JP2021155234A - Boehmite dispersion and its manufacturing metho - Google Patents

Abstract

To provide a boehmite dispersion containing pseudo boehmite powder having small deflocculation particle size and its manufacturing method.SOLUTION: Boehmite dispersion containing pseudo boehmite powder, in which the deflocculation particle size of the pseudo boehmite powder is 100 nm or smaller. The deflocculation particle size of the pseudo boehmite powder is preferably 50 nm or smaller. Preferably, the boehmite dispersion further contains sodium gluconate. More preferably, the boehmite dispersion further contains water, and the pseudo boehmite powder is dispersed in water.SELECTED DRAWING: Figure 11

Description

The present invention relates to a boehmite dispersion and a method for producing the same.

Boehmite (γ-AlOOH) is a kind of aluminum hydroxide oxide (alumina monohydrate). Among boehmite, those with low crystallinity are called pseudo-boehmite. Boehmite, including pseudo-boehmite, is chemically stable over a wide pH range and is practically insoluble in water and organic solvents. Taking advantage of this feature, it is used in a wide range of applications such as raw materials for ceramics and catalyst carriers, additives for plastics, and adsorbents.

In particular, powdered boehmite (boehmite powder) is useful as a precursor of _{α-alumina (α-Al 2} O ₃ ) and γ-alumina (γ-Al ₂ O _{3) used for ceramics-related members.} α-Alumina is excellent in mechanical properties, thermal stability and chemical stability, and is useful as an abrasive material such as abrasive grains and a structural material. Further, α-alumina can be made into a composite material by combining it with another material such as zirconia. γ-Alumina has a large surface area and can be made into a porous body. Therefore, it is used as an adsorbent, a separating agent and a catalyst carrier.

Manufacture of ceramic-related members using boehmite is known. For example, Patent Document 1 discloses a method for adjusting an α-alumina abrasive, which comprises adding and stirring a semi-finished product of boehmite or the like into a stirrer to form a raw material into a pulp property (Patent Document 1). 1). Further, Patent Document 2 discloses a method for producing an alumina-zirconia composite powder, which comprises dispersing a zirconium salt aqueous solution and boehmite and mixing a water / organic solvent solution (claim 2 of Patent Document 2). Further, Non-Patent Document 1 describes that boehmite (γ-AlOOH) powder, which is an aluminum oxyhydroxide, is important as a raw material for γ-alumina and α-alumina (No. 359 of Non-Patent Document 1). Left column of the page).

As a method for synthesizing boehmite (pseudo-boehmite), a neutralization reaction method, a hydrothermal synthesis method, a sol-gel method and the like are known. Of these, the neutralization reaction method is a method for synthesizing boehmite by a neutralization reaction between an alkaline solution containing aluminum ions and an acidic solution, and has an advantage that it is not necessary to use expensive equipment or raw materials.

Boehmite synthesis by the neutralization reaction method is known. For example, Patent Document 3 is characterized in that a basic solution containing one or both aluminum ions and an acidic solution are mixed and neutralized under high-speed rotary shear stirring, and the obtained neutralized product is washed and then dried. A method for producing aluminum hydroxide is disclosed (Patent Document 3, claim 3). Further, Patent Document 4 discloses a method for producing alumina hydrate fine particles in which an aqueous alkaline aluminum salt solution is reacted with an acidic substance and then an ammonium source is added (Patent Documents 4 [0018] to [0028] to [0028]. ]).

Further, although it is not intended for boehmite synthesis, Non-Patent Document 2 reports the result of examining the influence and role of chemical factors on colloidal agglutination in wastewater treatment.

Japanese Patent Application Laid-Open No. 2014-507509 Japanese Unexamined Patent Publication No. 1-301520 Japanese Unexamined Patent Publication No. 10-59713 Japanese Unexamined Patent Publication No. 2014-62011

Takayuki Tsukada et al., "Characterization of Pseudo-Behimite Powder and Foliction in Dilute Nitric Acid", Journal of the Ceramic Society of Japan, 1999, Vol. 107, No. 1244, pp. 359-364. Junichiro Matsumoto et al., "2. A few chemical factors related to aggregation", Proceedings of the Sanitary Engineering Research Discussion Group, Volume 2, Volume 2 (1965), pp. 9-23.

In response to the demand for higher quality ceramic-related members, there is a demand for miniaturization and high dispersion of the alumina precursor, which is a raw material thereof. Specifically, the primary particle size of the alumina precursor is required to be at the nano level, and is 100 nm or less as a guide. It is also desirable that the primary particles are dispersed as much as possible under the acidic conditions used (generally pH ≤ 4.0). Therefore, it is desired that the alumina precursor has a small gelatinization particle size. Here, the defibration particle size is a measure of the particle size in the defibration (dispersion) state when the alumina precursor is dispersed in a solvent, and specifically, particles that can move independently. It is the average value of the particle size of. Therefore, when the primary particles are aggregated to form the secondary particles, the deflocculation particle size corresponds to the diameter of the secondary particles. Further, in the present specification, the property of having a small glutinous particle size may be expressed as "easy glutinous".

For example, in the case of firing an alumina precursor to produce alumina abrasive grains which are ceramic-related members, there is a problem that if the unglazed particle size of the alumina precursor is large, the variation in abrasive characteristics such as BET specific surface area and hardness becomes large. There is.

