INVESTIGATION OF ALPHA-SIALON FORMATION BY HIGH-TEMPERATURE X-RAY DIFFERACTION

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 alpha-sialon with x=0.4. Powder compacts containing silicon nitride, aluminum nitride and yttria powders were pre-sintered at 1350 degrees C and then studied by HT-XRD at temperatures between 1450 and 1580 degrees 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 degrees C. X-ray diffraction results show the formation of a Y10Al2Si3O18N4 phase at 1350 degrees C, which dissolved to form alpha-sialon and other phases at higher temperatures. The amounts of alpha-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 -sialon transformation and resulted in a value of 330 kJ mol(-1).