Synthesis of Mg-alpha SiAlON powders from talc and halloysite clay minerals

Carbothermnl reduction and nitridation (CRN) of SiO2 is an attractive metho d to manufacture Si3N4 powders with controlled grain morphology. Some inexp ensive raw materials were previously used to synthesize p-sialon powder, re sulting in cheaper products to be useful for some engineering applications. In this work, Mg-alpha sialon (MgxSi12-m-nAlm+nOnN16-n) powders were achie ved by CRN of mixtures of talc (Mg-3(Si2O5)(2)(OH)(2)) and NZ halloysite cl ay (Al2Si2O5(OH)(4)) minerals. The final products consisted mainly of alpha -sialon and beta-sialon phases. Small amounts of 15R AIN-polytypoid and SiC were also identified in the synthesized powder. By adding a small amount o f alpha-Si3N4 powder as seeds to the starting composition, the conversion r ate of alpha-sialon phase was significantly enhanced and powders with up to 90 wt% of alpha-sialon were produced. (C) 2000 Elsevier Science Ltd. All r ights reserved.