In this respect, the pseudo-boehmite powder has fine primary particles and an extremely high BET specific surface area. Therefore, it is expected as a raw material (alumina precursor) for alumina-related members. However, in general pseudo-boehmite powder, primary particles are intricately entangled to form aggregated secondary particles. To show this, scanning electron micrographs (SEM images) and transmission electron micrographs (TEM images) of general pseudo-bemite powder are shown in FIGS. 1 and 2, respectively. As shown in the SEM image (FIG. 1), fine primary particles are aggregated to form coarse secondary particles. The secondary particles have an average particle size (D50) of about 20 μm. Further, as shown in the TEM image (FIG. 2), although the primary particles have a fine size of 10 to 30 nm, they are intricately intertwined to form a strong structure (secondary particles).

As described above, general pseudo-boehmite powder is composed of coarse aggregated secondary particles, and even if this is used as a raw material as it is, it is difficult to obtain a high-quality member. Further, the primary particles in the secondary particles have very strong aggregation, and it is difficult to disperse them uniformly. For example, in Non-Patent Document 1, pseudo-boehmite powder is dispersed under acidic conditions (in dilute nitric acid) to evaluate defibration. However, when the pseudo-boehmite powder is placed under acidic conditions, the structurally weak portion of the secondary particles is preferentially dissolved. Therefore, a part of the structurally weak primary particles is dissolved, and the secondary particles are in a chopped state. The secondary particles that have been cut into pieces and the dissolved primary particles cause significant unevenness in the quality of ceramic-related members.

In view of these conventional problems, the present inventor has conducted a study, and found that when the pseudo-pHe powder is produced by the neutralization reaction method, the neutralization treatment and the gelatinization treatment of the raw material solution are performed separately. It was found that it is effective and that the solution temperature and pH during the neutralization treatment and the glutinating treatment are important for obtaining a boehmite dispersion having a small glutinous particle size.

The present invention has been completed based on such findings, and an object of the present invention is to provide a boehmite dispersion containing pseudo-boehmite powder having a small gelatinization particle size and a method for producing the same.

The present invention includes the following aspects (1) to (10). In the present specification, the expression "~" includes the numerical values at both ends thereof. That is, "X to Y" is synonymous with "X or more and Y or less".

(1) A boehmite dispersion containing pseudo-boehmite powder.
A boehmite dispersion having a gelatinization particle size of 100 nm or less of the pseudo-boehmite powder.

(2) The boehmite dispersion according to (1) above, wherein the deflocculated particle size of the pseudo-boehmite powder is 50 nm or less.

(3) The boehmite dispersion according to (1) or (2) above, further comprising sodium gluconate.

(4) The boehmite dispersion according to any one of (1) to (3) above, which further contains water and the pseudo-boehmite powder is dispersed in water.

(5) The method for producing a boehmite dispersion according to any one of (1) to (4) above, wherein the following steps;
A step of preparing an alkaline aqueous solution and an acidic aqueous solution in which one or both contain aluminum ions, and
A step of mixing the alkaline aqueous solution and the acidic aqueous solution to obtain a mixed solution, and causing a neutralization reaction in the mixed solution to obtain a slurry containing a neutralized product.
The slurry is provided with a step of adding an acid to the slurry to perform a degluing treatment to maintain the pH at 4.0 or less.
A method of maintaining the temperature of the slurry at 20 ° C. or lower and the pH within the range of 10.5 to 11.5 during the neutralization reaction.

(6) The method of (5) above, wherein the alkaline aqueous solution is a sodium aluminate solution and the acidic aqueous solution is an aluminum sulfate solution.

(7) The method according to (5) or (6) above, further comprising a step of adding pure water to the slurry obtained by the neutralization reaction to dilute the slurry.

(8) The method according to any one of (5) to (7) above, further comprising a step of adding sodium gluconate to the slurry obtained by the neutralization reaction.

(9) The method of (8) above, wherein the temperature of the slurry is maintained at 30 to 40 ° C. when sodium gluconate is added.

(10) The method according to any one of (5) to (9) above, wherein the slurry is subjected to a high-speed shearing treatment during the neutralization reaction.

According to the present invention, there is provided a boehmite dispersion containing pseudo-boehmite powder having a small glutinous particle size and a method for producing the same. Therefore, it is possible to improve the quality of the ceramic-related member produced by using this boehmite dispersion.

An SEM image of a general pseudo-boehmite powder is shown. A TEM image of a general pseudo-boehmite powder is shown. The solubility of Al ₂ O for ₃ minutes in an aqueous solution is shown. The solubility of Al ₂ O for ₃ minutes in an aqueous solution is shown. Shows the abundance ratio of aluminum nuclides. The particle size distribution of the boehmite dispersion is shown. The relationship between the solution pH and the gelatin size is shown. The particle size distribution of the boehmite dispersion prepared by the high-speed shearing treatment is shown. The particle size distribution of the boehmite dispersion prepared by the low-speed shearing treatment is shown. The relationship between the slurry temperature when sodium gluconate is added and the deflocculation particle size of the obtained pseudo-boehmite powder is shown. The particle size distribution of the boehmite dispersion is shown. The SEM image of the boehmite dispersion part is shown. The relationship between the unglazed particle size of the boehmite dispersion and the BET specific surface area of the alumina abrasive grains is shown. The relationship between the unglazed particle size of the boehmite dispersion and the Knoop hardness of the alumina abrasive grains is shown.

