Pressure-volume-temperature relations in liquid and solid3He

Liquid and solid³He P-V-T relations were measured over 0.26–1.8 K with concentration on regions near the melting curve. The method used a cell whose volume was varied with diaphragms, the positions of which determined the volume and pressure. The molar volumes of liquidV_lm and solidV_sm along the melting curve were consistent with the directly measured volume change on melting V_m. Below 1 K,V_lm, V_sm, and V_m were greater than previous results. Along the melting curve, the compressibility of the solid became greater than the compressibility of the liquid atT<1.2 K, the difference rising to 12% at 0.32 K. The thermal expansion of the solid became negative below 0.30–0.35 K. The melting curve minimum was measured at 28.932±0.003 atm and 0.319±0.003 K. Starting with the minimum, the melting curve was calculated to 0.02 K, where it should be useful in thermometry. A set of self-consistent data is presented.Work performed under the auspices of the U.S. Atomic Energy Commission.