Industrial Diamond Substitutes: I, Physical and X‐Ray Study of Hafnium Carbide

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Abstract
A study of hard materials in an effort to find possible substitutes for industrial diamonds led to research on hafnium carbide. This compound was prepared from a mixture of hafnium dioxide and lampblack in a carbon resistance furnace by solid‐state reaction or from a melt. Some factors affecting the combined carbon content of the re‐ action products were qualitatively evaluated. A hafnium carbide prepared from a melt at a temperature slightly above 2800°C. with no holding time had a combined carbon content within 98% of the theoretical value. A curve was obtained by plotting combined carbon against cubic unit‐ cell dimension (a0) for the hafnium carbide‐ “hafnium monoxide” solid solution series. Extrapolation gave 4.641 ± 0.001 a.u. for the cell edge of hafnium carbide of theoretical composition; a0 was observed as high as 4.640 a.u. Density values within 99% of theoretical were obtained. Knoop microindentation hardness measurements with both dry and oil‐immersion objectives indicated a hardness in the silicon carbide range. Owing to its high cost and relatively low hard‐ ness, hafnium carbide is presently not considered to be a promising substitute for industrial diamonds.

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