Silicon-29 solid state MAS NMR investigation of silicon carbide powders prepared with a precursor method

Abstract

Carbon-silica hybrid precursors were synthesized from the liquid mixtures of tetraethyl orthosilicate and phenol resin by condensation reaction and pyrolysis. The precursors obtained by the pyrolysis at 1273 K yielded silicon carbide powders with various morphology after heat treatments at 1773-1973 K in an Ar atmosphere. Solid state 29Si MAS NMR is used for powder characterization. In the case that the crystallites are held at small size during heat treatments, the powders shows three signals at -16, -20 and -25 ppm in the NMR spectra. After coarsening of the crystallites and grains with heat treatment under no residual carbon, the powder shows the broad signal at - 19 ppm with a small spike at - 16 ppm. The signal at - 19 ppm would correspond to the "β-Sic" structure disordered by somewhat "α-SiC" areas.