Combustion synthesis of nanosized SiCxNy powders

Abstract

ABSTRACTSilane/acetylene/ammonia flames were used to produce fine powders of composition SiCxNy The experiments were conducted in a spherical reactor at 1 atmosphere total pressure with spark ignition in the center of the chamber. The composition was determined from complete quantitative analysis of the gas products and elemental analysis of the solids. IR spectra indicate little bound hydrogen in the powders, but oxygen was adsorbed on the high surface area powders (60–80 m2/g, N2 BET). The experimental stoichiometries of the nascent powders can be represented as mixtures with weight ratios of Si3N4/SiC ranging from about 0.2 to 2, and variable amounts of excess carbon or silicon. The powders, from TEM, consist of chains of nearly symmetrical particles with diameters around 40 nm. Helium pycnometry densities in the range of 2.9 to 3.2 g/cc are consistent with the theoretical densities for the Si3N4/SiC stoichiometries. The powders were amorphous or nanocrystalline, from X-ray diffraction (Cu Kα). Annealing in argon at 1773 K for 8 h resulted in preferential growth of crystalline SiC domains.