[1] The most energetic planetary collisions attain shock pressures that result in abundant melting and vaporization. Accurate predictions of the extent of melting and vaporization require knowledge of vast regions of the phase diagrams of the constituent materials. To reach the liquid-vapor phase boundary of silica, we conducted uniaxial shock-and-release experiments, where quartz was shocked to a state sufficient to initiate vaporization upon isentropic decompression (hundreds of GPa). The apparent temperature of the decompressing fluid was measured with a streaked optical pyrometer, and the bulk density was inferred by stagnation onto a standard window. To interpret the observed post-shock temperatures, we developed a model for the apparent temperature of a material isentropically decompressing through the liquid-vapor coexistence region. Using published thermodynamic data, we revised the liquid-vapor boundary for silica and calculated the entropy on the quartz Hugoniot. The silica post-shock temperature measurements, up to entropies beyond the critical point, are in excellent qualitative agreement with the predictions from the decompressing two-phase mixture model. Shock-and-release experiments provide an accurate measurement of the temperature on the phase boundary for entropies below the critical point, with increasing uncertainties near and above the critical point entropy. Our new criteria for shock-induced vaporization of quartz are much lower than previous estimates, primarily because of the revised entropy on the Hugoniot. As the thermodynamics of other silicates are expected to be similar to quartz, vaporization is a significant process during high-velocity planetary collisions.Citation: Kraus, R. G., et al. (2012), Shock vaporization of silica and the thermodynamics of planetary impact events,

We combine a recently developed high-resolution two-dimensional (2D) imaging velocimetry technique (velocity interferometer system for any reflector (VISAR)) with 1D VISAR measurements to construct a moving picture of heterogeneous deformation in shock-compressed single crystal silicon. The 2D VISAR takes an intensity snapshot of target velocity and reflectivity over a mm field-of-view while the compression history is simultaneously recorded by the 1D VISAR. Our data show particle velocity surface roughening due to the anisotropic onset of plasticity and, above ∼13 GPa, a structural phase transformation. Shock arrival at the Si free-surface is characterized by the formation of fracture networks and incipient velocity jetting.

Abstract. The goal of this experiment was to investigate the plastic response of Ta to dynamic loading at high strain rates. The samples used were derived from high purity rolled plate, polished down to thicknesses in the range 25-100 μm. Dynamic loading was applied by direct laser ablation of the sample, with pulses up to 10 ns long, at the Jupiter Laser Facility. The elastic-plastic wave structure was measured using two line VISAR systems of different sensitivity, and strain rates were inferred from the rise time of the waves. The elastic wave amplitudes indicated flow stresses between 2 and 3 GPa, depending on the sample thickness. Samples were recovered for post-shot metallographic analysis.

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