treatment is subjected to removal of alkali and alkali salts by ultrafiltration, cake filtration, ion exchange resin contact method, or the like.

  Next, in step (C) of the first aspect of the present invention, the aqueous suspension obtained in step (B) is desalted by adding water and an acid by an ultrafiltration method. To form an acidic aqueous alumina sol having a pH of 3 to 7.

  A modified diafiltration process is used for the ultrafiltration method. In the diafiltration method, alkali and alkali salts can be removed by adding water. When separation and purification is performed by using the ultrafiltration method and removing the alkali to the ultrafiltration membrane permeate side, the alkali always remains in the aqueous alumina sol in batch operation. Therefore, in the diafiltration method adopted, water and acid are added to the aqueous alumina sol side to form an acidic aqueous alumina sol having a pH of 3 to 7, while increasing the amount of permeate through the ultrafiltration membrane. As a result, the removal rate of alkali is increased, and the desalting treatment is efficiently advanced.

  As the ultrafiltration membrane to be used, an ultrafiltration membrane having a molecular weight cut off of 6,000 to 200,000 obtained as a commercial industrial product can be used. Further, a dynamic membrane (ultrafiltration membrane) in which a gel layer made of colloidal particles is formed on a microfiltration membrane used in a cross-flow filtration process can be used.

The desalting treatment is performed until the Al ₂ O ₃ concentration of the acidic aqueous alumina sol is 10% by mass and the electric conductivity is 1100 μS / cm or less, preferably 700 to 100 μS / cm. If the concentration of Al ₂ O ₃ acidic aqueous alumina sol of interest differs, correlation between the concentration of Al ₂ O ₃ and the electrical conductivity, directly proportional to the correlation between the electric conductivity of the described concentration of Al ₂ O ₃ 10 wt% based You can calculate as you do. And the desalination process temperature is 10-60 degreeC normally, and normal temperature may be sufficient.

  In this step, nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, acetic acid, formic acid, lactic acid or the like can be used as the acid. In this step, a batch type or a continuous type can be adopted as the operation method of the diafiltration method. The diafiltration apparatus is preferably a cross flow system.

Then, it can be concentrated to a maximum of 20 wt% as the concentration of Al ₂ O ₃ for the purpose, in diafiltration process and / or ultrafiltration.

  As the cake filtration method, it is preferable to employ a cross-flow filtration process.

  Next, in step (c) of the third aspect of the present invention, the aqueous suspension obtained in step (b) is desalted by adding water and acid by a cake filtration method. , Forming an acidic aqueous alumina sol having a pH of 3-7.

  In the desalting treatment by the cake filtration method, the salt generated from the acid used for neutralization and the alkali aluminate is added while adding water. Moreover, in order to maintain pH of 9-12, an alkali may be added to the desalination process reaction mixture which adds as needed. In addition, when separation / purification is performed by removing the alkali to the cake filtration membrane permeate side using the cake filtration method, salt always remains in the reaction mixture in the batch operation. Therefore, in the cross-flow filtration method, water and alkali are added to the reaction mixture side to increase the permeate amount of the cake filtration membrane while forming a desalination treatment mixture having a pH of 9 to 12. As a result, the salt removal rate can be increased and the desalting treatment can proceed efficiently.

The desalting treatment is performed until the Al ₂ O ₃ concentration of the desalting treatment mixture is 4% by mass and the electric conductivity is 500 μS / cm or less, preferably 300 to 100 μS / cm. When the Al ₂ O ₃ concentration of the target desalting treatment mixture is different, the correlation between the Al ₂ O ₃ concentration and the electric conductivity is the correlation with the electric conductivity based on the above-mentioned Al ₂ O ₃ concentration of 4% by mass. It may be calculated as being directly proportional. And the desalination process temperature is 10-60 degreeC normally, and normal temperature may be sufficient.

  In the desalting process using the cake filtration method, alkali metal hydroxide salt, alkaline earth metal hydroxide salt, alkali metal aluminate, alkaline earth metal aluminate can be added as necessary alkali. , Ammonium hydroxide, quaternary ammonium hydroxide, guanidine hydroxide, amines and the like. As the alkali metal hydroxide salt, sodium hydroxide, potassium hydroxide, cesium hydroxide and the like are preferable, and sodium hydroxide is particularly preferable. In addition, the alkali which an insoluble salt produces | generates as a by-product in a desalination process reaction mixture is naturally excluded.

In the desalting step by the cake filtration method, a batch method or a continuous method can be adopted as the operation method of the cross flow filtration method. A preferred industrial device is a continuous rotary filter press developed at the Czechoslovak National Institute of Organic Synthesis. (Details are described in K. Michel and V. Gruber, Chemie-Ingenieur-Technik, 43, 380 (1971) and FM Tiller, Filtration & Separation, 15, 204 (1978)).
A known filter cloth can be used for cake filtration. As the filter cloth, a microfiltration membrane is more preferable. As the microfiltration membrane, a microfiltration membrane having a nominal pore diameter of 0.05 μm to 10 μm obtained as a commercial industrial product can be used.

  Next, in step (C ′) of the fifth aspect, the aqueous suspension obtained in step (B ′) is contacted with a hydrogen type acidic cation exchange resin and a hydroxide type strongly basic anion exchange resin. In this step, an acidic aqueous alumina sol having a pH of 3 to 7 is formed.

