Comments on the analysis of experimental data in nonisothermal kinetics

A Preliminary Study of the Phase Transformations in Rolled Al-Fe-Si Alloy

“…An analysis of the transformed fraction is made using the isoconversional method, [11] which allows for a fixed conversion extent to consider constant the kinetic function dependent on that conversion extent. This method is of great use in the evaluation of the apparent activation energy of the diffusion processes.…”

“…This method is of great use in the evaluation of the apparent activation energy of the diffusion processes. In contrast to other equations reported in the literature, [12] Luiggi [11] introduces a new isoconversional equation (Eq. [1]) with an adjustable parameter N whose optimal value is that which permits the reproduction of the experimental activation energy.…”

“…It is, therefore, recommended that the trials be carried out at low values of F for changes to be detected and the apparent activation energy thus assessed. For this reason, only the apparent activation energy associated with the a phase is evaluated, using Luiggi's isoconversional relation, [11] ln…”

Adapting the condensation and evaporation model to the study of kinetics of phase transformations in binary metal systems

“…4. Once the transformed fraction is known, the activation energy is determined by following the isoconversional scheme for isothermal kinetics, with the following relationship [35]:…”

“…In the chemical reaction theory, the possibility that the same experimental data could be adjusted to different functions f (α) leads to erroneous interpretations of the characteristic kinetic triplet parameters, which has led to the so called isoconversional methods [33][34][35] in the study of phase transformations, where isothermal experimentation at fixed T allows the generation of pairs of values (Int, 1/T) or, in non-isothermal cases, pairs of values (Int β, 1/T) for a constant transformed fraction. As a result, any function of α associated to the transformation will be constant for α = constant, which easily allows for the evaluation of the activation energy of the process; however, due to ITAC agreements [36], such data shall be valid only if the other two kinetic triplet elements are generated (activation energy, Arrhenius prefactor and f (α)).…”