Isochoric measurement of the equation of state of solid argon at high pressure

Abstract

Isochoric P-T traces have been measured for solid argon at eight different molar volumes by using a capacitance technique which records the radial expansion of the vessel due to pressure. These measurements extend from melting curve temperatures down to 4 °K at pressures ranging up to 7 kbar. Analysis of the data indicates that, for the high temperature region (above 80 °K) the thermodynamic derivative ∂P/∂T r is independent of both temperature and density to within experimental errors. Using the fact that ∂P/∂T r is constant, it is possible to generate PVT and isothermal bulk modulus data at high temperatures. These data are compared with X-ray diffraction measurements and piston displacement data and are found to be in good agreement with both. The data also agree quite well with current theoretical predictions. The high-temperature bulk modulus data were found to have a simple exponential dependence on the molar volume, prividing another convenient representation of the high-temperature equation-of-state data.