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

The shape of a differential thermal analysis (DTA) curve depends on the sam ple 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 cel l containing the sample (or the reference), R-a (R-r). Having access to a d atabase that contains the values of the sample heat capacity, C-p, and thos e of the enthalpy of transformation, H, and calculating the parameters that depend on the apparatus, the cells and the reference, as well as the heati ng rate used, it is possible to determine the Delta T (T-a - T-r) values th rough the equation T-a - T-r = R(a)dH/dt + R(r)C(r)dT/dt - R(a)C(a)dT(a)/dt where C-a is the heat capacity of the cell + sample system and Cb the heat capacity of the cell + reference system. The comparison between the calcula ted and experimental values for Delta 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 anal ysis in general and of the apparatus used in particular. (C) 1999 Elsevier Science S.A. All rights reserved.