  In the ion exchange resin contact method, the aqueous suspension obtained in the hydrothermal treatment step is contact-treated with a hydrogen-type acidic cation exchange resin and a hydroxide-type strongly basic anion exchange resin. In this step, the alkali in the raw material alkali aluminate is removed by contact treatment with a hydrogen-type acidic cation exchange resin. Then, the content of the acid which is the stabilizer of the acidic aqueous alumina sol is adjusted by removing the acid used at the time of neutralization by the contact treatment with the hydroxide type strongly basic anion exchange resin.

  As the hydrogen-type acidic cation exchange resin to be used, a commercially available strong acid cation exchange resin and / or weak acid cation exchange resin is used after being subjected to ion exchange treatment and water washing treatment with an acid. And it is preferable to use the amount of hydrogen-type acidic cation exchange resin which is about 3 times equivalent with respect to the amount of alkali in the raw material alkali aluminate to be removed. The contact treatment method is usually a method in which the liquid to be treated is passed downward or upward through a column filled with resin, or the resin is added to the liquid to be treated and stirred and then filtered. The method can be adopted. The temperature of the contact treatment liquid is usually 10 to 60 ° C. and may be room temperature.

  Moreover, as a hydroxyl-type strong basic anion resin to be used, the strong basic anion resin marketed is used after performing an ion exchange process and a water washing process in sodium hydroxide aqueous solution. The amount of the resin used is intended to remove excess acid in the dealkalized acidic aqueous alumina sol as long as an acidic aqueous alumina sol having a pH of 3 to 7 is obtained. As the contact treatment method, a method of adding the resin to the liquid to be treated and holding it with stirring and then filtering the resin can be simply adopted. The temperature of the contact treatment liquid is usually 10 to 60 ° C. and may be room temperature.

The acidic aqueous alumina sol having a pH of 3 to 7 obtained in the step (C) of the third aspect of the present invention, the step (C) of the fifth aspect and the step (C ′) of the seventh aspect Until the maximum concentration of Al ₂ O ₃ is 20% by mass, it can be concentrated by a known concentration method such as a vacuum concentration method or an ultrafiltration method, and a stable acidic aqueous alumina sol can be obtained. According to an electron microscope observation, a rectangular plate-like primary particle having a size of one side of 10 nm to 40 nm and a thickness of 2.5 to 10 nm is formed by agglomeration between surfaces, and has a length of 50 to 400 nm. And a stable acidic aqueous alumina sol containing columnar secondary particles having a boehmite structure.

  In these steps, nitric acid, hydrochloric acid, sulfuric acid, perchloric acid, acetic acid, formic acid, lactic acid, or the like can be used as the acid. Here, in the desalting step, when the dynamic light scattering particle size distribution of the obtained acidic aqueous alumina sol having a pH of 3 to 7 is measured, particles having a hydrodynamic average particle size of 50 to 400 nm are recognized. And particles having a hydrodynamic average particle size of 50 to 400 nm and particles having a hydrodynamic average particle size of 600 to 1400 nm may be recognized. However, in this acidic aqueous alumina sol, the abundance ratio of secondary structure high-order aggregates, which is a particle group having a hydrodynamic average particle diameter of 600 to 1400 nm, is small.

  Therefore, it is considered that the secondary structure high-order aggregates have been peptized into secondary particles (colloid particles) by acid addition and desalting treatment. In addition, in the secondary particles, the surface-to-plane surfaces of the primary particles are condensed to form a columnar structure of 50 to 300 nm or an inclined columnar structure. Since the particles are in the form of secondary particles with the smallest specific surface area, the colloidal dispersion system (alumina sol) is a more stable system. Stability is also improved against the addition of electrolyte.

In the desalting step, an aqueous suspension containing an alumina hydrate having a boehmite structure is converted into a stable aqueous alumina sol by adding an acid and / or removing an alkali-derived electrolyte in the suspension. And the stability as a sol improves the said sol by adjusting the pH to 3-7, preferably 3.5-6.5 by the addition of the acid as a stabilizer. Therefore, a stable acidic aqueous alumina sol having an arbitrary Al ₂ O ₃ concentration of up to 20% by mass as the Al ₂ O ₃ concentration can be obtained. This sol is stable without being gelled even when stored at 50 ° C. for one month in a sealed state.

  The (D) step of the first aspect of the present invention, the (d) step of the third aspect and the (D ′) step of the fifth aspect are the length of one side of 10 to 40 nm and 2. Acidity having an alumina hydrate (secondary particle) having a columnar structure in which rectangular plate-shaped primary particles having a thickness of 5 to 10 nm are formed by condensation between planes or an inclined columnar structure and a boehmite structure In this step, the aqueous alumina sol is dried and calcined at 450 ° C. to 950 ° C. for 3 to 24 hours to obtain alumina powder having a γ-type crystal structure.

  Examples of the drying method include known drying methods such as a hot air dryer and a microwave dryer. In order to obtain finer particles, a spray dryer (spray dryer) or the like is preferable.

  Although the alumina hydrate having a boehmite structure is aggregated by drying to a mass of several μm to several tens of μm, the crystal structure after drying remains boehmite. In order to make the aggregated particles of alumina hydrate having a boehmite structure obtained by drying finer, the particles may be pulverized using a dry pulverizer such as a pin disk mill or an opposed pulverizer.

