Shock Melting and Decompression-Driven Solidification of Single Crystal Quartz

Quartz, along with other silicate materials, displays non-equilibrium melting behavior on shock compression. In these materials, the solid phase is overdriven above the liquidus and melts at significantly higher pressures and temperatures than what is seen with quasi-hydrostatic compression methods. Previous experiments approximated the overdriven melt pressure of quartz to be between approximately 117 and 120 GPa, with temperatures of ~6300-6500 kelvin. Similarly, quartz appears to be undercooled on melting, where the reported temperatures are ~4800-5000 K, several hundred kelvin below the melting curve. There is scarce experimental information observing the behavior of quartz during its transformation from the metastable solid state to a liquid, and even less observing how quartz behaves on decompression from a shocked liquid. We have conducted several experiments intentionally crossing this boundary, from approximately 120 GPa to 115 GPa, where a two-step pressure-temperature scheme was built into the target construction. Utilizing optical pyrometry diagnostics, we observed re-solidification of the quartz across this pressure step on a nanosecond time scale, where the emissive character and completeness of the solidification was subject to the quality of the primary and secondary shock transits through the sample. This effort provides further insight into the kinetic dependence of shock melting in quartz and other extended framework silicates.