TABLE OF CONTENTS The behaviour of any real, initially-solid sample is going to be considerably more complex than the idealized description given above. The success that has been achieved using this limited set of models can only be attributed to an averaging effect over the variety of processes occurring at the molecular level. When some of these processes have very different kinetic characteristics, none of the models may provide an adequate description of the experimental results.
There are several useful indicators of the possible occurrence of complex reactions [49]. From the experimental side, a lack of correspondence between DSC and DTG results indicates that the rate of change of enthalpy is not directly proportional to the rate of mass loss. Experiments at different heating rates also show up complexities.
Another important indication is the dependence of the value obtained for E upon the extent of reaction, ? [81]. It is thus essential to use a method of kinetic analysis that allows such a dependence to be detected. In isothermal studies, the occurrence of complex reactions may be detected by Arrhenius plots that are curved or give two linear regions [81]. The shapes of plots of ? against reduced-time also vary systematically with temperature.
The contributions to complex reactions are most easily separated when the activation energies of the individual reactions are considerably different. Reactions with low E values dominate the kinetics at low temperatures and slow heating rates, while those with high E
