Alumina ceramic sintering process, alumina ceramic sintering methods

What are the conventional sintering methods for alumina ceramics? Conventional sintering methods cannot meet the requirements for producing transparent alumina ceramics. Common sintering methods for producing transparent ceramics include: a. atmosphere and vacuum sintering, b. hot isostatic pressing sintering, and c. spark plasma sintering.

What are the conventional sintering methods for alumina ceramics?

1. Atmosphere and Vacuum Sintering

Alumina ceramics produced by atmospheric pressure sintering typically have 1-3% residual porosity. However, sintering in a vacuum or atmosphere creates a large number of oxygen vacancies in the alumina body, accelerating the diffusion of O₂⁻ and the densification rate, making it easier to eliminate the residual porosity.

2. Hot isostatic pressing

Hot isostatic pressing (HIP) is a production technology that combines high temperature and high pressure, capable of reaching temperatures of up to 2000°C. Using high-pressure inert gas or nitrogen in a sealed container as the pressure transmission medium, the operating pressure can reach over 200 MPa. The combined effects of high temperature and high pressure eliminate closed gas holes, which are difficult to eliminate during atmospheric sintering, and produce highly transparent submicron-grade alumina ceramics. The fine grain size of the transparent alumina ceramics produced using this method results in exceptional mechanical properties.

3. Spark Plasma Sintering

Spark plasma sintering (SPS) involves placing raw material powder into a mold made of a material such as graphite. Using upper and lower punches and powered electrodes, a specific sintering power source and pressing pressure are applied to the raw material powder. The sintering process is completed through discharge activation, thermoplastic deformation, and cooling. Due to its rapid sintering capabilities and ability to achieve densification of fine ceramic structures at relatively low temperatures, SPS has been widely used in the preparation of transparent alumina ceramics in recent years.