  As a firing method, alumina powder having a γ-type crystal structure is obtained by firing at 450 to 950 ° C. for 3 to 24 hours, preferably 500 to 800 ° C. for 5 to 10 hours.

  When the firing temperature is lower than 450 ° C., alumina having a γ-type crystal structure is hardly formed, and alumina having another crystal structure such as boehmite-type alumina is likely to be mixed. Further, when the temperature is higher than 950 ° C., δ-type alumina is the main component, and at higher temperatures, part of the alumina is α-type crystal structure, which is not preferable.

  If the firing time is shorter than 3 hours, the inside of the system at the time of firing becomes non-uniform, which is not preferable. If it exceeds 24 hours, the inside of the system can be uniformly fired, but the firing takes too much time, which is not economically preferable.

  The size of the primary particles of the alumina powder having the γ-type crystal structure obtained in the present invention is 2 or less as large as the primary particles of the alumina hydrate having the boehmite structure as a raw material according to electron microscope observation. The particle growth by firing is extremely small.

  The aggregated particle diameter of the alumina particles having a γ-type crystal structure obtained in the present invention is several tens of μm, and can be used as abrasive grains for abrasives, pigments, inorganic fillers, surface treatment agents, catalyst carriers, etc. Is possible. However, in order to produce a high-performance sol with a larger surface area and high reactivity, it should be mechanically dispersed to have the same size as the primary particles of alumina hydrate with boehmite structure as the raw material. Can do. As the mechanical dispersion treatment used at this time, a dry pulverizer or a wet pulverizer can be used. In order to avoid contamination of impurities from machines and devices, it is preferable to disperse using a wet pulverizer.

  In the present invention, in addition to using the sol obtained by the above-mentioned production method, by using an acidic aqueous alumina sol obtained from the method described in JP-A-10-087324, drying and baking, a γ-type suitable for the present invention is obtained. An alumina powder having a crystal structure can also be obtained.

In the seventh aspect of the present invention, by adding an acid such as nitric acid or acetic acid or an alkali such as quaternary ammonium, sodium or potassium to the alumina powder having a γ-type crystal structure obtained by the present invention, An aqueous alumina sol having an Al ₂ O ₃ concentration of up to 50% by mass can be obtained by mechanical dispersion treatment at a concentration. The obtained aqueous alumina sol is stable without being gelated even when stored at 50 ° C. for one month in a sealed state. Examples of the mechanical dispersion treatment in the seventh aspect include medium mill treatment, colloid mill treatment, high-speed shear stirring treatment, and high-pressure impact dispersion treatment. Specific examples of the apparatus used for the media mill treatment include a ball mill, an attritor, a sand mill, and a bead mill. Specific apparatuses used for the colloid mill treatment include a colloid mill, a stone mill, a cade mill, and a homogenizer. Specific apparatuses used for the high-speed shearing agitation treatment include what are called high-speed dispersers, high-speed impellers, and dissolvers as trade names. Specific apparatuses used for the high-pressure impact dispersion treatment include a high-pressure impact disperser using a high-pressure pump and an ultrasonic high-pressure impact disperser. The temperature of the mechanical dispersion treatment liquid is usually 10 to 60 ° C. and may be room temperature.

  When the dynamic light scattering particle size distribution of the aqueous alumina sol is measured, a particle group having a hydrodynamic average particle diameter of 10 to 40 nm, a particle group having a hydrodynamic average particle diameter of 50 to 400 nm, and 2500 to 3500 nm Three particle groups are observed with particles having a hydrodynamic average particle size of From the comparison with the observation result of the transmission electron microscope, the particle group having a hydrodynamic average particle diameter of 10 to 40 nm is a rectangular plate-like primary particle group having a length of one side of 10 to 40 nm. In the particle group having a hydrodynamic average particle diameter of 50 to 400 m, rectangular plate-like primary particles (colloid particles) having a length of one side of 10 to 40 nm are formed by condensation between surfaces. It is a columnar secondary particle group (colloid particle group) having a length of 400 nm. And the particle group which has a hydrodynamic average particle diameter of 2500-3500 nm is judged as the unaggregated high order aggregate.

  Therefore, the alumina powder having a γ-type crystal structure is peptized into its primary particles (colloid particles) and its secondary particles (colloid particles) by adding acid or alkali and mechanical dispersion treatment. it is conceivable that. In addition, the primary particles and the secondary particles condense between the faces of the primary particles to form a columnar structure of 50 to 300 nm or an inclined columnar structure. Since the particles are in the form of secondary particles with the smallest specific surface area, the colloidal dispersion system (alumina sol) is a more stable system. Stability is also improved against the addition of electrolyte.

  In the eighth aspect of the present invention, the aqueous alumina sol obtained in the seventh aspect can obtain a sol (organoalumina sol) in which alumina particles having a γ-type crystal structure are dispersed in an organic solvent by solvent substitution. Examples of the organic solvent include alcohols such as methyl alcohol and ethyl alcohol, and amides such as dimethylacetamide and dimethylformamide. As the solvent substitution method, a distillation substitution method or a membrane solvent substitution method using an ultrafiltration membrane can be used.

