Preliminary Thermodynamic Properties of Helium-3 between 1° and 100°K
The properties of the isotope He3 differ considerably from those of He4 at low temperatures because of quantum effects arising from the differences in their masses and in the statistics obeyed by the two molecules, At higher temperatares, where both substances behave classically, their properties become identical. Most of the previous work done on He3 has been in the liquid region in an attempt either to observe superfluid behavior or to establish the vapor-pressure curve as a primary temperature standard from 0.2° to 3.3°K. This study presents the P-V-T properties and C v for He3 in the temperature range from 4° to 20°K at pressures of up to 150 atm. These data and some of Keller’s data  have been fitted to a modified Strobridge equation and the derived thermodynamic properties S, H, and U have been obtained using this equation of state. In addition, using a quantum version of corresponding states, the P-V-T surface entropy and enthalpy have been predicted from 20° to 100°K. The correlation agrees well with the experimental results between 12° and 20°K. Combining the two regions, the properties of He3 have thus been determined from 1° to 100°K.
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