JPH08259225A - Alkaline alumina sol and production thereof - Google Patents

Abstract

PURPOSE: To improve stability and transparency in an alkali region by bringing an acidic alumina sol contg. specified cationic fine alumina particles into contact with an anion exchanger in an aq. phase in the presence of an alkali. CONSTITUTION: Crystalline alumina powder having <=10μm particle diameter and one or more kinds of crystal forms selected from among γ-, η-, δ-, ρ-, χ-, θ-, κ- and α-forms is suspended in water by 1-30wt.%, the resultant suspension is adjusted to pH2-8 by adding an acid and a cation exchanger is added. The suspension is then treated at room temp. to 100 deg.C for 0.5-50hr and the cation exchanger is separated to obtain an acidic alumina sol contg. cationic fine alumina particles. Aq. suspension contg. 1-20wt.% of the alumina sol is prepd., an alkali is added to the suspension by 1×10<-3> to 1mol per 1mol alumina and the suspension is brought into contact with an anion exchanger at room temp. to 100 deg.C for 0.5-50hr to obtain the objective alkaline alumina sol.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alumina sol in which crystalline alumina fine particles are dispersed, and more particularly to an alumina sol having excellent stability in an alkaline region and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, various alumina sols and methods for producing the same have been known. For example, JP-A-59-78925 discloses an acidic alumina sol composed of pseudo-boehmite crystals, and JP-A-53-112299 discloses an acidic alumina sol having a boehmite crystal lattice. . Further, according to Japanese Examined Patent Publication No. 3-52410, an alkaline alumina sol composed of alumina hydrate is also known.

However, the above-mentioned sol is conventionally called alumina sol, but it is actually aluminum hydroxide in a sol state, and its dispersoid is not aluminum oxide (alumina) but hydroxide. It is aluminum (alumina hydrate). Thus, at present, a stable alkaline alumina sol whose dispersoid consists essentially of aluminum oxide is not yet known.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an alkaline alumina sol having excellent stability, which comprises crystalline alumina (aluminum oxide) fine particles having a sharp particle size distribution as a dispersoid and a method for producing the same.

[0005]

In the alkaline alumina sol according to the first aspect of the present invention, the alumina fine particles are γ, η, δ, ρ, χ, θ,
It is characterized by comprising a single crystal or a plurality of crystals selected from κ and α forms.

The method for producing an alkaline alumina sol according to the second invention is γ, η, δ, ρ, χ, θ, κ, and α.
It is characterized in that an acidic alumina sol containing cationic alumina fine particles composed of single or plural crystals selected from the form is brought into contact with an anion exchanger in the presence of an alkali in an aqueous phase.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention will be specifically described below. First, the alkaline alumina sol according to the first invention will be described.

In the first aspect of the invention, fine alumina particles serving as dispersoids (hereinafter sometimes referred to as colloidal particles).
Is an aluminum oxide consisting essentially of single or multiple crystals selected from γ, η, δ, ρ, χ, θ, κ, and α forms. The crystal form of the alumina fine particles can be distinguished from alumina hydrates such as pseudo-boehmite, boehmite, bayerite, and gypsite, which constitute the conventional alumina sol, by identifying them by X-ray diffraction.

Further, since the alumina fine particles constituting the alkaline alumina sol of the present invention (hereinafter sometimes referred to as an alkaline alumina colloid solution) are aluminum oxide, the weight loss due to firing is small. That is, in the alumina sol of the present invention, the weight reduction of the alumina fine particles in the temperature range of 110 ° C. to 1000 ° C. is 10% by weight or less. The weight reduction of the alumina fine particles is obtained by sufficiently drying the alumina sol of the sample at 110 ° C.
₁ ) is measured, and then the sample is calcined at 1000 ° C. for 1 hour, and then the weight (W ₂ ) of the sample is measured to obtain the value by the formula 1. The weight loss of the alumina fine particles is particularly preferably 8% by weight or less.

[0010]

[Equation 1] Weight reduction = (W ₁ −W ₂ ) / W ₁ × 100 (%)

The fine alumina particles constituting the alkaline alumina sol of the present invention have a very narrow particle size distribution and have an average particle size of 1 to 300 nm, preferably 5 to 100 nm. Therefore, the alumina sol is excellent in transparency. ,
When a sol having an alumina concentration of 0.5% by weight is measured with a spectrophotometer, the absorbance at a wavelength of 800 nm is 1.0 or less,
It is preferably 0.5 or less, more preferably 0.2 or less, and the absorbance at a wavelength of 560 nm is 1.5 or less, preferably 1.0 or less, more preferably 0.5 or less. Furthermore, the absorbance at a wavelength of 400 nm is 3.
0 or less, preferably 2.0 or less, more preferably 1.0
It becomes the following.

