Hugoniot data in the pressure range 40 to 500 kbar for porous playa from Area 5 of the Nevada Test Site are ob tained by impedance-match methods using both in-contact and flyer-plate explosive arrangements. Two initial densities, 1.55 and 1.95 gcu cm crystal density, 2.66 gcu cm, of dry, reconstituted materials are examined. The data show regions in which the pressure is multivalued. This behavior is attributed to polymorphic phase transitions in one or more of the constituent minerals. A simple, closed form expression for the zero-degree isotherm is presented which converges asymptotically to the behavior of a free-electron gas at extreme pressure. It also contains the principal term representing the pressure-volume behavior predicted by the Thomas-Fermi model. Interpolation terms are added to fit known zero-pressure quantities, viz., initial density, compressibility, and sublimation energy. In addition an extensive review of the thermodynamics of equations of state is presented. Results of shock calculations in spherical geometry assuming hydrodynamic behavior of the medium are also presented. These calculations are intended to indicate the sensitivity of shock decay to uncertainties in the equation of state. The varied parameters include porosity, Gruneisens ratio, and the zero-degree isotherm. No large influence on shock decay due to these variations is evident. Author
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