The Effect of Powder Mixing Procedures on α-SiAlON

Various procedures of mixing starting powders for hot-pressing α-SiAlON ceramics were studied. They included different milling methods (attrition milling, ball milling, and sonication), liquid medium (water, isopropyl alcohol, and pyridine), and atmospheres (ambient air and nitrogen). These mixing procedures resulted in markedly different densification behavior and fired ceramics. As the powders experienced increasing oxidation because of mixing, the densification temperature decreased, the amount of residual glass increased, and α-SiAlON was destabilized and replaced by ß-SiAlON and AlN polytypes during hot pressing. These effects were mitigated when pyridine, nitrogen, and sonication were used. Several protocols that yielded nearly phase-pure, glass-free dense α-SiAlON were thus identified.