Phase properties of dilute mixtures of helium in near critical mercury

The properties of metallic hydrogen-nonmetallic helium mixtures are of cons iderable interest for planetary modelling. In the light of the unfavourable outlook for reliable measurements under the extraordinarily high temperatu res and pressures prevailing in the planet's interiors it becomes interesti ng to study the phases of fluid mercury-helium mixtures which might serve a s a model for the hydrogen-helium-system. At sufficiently high density, non metallic expanded mercury experiences a transition to a conducting state no t unlike that recently observed in hydrogen. The experimental results for m ercury-helium, which extend to pressures of 4000 bar and temperatures to 18 00 K, show that two distinct fluid phases exist at supercritical temperatur es and high pressures. (C) 1999 Elsevier Science B.V. All rights reserved.