Evidence for High-Temperature Forms of Zirconium and Tantalum Monocarbides

Evidence has been found which suggests the existence of high‐temperature crystalline modifications of both zirconium carbide and tantalum carbide. The high‐temperature inversion in zirconium carbide, indicated by a sharp decrease in spectral emisivity, in electrical resistivity, and in density, was reversible. No permanent changes in microhardness or in X‐ray diffraction patterns were found after cooling to room temperature. Emissivity measurements showed a hysteresis effect of approximately 400° C for zirconium carbide. A similar, although less sharply defined, effect was noted for tantalum carbide. No such effect was found in solid solutions of these two monocarbides.