  Further, in the ninth aspect of the present invention, an organoalumina sol is obtained by mixing the alumina powder having the γ-type crystal structure obtained in the first aspect to the sixth aspect and an organic solvent and subjecting the mixture to a mechanical dispersion treatment. Can do. According to this method, since it is dispersed in an organic solvent, it does not contain moisture and is advantageous when mixed with other organic solvents or organic compounds. Examples of the mechanical dispersion treatment in the ninth aspect include medium mill treatment, colloid mill treatment, high-speed shear stirring treatment, and high-pressure impact dispersion treatment. Specific examples of the apparatus used for the media mill treatment include a ball mill, an attritor, a sand mill, and a bead mill. Specific apparatuses used for the colloid mill treatment include a colloid mill, a stone mill, a cade mill, and a homogenizer. Specific apparatuses used for the high-speed shearing agitation treatment include what are called high-speed dispersers, high-speed impellers, and dissolvers as trade names. Specific apparatuses used for the high-pressure impact dispersion treatment include a high-pressure impact disperser using a high-pressure pump and an ultrasonic high-pressure impact disperser. The temperature of the mechanical dispersion treatment liquid is usually 10 to 60 ° C. and may be room temperature.

  The analysis method employed in the present invention is as follows.

(1) Composition analysis (i) Al ₂ O ₃ concentration Mass method (800 ° C. firing residue)
(Ii) Na ₂ O concentration Atomic absorption photometry (pretreatment is hydrochloric acid dissolution treatment)
(Iii) Acetic acid concentration Neutralization titration method.

(2) pH measurement It measured using pH meter D-22 (made by Horiba, Ltd.).

(3) Electrical conductivity The electrical conductivity was measured using ES-12 (manufactured by Horiba, Ltd.).

(4) Dynamic Light Scattering Particle Size Measurement was performed using a dynamic light scattering particle size measurement device DLS-6000 (registered trademark) (manufactured by Otsuka Electronics Co., Ltd.). The measurement analysis method employed the cumulant method, and the hydrodynamic average particle size in the liquid was measured.

    (Measurement conditions) Solvent Pure water (25 ° C.).

(5) Dynamic light scattering particle size distribution Measurement was performed using a dynamic light scattering particle size analyzer DLS-6000 (registered trademark) (manufactured by Otsuka Electronics Co., Ltd.). As the measurement analysis method, a modified Marquadt method (histogram analysis program) was adopted, and the hydrodynamic particle size distribution in the liquid was measured. The hydrodynamic average diameter in each particle group (mode) is obtained as a measurement result.

(6) Laser diffraction method particle size Measurement was performed using a laser diffraction scattering method particle size measurement apparatus Mastersizer 2000 (registered trademark) (manufactured by Malvern). The measurement analysis method employed a volume-based distribution based on Mie scattering theory, and measured the hydrodynamic average particle size in the liquid.

    (Measurement conditions) Solvent Pure water (25 ° C.).

(7) Specific surface area (BET method)
A sample dried in advance under predetermined conditions was measured using a nitrogen adsorption specific surface area meter MONOSORB MS-16 (manufactured by QUANTACHROME).

(8) Observation with transmission electron microscope After the sample was diluted with pure water, the sample was applied to a hydrophilic carbon-coated collodion film on a copper mesh and dried to prepare an observation sample. A transmission electron microscope JEM-1010 (manufactured by JEOL Ltd.) was used to photograph and observe an electron micrograph of the observed sample.

(9) Differential thermal analysis It measured using the differential thermal analyzer TG / DTA320U (made by Seiko Electronics Co., Ltd.).

  (Measurement conditions) Sample 16 mg, reference α? Alumina 16 mg.

Measurement temperature range 25 to 1100 ° C
Temperature increase rate 10 ° C / min.

(10) Powder X-ray diffraction Measurement was performed using an X-ray diffractometer XRD-6100 (manufactured by Shimadzu Corporation).

(11) Dispersion stability test (sedimentation test)
The sample was adjusted with pure water to an Al ₂ O ₃ concentration of 1.0% by mass, and then its dispersion stability in a centrifuge at 1000 rpm for 1 hour was evaluated. In the centrifugation process, two 30 g samples were processed. The supernatant of the obtained sample is collected and collected, and the Al ₂ O ₃ concentration in the sample before and after the centrifugation treatment is baked at 800 ° C. to measure the mass, and the residual rate of Al ₂ O ₃ is determined. It was measured.

(Measurement conditions) Centrifuge [Compact high-speed cooling centrifuge SRX-201, manufactured by Tommy Seiko; rotor TA-24BH type (minimum radius 35 mm, average radius 68 mm, maximum radius 99 mm)]
1000 rpm,
Centrifugation time 1 hour,
Centrifuge temperature 23 ° C,
Settling tube dimensions (23.6 mmφ, length 102.37 mm),
Sample amount 60g (30g x 2 points).

Example 1
1258 g of commercially available liquid sodium aluminate (AS-17, manufactured by Hokuriku Kasei Kogyo Co., Ltd., Al ₂ O ₃ concentration 19.13% by mass, Na ₂ O 19.46) in a stainless steel vessel equipped with a stirrer and a gas blowing tube. 4758 g of water was added to (mass%) and stirred vigorously. The liquid temperature of the diluted sodium aluminate aqueous solution at this time was 22 ° C. Gaseous carbon dioxide obtained by vaporizing liquefied carbon dioxide was introduced into this liquid for 95 minutes at a flow rate of 1.67 liters / minute. The liquid temperature of the reaction mixture (slurry) immediately after the introduction of gaseous carbon dioxide was 30 ° C., and the pH was 10.63. This reaction mixture was subsequently stirred at room temperature for 4 hours. Then, 6000 g of a reaction mixture (pH 10.80, Al ₂ O ₃ concentration 4.0% by mass) was obtained.

