Authors:P. Budrugeac, D. Homentcovschi, and E. Segal
The differential and integral isoconversional methods for evaluation the activation energy, described in the first note of
this series, were applied for:
a) simulated data for two successive reactions;
b) dehydration of calcium oxalate monohydrate.
It was shown that for these systems the activation energy depends on the conversion degree as well as on the method of evaluation.
Authors:P Budrugeac, D. Homentcovschi, and E. Segal
An analysis is presented of the consequences of the use of a one term equation containing apparent activation parameters,
instead of the true rate equation to describe two successive decomposition reactions undergone by a solid compound. It is
demonstrated that the apparent activation energy, obtained by means of isoconversional differential and integral methods,
varies with the conversion degree for a relatively narrow temperature range and with temperature at a given value of the conversion
degree. The activation energy values obtained with the isoconversional differential method are higher than the corresponding
values obtained with the isoconversional integral method.
Authors:Xiaomin Cao, Yun Tian, Zhiyong Wang, Yuwen Liu, and Cunxin Wang
The kinetics of bovine serum albumin (BSA) denaturation in the absence and the presence of urea was studied by the iso-conversional
method and the master plots method using differential scanning calorimetry (DSC). The observed denaturation process was irreversible
and approximately conformed to the simple order reaction, and the denaturation did not follow rigorously first-order kinetic
model or other integral order reaction models. The denaturation temperature (Tm), apparent activation energy (Ea), approximate order of reaction (n), and pre-exponential factor (A) all distinctly decreased as the 2 mol L−1 urea was added, which indicated that the urea accelerated the denaturation process of BSA and greatly reduced thermal and
kinetic stability of BSA. This study also demonstrated that the iso-conversional method, in combination with the master plots
method, provides a valuable and useful approach to the study of the kinetic process of protein denaturation.
Authors:X. Cao, Z. Wang, X. Yang, Y. Liu, and C. Wang
The kinetics of protein thermal transition is of a significant interest from the standpoint of medical treatment. The effect
of sucrose (0–15 mass%) on bovine serum albumin denatured aggregation kinetics at high concentration was studied by the iso-conversional
method and the master plots method using differential scanning calorimetry. The observed aggregation was irreversible and
conformed to the simple order reaction. The denaturation temperature (Tm), the kinetic triplets all increased as the sucrose concentration increased, which indicated the remarkable stabilization
effect of sucrose. The study purpose is to provide new opportunities in exploring aggregation kinetics mechanisms in the presence
Authors:M. López, M. Blanco, A. Vazquez, J. Ramos, A. Arbelaiz, N. Gabilondo, J. Echeverría, and I. Mondragon
The curing kinetics of nanocomposites based on phenolic resol cured with triethylamine (TEA) containing different amounts
of organic montmorillonite was analyzed by differential scanning calorimetry. Kissinger-Akahira-Sunose (KAS) model-free kinetics
has been applied to correlate the dynamic cure behaviour in the presence of modified montmorillonite. The effect in the curing
of the use of different clay modifiers has also been studied. A commercial clay with hydroxyl groups (Cloisite 30B) and a
customized montmorillonite (PheMMT) whose reactive groups induce condensation reactions with the resol matrix have been used.
Strong dependency of activation energy on apparent conversion has been observed for all compounds.
Authors:D. Válková, J. Kislinger, M. Pekař, and J. Kučerík
Humic acids represent a complicated mixture of miscellaneous molecules formed as a product of mostly microbial degradation
of dead plant tissues and animal bodies. In this work, lignite humic acids were enriched by model compounds and the model-free
method suggested by Šimon was used to evaluate their stability over the whole range of conversions during the first thermooxidative
degradation step. The kinetic parameters obtained were used to predict the stability at 20 and 180�C, respectively, which
served for the recognition of processes induced by heat and those naturally occurring at lower temperatures. Comparison of
the conversion times brought a partial insight into the kinetics and consequently into the role of individual compounds in
the thermooxidative degradation/stability of the secondary structure of humic acids. It has been demonstrated that aromatic
compounds added to humic acids, except pyridine, increased stability of humic acids and intermediate chars. The same conclusion
can be drawn for acetic and palmitic acids. Addition of glucose or ethanol decreased the overall humic stability; however,
the char of the former showed the highest stability after 40% of degradation.
The mathematical evaluation of the activation
energy, E, of non-isothermal degradation
reactions is usually made using the Ozawa/Flynn–Wall isoconversion principle
and involves the numerical resolution of a set of integrals without closed
form solution, which are solved by polynomial approximation or by numeric
integration. In the present work, the isoconversion principle, originally
described and maintained until now as an algebraic problem, was written as
a set of ordinary differential equations (ODEs). The individual ODEs obtained
are integrated by numeric methods and are used to estimate the activation
energy of simulated examples. A least square error (LSE) objective function
using the introduced ODEs was written to deal with multiple heating rate CaCO3
thermal decomposition TG experiments.