Shock wave equations of state using mixed‐phase regime data

Abstract

A method is given that uses Hugoniot data in the mixed‐phase regime to constrain further equation of state (EOS) parameters of low‐ and high‐pressure phases of materials under‐going phase transformations on shock loading. We compute the relative proportion of low‐ and high‐pressure phases present in the mixed‐phase region and apply additional tests to the EOS parameters of the separate low‐ and high‐pressure phases by invoking two simple requirements: the fraction of high‐pressure phase (1) must increase with increasing shock pressure, and (2) must approach one at the high‐pressure end of the mixed‐phase regime. We apply our analysis to previously published data for potassium thioferrite, KFeS2, and pyrrhotite, Fe0.9S. We find that including the mixed‐phase regime data in the KFeS2 analysis requires no change in the published high‐pressure EOS parameters. For Fe0.9S we must modify the high‐pressure phase EOS parameters to account for both the mixed‐phase and high‐pressure phase Hugoniot data. Our values of zero‐pressure density, bulk modulus and first pressure derivative of the bulk modulus of the high‐pressure phase of Fe0.9S are 5.3 Mg/m3, 106 GPa, and 4.9, respectively.