Formation of β-SiAlON as an intermediate oxidation product of SiC-AlN ceramics

• Published in: Journal of the American Ceramic Society 1995-10, Vol.78 (10), p.2753-2762
• Main Authors: YOUREN XU, ZANGVIL, A, RUH, R
• Format: Article
• Language: English
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Miscellaneous; Technical ceramics
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1995.tb08051.x

The oxidation mechanisms in SiC-AlN solid solutions, exposed at 1370 C for 200 h in air, have been investigated by SEM, HREM, and XRD. Five hot-pressed compositions, including pure SiC and pure AlN, were examined. Assuming parabolic rate behavior, the values of the parabolic rate constants based on oxide layer thickness increased by over 2 orders of magnitude by increasing AlN contents from 0 to 62 percent. A continuous amorphous phase containing cristobalite and mullite crystallites was present at the oxide layer in 13 percent and 27 percent AlN samples. Two reaction layers were found in the oxidized SiC-62 percent AlN solid solution. The inner layer consisted of a mixture of beta-SiAlON and graphite phases, while the outer layer consisted of mullite as a major phase and cristobalite as a minor phase. The oxidation proceeded in two stages: a partial oxidation of SiC-AlN to beta-SiAlON and carbon (graphite), and a final oxidation of beta-SiAlON to mullite + SiO2. (Author)