The alkaline alumina sol of the present invention has a pH of
8 or more, preferably pH 9 to 14, more preferably pH
It is very stable in the alkaline region of 9.5 to 12, and even if the aqueous sol whose alumina concentration is adjusted to 1% by weight is treated with a centrifuge at 1000 rpm for 30 minutes, the alumina fine particles do not settle. On the other hand, a paste-like semi-solid obtained by dispersing alumina powder in alkaline water (usually, such a semi-solid is also called a sol) is adjusted to an alumina concentration of 1% by weight and centrifuged. 1000r by machine
It is distinguished from the alkaline alumina sol of the present invention because it is separated into two layers when treated with pm for 30 minutes.

Since the alkaline alumina sol of the present invention has a low viscosity and an extremely high dispersion stability, the concentration of alumina can be increased. Alumina concentration is usually 1 to 40
It is adjusted to the range of% by weight. Moreover, a highly pure alkaline alumina sol can be obtained according to the purity of the acidic alumina sol used as a raw material. The amount of acid remaining in the alkaline alumina sol is usually 1% by weight or less, preferably 0.5% by weight or less, based on alumina.

Next, a method for producing the alkaline alumina sol according to the second invention will be described. As described above, the production method according to the present invention comprises contacting an acidic alumina sol containing cationic alumina fine particles composed of a single crystal or a plurality of crystals with an anion exchanger in the presence of an alkali in an aqueous phase. However, the acidic alumina sol is, for example, Japanese Patent Application No. 5-26160 filed by the applicant of the present application.
The acidic alumina sol described in No. 1 can be used.

The above-mentioned raw material alumina sol is especially used in Japanese Patent Application No.
-261601, that is, as the raw material alumina powder, one or two types of alumina composed of single or plural crystals selected from γ, η, δ, ρ, χ, θ, κ, and α forms. This alumina powder is suspended in water, a predetermined amount of acid is added to the obtained suspension, and then a cation exchanger is added and mixed by stirring, and then the cation exchanger is mixed. The acidic alumina sol obtained by separation is suitable.

The alumina powder may be used if it has a particle size of 10 μm or less, but preferably a small particle size of 1 μm or less. As such an alumina powder, commercially available ultrafine particle aluminum oxide can be used as it is or after further firing.
When using an alumina powder having a large particle diameter, it is preferable to grind this to reduce the particle diameter before use. The primary particle diameter of the alumina constituting the alumina powder is 100 n.
m or less, preferably 50 nm or less is desirable.

The concentration of the suspension of alumina powder is preferably in the range of 1 to 30% by weight, and the p of the suspension is p.
H is preferably in the range of 2-8. The stirring and mixing with the cation exchanger are carried out until the suspension of the alumina powder becomes a sol, but usually it becomes a sol when treated at a temperature range of room temperature to 100 ° C. for 0.5 to 50 hours. When the alumina powder contains a slight amount of an acid component such as chlorine, it is not necessary to add the acid again.

Examples of the acid used in the above method include mineral acids and organic acids, and examples thereof include monobasic acids such as hydrochloric acid, nitric acid, chloric acid, acetic acid, chloroacetic acid and benzoic acid, dibasic acids such as sulfuric acid, and phosphoric acid. And the like, and these acids are used alone or as a mixture. In the production of alumina sol, the amount of acid added is 5 × 10 ^{−4 to} 0.05 equivalent, preferably 1 equivalent of aluminum (Al),
It is desirable to set it in the range of 2.5 × 10 ^{−3 to} 0.025 equivalent.

Any cation exchanger can be used as long as it has a cation exchange ability, and examples thereof include a strongly acidic or weakly acidic cation exchange resin, a chelate resin, an ion exchange membrane and an ion exchange filter. To be done. These cation exchangers may be used alone or in combination, and in the case of a cation exchange resin, usually 1 kg of alumina (Al ₂ O 3
It is used in a ratio of 1 to 10 liters with respect to ₃ ).

