Production method of ultrafine aluminum hydroxide powder

The production of ultrafine aluminum hydroxide micropowder is divided into two categories: mechanical method and chemical method. Chemical methods include sodium aluminate solution seed decomposition method, metal alcohol salt method, microemulsion method, hypergravity method and water thermocouple method, etc. However, except for sodium aluminate solution seed decomposition method, which is low in cost and suitable for industrial production, several other chemical preparation processes are not convenient for industrialization due to high equipment requirements and high production costs.

1. Mechanical crushing method

The mechanical pulverization method is to process ordinary metallurgical-grade aluminum hydroxide into aluminum hydroxide micropowder after washing and drying. The aluminum hydroxide micropowder produced by the mechanical method has coarse particle size, wide particle size distribution, irregular particle morphology, and the largest particle can reach 15-20μm. The product has poor performance. In the production process of wires and cables, the processing performance is poor, the flexural strength and elongation are low, and its oxygen index is smaller than that of chemical aluminum hydroxide, and the flame retardant effect is poor.

2. Microemulsion method

W/O type microemulsion is a transparent or translucent thermodynamically stable system composed of water, water-insoluble organic solvent, surfactant and cosurfactant. Composition and properties of water, octane phenol polyoxyethylene ether, n-hexanol, cyclohexane microemulsion system, when the weight ratio of n-hexanol and octane phenol polyoxyethylene ether is 2:3, the microemulsion system has a wide and stable microemulsion phase region, which is an ideal system for preparing ultrafine particles. In this system, the ultrafine particles of aluminum hydroxide prepared by ammonia precipitation have an average particle size of 6 nm and have good dispersibility.

3. Sol-gel method

The sol-gel method is currently a method that has been widely studied and applied in the preparation of ultrafine powders. Using aluminum sulfate as raw material, under the reaction conditions of pH 3.5, sol concentration of 0.4mol/L, 0.3% water-soluble polymer dispersant, and reaction temperature of 80 ° C, a stable sol was obtained. After 5 hours of heat treatment at 100-150 ° C, ultrafine aluminum hydroxide particles were prepared with an average particle size of 70 nm, good dispersibility and uniform particle size distribution.

4. Metal alkoxide method

Under the action of an appropriate catalyst, isopropylaluminum is hydrolyzed in the H2O-NH3 system, and the resulting precipitation is filtered and dried to obtain ultrafine aluminum hydroxide particles with an average particle size of 90 nm. The advantage of this method is that the operation is simple and the obtained sample particle size is small; the disadvantage is that the sample agglomeration is serious and the cost of the organic raw materials used is high.

5. Aluminate decomposition method

Sodium aluminate seed decomposition method can be divided into two types: self-decomposing seed decomposition method and mechanical crushing seed decomposition method according to different seeds. The average particle size of the mechanical seed decomposition method product is relatively fine, which can reach 2 μm, but because the seeds used for decomposition are mechanically crushed, the finished product cannot avoid large particles of 10 μm or even 15 μm, which is a fatal defect in the production process of flame retardant materials, especially in the production process of wires, cables and engineering plastics. The product prepared by the two-stage decomposition method of self-decomposing seeds has fine particle size, the average particle size can be less than 1 μm, and the particle size distribution is narrow. The product has the advantages of high purity, good whiteness, regular particle uniformity, and easy dispersion.

The above are the production methods of several common ultrafine aluminum hydroxide micropowders. (jwl)