Two ultra-high-temperature materials, hafnium carbide and hafnium diboride, were oxidized in the temperature range 1400 to 2100°C. The two materials oxidized in distinctly different ways. The carbide formeda three-layer system consisting of a layer of residual carbide, a layer of reduced (partially oxidized) hafnium a oxide containing carbon, and a layer of fully oxidized hafnium dioxide. The diboride oxidized into only two layers. For the diboride system, the outer layer, mainly hafnium dioxide, contained several intriguing physical structures.