In the method of the present invention, the concentration of the acidic alumina sol is preferably in the range of 1 to 20% by weight, and the contact with the anion exchanger is carried out until the agglomerated alumina fine particles become colloidal. , Room temperature ~ 100 ℃
When treated in the temperature range of 0.5 to 50 hours, it is deflocculated and becomes a colloid. When the acidic alumina sol contains a trace amount of an alkali component such as sodium,
It is not necessary to add alkali again.

Examples of the alkali used in the present invention include hydroxides of alkali metal elements such as sodium hydroxide, potassium hydroxide and lithium hydroxide, ammonia, tetramethylammonium hydroxide and N-methyl-2-.
Examples thereof include nitrogen compounds such as pyrrolidone and trimethylamine, and these alkalis are used alone or in combination. In producing the alkaline alumina sol, the amount of alkali added is 1 × 10 ^{−3 to} 0.1 mol, preferably 5 × 10 ⁻³ , per 1 mol of alumina (Al ₂ O ₃ ).
It is desirable to be in the range of 0.05 mol.

In the present invention, the anion exchanger can be used as long as it has an anion exchange ability. In addition to a strongly basic or weakly basic anion exchange resin, a chelate resin, an ion exchange membrane, an ion exchange resin can be used. A filter etc. are illustrated. These anion exchangers may be used alone or in combination. In the case of an anion exchange resin, it is usually alumina (A
1 ₂ O ₃ ) Used at a ratio of 1 to 20 liters per 1 kg.

In the production method of the present invention, when the acid which is the stabilizer for the acidic alumina sol is removed by the anion exchanger and passes through the isoelectric point of alumina, the alumina fine particles are agglomerated, but on the alkaline side. , Alumina reacts with alkali to produce aluminum salt, and the aluminate ion of this aluminum salt is removed by the anion exchanger to regenerate alkali, so that the reaction with alumina is repeated and the alumina fine particles are peptized. It becomes colloidal particles (fine particles). In this method, even if the amount of alkali with respect to the alumina is small, the alkali is regenerated and repeatedly acts on the alumina, and therefore the alumina fine particles can be sufficiently deflocculated. Moreover, since the aluminate contained in the obtained alkaline alumina sol is very small, that is,
Since the content of salt in the sol is low, the colloidal particles sufficiently form an electric double layer and the stability of the sol is high.

On the other hand, in the conventional method for producing an alkaline alumina sol of hydrated alumina, a large amount of alkali is required in order to peptize the acidic alumina sol of hydrated alumina with alkali to form colloidal particles. The colloidal particles agglomerate as they pass through the electric point, and the electric double layer of the particles becomes thin due to the large amount of salt produced.As a result, the particles agglomerate, the dispersibility is low, and only the sol with poor transparency I can't get it. Further, a large amount of water and long-time washing are required to make the sol into a sol obtained by washing and removing the aluminum salt using an ultrafiltration membrane or the like, which is not efficient. Further, when the alumina powder is deflocculated with alkali in the same manner as in the case of the alkaline alumina sol of hydrated alumina, the desired alumina sol is difficult to obtain because the reactivity is very poor.

The alkaline alumina sol obtained by the above-mentioned production method can be made into an organosol by substituting water as a dispersion medium with an organic solvent by a known method such as a vacuum distillation method and an ultrafiltration method. As such an organic solvent, alcohols, glycols, esters, ketones, solvents such as aromatics can be used, and specifically, methanol, ethanol, propanol, ethylene glycol, propylene glycol, glycerin, acetone,
Examples thereof include organic solvents such as methyl ethyl ketone, propylene glycol monomethyl ether, methyl cellosolve, ethyl cellosolve, dimethylformamide, and N-methyl-2-pyrrolidone. Further, by subjecting the surface of the alumina particles to a surface treatment by a known method using a silane coupling agent, a titanium coupling agent, a surfactant, a higher fatty acid ester, or a salt thereof, low polarities such as xylene, toluene and dimethylethane. A sol having an organic solvent as a dispersion medium can also be used.

The alkaline alumina sol of the present invention is useful not only as a catalyst carrier but also in the following applications.

(1) Since it has a high binder strength, it can be used as a binder for various refractory materials to obtain a high-strength molded article. For example, if it is used as a binder in the lost wax method for precision casting, it has excellent strength. Can be obtained. Further, when used as a binder for inorganic fibers such as ceramic sheets, inorganic fibers having excellent strength can be obtained.

(2) Since it has little volume change or high thermal expansion at high temperature, it can be used for alumina and refractories containing alumina.

