The temperature of shock compressed iron

Abstract

Measurements of the temperature of Fe under shock compression were performed to Hugoniot pressures of 300 GPa. The samples consisted of thin Fe films, 0.5 to 9.5μm in thickness, or Fe foils in contact with a transparent anvil of either single‐crystal Al_2O_3 or LiF. Temperatures at the sample/anvil interface were obtained by measuring the spectral radiance of the interface for the duration of the shock transit through the anvil, using a four‐color optical radiometer. Results indicate that the Al_2O_3 anvil remains at least partially transparent to pressures of 230 GPa and to temperatures of over 9000 K. The experimental data that yield the lowest temperature at any given pressure define a narrow pressure‐temperature trajectory which we infer to be the best estimate of the Hugoniot temperatures of Fe. Although these results must strictly be considered as an upper bound on the Hugoniot temperatures of crystal‐density Fe, we have obtained a melting temperature for Fe along the Hugoniot of 6700±400 K at 243 GPa. Taken together with recent measurements of the melting temperature to static pressures of 100 GPa (WILLIAMS et al., 1987), our results imply a melting temperature for Fe of 7800±500 K at the pressure of the inner core‐outer core boundary.

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