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The consistency of the kinetic parameters derived from isothermal and nonisothermal
data should not be used, as it follows from Vyazovkin’s analysis, as a decisive criterion to
determine if the values are trustworthy. It is not a sufficient condition. He exemplifies
this on the fact that although fitting isothermal and nonisothermal data to single-step
models resulted in incorrect values of the kinetic triplets, the latter are also in perfect
agreement.
Vyazovkin [2000] further shows that there are some rather insignificant differences
between the E a -dependences obtained by using integral and differential methods. These
differences arise partially from the fact that the equations of the integral methods are
usually derived under the assumption of the constancy of the activation energy. On the
other hand, the differential methods may suffer from imprecise numerical differentiation,
even in the case of artificial data that are free of ‘experimental noise’.
In conclusion, he declares that model-free techniques have been very successful in
detecting multi-step kinetics in the data provided. Fitting data to multi-step kinetic
models has allowed the ‘true mechanism’ to be guessed for the simulated data. For the
real data, the mechanistic guesses happened to be uncertain. The fact that the obtained
E a -dependences allow one to unmistakably recognize a multi-step process taken alone is,
according to him, already a very important piece of mechanistic information.
Brown et al. [2000] say that use of small samples has decreased the problems of heat
transfer at the expense of a possible decrease in the homogeneity of the sample.
On the assumption that the data obtained are reliable and that random noise in the
data is negligible, one can proceed in the search for a mathematical description of the
data.
A mathematical description of the data is usually sought in terms of a ‘kinetic triplet’
(i.e. Arrhenius parameters A and E a , and the reaction model, f(α), also called the
conversion function).
Attempts have to be made to relate the computational results to the actual sequence of
physico-chemical processes occurring, i.e. the reaction mechanism. Formulation of such
a relationship is generally only possible with the aid of complementary information from
microscopic, spectroscopic and structural studies.
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