APPLICATION OF DYNAMIC DIFFERENTIAL SCANNING CALORIMETRY TO STUDY OF PHASE-TRANSITIONS

A dynamic differential scanning calorimeter (dynamic DSC) works simult aneously as a differential scanning calorimeter and an AC calorimeter, using the same apparatus with AC temperature modulation superposed on a linear temperature ramp. From AC calorimetric (ACC) operation in wh ich the part responding to AC temperature modulation is taken into acc ount, we can determine the absolute value of heat capacity by making t he best of the twin-type apparatus, although the temperature resolutio n is a little lower than in high precision AC calorimetry. Therefore, at a second order phase transition, ACC operation is useful for obtain ing temperature dependence of linear heat capacity and furthermore, th e frequency dispersion of the linear heat capacity is obtainable. On t he other hand, at a first order phase transition, the situation is com plicated. Nevertheless, latent heat at a first order phase transition can be estimated precisely from the both results of DSC operation and ACC operation. For further study, we have to pay attention to non-line ar heat capacity. When a first order transition takes place over a cer tain temperature range, the analysis of the waveform of AC temperature observed at a steady temperature in this range gives evidence for a k inetic mechanism. The experimental test is performed for sodium nitrit e, which undergoes both first and second order phase transitions.