Ultrafinealuminum hydroxideThe preparation methods are physical and chemical methods. The physical method usually refers to the mechanical method, and the chemical law includes the method of division, sol-gel method, precipitation method, hydrothermal synthesis method, carbon method, high gravity method and so on.

(1) Mechanical method

The mechanical method is to grind the washed and dried non-industrial grade aluminum hydroxide into ATH powder with fine particle size by stirring mill and air flow mill. The ATH powder produced by this method has irregular shape, coarse particle size and wide distribution, generally in the range of 5~15 μm, and poor product performance.

The aluminum hydroxide produced by this method is used in the production of wires and cables, and its processability, ductility and flame retardancy are far less than those produced by chemical methods. Although the mechanical method has simple preparation process and low experimental cost, the product has high impurity content and uneven particle size distribution, so it cannot be widely used.

(2) Methods of classification

The core of the commonly used seed method is to add ultrafine ATH seed crystals to the prepared sodium aluminate solution to prepare purer and finer ATH powders. Among them, the quality of seed crystal is an important factor affecting the particle size of ATH powder.
 

(3) Sol-gel method.

This method is mainly through the hydrolysis of aluminum compounds in a certain water bath temperature, stirring speed and pH value under the conditions of the formation of aluminum hydroxide colloid, and then under certain conditions into a gel, and finally by drying and grinding of aluminum hydroxide powder with smaller particle size.

(4) Precipitation method

There are two types of precipitation methods: direct and uniform precipitation. Direct precipitation refers to the addition of precipitant in aluminate solution to produce high-purity ultrafine aluminum hydroxide under certain conditions.

During the precipitation process, the mixing degree of precipitant and solution is the key factor affecting the properties of the final product. The uniform precipitation method is different from the direct precipitation, and its precipitation growth rate is slower.

(5) Hydrothermal synthesis method

The hydrothermal method is a method for preparing ATH by heating a closed reaction vessel and reacting the raw materials in an organic solvent medium at high temperature and high pressure.

(6) Carbon method

Carbon method is to pass CO2 into sodium aluminate solution, by controlling the reaction conditions to prepare aluminum hydroxide.