Densification process of a 95% alumina ceramic during the intermediate stage of sintering in air, and O2

Abstract

Sintering in pure O2 can enhance the densification of oxide ceramics during the final stage of sintering, but little attention has been paid on its effect on the densification process during the intermediate stage of sintering. This paper measures the shrinkage processes of a 95% alumina ceramic during the intermediate stage of sintering in air and O2 at different heating rates, and analyzes them by the master sintering curve (MSC) theory. It is found that the densification of the alumina ceramic sintered in air is obviously rapider than that in O2 at the heating rate of 15 K/min, while it is slower than that in O2 at the heating rate of 2.5 K/min. MSC analysis reveals that the apparent activation energy of sintering in O2 is lower than that in air, and this might be attributed to it that O2 restrains the diffusion of aluminum vacancies together with oxygen vacancies stoichiometrically, but favors the diffusion of aluminum vacancies and the transformation between O2 and aluminum vacancies on the surface.