HEAT-TRANSFER IN A DISC-TYPE DSC APPARATUS - IV - APPLICABILITY OF THE COUPLED CELLS MODEL TO PERIODIC TEMPERATURE MODULATION

The application of non-linear heating programs to a heat-flux DSC appa ratus has attracted much attention. On the basis of thermodynamics, th e change in enthalpy of a sample during a temperature change Delta T i s due, on the one hand to the true heat capacity of the sample Delta T C-p xi and on the other, to the enthalpy of some transformation occur ring in the sample Delta(r)H Delta xi. These contributions can be sepa rated on the basis of the kinetics of the transformation. The coupled cells model of a disc type, heat flux DSC apparatus has been tested, u sing true heat capacities and a sine modulation of the temperature of the furnace around a constant temperature. In the range from 2 to 60 m Hz, the amplitude and phase shift of the calorimetric signal were meas ured at several frequencies. Theoretical equations, based on the model , and using the thermal Ohm's law explains the results with a reasonab le accuracy. A non-linear DSC experiment affords two ways of determina tion of the heat capacity of a sample making possible a distinction be tween the enthalpic effect and heat capacity.