Thermal expansion studies on the subcarbides of group V and VI transition metals

Abstract

The thermal expansions of the high and low temperature modifications of V 2C and Mo 2C and the low temperature modifications of Ta 2C and W 2C have been studied with the aid of X-ray powder diffraction. All the carbides display thermal anisotropy with larger thermal expansion coefficients perpendicular to the basal plane than parallel to it, an exception being Ta 2C which displays the reverse behaviour. The thermal anisotropy of V 2C and Mo 2C increases markedly as the hexagonal, high temperature modifications transform into the orthorhombic, low temperature modifications, a fact which can be related to the ordering schemes of the carbon atoms. The mean thermal expansion coefficients of the carbides can be correlated to their melting points.