Phase equilibria in fluid mixtures at high pressures: the helium + argon system

Abstract

An experimental study of phase equilibria in the system helium + argon has been carried out at temperatures from 98 to 160 K and pressures to 4000 atm. The mixture critical line and the three-phase region solid + liquid + gas have been located over most of this pressure range, and a region of fluid-fluid equilibria has been observed at temperatures above the critical temperature of argon. At pressures above about 1000 atm, in the two-phase region, the mutual solubilities of helium and argon decrease with increasing pressure at all temperatures. The relevance of these findings to problems of deep atmosphere structures in the outer planets is briefly discussed.