(3) Since the colloidal particles have a high hardness, when used as a hard coat film in combination with various abrasives, various cutting tools, or a matrix of resin, alkoxide hydrolyzate such as ethyl silicate, etc. Excellent effect can be obtained. Further, when used as an abrasive, the polishing rate can be adjusted depending on the difference in particle size or crystal form.

(4) Since it has a large Young's modulus, when it is added to a coating composition such as an electromagnetic steel sheet, the tension of the coating can be greatly improved and a low iron loss electromagnetic steel sheet can be obtained.

(5) In particular, since the particle size distribution is narrow, the mechanical strength and running stability can be greatly improved when it is used as a filler for various plastics and rubbers. For example, when it is used as a filler for a polyester film, a biaxially oriented film having high strength, smoothness, and excellent abrasion resistance and slipperiness can be obtained.

(6) In addition, ink jet film fillers, papermaking, fiber surface treatment agents, cosmetic compounding agents,
It is suitable for use as a lubricant, a thickener, and an aluminum casting alloy.

[0033]

EXAMPLES The present invention will be described in detail below with reference to preferred examples.

Reference Example 1 Commercially available aluminum oxide powder (specific surface area: 110 m ² /
g, average particle diameter of powder: 0.9 μm, main crystal form: δ form, hydrochloric acid content (amount converted as HCl): 0.4% by weight)
100 g and 400 g of pure water are mixed and stirred at room temperature while being strongly acidic cation exchange resin (DA manufactured by Mitsubishi Kasei, DA
IAION, SK-1B) 400cc is gradually added,
After stirring for 20 hours, remove the ion exchange resin,
An aqueous solution of acidic alumina colloid was obtained.

The average particle size of the colloidal particles dispersed in this aqueous alumina colloidal solution was 50 nm. The obtained acidic alumina colloidal aqueous solution is concentrated to obtain 2 as an oxide.
The colloidal solution was 0% by weight and had a pH of 4.8.

Example 1 100 g of the acidic alumina sol (solid content: 20% by weight) obtained in Reference Example 1 was mixed with 290 g of pure water, and a strong basic anion exchange resin (Mitsubishi 200 cc of DAIAION, SA-20A) manufactured by Kasei Co., Ltd. was gradually added, 10 g of 1% by weight sodium hydroxide was added, and stirring was continued for 10 hours. Then, the ion exchange resin was removed to obtain an aqueous alkaline alumina colloid solution.

The average particle size of the colloidal particles dispersed in this aqueous colloidal solution was 40 nm. The crystal form of the colloidal particles was δ form, which was the same as that before the treatment. The obtained alkaline alumina colloid aqueous solution was concentrated to obtain a 20 wt% colloidal solution as an oxide.

The preparation conditions of the colloidal solution thus prepared are shown in Table 1 together with the following Examples 2 to 6 and Comparative Example 1.
Shown in The properties of this colloidal solution and colloidal particles were measured and observed by the following methods, and the results are shown in Tables 2 and 3.
, Respectively.

(1) Average Particle Size of Colloidal Particles The colloidal aqueous solution was diluted with pure water and measured using a centrifugal sedimentation type particle size distribution measuring device (CAPA-700, manufactured by Horiba, Ltd.).

(2) Particle size distribution of colloidal particles It was measured by the same measuring device as above. The symbols in Table 3 have the following meanings. ○ ・ ・ ・ Sharp particle size distribution △ ・ ・ ・ Broad particle size distribution × ・ ・ ・ Very broad particle size distribution

(3) Coefficient of variation of colloidal particles: Measured with the same measuring device as above. However, coefficient of variation (%) =
(Standard deviation / average particle diameter) × 100.

(4) Loss on ignition of colloidal particles One sample was prepared by drying an aqueous colloidal solution at 110 ° C. for 20 hours.
The weight loss was determined by firing at 000 ° C for 1 hour.

(5) Crystal form of colloidal particles After the aqueous colloidal solution was dried by a freeze dryer, it was heated to 110 ° C.
The sample dried at 20 ° C. for 20 hours was measured using a high-power X-ray diffractometer (RINT-1400, manufactured by Rigaku Denki) under the conditions of Cu tube, 60 KV and 200 mA, and JCPD
The crystal form was qualified using S software.

(6) Particle shape of colloidal particles A sample obtained by diluting colloidal particles with distilled water was observed using a transmission electron microscope (H-800 manufactured by Hitachi, Ltd.).

