Temperatures of shock-induced shear instabilities and their relationship to fusion curves

Abstract

New emission spectra for MgO and CaAl_2Si_2O_8 (glass) are observed from 430 to 820 nm. Taken with previous data, we suggest that transparent solids display three regimes of light emission upon shock compression to successively higher pressures: (1) characteristic radiation such as observed in MgO and previously in other minerals, (2) heterogeneous hot spot (greybody) radiation observed in CaAl_2Si_2O_8 and previously in all transparent solids undergoing shock-induced phase transformations, and (3) blackbody emission observed in the high pressure phase regime in NaCl, SiO_2, CaO, CaAl_2Si_2O_8, and Mg_2SiO_4. The onset of regime (2) may delineate the onset of shock-induced polymorphism whereas the onset of regime (3) delineates the Hugoniot pressure required to achieve local thermal equilibrium in the shocked solid. We also propose that the hot spot temperatures and corresponding shock pressures determined in regime (2) delineate points on the fusion curves of the high pressure phase.

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