A specific embodiment of the present invention (hereinafter, referred to as “the present embodiment”) will be described. The present invention is not limited to the following embodiments, and various modifications can be made without changing the gist of the present invention.

Boehmite dispersion The boehmite dispersion of the present embodiment contains pseudo-boehmite powder. Boehmite (γ-AlOOH), together with diaspore (α-AlOOH), constitutes an alumina hydroxide oxide (alumina monohydrate). In a completely crystalline state, boehmite has a crystal structure in which two sheet structures are bonded in the b-axis direction by hydrogen bonds. This sheet structure is formed by connecting AlO ₆ octahedrons centered on aluminum ions in a zigzag shape in the a-axis and c-axis directions so as to share a ridge. This crystal structure can also be said to be a layered structure in which unit layers having an AlO (OH) composition are stacked so as to form a double layer structure of (OH), Al, O, Al, and (OH).

Boehmite is classified into low crystalline boehmite (Pseudo-boehmite) and highly crystalline boehmite (Boehmite) according to the size of crystallinity. The water content of highly crystalline boehmite is theoretically about 15% by mass, but the water content of pseudo-boehmite is more than 15% by mass. In pseudo-boehmite, it is considered that adsorbed water has penetrated between the layers of the sheet structure in the crystal structure. The composition of the pseudo-boehmite is typically 0.5 ≦ n ≦ 2.5 when expressed by _{the formula: Al 2} O ₃ · nH _{2 O.}

The pseudo-boehmite powder of the present embodiment has a gelatinization particle size of 100 nm or less. Here, the deflocculation particle size is a guideline for the particle size in the deflocculation state, and is obtained by the dynamic light scattering method described later. In general pseudo-boehmite powder, fine primary particles are intricately intertwined to form strong aggregated secondary particles. Therefore, the deflocculated particle size is over 100 nm. If the defibration particle size is more than 100 nm, the quality of the final product may deteriorate. For example, when the boehmite dispersion is fired to produce alumina abrasive grains, if the defibrated particle size of the pseudo-boehmite powder is more than 100 nm, the BET specific surface area and hardness of the abrasive grains vary widely. On the other hand, in the boehmite dispersion of the present embodiment, the primary particles are dispersed so as to exist substantially independently. Therefore, it is possible to improve the quality of the final product. The defibration particle size is preferably 50 nm or less. The lower limit of the defibration particle size is not particularly limited. However, if the deflocculated particle size is too small, it may be difficult to filter during production. Therefore, the defibration particle size is preferably 10 nm or more, more preferably 30 nm or more.

The unglazed particle size can be determined by a dynamic light scattering method. Specifically, 0.18 parts by mass of boehmite dispersion is diluted with 24.8 parts by mass of pure water, placed in a 50 cc container, and sufficiently stirred using a magnetic stirrer. Next, the container containing the boehmite dispersion is set in a particle size / zeta potential / molecular weight measuring device (Malvern Panasonic, zetasizer) to determine the distribution of particle size. In the particle size distribution, the particle size that maximizes the scattering intensity is obtained, and this is used as the deflocculation particle size. The unglazed particles are in Brownian motion. In the dynamic light scattering method, the rate of Brownian motion (diffusivity) of a particle is obtained, and the particle size is calculated using the Stokes Einstein equation. By using the dynamic light scattering method, it is possible to accurately evaluate the particle size of the unglazed particles, not the agglutinated secondary particles or the primary particles constituting the aggregated secondary particles.

The boehmite dispersion typically contains a solvent in addition to the pseudo-boehmite powder. The solvent is not particularly limited. However, water and / or alcohol is preferred, with water particularly preferred. Boehmite contains a hydroxyl group (OH ⁻ ). Therefore, the pseudo-boehmite powder can be highly dispersed in water. It is preferable that the boehmite dispersion further contains water and the pseudo-boehmite powder is dispersed in water. Further, the boehmite dispersion may contain an additive such as a dispersant in addition to the pseudo-boehmite powder and the solvent. Examples of the dispersant include ammonium polyacrylate and the like. Any additive can be used as long as it does not contain a component such as silicon (Si) that inhibits the sinterability of the ceramics.

The boehmite dispersion may _{further comprise sodium gluconate (C 6} H ₁₁ Na). Sodium gluconate is a component that acts as a precipitation inhibitor that delays the reaggregation of pseudoboehmite powder during the production of boehmite dispersions. Therefore, by using sodium gluconate, it becomes possible to efficiently obtain a boehmite dispersion having a small gelatin particle size. The content of sodium gluconate is 3.0 to 9.0% by mass (2.6 to 7.7% by mass in terms of AlOOH) with respect to _{3 minutes of precipitated Al 2} O.

Method for Producing Boehmite Dispersion The method for producing boehmite dispersion according to the present embodiment is as follows: a step of preparing an alkaline aqueous solution and an acidic aqueous solution in which one or both of them contain aluminum ions (preparation step), and the alkaline aqueous solution. A step of mixing an acidic aqueous solution to make a mixed solution and causing a neutralization reaction in this mixed solution to make a slurry containing a neutralized substance (slurry step), and a step of adding an acid to this slurry to make a pH 4.0. It is provided with a step of performing a defibration treatment to be maintained below (a deflocculation step). Further, during the neutralization reaction, the temperature of the slurry is maintained at 20 ° C. or lower and the pH is maintained within the range of 10.5 to 11.5. Details of each step will be described below.

