Temperature modulated differential scanning calorimetry. Part III. Effect of heat transfer on phase angle in quasi-isothermal ADSC

The effect of heat transfer on the phase measurements of alternating differential scanning calorimetry (ADSC, Mettler-Toledo) has been investigated, continuing previous work, using quasi-isothermal experiments. A new model for the prediction of the effects of heat transfer has been suggested in this work, acid more closely simulates the practical conditions than did the earlier model. In particular, the reference sensor temperature is compared with the sample sensor temperature rather than with the sample temperature itself, as was used in the previous model. Both theoretical simulation and experimental results show that, a phase angle is introduced simply by virtue of heat transfer effects, and that it depends on many experimental parameters. In particular, it is independent of the amplitude of temperature modulation, but depends strongly (and non-linearly) on the frequency and approximately linearly on the sample mass, To a large extent, these dependencies are well predicted by the theoretical model, which also predicts a strong influence of the heat transfer coefficient characterising the quality of the interface been sample and pan. It is shown that the use of a heat transfer fluid can largely eliminate the inconsistencies in the interfacial contact between sample and pan. (C) 1999 Elsevier Science B.V. All rights reserved.