(7) Absorbance of colloidal solution The colloidal solution was diluted with pure water to adjust the concentration of alumina to 0.5.
The weight% of the sample was measured with a spectrophotometer (U-2000, manufactured by Hitachi, Ltd.).

(8) Dispersion stability of colloidal solution A sample having a concentration of alumina of 1% by weight was prepared by diluting the aqueous colloidal solution with pure water at 1000 rpm with a small centrifuge (H-18 manufactured by Domestic Centrifuge). Centrifugation was performed for 30 minutes. The symbols in Table 2 have the following meanings. ○: Colloidal solution does not settle and separate ×: Colloidal solution does not settle and separate

(9) Change with time of colloidal solution A colloidal aqueous solution was allowed to stand in a constant temperature bath at 70 ° C. for one month, and a sample was diluted with pure water, and a centrifugal sedimentation type particle size distribution analyzer (Horiba Seisakusho, CAPA-700) was used. ) Was used for the measurement. The symbols in Table 2 have the following meanings. ◯: Within ± 20% of the average particle size immediately after preparation Δ: Within ± 50% of the average particle size immediately after preparation ×: With respect to the average particle size immediately after preparation More than ± 50%

(10) Viscosity of colloidal solution The colloidal aqueous solution was diluted with distilled water to adjust the alumina concentration to 10
The weight% of the sample was measured with an Ostwald viscometer at 25 ° C.

(11) Specific surface area of fine alumina powder After the colloidal aqueous solution was dried by a freeze dryer, it was heated to 110 ° C.
The sample dried for 20 hours was measured by a nitrogen adsorption method (BET method) using a specific surface area measuring device (Multisorb 12 manufactured by Yuasa Ionics).

(12) Zeta Potential of Alumina Colloid Particles An ultrasonic zeta potential measuring device (ESA-800 manufactured by Matec) was used to dilute the colloidal aqueous solution with distilled water to have an alumina concentration of 2% by weight and a pH of 10.5. )
Was measured by

Example 2 1000 g of acidic alumina sol (solid content concentration: 20% by weight, average particle size: 20 nm, main crystal form: δ form) prepared in the same manner as in Reference Example 1 and 6800 g of pure water at 50 ° C. While stirring, 2000 cc of a strongly basic anion exchange resin (manufactured by Mitsubishi Kasei, DAIAION, SA-10A) was gradually added thereto, and then 200 g of 1% by weight tetramethylammonium hydroxide was added, followed by stirring for 16 hours. It was Then, after cooling to room temperature, the ion exchange resin was removed to obtain an alkaline alumina colloid aqueous solution.
This colloidal aqueous solution is concentrated to 20% by weight as an oxide.
Was used as the colloidal solution.

Example 3 400 g of ethylene glycol was added to 500 g of the aqueous alumina colloid solution (solid content 20% by weight) obtained in Example 2.
Was added and solvent substitution was carried out at 90 ° C. with a rotary evaporator to obtain an alumina colloidal solution containing 20% by weight of ethylene glycol as a dispersion medium as an oxide.
This colloidal solution was diluted with distilled water so as to be 1% by weight as an oxide, and then 1000 rpm with a small centrifuge.
After 30 minutes of centrifugation, no precipitation of colloidal particles was observed.

Example 4 1000 g of acidic alumina sol (solid content concentration: 20% by weight, average particle size: 60 nm, main crystal form: γ type), pure water 8950 g, and 4% by weight water prepared by the same method as in Reference Example 1 While stirring 50 g of potassium oxide at 50 ° C., a strong basic anion exchange resin (manufactured by Mitsubishi Kasei, DAIAIO
N, SA-10A) 1000 cc was gradually added, and 20
Stir for a period of time. Then, after cooling to room temperature, the ion exchange resin was removed to obtain an alkaline alumina colloid aqueous solution. This colloidal aqueous solution was concentrated to give a 30% by weight colloidal solution as an oxide.

Example 5 While adding 400 g of ethyl alcohol to 500 g of the aqueous alumina colloid solution (solid content 20% by weight) obtained in Example 4, an ultrafiltration membrane (SIP-10 manufactured by Asahi Kasei Kogyo Co., Ltd.) was used.
Solvent substitution was performed in 13) to obtain an alumina colloidal solution containing 20 wt% of ethyl alcohol as a dispersion medium as an oxide. After diluting this colloidal solution as an oxide to 1% by weight with distilled water, 100% with a small centrifuge.
After centrifugation at 0 rpm for 30 minutes, no precipitation of colloidal particles was observed.

