Effect of Sintering Atmosphere on Densification of MgO‐Doped Al 2 O 3

The densification behavior of Al 2 O 3 ‐MgO (0.1 wt%) has been studied in O 2 and N 2 atmospheres. Powder compacts have been sintered at 1600°C for 0.5 to 8 h. For some specimens the sintering atmosphere has been changed after 30 min of sintering. Irrespective of sintering atmosphere, sintered densities are approximately the same up to 99% relative density, implying that the capillary pressure effect dominates the atmosphere effect for most of the densification stage. During extended sintering treatment the density of specimens sintered in O 2 becomes higher than that in N 2 . When the sintering atmosphere is changed from O 2 to N 2 , enhanced densification results, and vice versa. Such an effect of sintering atmosphere is explained by the diffusiveness of gases entrapped in pores, as well as by oxygen potential differences inside and outside of the specimen. Differences in grain growth rate in various atmospheres are discussed on the basis of different densification rates.