JPH06263436A - Production of fine acicular boehmite particles - Google Patents

Abstract

PURPOSE:To reduce treatment temp., to accelerate the crystallization of boehmite and to reduce the cost of production by hydrolyzing a water-soluble aluminum compd. and hydrothermally treating a prepd. pseudo-boehmite sol in coexistence with hydrogen peroxide. CONSTITUTION:One or more kinds of water-soluble aluminum compds. selected among inorg. acid salts, lower fatty acid salts, alkoxides and modified alkoxides each having a functional group substd. for part of alkoxy groups are hydrolyzed in an alkaline soln. contg. hydrogen peroxide and/or a metal peroxide and the resulting aluminum hydroxide is oxidized with oxygen generated at the time of the reaction to obtain amorphous pseudo-boehmite. Impurity ions such as Na and K ions are removed from the pseudo-boehmite by washing and then the pseudo-boehmite is dispersed in water and brought into a hydrothermal reaction in a perfectly dispersed state at 150-250 deg.C in the presence of hydrogen peroxide in a closed system to obtain high purity crystalline acicular fine powder.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing fine needle-shaped boehmite powder.

[0002]

2. Description of the Related Art Conventionally, as a method for producing boehmite,
A method is employed in which aqueous ammonia is added to an aluminum salt to precipitate gel aluminum hydroxide, which is washed, dehydrated and dried, and then heat treated at 200 to 500 ° C.

[0003]

However, according to this method, it is difficult to obtain acicular boehmite fine particles because the aluminum hydroxide cake is in the state of agglomerated particles. In addition, aluminum hydroxide is 200 to 500
When heat-treated at a temperature of ℃, not only boehmite but also diaspore of the same molecular formula is produced at the same time, so high-purity boehmite cannot be obtained.
When it is performed at a high temperature of 500 ° C., there is a problem that a part of the produced diaspore may change to α-Al ₂ O ₃ .

The present invention is therefore aimed at obtaining pure, acicular, boehmite fine powders.

[0005]

[Means for Solving the Problems] As a means for solving the above problems, the present invention hydrolyzes a water-soluble aluminum compound in an alkaline solution containing hydrogen peroxide and / or an alkali metal peroxide to produce a product. The above pseudo boehmite sol is hydrothermally treated in the presence of hydrogen peroxide.

As the water-soluble aluminum compound,
At least one compound selected from the group consisting of an inorganic acid salt, a lower fatty acid salt, an alkoxide and a modified alkoxide in which a part of the alkoxy group is substituted with another functional group may be used. Examples of the inorganic acid salt include aluminum chloride, aluminum sulfate and aluminum nitrate,
A typical example of the lower fatty acid salt is acetate. Furthermore, as the alkoxide, for _{example, Al (OCH 3) 3,} Al (OC 2 H 5) 3, Al (OC 3 H 7 -
n) ₃ , Al (OC ₃ H ₇ -i) ₃ , Al (OC ₄ H ₉ ) ₃ , Al (OC _{4
H 9 -i) 3, Al (} OC 4 H 9 -sec) 3, Al (OC 4 H 9 -tert)
₃ are typical examples, but the present invention is not limited to these.

As the alkaline solution, an aqueous solution of at least one hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide and lithium hydroxide and hydrogen peroxide, or sodium peroxide,
An aqueous solution of at least one alkali metal peroxide selected from the group consisting of lithium peroxide and potassium peroxide may be used.

[0008]

In the present invention, when a water-soluble aluminum compound is hydrolyzed in an alkaline solution containing hydrogen peroxide or an alkali metal peroxide, aluminum hydroxide is produced. Oxidizing action of oxygen generated during the synthesis reaction. In response, AlOOH, that is, amorphous pseudo-boehmite is generated. This pseudo-boehmite has extremely low cohesiveness as compared with aluminum hydroxide, and it is washed with Na ions and K
After removing impurity ions such as ions and Li ions,
When dispersed in water, hydrothermal treatment is performed in a completely dispersed state. If this hydrothermal treatment is carried out in the presence of hydrogen peroxide in a closed system, the oxygen gas generated by the decomposition of hydrogen peroxide will significantly increase the pressure in the reaction system and promote the crystallization of boehmite, which is dispersible. Combined with the hydrothermal treatment of good pseudo-boehmite, it enables the hydrothermal treatment at a low temperature and contributes to the production of highly crystalline acicular boehmite fine particles free from aggregation.