4000 g of the obtained reaction mixture was charged in a stainless steel autoclave container and hydrothermally treated at 140 ° C. for 15 hours. The obtained aqueous suspension had a pH of 10.30, an electric conductivity of 56.4 mS / cm, and an Al ₂ O ₃ concentration of 4.0% by mass. When the dynamic light scattering particle size distribution of this aqueous suspension was measured, a particle group having a hydrodynamic average particle size of 182 nm (standard deviation 23 nm) and a hydrodynamic average particle size of 920 nm (standard deviation 115 nm) were obtained. And having particles.

After the aqueous suspension was taken out, 5000 g of pure water and 14.8 g of acetic acid were added to the total amount of the aqueous suspension and stirred to adjust the pH to 6.10. Then, an ultrafiltration membrane (fractionated molecular weight of 5 In addition, 7000 g of pure water was added for desalting in an automatic continuous pressure filtration apparatus with a stirrer, and then concentrated in the apparatus to obtain 1680 g of acidic aqueous alumina sol. The obtained acidic aqueous alumina sol had a pH of 6.80, an Al ₂ O ₃ concentration of 9.5 mass%, an Na ₂ O concentration of 88 mass ppm, an electric conductivity of 104 μS / cm, a viscosity of 25 mPa · s, and an acetic acid concentration of 0.18 mass%. Yes, a specific surface area of 108 m ² / g was measured by the BET method of the powder dried at 300 ° C. with a dynamic light scattering particle size of 265 nm.

  When the dynamic light scattering particle size distribution of the obtained acidic aqueous alumina sol was measured, only particles having a hydrodynamic average particle size of 260 nm (standard deviation 60 nm) were recognized. According to transmission electron microscope observation, primary particles of alumina hydrate in the obtained acidic aqueous alumina sol have rectangular plate-like particles having a side length of 10 to 20 nm and a thickness of 2.5 to 7.5 nm. Met. Then, secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between the surfaces are formed.

  The morphology of the secondary particles is similar to a columnar structure (rouleax: French, long cylindrical and branched structures: English) formed by the aggregation of red blood cells in the blood.

Further, when the powder obtained by drying the acidic aqueous alumina sol at 110 ° C. is subjected to thermal analysis up to 1100 ° C., the colloidal particles of the alumina hydrate have a H ₂ O / Al ₂ O ₃ molar ratio of 1.09, Similarly, from the powder X-ray diffraction result (Table 1) of the powder dried at 110 ° C., it could be identified as alumina hydrate having a boehmite structure. This acidic aqueous alumina sol was stable without being gelled even after being kept at 50 ° C. for one month in a sealed state.

  This operation was repeated, and 20000 g of the obtained acidic aqueous alumina sol having a boehmite structure was dried with a hot air dryer at 110 ° C. for 24 hours. Thereafter, the mixture was pulverized using an alumina mortar to obtain 1900 g of alumina powder having a boehmite structure under 100 mesh. The alumina powder having the boehmite structure was put in a magnetic mortar, fired in an electric furnace at 700 ° C. for 5 hours, and cooled to room temperature to obtain 1500 g of alumina powder.

The obtained alumina powder has a specific surface area of 101 m ² / g and a powder X-ray diffraction result (Table 2), and has a γ-type crystal structure. It was a rectangular plate-like particle having a side length of 40 nm and a thickness of 5 to 10 nm. And there existed secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between planes.

Example 2
The same operation as in Example 1 was performed, and 90 g of the obtained alumina powder having a boehmite structure was put in a magnetic mortar, fired in an electric furnace at 950 ° C. for 5 hours, and cooled to room temperature to obtain 71 g of alumina powder.

The obtained alumina powder has a specific surface area of 87 m ² / g, and has a γ-type crystal structure based on the results of powder X-ray diffraction. According to observation with a transmission electron microscope, the primary particles have a side length of 15 to 45 nm. And rectangular plate-like particles having a thickness of 7 to 15 nm. And there existed secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between planes.

Example 3
The same operation as in Example 1 was carried out, and 2136 g of pure water and 67.7 g of a nitric acid aqueous solution having a nitric acid concentration of 62 mass% were added to 1500 g of the obtained alumina powder having a γ-type crystal structure, and 7400 g of zirconia beads (diameter 1 mm). The whole amount was placed in a 5 L polybin containing, and ball mill dispersion was performed at a rotation speed of 60 rpm for 48 hours.

Thereafter, zirconia beads for pulverization were separated to obtain 3600 g of an aqueous alumina sol in which alumina particles having a γ-type crystal structure were dispersed. The physical properties of the obtained aqueous alumina sol are: specific gravity 1.364, pH 3.99, Al ₂ O ₃ concentration 36.5% by mass, viscosity 7.7 mPa · s, dynamic light scattering particle size 76 nm, laser diffraction method average particle size It had a specific surface area of 106 m ² / g and a nitric acid of 1.22 mass% when dried at 0.107 μm and 300 ° C. Similarly, when the dynamic light scattering particle size distribution of the obtained acidic aqueous alumina sol is measured, a particle group having a hydrodynamic average particle size (standard deviation of 13.9 nm) of 17.3 nm and a fluid dynamics of 150.8 nm are obtained. Three particle groups were observed, a particle group having an average particle size (standard deviation 65.4 nm) and a particle group having a hydrodynamic average particle size (standard deviation 633.2 nm) of 3153.0 nm. In the evaluation of the dispersion stability test, the residual ratio of Al ₂ O ₃ was 97.2%.

