Effects of residual gas on densification and microstructure development of Al₂O₃ and ZrO₂-8 mol%Y₂O₃ ceramics sintered in air

Measurements of gas emission during fracture of Al₂O₃ and ZrO₂-8 mol%Y₂O₃ sintered in air were carried out under ultrahigh vacuum using a mass spectrometer in order to examine the effect of entrapped gas on densification and microstructure development of the materials. Analysis of the spectrometer revealed that nitrogen being introduced from the sintering atmosphere was mainly emitted at the moment of fracture for both materials. During prolonged sintering, the density of Al₂O₃ tended to decrease and the amount of emitted gas increased. In contrast, the density of ZrO₂-8 mol%Y₂O₃ did not decrease and the emitted gas tended to decrease in the course of sintering. These results of sintering behavior were concluded to result from the difference in nitrogen diffusivity between the materials.