Alumina ceramics is a ceramic material with alumina (Al2O3) as the main body. It is one of the inorganic non-metallic materials. The alumina ceramics produced by UNIPRETEC have good thermal conductivity, mechanical strength and high temperature resistance. The application has become more and more extensive, satisfying the needs of daily use and special industries. A very important part of alumina ceramic production is sintering, which has a great influence on the physical and chemical properties of alumina ceramic products. The following is a brief introduction about the factors that affect the sintering of alumina ceramics.
1. According to the needs, select the appropriate forming method to obtain a green body with uniform microstructure and uniform phase distribution. By controlling and eliminating defects in the forming process, the sintering temperature and the shrinkage rate of the green body can be effectively reduced, and the densification process can be accelerated, and the amount of machining of sintered products can be also reduced.
2. Influence of sintering system
Properly increasing the sintering temperature is conducive to diffusion and sintering, speeds up the sintering speed, and promotes densification. The control of the heating rate is very important for the sintering of alumina ceramics. Usually it should be slow below 600℃, and should be strictly controlled and as slow as possible during the medium temperature stage of 1,000-1,500℃; the heating speed can be accelerated above 1500℃ to prevent the appearance of coarse crystals. The pressure also promotes the reduction of the gap between the powder particles and the reduction of the diffusion distance.
3. Influence of sintering atmosphere
The atmosphere has a great influence on the sintering of alumina ceramics, and a suitable atmosphere contributes to densification. Generally speaking, the lower the partial pressure of oxygen ions in the atmosphere, the more favorable the sintering of alumina. Sintering in a hydrogen atmosphere is beneficial to eliminate closed pores due to the small radius of hydrogen atoms and easy diffusion, and a sintered body with a density close to the theoretical density can be obtained. The CO-H2 atmosphere can easily lose oxygen ions in the alumina lattice, form vacancies, and accelerate the diffusion of cations, thereby effectively promoting sintering and obtaining good density, which is easier to sinter than hydrogen atmosphere.
4. Influence of additives
Because the alumina ceramic billet has a high melting point, it is difficult to sinter. If some additives are added, the sintering performance can be improved and sintering can be promoted.
5. Influence of sintering method
The correct choice of sintering method is the key to making alumina ceramics have an ideal structure and predetermined properties. A suitable sintering method can effectively reduce the sintering temperature. Al2O3 ceramics can be sintered at normal pressure above 1,600°C and hot-pressed (20MPa) sintered at about 1,500°C to obtain products close to the theoretical density, while high-temperature isostatic pressure sintering (400MPa) has reached densification at about 1,000°C.
