Phase equilibria in binary mixtures containing fluorocarbons at high pressures and low temperatures VI. Liquid-solid equilibria for {(1− x)CF 4 + xAr}, {(1− x)CF 4 + xKr}, and {(1− x)CF 4 + xXe} up to 200 MPa

Abstract

Liquid-solid equilibria in { xAr + (1− x)CF 4}, { xKr + (1− x)CF 4}, and { xXe + (1− x)CF 4} were investigated at pressures up to 200 MPa in an optical high-pressure low-temperature cell according to the synthetic method. The liquidus curves experimentally obtained show a complex behaviour because of the existence of a solid-to-solid transition in pure CF 4 about 13 K below its melting temperature at 0.1 MPa. All three mixtures belong to a eutectic type with more or less formation of mixed crystals at high pressures. For { xAr + (1− x)CF 4} a T( x) diagram for 0.1 MPa was extrapolated that even allows complete miscibility in the solid phase with a minimum temperature within the errors of extrapolation. The results are discussed from a phasetheoretical point of view. Calculations of the liquidus curves using an extended regular-solution theory by Preston and Prausnitz as well as the Wilson equation, show good agreement with the experimental results.