LIQUID-SOLID PHASE TRANSITION IN HE3-HE4 MIXTURES

Measurements on the liquid-solid phase transition of He3-He4 mixtures have been performed by means of a strain-gauge technique. It was found that the freezing curves of mixtures with initial concentrations of greater than 5% He3 merged into a common curve with negative slope in the P-T plane. This curve is interpreted to be a three-phase equilibrium line or univariant involving the coexistence of bcc solid helium and the two phase-separated liquids, one rich in He3 and the other rich in He4. A number of other univariant lines involving these and other phases of helium have also been observed. Univariants intersect at quadruple points which are defined as points where four phases coexist. A quadruple point has been observed in these experiments involving coexistence of bcc solid helium, hcp solid helium, and the two phase-separated liquids at a temperature T=0.37°K and a pressure P=26 atm. The data is discussed in terms of a three-dimensional phase diagram which is consistent with the Gibbs phase rule and with the results obtained by other investigators. © 1969 The American Physical Society.