COMPRESSIONAL SOUND-VELOCITY, EQUATION OF STATE, AND CONSTITUTIVE RESPONSE OF SHOCK-COMPRESSED MAGNESIUM-OXIDE

Wave profile and equation of state (EOS) data are reported for low-porosity polycrystalline magnesium oxide under shock compression. The Hugoniot equation of state between 14 and 133 GPa is U-S 6.87(10) + 1.24(4)u(p), where the numbers in parentheses are one standard deviation uncertainties in the last digit(s). Reverse-impact wave profiles constrain the compressional sound velocity, V-P, at 10-27 GPa to +/-2%. Measured V-P values are consistent with ultrasonic data extrapolated from 3 GPa. By combining the Hugoniot results with ultrasonic data, the adiabatic bulk modulus and its first and second pressure derivatives at constant entropy are 162.5(2) GPa, 4.09(9), and -0.019(4) GPa(-1). The shear modulus and its first and second pressure derivatives are 130.8(2) GPa, 2.5(1), -0.026(45) GPa(-1) Polycrystalline MgO has a compressive yield strength of 1-1.5 GPa at the elastic limit which increases to 2.7(8) GPa along the Hugoniot and is similar at unloading. Wave profiles for MgO at 10-39 GPa are described using a modified elastic-plastic model. There are significant differences in the dynamic response of single-crystal and polycrystalline MgO.