The Key Point of Densification of Alumina Ceramics.
When the alumina ceramic is completely densified, the light transmittance is greatly improved and becomes translucent. It can be used to replace single crystal sapphire to make high-pressure sodium lamp arc tubes, infrared optical components, microwave integrated circuit substrates and other devices. Not only that, the increase in density can also improve the mechanical properties of alumina ceramics.
Therefore, it's generally believed that there are two main ways to improve the density of alumina ceramics. Firstly, by increasing the sintering temperature or providing a reducing atmosphere, the atoms of ceramics are easy to diffuse to realize sintering at high temperature, and the gas phase of ceramics is easy to diffuse out of grains and sintered into compact ceramics.
The second is to improve the ceramic compactness through additives.
In addition, in the actual production, the selection of raw materials and production process are also the key points affecting the densification of alumina ceramics.
The finer the particle of raw material, the shorter the sintering time. This is because the finer the particles, the closer the contact between them, the shorter the diffusion path during sintering, and the larger the sintering driving force - surface energy. However, because the surface energy of the ultrafine powder particles is larger, the grain grows rapidly or abnormally in the process of high temperature sintering, and the surface activity of the ultrafine particles is relatively high, which may adsorb impurities, resulting in the impurity of the powder, and the molding will be more difficult.
In order to reduce the sintering temperature of alumina ceramics, the powder should be added with appropriate additives before sintering, so the level of mixture is also an important factor affecting the sintering body of ceramic.
The purpose of mixing is to make the powder composition uniform. If the composition distribution is not uniform, the local composition will deviate from the overall ratio, there is less local additives, alumina is difficult to sintering at low temperature, and more additives where the melting point is low, easy to appear liquid phase, grain rapid growth, eventually lead to the microstructure of the product is not uniform, resulting in low density.
