Relationship between the DTA peak and the phase diagram: symbiosis between a thermodynamic database and a DTA curve

Abstract

The shape of a differential thermal analysis (DTA) curve depends on the sample and the reference, the heating or cooling rates used in the experiment as also the thermal resistance to heat flow from the heat source to the cell containing the sample (or the reference), R a ( R r). Having access to a database that contains the values of the sample heat capacity, C p, and those of the enthalpy of transformation, H, and calculating the parameters that depend on the apparatus, the cells and the reference, as well as the heating rate used, it is possible to determine the Δ T ( T a − T r) values through the equation T a −T r =R a dH dt +R r C r dT r dt −R a C a dT a dt where C a is the heat capacity of the cell + sample system and C b the heat capacity of the cell + reference system. The comparison between the calculated and experimental values for Δ T enables an assessment to be made as to whether the modelled parameters are in agreement with the experimental information. This procedure enables a deeper perception of the thermal analysis in general and of the apparatus used in particular.