<Preparation process>
In the preparation step, an alkaline aqueous solution and an acidic aqueous solution are prepared. Either or both of the alkaline aqueous solution and the acidic aqueous solution contain aluminum ions. Examples of the alkaline aqueous solution include solutions of alkaline hydroxides such as sodium hydroxide and potassium hydroxide, and aqueous ammonia. Examples of the alkaline aqueous solution containing aluminum ions include an alkali aluminate solution such as sodium aluminate and potassium aluminate. Of these, a sodium aluminate (sodium aluminate) solution, which is easily available and inexpensive, is preferable. When a sodium aluminate solution is used, its concentration is not limited. However, a _{solution containing 100 to 200 g of Al 2} O ₃ minutes per liter (100 to 200 g-Al ₂ O ₃ / L) is preferable. On the other hand, as the acidic aqueous solution, either an inorganic acid or an organic acid can be used. As the inorganic acid, sulfuric acid, hydrochloric acid, nitric acid, phosphoric acid, perchloric acid, boric acid and the like can be used. Examples of the organic acid include carboxylic acids such as formic acid, acetic acid and propionic acid, dicarboxylic acids such as oxalic acid, and hydroxycarboxylic acids such as gluconic acid. Examples of the acidic aqueous solution containing aluminum ions include a solution of an inorganic salt such as aluminum sulfate and aluminum nitrate, and a solution of an organic salt such as aluminum acetate. Of these, an aluminum sulfate (aluminum band) solution that is inexpensive and easily available is preferable. When using an aluminum sulfate solution, its concentration is not limited. However, if the concentration is too high, the resulting boehmite slurry becomes highly viscous and difficult to handle. Further, if the concentration is too low, the processing volume at the time of solid-liquid separation becomes large, which is economically disadvantageous. Therefore, a solution having an aluminum concentration of 0.8 to 1.6% by mass in terms of _{Al 2} O _{3 is preferable.} It is preferable that the alkaline aqueous solution is a sodium aluminate solution and the acidic aqueous solution is an aluminum sulfate solution.

<Slurry process>
In the slurrying method, the prepared alkaline aqueous solution and acidic aqueous solution are mixed and mixed, and a neutralization reaction is caused in this mixed solution to obtain a slurry containing a neutralized product (pseudo-bemite). During the neutralization reaction, the reaction represented by the following formula (1) proceeds in the mixed solution to form pseudoboehmite (γ-AlOOH). Pseudo-boehmite is sparingly soluble in water. Therefore, the solution after the reaction becomes a slurry (suspension) in which boehmite fine particles are dispersed.

In this embodiment, the pH of the solution is maintained in the range of 10.5 to 11.5 during the neutralization reaction. This makes it possible to form pseudo-boehmite powder with a small defibration particle size. On the other hand, when the pH is less than 10.5 or more than 11.5, the deflocculation particle size of the pseudo-boehmite powder becomes large. It is speculated that the mechanism described below may be working as the reason why the deflocculation particle size becomes smaller in the pH range of 10.5 to 11.5.

Aluminum ions in an aqueous solution are aco ions (aqua ions) and exist as ligands with water molecules. For example, if it is sufficiently acidic, it exists as an aco complex (complex ion) ([Al (OH ₂ ) ₆ ] ^3+). In weak acidity, part of the ligand dissociates ^{and releases hydrogen ions (H +} ), and the hydroxyaco complex ([Al (OH ₂ ) ₅ (OH)] ²⁺ , [Al (OH ₂ ) ₄ (OH)) ₂ ] ⁺ etc.) is formed. Further, when hydrogen ion release proceeds sequentially, tetrahydroxydoaluminate ion ([Al (OH) ₄ ] ⁻ ) is generated. Then, the tetrahydroxydoaluminate ion and the aluminum ion cause a neutralization reaction represented by the above formula (1) to generate boehmite (γ-AlOOH).

By the way, under a certain environment, aco-complexes and hydroxyaco-complexes are polymerized with each other to form a polynuclear complex (multinuclear complex ion) by a dehydration condensation reaction mediated by ^{a hydroxy ion (OH −).} Such as hydroxy aquo complexes _{([Al (OH) (OH} 2) 5] 2+) may undergo a polymerization reaction of the following formula (2), polynuclear complexes _{([Al 2 (OH) 2} (OH 2) 8] 4+ )become.

If the formation of such a polynuclear complex progresses excessively, it becomes difficult to synthesize a pseudo-boehmite powder having easy gelatinization. That is, as a result of repeated bonding between the polynuclear complexes, a larger complex is formed, and the primary particles of the finally obtained pseudo-boehmite powder become large. Further, even if the primary particles of the pseudo-boehmite powder are small, the bonds between the primary particles become strong. Usually, with pseudo-boehmite obtained by the neutralization reaction, it is not easy to control the progress of the dehydration condensation reaction which is extremely fast at the initial stage of the neutralization reaction. Therefore, the precipitated primary particles of pseudo-boehmite repeatedly collide with each other and aggregate with each other, and are stretched around like a mesh to form strong secondary particles. The secondary particle structure of pseudoboehmite formed in this way is not easily decomposed and decomposed by external factors such as acid or alkali. In addition, if the concentration of acid or alkali is increased to promote decomposition and decomposition, or if the operating temperature is raised, partial dissolution of the primary particles of boehmite will occur, and only the target fine primary particles of beamite will be dissolved. Difficult to obtain.