The temperature of the hydrothermal treatment is 150 to 250 ° C.
The reason is that crystallization is not sufficiently carried out at a temperature of less than 150 ° C. and is less than 90%, and if it exceeds 250 ° C., a highly heat-resistant reaction vessel is required, resulting in an increase in cost in terms of energy and equipment. Because.

[0010]

Example 1 0.1 mol of aluminum sulfate was added to 100 parts of pure water.
After dissolving in 0 ml and adding 70 ml of 30% hydrogen peroxide solution, 28% ammonia water was added with high speed stirring to adjust the pH.
Was set to 9, and a pseudo-boehmite sol was synthesized. After washing the obtained pseudo-boehmite sol 5 times with pure water, 1000 ml
Disperse in 250 ml of pure water and collect 250 ml of it
Place in a 0 ml Teflon container and add 30% hydrogen peroxide solution 1 to it.
2 ml was added. Next, this Teflon container was placed in an autoclave and subjected to hydrothermal treatment at 200 ° C. for 8 hours. After completion of the reaction, the mixture was allowed to cool, and after the temperature dropped to 50 ° C., the Teflon container was taken out and solid-liquid separation was performed using a centrifugal separator.
The generated powder is dehydrated by displacement with ethyl alcohol, and 5
It was dried at 0 ° C. to obtain a dry powder.

X-ray diffraction analysis of the obtained powder revealed that
The product was confirmed to be boehmite. The shape of the obtained powder was observed by TEM analysis.
It was a needle-like crystal having a thickness of 35 nm, a length of 360 nm and an aspect ratio of about 10.

[0012]

As is apparent from the above description, according to the present invention, a water-soluble aluminum compound is hydrolyzed in an alkaline solution containing hydrogen peroxide or an alkali metal peroxide to give aluminum hydroxide. Amorphous pseudo-boehmite with extremely less cohesiveness was generated, and the sol was hydrothermally treated in the presence of hydrogen peroxide, so that needle-shaped boehmite fine powder can be produced without causing agglomeration, and Since hydrogen peroxide is allowed to coexist during the hydrothermal treatment, the internal pressure of the reaction system is increased and the hydrothermal treatment can be performed at a low temperature, and at the same time, the crystallization of boehmite can be promoted, which reduces the manufacturing cost. Can be achieved. Furthermore, since the reaction temperature is as low as 150 to 250 ° C., water of crystallization does not desorb from the boehmite structure,
Excellent effects such as the possibility of producing high-purity acicular boehmite fine powder without fear of transformation of boehmite into γ-Al ₂ O ₃ can be obtained.

Claims (5)

[Claims] 1. A method of hydrolyzing a water-soluble aluminum compound in an alkaline solution containing hydrogen peroxide and / or an alkali metal peroxide, and subjecting the produced pseudo-boehmite sol to hydrothermal treatment in the presence of hydrogen peroxide. And a method for producing acicular boehmite fine powder. 2. The alkaline solution is an aqueous solution containing hydrogen peroxide and at least one hydroxide selected from the group consisting of sodium hydroxide, potassium hydroxide, ammonium hydroxide and lithium hydroxide. 1. A method for producing fine needle-shaped boehmite powder. 3. The method for producing fine needle-shaped boehmite powder according to claim 1, wherein the alkaline solution is an aqueous solution of at least one peroxide selected from the group consisting of sodium peroxide, lithium peroxide and potassium peroxide. . 4. The aluminum compound is an inorganic acid salt,
The needle-shaped boehmite fine powder according to claim 1 or 2, which is at least one compound selected from the group consisting of a lower fatty acid salt, an alkoxide, and a modified alkoxide in which a part of the alkoxy group is substituted with another functional group. Production method. 5. The method for producing fine acicular boehmite powder according to claim 1, wherein the hydrothermal treatment is performed at a temperature within a range of 150 to 250 ° C.