β-Si3N4 Microcrystals Prepared by Carbothermal Reduction-Nitridation of Quartz

Single phase beta-Si3N4 with microcrystals was synthesized via carbothermal reduction-nitridation (CRN) of quartz and carbon coke powder as starting materials. The effects of reaction parameters, i.e., heating temperature, holding time, C/SiO2 ratio, Fe2O3 additive and beta-Si3N4 seeds on the phase transformation and morphology of products were investigated and discussed. Rather than receiving a mixture of both alpha- and beta- phases of Si3N4 in the products, we synthesized powders of beta-Si3N4 single polymorph in this work. The mechanism for the CRN synthesis of beta-Si3N4 from quartz and the formation mechanism of Fe3Si droplets were discussed. We also firstly reported the formation of Fe3Si Archimedean solids from a CRN process where Fe2O3 was introduced as additive. Comparing to the gear-like short columnar morphology observed in samples without beta-Si3N4 seeding, the addition of beta-Si3N4 seeds led to an elongated morphology of final products and much finer widths. In addition, the beta-Si3N4 microcrystals exhibited a violet-blue spectral emission range, which could be highly valuable for their future potential optoelectronic applications.