Thus in order to obtain a pseudo-boehmite powder having excellent peptizing property, while as many frequency of occurrence of aquo complexes _{([Al (H 2 O)} 6] 3+), and as much as possible the formation of polynuclear complexes according to the dehydration condensation reaction slow It is preferable to cause a neutralization reaction in the region to be subjected to. In this regard, the present inventor _{paid attention to the solubility of Al 2} O ₃ minutes under acid / alkaline conditions, and considered that easy glutinous property was exhibited in the region immediately before the formation of the polynuclear complex.

FIG. 3 shows the solubility _{of Al 2} O for ₃ minutes when the pH is changed from the acid condition to the alkaline condition. Further, FIG. 4 shows the solubility _{of Al 2} O for ₃ minutes when the pH is changed from the alkaline condition to the acid condition. This solubility is obtained from the solubility product when aluminum hydroxide undergoes a dissolution reaction. That is, aluminum hydroxide ^{has an extremely low concentration of hydroxy ions (OH −} ) in the acid region, and the reaction represented by the following equation (3) proceeds and the equilibrium shifts in the dissolution direction. The solubility product (Ksp) in this reaction is 5 × ^10-33 . On the other hand, in the alkaline region, the reaction represented by the following formula (4) proceeds to form a ^{coordination bond by hydroxy ion (OH −} ), and tetrahydroxydoaluminate ion ([Al (OH) ₄ ] ⁻ ) is generated. Generate. The solubility product (Ksp) in this reaction is 4 × 10 ^-13 .

_{As shown in FIGS. 3 and 4, the solubility of Al 2} O ₃ minutes becomes significantly higher in the region where the pH is less than 4.0 and more than 11.0. From this, it is considered that the bond end state of the polynuclear complex is weakened in the two regions where the pH is around 4.0 and 11.0, and the aggregation of the primary particles constituting pseudoboehmite is weakened.

Next, we focus on the abundance ratio of aluminum nuclides (complexes). FIG. 5 is taken from Non-Patent Document 2 (Fig. 4 on page 13) and shows the abundance ratio of aluminum nuclides in solution under acid / alkaline conditions. As shown in FIG. 5, a large number of nuclides (Al ³⁺ , [Al ₂ (OH)] ²⁺ , [Al ₂ (OH) ₂ ] ^4+, etc.) are dissolved in the acid region. In addition, the abundance ratio of aluminum nuclides changes significantly in response to slight fluctuations in pH. As described above, the equilibrium state of aluminum nuclides is considerably complicated in the acidic region, and it can be said that it is difficult to stably and continuously synthesize boehmite in this region. On the other hand, the equilibrium state of nuclides is not so complicated in the alkaline region. Therefore, it is presumed that pseudoboehmite powder having excellent defibration property can be stably synthesized in the region where the pH is around 11.0.

In the region where the pH is less than 10.5, the amount of pseudoboemite produced increases exponentially as the pH decreases, but these easily form secondary agglutinated particles, so that the hydrolysis of the polynuclear complex progresses further. It ends up. Therefore, only a very general pseudo-boehmite having no easy-to-glue property can be obtained. On the other hand, in the region above pH 11.5, _{the solubility of Al 2} O ₃ minutes increases exponentially, so that pseudo-boehmite with easy gelatinization is instantaneously generated, but the solubility is still sufficiently high. , The generated pseudo-boehmite is redissolved in the solution. As a result, pseudo-boehmite consisting of only strong secondary agglutinating particles that survived without being redissolved can be obtained. On the other hand, in the region of pH 10.5 to 11.5, which is the region where the supersaturated region is switched to the saturated region, it becomes possible to obtain a pseudo-boehmite powder having excellent defibration property in a sufficient yield.

The temperature of the slurry is maintained below 20 ° C. during the neutralization reaction. If the temperature of the neutralization reaction exceeds 20 ° C., the dehydration condensation reaction at the initial stage of the neutralization reaction proceeds excessively quickly, and the precipitated pseudo-boemite particles repeatedly collide and aggregate with each other, resulting in a strong secondary particle structure. Will form. The slurry temperature is preferably 15 ° C. or lower. On the other hand, if the slurry temperature is excessively low, the neutralization reaction will not proceed easily, and boehmite will not be synthesized. The slurry temperature is preferably 5 ° C. or higher.

The slurry may be subjected to high-speed shearing during the neutralization reaction. In the boehmite reaction, the dehydration condensation reaction at the initial stage of the reaction proceeds extremely quickly. Therefore, the neutralization reaction may occur non-uniformly, especially when a raw material solution having a high aluminum concentration (alkaline aqueous solution and acidic aqueous solution) is used. On the other hand, by subjecting the solution (slurry) to a high-speed shearing treatment, the neutralization reaction can proceed uniformly. Therefore, a high-concentration raw material solution can be used, which contributes to the efficient production of boehmite dispersion.

For the high-speed shearing treatment, the raw material solution may be treated using a high-speed rotary shearing stirrer such as a homomixer or a homogenizer. The high-speed shearing treatment is ^{preferably performed under the condition that the velocity gradient is 1000 seconds-1} or more, and more preferably 10,000 seconds- ¹ or more. Here, the speed gradient is x / y × 10 when the peripheral speed of the turbine (rotor) of the stirrer is x (m / sec) and the clearance between the turbine (rotor) and the status (screw) is y (mm). It is represented by ³ (seconds- ^1).

