High purity alumina refers to the purity of more than 99.99%, and the uniform size of the ultra-fine powder material. It has the characteristics of high hardness, high strength, abrasion resistance, corrosion resistance, high temperature resistance, good oxidation resistance, good insulation property, small thermal expansion coefficient, good thermal shock resistance and low dielectric loss. It is widely used in insulating materials, Products, wear-resistant materials and aerospace materials and other high-tech cutting-edge industries.
At present, high purity alumina powder preparation methods are pyrolysis, organic aluminum alkoxide hydrolysis, sol-gel method and hydrochloric acid ammonia method.
China's alumina products to industrial alumina-based, high-purity, ultra-fine alumina production has not yet reached the level of industrialization, products mainly rely on imports. With the continuous development of high-tech industries, high-quality, multi-species alumina demand continues to increase. Therefore, the study of the production of high quality alumina is promising.
1, pyrolysis method
Pyrolysis method is divided into ammonium aluminum sulfate pyrolysis method and ammonium aluminum sulfate thermal decomposition method.
(NH4) 2 SO4 was prepared by dissolving H2SO4 to dissolve Al (OH) 3 to obtain NH2 (SO4) 3 solution. NH4Al (SO4) 2 was obtained by the reaction of NH4 (2) (SO4) 2 dehydration and then in the high temperature furnace thermal decomposition of AL2O3
Ammonium sulfate ammonium pyrometallurgical production of alumina with stable operation, high purity products, alumina than the surface characteristics of large, and the production of ultra-fine powder particles smaller, reunited lighter. But in the production process of greater impact on the environment, will produce a large number of SO2, SO3 and NH3 emissions. Due to the complexity of the production process, serious environmental pollution, the production process is gradually being eliminated.
(2) ammonium aluminum carbonate pyrolysis method is the current high purity alumina powder industrial production of the main application technology, the principle is: the reaction temperature of 35 ℃, ammonium bicarbonate and ammonium sulfate by material ratio of 1: (10 ~ 15). The high purity α-Al2O3 powder with purity greater than 99.99%, average particle size of 0.35μm and specific surface area of 10m2 / g can be obtained by thermal decomposition of aluminum carbonate.
Aluminum carbonate pyrolysis method to overcome the pollution of SO2 and SO3, but the resulting particle size and agglomeration than ammonium sulfate pyrolysis method is poor, and the production process is long, high cost;
The key to the ammonium aluminum carbonate pyrolysis process is the synthesis of basic ammonium aluminum carbonate, which directly affects the properties and quality of high purity ultrafine alumina and its finished products.
2, organic aluminum alkoxide hydrolysis method
Organic Alcohol Alcohol Hydrolysis is also the main application process for mass production of high purity alumina in China. The method comprises the following steps: the metal aluminum is reacted with the organic alcohol to produce the precursor metal alcohol, the precursor metal alkoxide is dissolved in water or an organic solvent to form a uniform solution and hydrolyze (alcoholysis) reaction; the hydrolyzate is condensed to about 1 nm Of the sol particles, and then gathered into a gel, then the gel dry, calcined, and finally get inorganic nanoparticles.
3, sol-gel (Sol-gel) method
The sol-gel method is the first principle that the inorganic salt or metal alkoxide is directly polymerized to form a sol by hydrolysis, then the sol is gelatinized by adding water, and then calcined at high temperature after drying to obtain high purity alumina powder.
Sol-gel method is one of the most important means to prepare high purity alumina powder at lower temperature. The disadvantage is that the phenomenon of hard agglomeration occurs during the preparation process, which requires the addition of surfactants to inhibit the production of aggregates. If the use of raw materials for the aluminum salt, in the reaction process and calcination will produce corrosive gases, polluting the environment; if the use of raw materials for the organic alkoxide, there is a high cost, strong activity is not easy to store shortcomings.
4, hydrochloric acid ammonia method
Hydrochloric acid aqueous ammonia preparation of high purity alumina powder is the industrial aluminum hydroxide or sodium aluminate and hydrochloric acid in the sealed reaction tank to get aluminum chloride solution; aluminum chloride solution after filtration, by evaporation, crystallization The aluminum hexahydrate aluminum trichloride crystals are dehydrated under the protection of hydrogen chloride gas to obtain anhydrous aluminum trichloride powder. The aluminum trichloride powder is purified by sublimation in a vacuum furnace to obtain the purity 99.999% aluminum trichloride; high purity aluminum trichloride dissolved in aqueous ammonia solution, after concentration, crystallization, filtration, drying obtained high purity aluminum hydroxide crystal; aluminum hydroxide crystal after high temperature calcination to produce a purity of 99.993% High purity α-Al2O3 powder having an average particle diameter of 0.3 μm and a specific surface area of 21 m2 / g.
We're Here to Help