Concentration dependence of the excess molar volumes of 3He–4He mixtures

On the basis of dielectric constant measurements, P–V–T relationships are derived for the first time for 3He–4He mixtures at different 3He concentrations from 0 to 100% in the temperature range 4.5–9 °K and at pressures from 0.3 to 20 atm, i.e. in the range where the molar volumes of mixtures differ considerably from additive values. Excess molar volumes of the mixtures (VE) are calculated and the concentration dependence of VE is studied in the entire temperature and pressure range investigated. It is shown that in various temperature and pressure intervals the character of this dependence is different. For each composition there exists a region of P and T values where the concentration dependence of VE is sign-alternating. Calculations of VE on the basis of Prigogine’s model are carried out. It is shown that, on the whole, this theory describes the behavior of VE as a function of all the parameters, i.e., temperature, pressure, and 3He concentration, adequately. Quantitative discrepancy between theory and experiment is pronounced only at high densities, which is associated with the contribution of quantum-statistical effects to the excess functions of the 3He–4He system.

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