Low temperature sintering of high wear resistant alumina ceramic granulation powder
Alumina ceramic is a kind of ceramic material with alumina as the main raw material. Because of its high mechanical strength, low high frequency dielectric loss, high temperature insulation resistance, chemical corrosion resistance and other excellent properties, as well as a wide range of raw materials, relatively cheap price and other advantages, alumina ceramics has been widely used in electronics, machinery, chemical industry, metallurgy, aerospace and other industries, and has become the most widely used in the world Large oxide ceramic materials.
However, the melting point of alumina is as high as 2050 ℃, which makes it difficult to sinter because the sintering is based on the material migration under the action of surface tension, and alumina has larger lattice energy and more stable structural state, so the particle migration needs higher activation energy, that is, lower activity. For this reason, alumina ceramics need to use high temperature heater and high-grade refractory materials as kiln and kiln furniture, which limits its production and wider application to a certain extent. Therefore, how to reduce the sintering temperature of alumina ceramics, thereby reducing the production cost, has always been a subject of concern and urgent need to be solved in the industry.
At present, the most effective way to reduce the sintering temperature of alumina ceramics is to use monodisperse ultrafine alumina powders with small grain size, large specific surface area and high surface activity as raw materials. Because of the short diffusion distance between particles, only low sintering temperature and activation energy are needed. According to C. herring conversion rule (see table for the corresponding values of specific particle size and sintering temperature), if the particle size can be reduced to less than 20nm, the sintering temperature can be reduced to below 1000 ℃, and the grain size of Al2O3 ceramics can be reduced to less than 100nm.
However, the superfine alumina powder also has its own limitations. Due to the large surface energy, these ultra-fine powders are easy to agglomerate into irregular shapes, resulting in poor fluidity. When pressed, the mold can not be filled evenly. Finally, the problems such as cavity, non compact corner, spalling, elastic aftereffect and so on appear in the ceramic body. Finally, the quality of the sintered body is affected. Therefore, in order to avoid these problems, it is necessary to process the raw material powder into granulated powder with ideal shape, size and reasonable particle size distribution, so as to ensure the sintering density after porcelain forming.