<Glue process>
In the degluing step, the slurry obtained in the slurrying step is subjected to a degluing treatment. This degluing treatment is carried out by adding an acid to maintain the pH of the slurry at 4.0 or less. In the pseudo-boehmite powder obtained in the slurrying step, the primary particles are weakly bonded to form secondary particles. Therefore, by adding an acid, the bonds between the primary particles constituting the secondary particles are separated, and it becomes possible to highly disperse the fine primary particles in the solution. The pH is preferably 3.5 or less. On the other hand, if the pH is excessively low, the primary particles themselves will dissolve. Therefore, the pH is preferably 2.0 or higher, more preferably 2.5 or higher. As the acid, known inorganic acids and / or organic acids can be used. Examples of the inorganic acid include nitric acid, hydrochloric acid, sulfuric acid, phosphoric acid, boric acid, and hydrofluoric acid. Organic acids include formic acid, acetic acid, butanoic acid, propionic acid, pentanoic acid, hexanoic acid, heptanic acid, octanoic acid, nonanoic acid, decanoic acid, dodecanoic acid, tetradecanoic acid, pentadecanoic acid, 9-hexadecanoic acid, heptadecanoic acid, octadecane. Examples thereof include acids, glucolic acid, citric acid, apple acid, lactic acid, fumaric acid, maleic acid, adipic acid, oxalic acid, malonic acid, succinic acid and tartrate acid. Inorganic acids are preferred, and nitric acid is particularly preferred. In this way, the boehmite dispersion of the present embodiment can be obtained.

If necessary, a step (dilution step) of adding pure water to the slurry obtained in the slurrying step to dilute it may be provided. The slurry after the slurrying step is in a supersaturated region near pH 11, and a large amount of Al ₂ O ₃ minutes is dissolved in the solution even after the pseudo-boehmite powder is precipitated. This Al ₂ O ₃ minute exists in the form of dissolved aluminum ion (Al ³⁺ ), acocomplex ([Al (OH ₂ ) ₆ ] ³⁺ ), and an aggregate thereof ([Al _n (OH) _{3n + 1} ] ^−). This dissolved Al ₂ O ₃ minutes may precipitate due to a hydrolysis reaction over time, causing the pseudo-boehmite powder to reaggregate. By diluting the slurry with pure water, the hydrolysis reaction can be suppressed and the reaggregation of the pseudoboehmite powder can be delayed.

If necessary, a step (addition step) of adding _{sodium gluconate (C 6} H ₁₁ Na) to the slurry obtained in the slurrying step may be provided. This makes it possible to delay the reaggregation of the pseudo-boehmite powder. Sodium gluconate functions as a masking agent for ionic nuclides. Therefore, it acts as a precipitation inhibitor that suppresses the hydrolysis reaction of _{dissolved Al 2} O ₃ minutes (Al ³⁺ , [Al (OH ₂ ) ₆ ] ³⁺ , [Al _n (OH) _{3n + 1} ] ^{−, etc.).} The amount of sodium gluconate added is preferably 3.0 to 9.0% by mass with respect to the _{precipitated Al 2} O _{3 minutes.} If the amount added is less than 3.0% by mass, the effect as a precipitation inhibitor cannot be sufficiently exerted. On the other hand, if it exceeds 9.0% by mass, the independence of the obtained pseudo-boehmite is too high, and there is a problem that the filtration / cleaning property is significantly deteriorated. The addition amount is more preferably 4.0 to 6.0% by mass.

When adding sodium gluconate, the temperature of the slurry is preferably maintained at 10 to 50 ° C, more preferably 30 to 40 ° C. The higher the slurry temperature when sodium gluconate is added, the smaller the deflocculation particle size of the obtained pseudo-boehmite powder. _{This is because the masking reaction between sodium gluconate and Al 2} O ₃ minutes still dissolved in the slurry is facilitated, and the independence of the primary particles is further promoted. However, if the slurry temperature is excessively high, the deflocculated particle size becomes too small, and it becomes difficult to perform filtration cleaning in a subsequent step. Therefore, it is preferable to keep the slurry temperature within the above range.

The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to the following examples.

[Experimental Example 1]
In Experimental Example 1, a boehmite dispersion was prepared using a high-speed rotary shear stirrer and evaluated.

(1) Preparation of boehmite dispersion <Preparation step>
Sodium aluminate (sodium aluminate) solution and aluminum sulfate (sulfate band) solution were prepared as raw material solutions, respectively. The sodium aluminate solution had a sodium concentration of 150 g / L in terms of _{Na 2} O and an aluminum concentration of 150 g / L in terms of _{Al 2} O _3. The aluminum sulfate solution had an aluminum concentration of 8.0% by mass in terms of _{Al 2} O _3.

<Slurry process>
Next, the prepared sodium aluminate solution was introduced into the reactor and neutralized under low temperature conditions of 20 ° C. or lower. At the time of the reaction, the solution (slurry) was subjected to a high-speed shearing treatment using a high-speed rotary shearing stirrer. A baffle reactor equipped with a dissolver stirrer was used as the high-speed rotary shear stirrer. This reactor was equipped with a reaction vessel (φ100 mm) and a rotatable dissolver blade (φ50 mm, width 15 mm). The reaction tank was provided with four obstruction plates (height 30 mm, width 23 mm) fixed to the lower part of the side wall, and was provided with a lower introduction port. The clearance between the dissolver wing and the baffle plate was 2 mm.

