Mixtures of silicon (which converts to Si3N4) and alumina (Al2O3) were heated in nitrogen to prepare a composite sialon body. The effect of a range of nitridation additives designed to improve the yield and the rate of reaction have been explored, together with a range of sintering aids. The additives included are oxides of calcium, titanium, zirconium, iron, a refractory cement, gibbsite raw material to replace alumina and boron nitride. The nitridation and sintering were performed separately to assess the specific effects of each additive. Thermogravimetric analysis informed the choice of nitridation and sintering firing temperatures. The nitridation firings at 1400 deg C formed mainly b-sialon with minor amounts of O-sialon, mullite, corundum and other sialon phases. After sintering, all the samples contained b-sialon and X-phase as predicted from the position of the target composition on the sialon phase diagram. The samples with calcium hydroxide or calcium aluminate cement exhibited the best porosity and density.
