Three preparation techniques of high purity alumina
Sapphire is a single crystal of alumina (-Al2O3), also known as corundum. Sapphire, as an important technical crystal, has been widely used in many fields of science and technology, national defense and civil industry. Over the past two years, there have been more than 40 enterprises investing in the production of sapphire crystal in China. The sapphire enterprises in China will continue to grow, and many foreign enterprises will also come to China to establish production bases. The LED market in the future will flock to China. Sapphire long crystal on alumina demand will be increasing, high purity alumina market prospect is very considerable.
1) Cholinergic aluminum hydrolysis:
At present, domestic manufacturers using this method mainly include Hebei Pengda and Chongqing Tongtai. The production process is as follows: Firstly, aluminum blocks with a purity of 99.95% are made into aluminum foil with a thickness of about 0.1 mA by cutting tools, and choline chloride is converted into choline by using strong anion exchange resin. Then a certain amount of aluminum foil was added to the choline solution with a concentration of 0.1 ~ 0.2M for the reaction. The reaction temperature of the hydrolysis reaction shall be controlled at 80. C. During the reaction, the reaction speed was determined according to the speed of hydrogen escaping monitored. When the reaction speed was very low or stopped, the slurry was removed for solid-liquid separation, and at the same time, the refined aluminum was added periodically to make the above process circulate. Fine alumina powder can be obtained by filtering, spray drying and calcining the alumina produced by hydrolysis reaction.
There is no purification process in the production of this technology. Aluminum blocks are made of aluminum foil with cutting tools, and impurities are easily brought in. Product purity is generally only 99.95%- 99.98%.
2) Aluminum ammonium sulfate pyrolysis
In the pyrolysis process of aluminum ammonium sulfate, aluminum sulfate solution was prepared by dissolving aluminum hydroxide with sulfuric acid, then ammonium sulfate was added into the solution to react with the solution to produce ammonium vanadium, and then refined ammonium vanadium was obtained by repeated recrystallization according to the requirements of purity. Then the refined ammonium vanadium will be obtained at 1250. The aluminum oxide powder is obtained by decomposition under C.
Although the process is relatively simple and the cost is relatively low, this method is being phased out due to its long production cycle, thermal dissolution and serious environmental pollution caused by SO3 and NH3 generated in the decomposition process.
3) Alcohol-aluminum hydrolysis
The organic alcohol brine hydrolysis, isopropanol aluminum hydrolysis, is the main industrial production technology for the preparation of high purity alumina oxide powder for sapphire abroad. The high purity ultrafine alumina powder was prepared by organic synthesis of aluminum and isopropanol with catalyst through synthesis, purification, hydrolysis and calcination. The alumina powder produced by this method is of high purity and small particle size. The process has strong control over the purity of the product, and the product is of high purity, which can meet the requirements of sapphire long crystal. The purification can be divided into distillation and rectification, in which rectification USES 8-12 column plates and the purity can reach 99.999%. The purity of distillation is somewhat lower than that of rectification.
