Synthesis of Si3N4 using sepiolite and various sources of carbon

Abstract

Sepiolite of Turkish origin was used as Si precursor in the syntheses of silicon nitride (Si3N4) powders by carbothermal reduction-nitridation (CRN) by mixing with several reducing agents i.e. charcoal, carbon black and petroleum coke as discrete particles and acrylonitrile as an intercalation medium. Purified sepiolite samples with a pre-determined C/SiO2 ratio of 4 yielded Si3N4 powders after firing at temperatures 1300-1475 degreesC under continuous nitrogen flow. The various sepiolite-reducing agent combinations were evaluated. The alpha/beta ratio and secondary phase content of the powders after CRN were found to depend on temperature, time, heating rate and on the physicochemical properties of the precursor used such as, surface area and mixing of the reactants. (C) 2001 Kluwer Academic Publishers.