A technique for following sialon formation in situ by high temperature x-ray diffraction (HT-XRD) was developed. The composition chosen for study was an yttrium α-sialon with x = 0.4. Powder compacts containing silicon nitride, aluminum nitride and yttria powders were pre-sintered at 1350 °C and then studied by HT-XRD at temperatures between 1450 and 1580 °C and nitrogen pressures of 0.11 MPa. The furnace was made from graphite coated with porous silicon nitride/silicon carbide. The coating prevented silicon carbide formation in the sample up to 1600 °C. X-ray diffraction results show the formation of a Y10Al2Si3O18N4 phase at 1350 °C, which dissolved to form α-sialon and other phases at higher temperatures. The amounts of α-sialon formed are similar to the amounts reported by other authors. An empirical method was used for the calculation of activation energy for the silicon nitride to α-sialon transformation and resulted in a value of 330 kJ mol-1.
Godkänd; 1994; 20070507 (cira);
ISBN for host publication: 0-87849-668-8