Oxidation of Hafnium Carbide in the Temperature Range 1400° to 2060°C

Abstract

After hafnium carbide has been oxidized at temperatures in the range of 1400° to 2060°C, three distinct layers are present in the film cross section: (a) a residual carbide layer with dissolved oxygen in the lattice, (b) a dense‐appearing oxide interlayer containing carbon, and (c) a porous outer layer of hafnium oxide. Experimental measurements of layer thicknesses and oxygen concentrations are combined with an extended formulation of moving‐boundary diffusion theory to obtain the diffusion constants of oxygen in each of the three layers. The results indicate that the oxide interlayer is a better diffusion barrier for oxygen than either of the other layers. Based on X‐ray microanalysis, X‐ray diffraction, and resistance measurements, the interlayer is an oxygen‐deficient oxide of hafnium with a carbon impurity. The interlayer hardness equals that of the residual carbide layer.