where D1, D2, D3 are the three DSC signals with empty pans, the signal of the reference, and the signal of the sample. mr and m are the masses of the reference and the sample, respectively, and crp is the heat capacity of the reference. Using this heat capacity cp(T) obtained with DSC measurements, one is able to calculate the enthalpy of the specimen by integrating the heat capacity signal with respect to temperature and adding the room temperature enthalpy H(298) to the result:
where H(T) is the enthalpy and cp is the specific heat capacity. The assumption in this equation of a constant heat capacity between 298 K and 473 K is taken into consideration for the uncertainty of the enthalpy values. Therefore, the enthalpy versus temperature dependence for a given material can be calculated directly from DSC measurements. This enthalpy - temperature dependence can further be used to obtain the inverse dependence, temperature versus enthalpy. With this result, we are able to extend our electrical measurements (i.e., enthalpy or electrical resistivity) of the pulse-heating experiment to lower temperatures by combining the temperature scale from the DSC (temperature versus enthalpy) with the electrical measured properties versus enthalpy. It has to be noted that the above mentioned procedure is only applicable as long as there are no phase transitions in the solid sate of the material under investigation. Phase transitions can easily be observed with DSC measurements, but can be wholly or partially suppressed under pulse-heating conditions as applied within this experiment, due to the extreme high heating rates of 108K×s-1. This procedure enables us to extend the results for enthalpy versus temperature and resistivity versus temperature to lower temperature regions, starting now at the onset temperature of the DSC (500 K). Up to now access to these temperature regions when using pulse-heating techniques was only possible by experiments with millisecond time resolution.
Institut of Experimental Physics
Graz University of Technology
ao. Univ.-Prof. Dr. Tel.: +43 (0) 316 / 873 - 8149
Fax: +43 (0) 316 / 873 - 8655 pottlachernoSpam@tugraz.at