PHASE-DIAGRAM AND CONCENTRATION SUSCEPTIBILITY OF HE-3-HE-4 MIXTURES NEAR THE TRICRITICAL POINT

The inverse concentration susceptibility (∂Φ/∂x)T of 3He-4He mixtures has been calculated from high-resolution vapor-pressure measurements and in situ measurements of the dielectric constant very close to the tricritical point. The measurements have been fitted to a scaling-law equation of state. In the normal fluid a logarithmic correction term was necessary to obtain a good fit. In the superfluid a regular correction term, proportional to (x - xt)2, was evaluated. New measurements of the phase-separation curve confirm our earlier measurements on the 3He-rich side and extend the measurements much closer to the tricritical point on the 4He-rich side. The tricritical point is at temperature T = 0.8669 ± 0.0005 K and mole fraction x = 0.6716 ± 0.0014. © 1979 Plenum Publishing Corporation.