T-History

In a T-History measurement, the PCM sample and a reference material with well-known thermo-physical properties are located symmetrically in a temperature-controlled ambience. Sample as well as reference are placed inside identical specimen containers and these inside identical insulations. It is decisive for accurate T-History measurements to arrange the setup of the calorimeter in such a way that PCM and reference are subjected to the same temperature program. To obtain such conditions, PCM and reference have to be placed symmetrically inside the temperature-controlled ambience. Deviations from perfect symmetry are taken into account through the calibration. To measure the enthalpy curve, sample and reference are simultaneously exposed to a sudden change in temperature. During the temperature adjustment of PCM and reference, the ambience is kept isothermal. From the thermal response of the reference, the heat flow to the reference as a function of temperature is determined. Following this, the heat flow to the sample and the enthalpy curve are calculated.

Typical T-History calorimeters allow the investigation of samples of about 10 to 100 g that are approximately 1000 times larger than typical DSC samples. Due to its large sample size, the T-History method is interesting in particular for heterogeneous materials and materials with volume-dependent behaviour, such as compound materials or substances that show separation and/or supercooling effects. Moreover, large samples together with constant charging and discharging temperatures ensure that the measured enthalpy curves are close to the behaviour of the bulk material.