  This aqueous alumina sol was stable without being gelated even after being kept at 50 ° C. for one month in a sealed state.

Example 4
The same operation as in Example 1 was performed. To 1393 g of the obtained alumina powder having a γ-type crystal structure, 1901.6 g of pure water and 19.9 g of nitric acid aqueous solution having a nitric acid concentration of 62% by mass were added, and zirconia beads (diameter 1 mm) A total volume was put into a 4 L wet media agitation type batch grinder (product name: Attritor, model; MA1SE-X, manufactured by Mitsui Mining Co., Ltd.) containing 10800 g and dispersed at a rotation speed of 300 rpm for 11 hours. .

Thereafter, zirconia beads for pulverization were separated to obtain 2400 g of an aqueous alumina sol in which alumina particles having a γ-type crystal structure were dispersed. The physical properties of the obtained aqueous alumina sol are: specific gravity 1.370, pH 5.05, Al ₂ O ₃ concentration 37.5% by mass, viscosity 12.1 mPa · s, dynamic light scattering particle size 103 nm, laser diffraction method average particle size It was 0.105 μm, dried at 300 ° C., specific surface area 110 m ² / g, and nitric acid 0.39% by mass. This aqueous alumina sol was stable without being gelated even after being kept at 50 ° C. for one month in a sealed state.

  Using a reduced pressure rotary concentrator (rotary evaporator) in a water bath at a bath temperature of 50 ° C., the obtained aqueous alumina sol was put into 498.3 g in a 1 L eggplant type flask while introducing 7086 g of methanol. Solvent substitution was performed to obtain 860.5 g of an organoalumina sol (methanol alumina sol) in which alumina particles having a γ-type crystal structure were dispersed in a methanol solvent.

The physical properties of the obtained methanol alumina sol were Al ₂ O ₃ concentration of 21.6% by mass, residual moisture of 0.93% by mass, viscosity of 10.9 mPa · s, dynamic light scattering particle diameter of 136 nm, and 50 ° C. in a sealed state. And kept stable for 1 month without gelation.

Example 5
The reaction mixture was prepared in the same manner as in Example 1 to obtain 4200 g (pH 10.79, Al ₂ O ₃ concentration 4.0 mass%) of the stirred reaction mixture. 4150 g of this reaction mixture was charged into a stainless steel autoclave container and hydrothermally treated at 140 ° C. for 15 hours. The obtained aqueous suspension had a pH of 10.45, an electric conductivity of 62.6 mS / cm, and an Al ₂ O ₃ concentration of 4.0% by mass.

  After this aqueous suspension was taken out, 4150 g of water was added to the aqueous suspension, and then 2739 g of a hydrogen type cation exchange resin (Amberlite IR-120B (registered trademark), manufactured by Rohm and Haas) was added. I put it in. Thereafter, 4.2 g of an acetic acid aqueous solution having an acetic acid concentration of 20% by mass was further added to adjust the pH to 4.69, followed by concentration under reduced pressure to obtain 1126 g of an acidic aqueous alumina sol.

The obtained acidic aqueous alumina sol had a pH of 5.34, an Al ₂ O ₃ concentration of 14.3% by mass, an electric conductivity of 529 μS / cm, a dynamic light scattering particle size of 363 nm, and a powder dried at 300 ° C. The specific surface area according to the BET method was 104 m ² / g. According to transmission electron microscope observation, colloidal particles of alumina hydrate contained in the obtained acidic aqueous alumina sol have rectangular plate-like particles having a side length of 10 to 20 nm and a thickness of 2.5 to 7.5 nm. Met. Then, secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between the surfaces are formed.

  The acidic aqueous alumina sol was stable without being gelated even after being kept sealed at 50 ° C. for 1 month.

  500 g of the obtained acidic aqueous alumina sol having a boehmite structure was dried with a hot air dryer at 110 ° C. for 24 hours. Thereafter, the mixture was pulverized using an alumina mortar to obtain 71.5 g of alumina powder having a boehmite structure under 100 mesh. The alumina powder having the boehmite structure was placed in a magnetic mortar, fired in an electric furnace at 700 ° C. for 5 hours, and cooled to room temperature to obtain 58.3 g of alumina powder.

The obtained alumina powder has a specific surface area of 101 m ² / g and a powder X-ray diffraction result (Table 2), and has a γ-type crystal structure. It was a rectangular plate-like particle having a side length of 40 nm and a thickness of 5 to 10 nm. And there existed secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between planes.

Example 6
The reaction mixture was prepared in the same manner as in Example 1 to obtain 4450 g (pH 10.79, Al ₂ O ₃ concentration 4.0% by mass) of the stirred reaction mixture. 4400 g of this reaction mixture was charged into a stainless steel autoclave container and hydrothermally treated at 140 ° C. for 15 hours. The obtained aqueous suspension had a pH of 10.45, an electric conductivity of 62.6 mS / cm, and an Al ₂ O ₃ concentration of 4.0% by mass.

