Results obtained on the thermooxidative degradations of LDPE (low-density polyethylene) and NBR (nitrile-butadiene rubber)
are presented. The activation energies for the thermooxidations leading to solid products were estimated. For LDPE, the activation
energies obtained from non-isothermal data are in satisfactory agreement with those obtained from isothermal data. For NBR,
the isothermal activation energy is ≉16% higher than the non-isothermal one. This difference is due to the morphological changes
undergone by NBR during its heating at the rather high temperatures at which isothermal measurements were performed.
Authors:V. Mamleev, S. Bourbigot, M. Bras, and J. Lefebvre
Two well-known isoconversion methods, the first one developed by Ozawa-Flynn-Wall and the second one developed by Friedman,
are confronted with calculations made using modulated thermogravimetry (MTG). The latter variant is free from a number of
assumptions and restrictions made in the isoconversion computations. In particular, it allows the use of a single decomposition
curve and it remains in force even in the case of multistage decomposition with conjugated processes. To obtain the model-fitting
methods from the model-free methods one should replace some functions averaged over isoconversion levels by the functions
calculated on the basis of kinetic models. In the Ozawa-Flynn-Wall method it is the averaged reduced time (integral of Arrhenius
exponential over time). In the method of Friedman it is the averaged differential conversion function. In MTG, the perturbations
caused by the sinusoidal temperature modulation are connected with derivatives of mass loss by simple scaling, where activation
energy plays a role of a scaling parameter. The ratio of the experimentally measured perturbations to the experimental derivative
is used for the model-free computation of activation energy. If a theoretical derivative replaces the experimental one, this
procedure leads to the model-fitting method. Even a rough approximation of the experimental derivative should not lead to
an excessive error in activation energy. If in a vicinity of peaks' maxima in derivatives of mass loss the decomposition is
controlled by single rate-limiting processes, modulated thermogravimetry should give realistic activation energies for these
processes. Inasmuch as the results of MTG are weakly sensitive to selection of kinetic models, this method should have a high
A weighted mean activation energy method was applied to describe the reactivity and combustibility of crude oils via simultaneous TG/DTG. Thermal experiments were conducted with a non-isothermal method at a heating rate of 10‡C min−1 with excess air. Reaction rates increased progressively with increasing temperature. The rate data were fitted to an Arrhenius equation; the plots showed three distinct reaction regions. Weighted mean activation energies (Ewm), of the crude oils were calculated and a correlation was established betweenEwm, API gravity and peak temperatures during high-temperature oxidation.
Poly(bisphenol A acryloxyethyl phosphate) (BPAAEP) was blended in different ratios with a commercial urethane acrylate to
obtain a series of UV curable flame-retardant resins. The thermal oxidative degradation mechanism of their cured films in
air were studied by thermogravimetric analysis at several heating rates between 5 and 20�C min−1. The activation energies were determined using Kissinger method, Friedman method, Flynn-Wall method, Horowitz-Metzger method
and Ozawa method. The results showed that the activation energies of the blends were lower than that of pure urethane acrylate
at lower degree of degradation, whereas the higher activation energies were obtained at higher degree of degradation.
When ethylene-vinyl acetate copolymer, EVA, is heated, a two-stage thermal degradation occurs following its melting. The vinyl
acetate content of the copolymer was determined to be 43.8% by using TA 2950 and TA 2050 thermogravimetric instruments. TG/FTIR
was used to detect the evolved gas. Acetic acid and trans-1-R-4-R'-cyclohexane were the main products evolved from EVA in
the first and second stage, respectively. The apparent activation energies were determined for both stages by differential
Using the earlier theoretical achievements, it was possible to elaborate a full description of adequate transport properties,
including the determination of activation energy for the sorption of such gases as CO2 and CH4 on coal, as well as the formulation of model solutions. The interrelation of the kinetic-diffusion parameters was also demonstrated.
We then analyse the experimental kinetic curve over the entire time range with a constant of a kinetic character and with
the application of two typical solutions of Fick’s law, for fast and slow processes. These three constants may be compared
with one another, since they are expressed using the same unit, and, in effect, may be used to determine the isokinetic effect.
Finally, we suggest a new approach to the estimation of the activation energy, despite the fact that the measurements were
performed at two close temperatures, 293 and 303 K.
In the presented investigations, the isokinetic effect for sorption process has been found to be statistically less significant
when compared with that of chemical reactions/processes.
Results of differential scanning calorimetry (DSC) at different heating rates on Se2Ge0.2Sb0.8 chalcogenide glass are reported and discussed. As the heating rate (α) changed, also the glass transition temperature (Tg) and onset temperature of crystallization (Tc) changed. As the value of the transition activation energyEt changed, the crystallization fraction (χ), heat flow (Δq and the crystallization peak temperature (Tp) also changed. The value of the effective activation energy of crystallizationEc was calculated by means of six different methods. The Se2Ge0.2Sb0.8 chalcogenide glass has two crystallization mechanisms, a one-dimensional and an other surface crystallization growth. The average value ofEt for Se2Ge0.2Sb0.8 is equal to 194.95±3.9 kJ·mol−1 and the average value ofEc is equal to 164±3.3 kJ·mol−1.
The dependence of the frequency factor on the temperature (A=A0Tm) has been examined and the errors involved in the activation energy calculated from some integral methods without considering
such dependence have been estimated. Investigated integral methods are the Coats-Redfern method, the Gorbachev-Lee-Beck method,
the Wanjun-Yuwen method and the Junmeng-Fusheng method. The results have shown that the error in the determination of the
activation energy calculated ignoring the dependence of the frequency factor on the temperature can be rather large and it
is dependent on x=E/RT and the exponent m.
Authors:A. Ortega, L. Pérez-Maqueda, and J. Criado
It has been demonstrated that a single plot of the values of Δlnα1/2/Δln(1-α) (taken from a single α−T curve obtained under a controlled linear increase of the reaction rate) as a function of the corresponding values of Δ(1/T)/Δln(1−α) permits the simultaneous determination of both the activation energy and the kinetic model in accordance with a
solid state reaction.
Authors:T. M. Carvalho, A. T. Adorno, A. G. Magdalena, and R. A. G. Silva
mass%Ag; ( c ) Cu–11 mass%Al– X mass%Ag
The methods of Kissinger and Ozawa were used to study the influence of additions of 4, 6, 8, and 10 mass%Ag on the activationenergy of the (α + γ 1 ) → β reverse eutectoid