The Use of Plastic Crystals as Pressure Calibration Devices.
Final rept. 1980-1981,
NAVAL ACADEMY ANNAPOLIS MD
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The permittivity of carbon tetrachloride, cyclohexane, and cyclohexanol has been studied at audio frequencies and various pressures and temperatures. The permittivity of the liquid phase was determined to agree well with previous work. The first measurements on carbon tetrachloride in the superpressed state were performed and it was determined that the superpressed state is an extension of the liquid phase with no anomalies. Because of the superpressing, the liquid to rhombohedral phase transition is unacceptable as a possible pressure fixed point. However, the rhombohedral to liquid transition is well defined and could make a good transfer point. In addition, the variation of permittivity of liquid carbon tetrachloride with pressure is found to be extremely reproducible and thus could be used as a pressure gage. Finally, the melting of the rhombohedral phase was found to be diffuse. This property was found to be intrinsic to carbon tetrachloride and several explanations of the behavior are proposed. Author