Shock compression of powder compacts of CaF2

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Abstract
Particle velocity gauges were used to measure the Hugoniots to 30 GPa of CaF2 powder compacts having initial porosities of 15% and 35%. The Hugoniot of the material with 15% porosity is concaved upward over the range to 30 GPa and lies close to the solid Hugoniot in the stress range above 15 GPa. The Hugoniot of the material with 35% porosity becomes an isovolume curve, at about the zero‐pressure volume, in the stress range above about 10 GPa. Studies of recovered shock loaded samples indicate that the temperature distributions in the shock‐compressed samples were very heterogeneous. It is inferred that the higher stress Hugoniot measurements pertain to a nonequilibrated mixture of the solid and liquid phases of CaF2. In view of this evidence against thermal equilibrium, one may question the validity of the Hugoniot data on the initially porous samples to obtain data on Grüneisen’s ratio at high pressures.