Abstract
New optical wavelength emission spectra recorded during dynamic compression of MgO shocked to 55-63 GPa, and CaAl 2 Si 2 O 8 (glass) shocked to 37-40 GPa, and a control sample of steel shocked to 40 GPa suggest that transparent brittle solids exhibit both thermal and characteristic line spectra. These spectra are related to the state of brittle materials shocked to successively higher pressures and temperatures. Three regimes of emission spectra behavior are proposed to occur in transparent solids upon shock compression: (1) the characteristic line spectrum regime such as observed in MgO and previously in SiO 2 , CaSO 4 H 2 O, CaCO 3 , and NaCl, (2) the heterogeneous hot spot (greybody) radiation regime observed in CaAl 2 Si 2 O 3 (glass) and previously in all solids undergoing shock-induced phase transformations, and (3) the blackbody emission regime observed in the high pressure phase regime of NaCl, SiO 2 , CaO, CaAl 2 Si 2 O 8 , and Mg 2 SiO 4 . The onset of regime (2) appears to be useful for delineating shock-induced polymorphism whereas the onset of regime (3), where the emissivity approaches unity, represents achievement of local thermal equilibrium in the shocked solid.
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