Example 6 100 g of acidic alumina sol (solid content concentration: 20% by weight, average particle size: 110 nm, main crystal form: mixture of α form and θ form) prepared by the same method as in Reference Example 1 and 295 g of pure water And 5 g of 1% by weight lithium hydroxide were stirred at 50 ° C., and a strong basic anion exchange resin (manufactured by Mitsubishi Kasei, D
(AIAION, SA-10A) 500 cc was gradually added, and the mixture was stirred for 20 hours. Then, after cooling to room temperature, the ion exchange resin was removed to obtain an alkaline alumina colloid aqueous solution. This colloidal aqueous solution was concentrated to give a 40% by weight colloidal solution as an oxide.

Comparative Example 1 While stirring 100 g of the acidic alumina sol of Reference Example 1 and 250 g of pure water at room temperature, 50 g of 1% by weight sodium hydroxide was added, and stirring was continued for 10 hours. Then, while adding pure water, the ultrafiltration membrane (Asahi Kasei Kogyo, SIP-
In 1013), the product was washed until the electric conductivity became 3 mS / cm and then concentrated to obtain a colloidal solution of 20 wt% as an oxide. When this solution was allowed to stand for a while, precipitation of agglomerated alumina colloid particles was observed, and a stable colloid aqueous solution could not be obtained.

[0057]

[Table 1] Preparation of colloidal solution Preparation condition Mixing ratio Solid concentration of alkali pH (* 1) Type Addition ratio (* 2) (* 3) (* 4) Example 1 10 NaOH 0.64 × 10 ^-2 5 10.9 Example 2 10 TMAH 0.56 x 10 ^-2 2.5 10.6 Example 4 5 KOH 0.91 x 10 ^-2 2 11.1 Example 6 25 LiOH 0.53 x 10 ^-2 5 10.5 Comparative Example 1-NaOH 0.38 x 10 ^-1 5 11.5 (* 1) Mixing ratio = Ion exchange resin (cc) / Al ₂ O ₃ (g) (* 2) Addition ratio = Alkali equivalent / Al equivalent (* 3) Solid concentration of acidic alumina sol (wt% ) (* 4) pH of alkaline alumina sol

[0058]

TABLE 2 Co B A de soluble liquid sexual shaped solids Absorbance dispersion time ζ potential pH Viscosity Concentration 8 00nm 5 60nm 4 00nm Stability Stability Example 1 20 wt% of the 0.1 0.4 1.7 ○ ○ -22mV 10.5 4cp embodiment Example 2 20 0.1 0.3 1.0 ○ ○ -21 10.4 4 Example 4 30 0.1 0.3 1.6 ○ ○ -29 11.1 5 Example 6 40 0.9 1.1 1.2 ○ ○ -24 10.5 2 Comparative Example 1 20 1.1 1.9 2.8 × × -14 10.6 13

[0059]

[Table 3] Properties of colloidal particles Average particle size fluctuation ratio table Weight Crystalline particles Particle size distribution coefficient Area reduction shape Example 1 50nm ○ 40% 120m ² / g 2.3% δ chain Example 2 20 ○ 50 131 2.2 δ Dice Example 4 50 ○ 40 310 5.8 γ Fibrous Example 6 100 ○ 30 20 0.9 α, θ Dice Comparative Example 1 550 × 36 112 2.3 δ Chain

[0060]

EFFECT OF THE INVENTION The alkaline alumina sol according to the first aspect of the present invention uses crystalline alumina fine particles as a dispersoid, is stable in an alkaline region of pH 8 or more, and is excellent in transparency. Various applications can be applied to other uses.

In the method for producing an alkaline alumina sol according to the second aspect of the present invention, since alkali is regenerated and acts on alumina repeatedly, it is possible to sufficiently peptize the alumina fine particles even if the amount of alkali added to alumina is small. , Economical as a manufacturing process. In addition, it is possible to prepare an alkaline alumina sol having high dispersion stability, which can be said to be an excellent manufacturing method.

Claims (2)

[Claims] 1. Alumina fine particles are γ, η, δ, ρ,
An alkaline alumina sol characterized by comprising a single crystal or a plurality of crystals selected from χ, θ, κ, and α forms. 2. γ, η, δ, ρ, χ, θ, κ, and α
A method for producing an alkaline alumina sol, which comprises contacting an acidic alumina sol containing cationic alumina fine particles composed of single or plural crystals selected from the form with an anion exchanger in the presence of an alkali in an aqueous phase. .