First, 140 mL of sodium aluminate solution was placed in a reaction vessel, and the dissolver blade was rotated at a rotation speed of 5130 rpm. The velocity gradient at this time was 11000 seconds ^-1 . Then, 110 mL of aluminum sulfate solution was gradually added from the lower inlet of the reaction vessel so as to have a pH in the range of 10.5 to 11.5 to complete the neutralization reaction. The solution temperature was maintained at 15 ° C. during the reaction. The neutralization reaction was carried out by gradually adding aluminum sulfate using a roller pump until the pH was in the range of 10.5 to 11.5. At this time, the pH gradually decreased from about 14, the neutralization reaction proceeded, and pseudoboehmite began to precipitate from around the pH below 12. _{As described above, since the solubility of Al 2} O ₃ minutes is extremely high in the region where the pH exceeds 11.0, the pseudo-boehmite precipitated so far was immediately redissolved due to the convenience of solubility. The reaction was completed when neutralized to the range of pH 10.5 to pH 11.5. This reaction gave a slurry containing a neutralized product.

<Glue process>
The obtained slurry was solid-liquid separated and washed with a centrifuge to obtain a slurry having a water content of 80 to 95%. The slurry was then subjected to a degluing treatment. Specifically, while stirring the slurry, diluted nitric acid was added thereto to maintain the pH at 3.5. As a result, a boehmite dispersion in which the pseudo-boehmite powder was deflated (dispersed) in an aqueous solution was obtained.

(2) Evaluation The following evaluation was performed on the boehmite dispersion obtained in Experimental Example 1.

<Glue particle size>
The unglazed particle size of the boehmite dispersion was determined by a dynamic light scattering method. Specifically, 5 g of the boehmite dispersion was diluted with 100 g of pure water, 25 g of this was weighed and placed in a 50 cc container, and the mixture was sufficiently stirred using a magnetic stirrer. Next, the container containing the boehmite dispersion was set in a particle size / zeta potential / molecular weight measuring device (Malvern Panasonic, Zeta Sizar) to measure the particle size. At this time, the dispersion solvent: pure water and the temperature: 25 ° C. were input as the measurement conditions.

(3) Evaluation result The distribution of particle size of the boehmite dispersion is shown in FIG. The relationship between the solution pH and the gelatinization particle size after the completion of the neutralization reaction is shown in FIG. Here, the defibration particle size is the particle size at which the scattering intensity is maximized in the particle size distribution. As shown in FIGS. 6 and 7, the deflocculation particle size became the minimum near pH 11.0, and the deflocculation particle size increased sharply before and after that. From this, it was found that the deflocculated particle size became smaller when the pH was in the range of 10.5 to 11.5.

The particle size distribution of the boehmite dispersion prepared with the solution pH at 11.4 is shown in FIG. This boehmite dispersion had a small glutinous particle size of 60 to 70 nm and a uniform particle size.

[Experimental Example 2]
In Experimental Example 2, a boehmite dispersion was prepared from a diluted raw material solution using a general reactor (low-speed rotary shear stirrer) and evaluated.

(1) Preparation of boehmite dispersion A raw material solution (sodium aluminate solution, aluminum sulfate solution) diluted 6-fold with pure water was used. Further, during the slurrying step, a neutralization reaction was carried out under low speed conditions using a reaction apparatus equipped with a general reaction vessel and a stirring blade. The reaction temperature was 5.5 ° C., the pH of the solution after the completion of the neutralization reaction was 11.2, and the stirring speed was 600 rpm. A boehmite dispersion was prepared in the same manner as in Experimental Example 1 except for the above.

(2) Evaluation The deflocculation particle size of the obtained boehmite dispersion was measured in the same manner as in Experimental Example 1.

(3) Evaluation result The particle size distribution of the boehmite dispersion is shown in FIG. This boehmite dispersion had a small thawing particle size of 100 nm or less and a uniform particle size. This result is almost the same as the result obtained in Experimental Example 1. Therefore, it was found that a boehmite dispersion having a small gelatinization particle size can be obtained even by using a general reactor.

[Experimental Example 3]
In Experimental Example 3, sodium gluconate was added when preparing the boehmite dispersion, and its effect was investigated.

(1) Preparation of boehmite dispersion <Preparation step>
Sodium aluminate solution and aluminum sulfate solution were prepared as raw material solutions. The sodium aluminate solution and the aluminum sulfate solution used were the same as those used in Experimental Example 1.

<Slurry process>
Next, the prepared sodium aluminate solution and aluminum sulfate solution were introduced into the homogenizer. Sodium aluminate solution was introduced at a flow rate of 23 L / hour for 1 hour. The aluminum sulfate solution was diluted 21-fold with pure water and then introduced at a flow rate of 380 L / hour for 1 hour. During the neutralization reaction with a homogenizer, the solution temperature changed from 9.4 ° C to 17.4 ° C.

The slurry after the neutralization reaction was placed in a stirring tank. As the stirring tank, a heater provided around the stirring tank capable of heating the contents was used. 247 g of sodium gluconate and 926 g of pure water were added to the slurry, and the mixture was stirred for 3 hours. The heater was operated during stirring to change the temperature of the stirred product (slurry) from room temperature to 40 ° C.

