Low Temperature Sintering Of Alumina Ceramics
However, the high melting point of alumina also leads to a higher sintering temperature during production and processing. Therefore, additives are often used to reduce the sintering temperature of alumina ceramics, and the sintering temperature of alumina ceramics is proportional to its purity.
The sintering of alumina ceramics is mainly affected by two main factors:
①The atomic radius of the alumina crystal is small and the ionic bond is strong, resulting in low diffusion difficulty and high sintering temperature;
②In the middle and later stages of the sintering process, it has a great influence on the grain growth. At this time, the grains may grow abnormally, resulting in uneven structure, and even large internal closed pores, which reduces the bonding strength between grains, resulting in a decrease in the performance of the material.
There are currently 3 main methods to reduce the sintering temperature of aluminium oxide:
①Reduce the particle size of alumina powder;
②Adopt other modern advanced sintering technology;
③Add sintering aids.
Because of its simple operation, low cost and high efficiency, sintering aids have become one of the best technologies to reduce the sintering temperature of alumina ceramics.
The electrical properties of alumina ceramics can also be significantly improved by modifying the addition process.
The sintering aid mainly forms a solid solution with the alumina matrix. Increase the lattice distortion, increase the diffusion rate, and reduce the sintering temperature of alumina ceramics.
Such additives are commonly found in MnO2, TiO2, Fe2O3, etc., which have similar lattice constants to alumina and can form different types of solid solutions with alumina. For example, Fe2O3 and Cr2O3 can form infinite solid solutions with alumina, MnO2 and TiO2 can form limited solid solutions with alumina, and most of these additives contain valence elements, and the valence effect enhances lattice distortion, particle diffusion or interface movement during sintering. It promotes lattice activation and improves the sintering properties of the matrix.
In addition, the additive itself or between the additive and the alumina matrix forms a liquid phase at high temperature, which promotes sintering through the dissolution-precipitation mechanism, and the generation of the liquid phase is the main factor to reduce the sintering temperature of alumina ceramics.
When the sintering temperature reaches the melting point or eutectic temperature of the additive, the liquid phase begins to appear, which promotes the migration and diffusion of particles in the sintered body and improves the sintering performance of alumina ceramics. Adding one or more of these additives to the matrix can form binary, ternary or more complex eutectic to obtain a stable liquid phase.
