HARDNESS, INDENTATION FRACTURE-TOUGHNESS AND COMPOSITIONAL FORMULA OFX-PHASE SIALON

The hardness and indentation fracture toughness, K-IC of sintered X-ph ase sialon, produced by simultaneous carbothermal reduction and nitrid ing of kaolinitic clays, are determined. By comparing the values obtai ned for the sialon with those for a commercially pure mullite, it is s uggested that X-phase sialon is a material with potential for similar applications to those in which mullite is currently used. On the basis of the oxygen/nitrogen ratios of the sialon determined by the inert g as fusion method; the analysis of the energy of the dispersed X-rays ( EDAX) from thinned samples in the transmission electron microscope (TE M) and the aluminium/silicon ratios, also determined by the TEM EDAX m ethod, a modified compositional formula is proposed for X-phase.