<Glue processing>
The obtained slurry was subjected to a gelatinizing treatment in the same manner as in Experimental Example 1 to obtain a boehmite dispersion in which pseudo-boehmite powder was dispersed in an aqueous solution.

(2) Evaluation The boehmite dispersion (pseudo-boehmite powder) obtained in Experimental Example 3 was evaluated as shown below.

<Glue particle size>
The unglazed particle size of the boehmite dispersion was measured. The measurement was performed by the same method as in Experimental Example 1.

<SEM observation>
The boehmite dispersion was observed using a scanning electron battery microscope (SEM). Observation was performed using a scanning electron microscope (Hitachi High-Tech Science Corporation, S-4700).

<Component analysis>
The components of the boehmite dispersion were analyzed. First, a desired amount of sample was melted together with a lithium borate melting agent by a glass bead method to prepare a glass beaded sample. After setting the obtained sample in a fluorescent X-ray analyzer (Rigaku Co., Ltd., ZSX PrimusII), the fluorescent X-ray intensity was measured and the amount of each component was quantified using a calibration curve.

(3) Evaluation Results FIG. 10 shows the relationship between the slurry temperature when sodium gluconate was added and the gelatinization particle size of the boehmite dispersion. The higher the slurry temperature, the more monotonous the defibration particle size tended to be.

The particle size distribution and SEM image of the boehmite dispersion prepared by setting the slurry temperature at the time of adding sodium gluconate to 30 ° C. are shown in FIGS. 11 and 12, respectively. This boehmite dispersion had a small thawing particle size of 50 nm or less and a uniform particle size. In the SEM image, dispersed primary particles were observed, but no aggregated secondary particles were observed.

Table 1 shows the component analysis results of the boehmite dispersion prepared by setting the slurry temperature at the time of adding sodium gluconate to 30 ° C. In Table 1, the amount of each component in the dispersion is shown in terms of oxide. The obtained boehmite dispersion had an extremely high purity with an impurity content of 0.1% by mass or less.

[Experimental Example 4]
In Experimental Example 4, alumina abrasive grains were prepared using a boehmite dispersion, and their characteristics were evaluated.

(1) Preparation of Alumina Abrasive Grains Alumina abrasive grains were prepared using a boehmite dispersion having various types of defibrated particle size as a raw material. Specifically, the gelatinized dispersion was dried at 100 ° C. for 6 hours to obtain a dry product. This was fired at 1300 to 1500 ° C., then crushed and sized to obtain alumina abrasive grains having a center diameter of about 200 to 400 μm.

(2) Evaluation The obtained alumina abrasive grains were evaluated as shown below.

<BET specific surface area>
The BET specific surface area of the alumina abrasive grains was measured using an automatic specific surface area measuring device (Shimadzu Corporation, Tristar 3000).

<Knoop hardness>
The Knoop hardness of the alumina abrasive grains was measured using a hardness tester (Matsuzawa Co., Ltd., PMT-X7A). At this time, a noup indenter was used, and the measurement was performed under the condition of a test force of 100 gf (980.7 mN).

(3) Evaluation Results The BET specific surface area and Knoop hardness of the alumina abrasive grains are shown in FIGS. 13 and 14, respectively. Here, the horizontal axis of FIGS. 13 and 14 represents the gelatinization particle size of the boehmite dispersion used as a raw material.

As shown in FIGS. 13 and 14, the BET specific surface area and Knoop hardness of the abrasive grains began to fluctuate significantly when the unglazed particle size of the boehmite dispersion exceeded 100 nm. From this, it was found that the quality of the final product begins to be adversely affected above the deflocculation particle size of 100 nm of the boehmite dispersion.

Claims (10)

A boehmite dispersion containing pseudo-boehmite powder
A boehmite dispersion having a gelatinization particle size of 100 nm or less of the pseudo-boehmite powder. The boehmite dispersion according to claim 1, wherein the defibrated particle size of the pseudo-boehmite powder is 50 nm or less. The boehmite dispersion according to claim 1 or 2, further comprising sodium gluconate. The boehmite dispersion according to any one of claims 1 to 3, further comprising water and the pseudo-boehmite powder being dispersed in water. The method for producing a boehmite dispersion according to any one of claims 1 to 4, wherein the following steps;
A step of preparing an alkaline aqueous solution and an acidic aqueous solution in which one or both contain aluminum ions, and
A step of mixing the alkaline aqueous solution and the acidic aqueous solution to form a mixed solution, and causing a neutralization reaction in the mixed solution to form a slurry containing a neutralized product.
The slurry is provided with a step of adding an acid to the slurry to perform a degluing treatment to maintain the pH at 4.0 or less.
A method of maintaining the temperature of the slurry at 20 ° C. or lower and the pH within the range of 10.5 to 11.5 during the neutralization reaction. The method according to claim 5, wherein the alkaline aqueous solution is a sodium aluminate solution, and the acidic aqueous solution is an aluminum sulfate solution. The method according to claim 5 or 6, further comprising a step of adding pure water to the slurry obtained by the neutralization reaction to dilute the slurry. The method according to any one of claims 5 to 7, further comprising a step of adding sodium gluconate to the slurry obtained by the neutralization reaction. The method of claim 8, wherein the temperature of the slurry is maintained at 30-40 ° C. when sodium gluconate is added. The method according to any one of claims 5 to 9, wherein the slurry is subjected to a high-speed shearing treatment during the neutralization reaction.

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