2025 Volume 72 Issue 3 Pages 61-66
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.
