Production process of alumina ceramics

Alumina ceramics are currently divided into two types: high-purity type and ordinary type. The high-purity alumina ceramic system is a ceramic material with an Al2O3 content of over 99.9%. Due to its high sintering temperature of 1650-1990 ℃ and transmission wavelength of 1-6 μ m. Generally, molten glass is made to replace platinum crucibles: its transparency and resistance to alkali metal corrosion are used as sodium lamp tubes; It can be used as an integrated circuit substrate and high-frequency insulation material in the electronic industry. The ordinary alumina ceramic series is divided into 99 porcelain, 95 porcelain, 90 porcelain, 85 porcelain and other varieties according to the different Al2O3 content. Sometimes, those with an Al2O3 content of 80% or 75% are also classified as the ordinary alumina ceramic series. Among them, 99 alumina ceramic materials are used for making high-temperature crucibles, refractory furnace tubes, and special wear-resistant materials, such as ceramic bearings, ceramic seals, and water valve plates; 95 alumina porcelain is mainly used as corrosion-resistant and wear-resistant components; Due to the frequent incorporation of some talc into 85 ceramics, their electrical properties and mechanical strength are improved. They can be sealed with metals such as molybdenum, niobium, and tantalum, and some are used as vacuum devices. The production process is as follows:

Prepare the incoming aluminum oxide powder into powder materials according to different product requirements and forming processes. The particle size of the powder is within 1 μ If the manufacturing of high-purity alumina ceramic products is below m microns, in addition to alumina purity of 99.99%, ultrafine grinding and uniform particle size distribution are also required. When using extrusion molding or injection molding, binders and plasticizers need to be introduced into the powder, usually thermoplastic plastics or resins with a weight ratio of 10-30%? The organic binder should be evenly mixed with the alumina powder at a temperature of 150-200 ℃ to facilitate the molding operation. The powder raw materials formed by hot pressing process do not require the addition of binders. If semi-automatic or full-automatic dry pressing molding is adopted, there are special process requirements for the powder, and the powder needs to be treated by spray granulation to make it spherical, so as to improve the powder fluidity and facilitate automatic filling of mold wall during molding. In addition, to reduce the friction between the powder and the mold wall, it is necessary to add 1-2% lubricant? Like stearic acid? And adhesive PVA.

For dry pressing, the powder needs to be spray granulated, in which polyvinyl alcohol is introduced as the binder. In recent years, a research institute in Shanghai has developed a water-soluble paraffin as the binder for Al2O3 spray granulation, which has good fluidity under heating. The powder after spray granulation must have good fluidity, loose density, and flow angle friction temperature less than 30 ℃. Ideal particle size ratio and other conditions are required to obtain a higher green density.

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