Deconvolution of Superimposed Endotherms

With slower heating rates, transformation peaks in DTA and DSC often show features implying the superposition of multiple peaks. If these individual peaks could be isolated, much information about the onset temperatures, rates, and mutual interdependence of individual reactions governing an overall transformation could be discerned. 

The superposition principle for heat flow as measured by power-compensated DSC should apply—just as it would be expected that the water flow into one tank from two pipes would be additive. Assuming Fourier s law holds (steady state heat flow proportional to temperature gradient), the temperature differences measured in DTA (and heat-flux DSC) are additive via contributions from multiple transformation sources within the sample material. 

The process of deconvolution of superimposed endotherms and exotherms requires modeling individual reactions to heat flow functions, which when added together, emulate the exper- 

In addition to deconvolution, the computer fitting of model equations to single transformation peaks has the utility of establishing important parameters of the reaction, such as reaction order and activation energy. This sort of modeling has previously been undertaken by sometimes cumbersome and questionable [2, 3] mathematical manipulation of experimental data. 

Before actual data can be fit to a model, extraneous effects manifested in the trace must be removed, such as the shift in baseline as a result of the change in heat capacity of the sample during the transformation (see section 3.7.2). It may, for some device designs (e.g. post-type DTA), be difficult to purify the instrument output to represent only the latent heat from the transformation because of random baseline float. Hence, the data set fitting a particular model is a necessary but insufficient criterion for guaranteeing that the model describes the measured phenomenon. 

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