High pressure differential scanning calorimetry: Aspects of calibration

A high pressure differential scanning calorimeter (HP-DSC) based on an original design of Höhne and co-workers has been constructed at the University of Aberdeen to allow the characterisation of the thermal behaviour of materials under pressure in both fundamental and technological research areas, for example, in the offshore and pharmaceutical industries. The HP-DSC is equipped with an autoclave using silicone oil as the pressurising medium and may be operated in a temperature range from 20 °C to 300 °C at pressures from 0.1 MPa to 500 MPa and with various heating and cooling rates (from 0.5 K min−1 to 20 K min−1). For calibration purposes, the pressure dependence of the melting temperatures and associated enthalpy changes of both indium and tin have been investigated and compared to the data obtained by Höhne and co-workers for indium and from other published data in the literature for tin. From the heat flow calibration, a dimensionless enthalpy correction factor Rcorr(p) has been determined which may be used to correct the measured enthalpy values over the whole temperature range and for any given pressure value. Likewise a calibration diagram has been constructed from the temperature calibration over the full range of pressure up to 500 MPa to allow the corrected temperature to be determined from the measured temperature for a thermal event occurring at any pressure.