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. Comments Copyright The American Ceramic Society. Reprinted from Journal of the American Ceramic Society, Volume 89, Issue 3, 2006, pages 1110-1113. This journal article is available at ScholarlyCommons: http://repository.upenn.edu/mse_papers/103 The Effect of Powder Mixing Procedures on a-SiAlON Roman Shuba and I-Wei Chen Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6272 Various procedures of mixing starting powders for hot-pressing a-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 a-SiAlON was destabilized and replaced by b-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 a-SiAlON were thus identified.