While adding water to this aqueous suspension so that the liquid amount was constant, desalting was performed while circulating using an automatic continuous pressure filtration apparatus with a stirrer equipped with a microfiltration membrane having a nominal pore size of 0.2 μm. The desalting treatment reaction mixture had a pH of 10.26, an electric conductivity of 230 μS / cm, and an Al ₂ O ₃ concentration of 8.0% by mass.

  After removing this desalting treatment reaction mixture, 6.7 g of an acetic acid aqueous solution having an acetic acid concentration of 20% by mass was added to the total amount of the desalting treatment reaction mixture and stirred to adjust the pH to 5.50, followed by concentration under reduced pressure. 1141 g of acidic aqueous alumina sol was obtained.

The obtained acidic aqueous alumina sol had a pH of 6.00, an electric conductivity of 700 μS / cm, an Al ₂ O ₃ concentration of 14.8%, a viscosity of 12.3 mPas, a dynamic light scattering particle size of 282 nm, and was dried at 300 ° C. The specific surface area of the powder by the BET method was 106 m ² / g.

According to transmission electron microscope observation, colloidal particles of alumina hydrate contained in the obtained acidic aqueous alumina sol have rectangular plate-like particles having a side length of 10 to 20 nm and a thickness of 2.5 to 7.5 nm. Met. Then, secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between the surfaces are formed.
Further, even after this sol was kept at 50 ° C. for 1 month in a sealed state, it did not gel and was stable.

  500 g of the obtained acidic aqueous alumina sol having a boehmite structure was dried with a hot air dryer at 110 ° C. for 24 hours. Thereafter, the mixture was pulverized using an alumina mortar to obtain 74.0 g of alumina powder having a boehmite structure under 100 mesh. The alumina powder having the boehmite structure was put in a magnetic mortar, fired in an electric furnace at 700 ° C. for 5 hours, and cooled to room temperature to obtain 60.4 g of alumina powder.

The obtained alumina powder has a specific surface area of 101 m ² / g and a powder X-ray diffraction result (Table 2), and has a γ-type crystal structure. It was a rectangular plate-like particle having a side length of 40 nm and a thickness of 5 to 10 nm. And there existed secondary particles having a columnar structure having a length of 50 to 300 nm or an inclined columnar structure formed by the primary particles condensing between planes.

Comparative Example 1
90 g of alumina powder having a boehmite structure obtained by the same operation as the method of Example 1 was put in a magnetic mortar, fired in an electric furnace at 400 ° C. for 24 hours, and cooled to room temperature to obtain 70 g of alumina powder. .

The obtained alumina powder has alumina of the boehmite type crystal structure and γ type crystal structure from the powder X-ray diffraction result, and according to observation with a transmission electron microscope, the primary particle has a side of 10 to 40 nm. It was a rectangular plate-like particle having a length and a thickness of 3 to 10 nm.
Comparative Example 2
90 g of alumina powder having a boehmite structure obtained by the same operation as the method of Example 1 was put in a magnetic mortar, fired in an electric furnace at 1000 ° C. for 4 hours, and cooled to room temperature to obtain 72 g of alumina powder. .

The obtained alumina powder has alumina of δ type crystal structure from the powder X-ray diffractometry, and according to observation with a transmission electron microscope, the primary particles have a side length of 20 to 60 nm and a length of 10 to 20 nm. A rectangular plate-like particle having a thickness.
Comparative Example 3
90 g of alumina powder having a boehmite structure obtained by the same operation as the method of Example 1 was placed in a magnetic mortar, fired in an electric furnace at 1100 ° C. for 4 hours, and cooled to room temperature to obtain 72 g of alumina powder. .

  The obtained alumina powder has [alpha] -type crystal structure alumina from the powder X-ray diffraction results, and according to observation with a transmission electron microscope, the primary particles have a side length of 20 to 60 nm and a length of 10 to 20 nm. A rectangular plate-like particle having a thickness.

  The alumina powder having the γ-type crystal structure and the aqueous alumina sol in which the alumina particles having the γ-type crystal structure obtained by the present invention are dispersed in, for example, an alumina hydrate having a commercially available boehmite structure as compared with the conventional aqueous alumina sol. Between an aqueous alumina sol containing hexagonal plate particles and / or rectangular plate particles having a high dispersibility and an aqueous alumina sol containing fibrous particles having high thixotropic properties of alumina hydrate having a boehmite structure on the market The behavior results in improvements not previously available for various applications.

  Components added to a conventional alumina sol to make a composition can also be added to the alumina powder and alumina sol having a γ-type crystal structure of the present invention. It includes silica sol, hydrolyzed alkyl silicate, other metal oxide sol, water-soluble resin, resin emulsion, thickener, antifoaming agent, surfactant, refractory powder, metal powder, pigment, coupling agent, etc. Is mentioned.

  Easily prepare inorganic paints, heat-resistant paints, anticorrosive paints, inorganic / organic composite paints, etc. by blending alumina powder and alumina sol having the γ-type crystal structure of the present invention together with various paint components used conventionally. can do. The dry coating film formed from the coating material containing the alumina sol of the present invention has few pinholes and almost no cracks. This is because in the formation of the coating film, the columnar secondary particles of 50 to 400 nm contained in the alumina sol do not cause segregation in the coating film as seen in general colloidal particles. This is considered to form a robust cross-linked structure. Further, since the hardness is higher than that of the dried alumina sol having a boehmite type crystal structure, there is an advantage that the coating film is hardly damaged.

