Influence of process parameters and initial composition on synthesis of O′-sialon powder by carbothermal reduction-nitridation

With nano SiO₂, Al(OH)₃ and carbon black as raw materials, O′-sialon powder was synthesized by carbothermal reduction-nitridation (CRN). The phase composition of reaction products was determined by XRD. The influence of synthesis temperature, selection of protective powder, N₂ flow rate and initial composition on the synthesis was studied. The results show that the synthesis temperature affects the formation of O′-sialon significantly. The content of O′-sialon in the products increases with the increase of synthesis temperature, reaching the maximum at 1400°C, which is assumed to be the optimum synthesis temperature. The positive effect of Si₃N₄+SiO₂ protective powder is not as obvious as expected and larger mass loss of samples is aroused. 20 ml/min is an appropriate N₂ flow rate, which is most favorable for the synthesis of O′-sialon. While the initial composition is varied, the influence of it on the phase composition at the synthesis temperature of 1400°C is more dramatic than that at 1350°C. An increase of C content in the initial composition will promote the CRN process, and an excess of C will lead to the conversion of O′-sialon to β′-sialon. The best results are obtained with a stoichiometric content of C.