Construction of an Adiabatic High-Pressure Calorimeter Using Helium Gas for Pressurization

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Abstract
A novel adiabatic high-pressure calorimeter was constructed with using helium gas as a pressure transmitting medium. It works under a constant pressure up to 250 MPa in the temperature range from 12 to 370 K. Sample cell is made of Be–Cu alloy and has internal volume of 26 cm3. The pressure transmitting tube is connected to an external pressure-control system, which enables to keep automatically the inner pressure constant within ±1 kPa over the whole pressure and temperature ranges. Thus the thermodynamic path that any specimen follows during the heat capacity measurement can be described unambiguously. Heat capacities of the sample cells loaded without and with 158.9 MPa He gas were measured in the temperature range from 25 to 370 K. The imprecision of heat capacity data of the compressed He gas was within 0.3%. Thus the present calorimeter enables us to extend the low-temperature thermodynamic study on various kinds of materials to high pressures without a significant loss of the claimed precision.