Manufacturing process of high-purity alumina
High purity aluminum oxide is a white micro powder with uniform particle size, easy dispersion, stable chemical properties, moderate high-temperature shrinkage, and good sintering performance. It has optical, electrical, magnetic, thermal and mechanical properties unmatched by ordinary aluminum oxide powder, and has been widely used in high-tech materials and modern industrial fields.
(1) Improved Bayer method
It is difficult to remove impurities in the traditional Bayer method to prepare alumina. The improved method mainly improves the preparation of sodium hydroxide and the removal of sodium. After the desilication and iron removal of sodium aluminate, the decomposition conditions are adjusted to obtain high-purity aluminum hydroxide. Aluminum hydroxide precipitates slowly in the preparation process, effectively reducing the occurrence of abnormal crystal nuclei, reducing the mixing of sodium and silicon impurities, and then calcines and grinds at high temperature to obtain high-purity aluminum oxide. The raw materials used in the modified Bayer process are cheap and easy to obtain, and the preparation process has zero pollution.
(2) Thermal decomposition of inorganic aluminum salt
According to different raw materials, it can be divided into ammonium aluminum sulfate pyrolysis and ammonium aluminum carbonate pyrolysis. Ammonium aluminum sulfate pyrolysis method is to dissolve aluminum hydroxide with sulfuric acid to obtain aluminum sulfate, then add ammonium sulfate, adjust the pH and composition to obtain ammonium aluminum sulfate, remove impurities through multiple crystallization, and calcine and decompose it at high temperature. Ammonium aluminum sulfate cracking has the advantages of simple operation, high product purity, non caking and mature technology, which is suitable for industrial production. Aluminum ammonium carbonate pyrolysis is an improved method based on ammonium aluminum sulfate pyrolysis. The improved pyrolysis method of ammonium aluminum carbonate avoids the emission of pollutants, and the product particles are evenly distributed.
(3) Hydrolysis of Organic Aluminum Alcohols
The hydrolysis of organic aluminum alkoxide is that the catalyst promotes the reaction of aluminum and organic alcohol to generate aluminum alkoxide solution, which is purified, hydrolyzed and calcined to generate high-purity aluminum oxide. This method will not produce harmful gases and pollution. Organic alcohol can be recycled and high-purity aluminum oxide has high purity.
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