Previous studies report that WC oxidises in air more readily than W.
However, systematic thermogravimetric studies reveal considerably slower
oxidation kinetics in WC samples, which outperform previous measurements by
1-2 orders of magnitude. By combining X-ray diffraction and electron
microscopy, the enhanced stability in WC is explained by a dense interlayer of
sub-stoichiometric WO3, approximately 10 microns in thickness, which forms
adjacent to the substrate/oxide interface. The faster oxidation kinetics from
previous studies are explained by the comparatively low densities of samples
used.