EVALUATION OF TEMPERATURE-MODULATED DIFFERENTIAL SCANNING CALORIMETRIC MEASUREMENTS BY PHASE-SENSITIVE RECTIFICATION TECHNIQUES

The phase-sensitive rectification method (lock-in technique) is presen ted and tested to serve as another evaluation method for temperature-m odulated differential scanning calorimetric measurements. This is done by model calculations with a mathematical computation system, using s imple models of events often measured in this type of calorimeter: cha nges in heat capacity, cold crystallization, a chemical reaction anti the glass transition. The advantages of the new evaluation method are: a lower numerical expenditure; a well-defined connection between time resolution and smoothing interval; and a reliable decrease in fluctua tions of the results. It has furthermore been demonstrated that numeri cal calculations can be a powerful tool to test different models and t heir influence on the measured signal and the evaluated results. This is especially significant in cases, where a certain process produces n on-linear distortions of the heat-flow rate signal. (C) 1997 Elsevier Science B.V.