Sintering is an important step in the production of alumina ceramics, which has great influence on the physical and chemical properties of alumina ceramics. Sintering is the process of heating powder or powder compact to a temperature below the melting point of the basic components, and then cooling to room temperature in a certain way.

Alumina ceramics is a kind of ceramic material with alumina (Al2O3) as the main body, but no matter what type of ceramic products are inseparable from the sintering process, alumina ceramics are no exception. The driving force for the sintering of alumina ceramics is mainly the change of the surface energy of the powder, that is, the surface energy of the powder decreases, the surface area decreases, and the ceramics achieve densification.

What is the conventional sintering method of alumina ceramics?

Conventional sintering methods can not meet the requirements of preparing transparent alumina ceramics. The common sintering methods for preparing transparent ceramics are: a atmosphere and vacuum sintering, b hot isostatic pressing sintering, c discharge plasma sintering, etc.

What is the conventional sintering method of alumina ceramics

1, atmosphere and vacuum sintering

Alumina ceramics prepared by atmospheric pressure sintering usually have 1~3% residual pores, and by sintering in vacuum or atmosphere, alumina blanks can produce a large number of oxygen vacancies, accelerate the diffusion of O2-, and accelerate the densification rate of the blanks, which can make the residual pores easier to eliminate.

2, hot isostatic pressing sintering

Hot isostatic pressing (HIP) is a process production technology that integrates high temperature and high pressure, and the heating temperature can reach 2000℃. By using the high-pressure inert gas or nitrogen in the closed container as the pressure transmission medium, the working pressure can reach more than 200MPa. Under the joint action of high temperature and high pressure, the closed air port which is difficult to eliminate under normal pressure sintering can be eliminated, and the submicron alumina ceramics with high transparency can be prepared. Because of the small grain size of alumina transparent ceramics prepared by this method, the mechanical properties of the ceramics are very excellent.

3, discharge plasma sintering

Discharge plasma sintering (SPS) is the raw material powder into the mold made of graphite and other materials, the use of upper and lower die punch and energized electrodes to apply specific sintering power and pressing pressure to the raw material powder, through discharge activation, thermoplastic deformation and cooling to complete the sintering process. SPS has been widely used in the preparation of alumina transparent ceramics in recent years because of its rapid sintering and the densification of fine ceramic structures at low temperatures.

Through the process of sintering densification, the material transfer can be carried out by solid phase diffusion, including surface diffusion, grain boundary diffusion, lattice diffusion, etc., so as to help you get better quality alumina ceramics.