2段階昇温パルス通電焼結したアルミナセラミックスの透光性に及ぼす焼結雰囲気の影響

抄録

The influence of various sintering atmospheres (vacuum, CO₂ and N₂) on the transparency of alumina ceramics was investigated using the two-step pulsed electric current sintering (TS-PECS). Samples sintered under a CO₂ atmosphere exhibited lower transparency with a darker coloration due to carbon contamination resulting from CO₂ gas during TS-PECS. In contrast, sample darkening was reduced by switching from CO₂ to vacuum during the TS-PECS process. Switching between CO₂ and vacuum atmospheres suppressed carbon deposition caused by CO gas generated from the CO₂ and graphite die/sheet. Samples sintered under an N₂ atmosphere exhibited lower transparency and density compared to those sintered in vacuum. This is due to the slow diffusion of N₂ in alumina, which leads to N₂ retention in closed pores and impedes densification. Notably, higher transparency was observed in samples sintered by switching the atmosphere from vacuum to N₂ during the TS-PECS process compared to those sintered solely under vacuum. Optimizing gas and atmosphere profiles during PECS is essential for achieving the desirable transparency and density of alumina ceramics.