  These paints and adhesives containing alumina powder and alumina sol having a γ-type crystal structure of the present invention are applied to the surface of various substrates such as glass, ceramics, metals, plastics, wood, fibers, paper, etc. Can be applied. The alumina sol of the present invention can be impregnated with a felt-like material such as ordinary glass fiber, ceramic fiber, and other inorganic fibers.

  Since the alumina powder and alumina sol having a γ-type crystal structure of the present invention have a columnar structure of 50 to 400 nm which is the size of secondary particles of alumina sol having a boehmite structure as a raw material, an interlayer insulating film in a multilayer wiring semiconductor device It is also useful as a surface polishing agent for the surface of metal wiring such as aluminum, copper, tungsten or alloys thereof, and for plating layers such as Ni-P provided on a substrate such as a disk for a magnetic recording medium. is there.

The alumina sol having a γ-type crystal structure of the present invention exhibits high stability and has the property of eventually turning into a gel upon removal of the medium, but the secondary particles contained in the alumina sol have columnar shapes of 50 to 400 nm. Due to its structure, it exhibits unique properties derived from this alumina sol when it gels or after curing. It will be readily understood that the present invention is useful in various applications other than the above applications.

Claims (9)

A method for producing an alumina powder having a γ-type crystal structure, comprising the following steps (A), (B), (C) and (D).
(A): A step of generating a reaction mixture having a pH of 10.5 to 11.5 by adding liquid or gaseous carbon dioxide to an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C.
(B): A step of producing an aqueous suspension containing an alumina hydrate having a boehmite structure by hydrothermally treating the reaction mixture obtained in the step (A) at a temperature of 110 to 250 ° C.
(C): An acidic aqueous alumina sol having a pH of 3 to 7 by subjecting the aqueous suspension obtained in the step (B) to desalination by adding water and an acid by an ultrafiltration method. And (D): The acidic aqueous alumina sol obtained in the step (C) is dried and calcined at 450 to 950 ° C. for 3 to 24 hours to obtain an alumina powder having a γ-type crystal structure. Generating step.   The method for producing an alumina powder having a γ-type crystal structure according to claim 1, wherein in step (B), the reaction mixture obtained in step (A) is pretreated by stirring for 2 to 24 hours before hydrothermal treatment. . A method for producing an alumina powder having a γ-type crystal structure, comprising the following steps (a), (b), (c) and (d):
(A): A step of generating a reaction mixture having a pH of 10.5 to 11.5 by adding liquid or gaseous carbon dioxide to an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C.
(B): a step of hydrothermally treating the reaction mixture obtained in step (a) at a temperature of 110 to 250 ° C. to produce an aqueous suspension containing an alumina hydrate having a boehmite structure;
(C): The aqueous suspension obtained in the step (b) is desalted by adding water and an acid by a cake filtration method, whereby an acidic aqueous alumina sol having a pH of 3 to 7 is obtained. And (d): the acidic aqueous alumina sol obtained in the step (c) is dried and calcined at 450 to 950 ° C. for 3 to 24 hours to produce an alumina powder having a γ-type crystal structure. Process.   The method for producing an alumina powder having a γ-type crystal structure according to claim 3, wherein in step (b), the reaction mixture obtained in step (a) is pretreated by stirring for 2 to 24 hours before hydrothermal treatment. . A method for producing an alumina powder having a γ-type crystal structure, comprising the following steps (A ′), (B ′), (C ′) and (D ′).
(A ′): a step of generating a reaction mixture having a pH of 10.5 to 11.5 by adding liquid or gaseous carbon dioxide to an aqueous alkali aluminate solution at a liquid temperature of 5 to 35 ° C.,
(B ′): A step of producing an aqueous suspension containing an alumina hydrate having a boehmite structure by hydrothermally treating the reaction mixture obtained in the step (A ′) at a temperature of 110 to 250 ° C. And (C ′): The aqueous suspension obtained in the step (B ′) is brought into contact with a hydrogen-type acidic cation exchange resin and a hydroxyl-type strongly basic anion exchange resin to obtain 3- A step of forming an acidic aqueous alumina sol having a pH of 7, and (D ′): by drying the acidic aqueous alumina sol obtained in the step (C ′) and calcining at 450 to 950 ° C. for 3 to 24 hours. producing alumina powder having a gamma-type crystal structure;   The alumina powder having a γ-type crystal structure according to claim 7, wherein in step (B ′), the reaction mixture obtained in step (A ′) is pretreated by stirring for 2 to 24 hours before hydrothermal treatment. Production method.   A step of mixing mechanically dispersing the alumina powder having a γ-type crystal structure obtained by the production method according to any one of claims 1 to 6, water, an acid or an alkali, and performing a mechanical dispersion treatment. A method for producing an aqueous alumina sol.   The manufacturing method of the organo alumina sol including the process of carrying out solvent substitution of the aqueous | water-based alumina sol obtained by Claim 7 with the organic solvent. An organoalumina sol comprising a step of mixing alumina powder having a γ-type crystal structure obtained by the production method according to any one of claims 1 to 6 and an organic solvent, and subjecting the mixture to a mechanical dispersion treatment. Manufacturing method.