Shock Compression of Argon

Abstract

Liquid argon has been shock compressed from two initial states at 86°K and 2 bar, and 148.2°K and 70 bar. The highest pressure of 700 kbar and temperature of 13 000°K were obtained by reflecting a shock wave with a pressure of 270 kbar from a tungsten wall. These shock loci allow a test of the interatomic potential over a wide region and show that the potential can be represented by a sum of pair interactions up to a pressure of 400 kbar. The pair potential is furthermore found to be considerably less repulsive at small interatomic distances than the 12‐power repulsive law. In fact, an exponential form yields good results up to 360 kbar. Above this pressure range the reflected‐shock data require a large change in the potential form which is interpreted to be due to a pressure‐induced electronic transition to the conduction band. Calculations show that a discontinuity in the Hugoniot data at 50 kbar and 1200°K could be identified with the melting line. This temperature corresponds to three times the highest reduced melting temperature observed so far.