Shock loading and unloading in bismuth

Abstract

Shock loading and unloading was performed on bismuth specimens for initial temperatures of 293 and 473 K. Wave velocity profiles transmitted through the specimen were determined with an interferometer system. The maximum pressure achieved at room temperature was sufficient to induce a polymorphic transition to the high‐pressure solid phase of bismuth. At elevated temperatures, the pressures obtained in some experiments caused partial melting during shock compression. The stress‐volume states achieved during compression at 473 K agree closely with the calculated equilibrium hydrostat, and therefore give direct evidence that melting occurs. The measured initial unloading wave velocities from the shocked state show no major change at the onset of the polymorphic transition. However, a large decrease in the initial unloading wave velocity occurs for partial melting. The volume states achieved during unloading from states of partial melt indicate that refreezing back to the initial solid phase does occur, although there appears to be substantial rate effects associated with refreezing.