Carbothermal reduction and nitridation reaction of $SiO_x$ and preoxidized $SiO_x$: Formation of $\alpha - Si_3N_4$ fibers

Ramesh, PD and Rao, KJ (1994) Carbothermal reduction and nitridation reaction of $SiO_x$ and preoxidized $SiO_x$: Formation of $\alpha - Si_3N_4$ fibers. In: Journal of Materials Research, 9 (9). pp. 2330-2340.

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Abstract

The chemical composition of amorphous $SiO_x$ has been analyzed by oxidation studies and is found to be $SiO_{1.7}.$ $SiO_{1.7}$ appears to be a monophasic amorphous material on the basis of $^{29}Si$ nuclear magnetic resonance, high resolution electron microscopy, and comparative behavior of a physical mixture of Si and $SiO_2$. Carbothermal reduction and nitridation reactions have been carried out on amorphous $SiO_{1.7}$ and on amorphous $SiO_2$ obtained from oxidation of $SiO_{1.7}$. At 1623 K reactions of $SiO_{1.7}$ lead exclusively to the formation of $Si_2N_2O$, while those of $SiO_2$ lead exclusively to the formation of $Si_3N_4$. Formation of copious fibers of $\alpha - Si_3N_4$ was observed in the latter reaction. It is suggested that the partial pressure of SiO in equilibrium with reduced $SiO_{1.7}$ and $SiO_2$ during the reaction is the crucial factor that determines the chemistry of the products. The differences in the structures of $SiO_2$ and $SiO_{1.7}$ have been considered to be the origin of the differences in the SiO partial pressures of the reduction products formed prior to nitridation. The effect of the ratios, $C: SiO_{1.7}$ and $C: SiO_2$, in the reaction mixture as well as the effect of the temperature on the course of the reactions have also been investigated.

Item Type: Journal Article The copyright of this article belongs to Materials Research Society. Ceramics;Chemical synthesis;Structural materials Materials;Si3N4(fiber) Division of Chemical Sciences > Materials Research Centre 22 Aug 2006 19 Sep 2010 04:30 http://eprints.iisc.ernet.in/id/eprint/8061