Development of the phase composition in the carbothermally derived beta-sialon ceramics.

Carbothermally derived beta-sialon powders with different phase composition were presureless sintered with or without yttria additives. Then they were isothermally annealed in nitrogen. XRD study has shown changes in the phase composition after sintering and annealing at 1450 degrees centigrade. Development of the phase composition was dependent on the composition of the starting beta-sialon powders (presence of AlN or 15R phase) and yttria admixture. It has been found that sintering of carbothermally derived powders shifted the composition of the ceramics towards beta-sialon with higher z-value. Further annealing in nitrogen could lead to decomposition of sialon polytypoid phases and was accompanied by slow oxidation at low oxygen partial pressure.