Authors:Hu Rongzu, Wu Shanxiang, Liang Yanjun, Sun Lixia, and Yang Zhengquan
A numerical method of computing the kinetic parameters (the activation energy (E), the preexponential constant (A) and the reaction order (n)) of exothermic decomposition of energetic materials via the exothermic rate equation is presented. The values ofE, A, andn are reported for the exothermic decomposition of six typical energetic materials, 1,6-diazido-2,5-dinitrazahexane (I), 1,5-diazido-3-nitrazapentane
(II), 2,2,4,7,9,9-hexanitro-5-methyl-4,7-dinitrazadecane (III), 2,2,2-trinitroethyl-4,4,4-trinitrobutyrate (IV), 1,4-dinitro-2,3-dioxo-1,4-dinitrazacyclohexane
(V) and 1,3,5-trianitro-1,3,5-triazafurazano[3,4-f]cycloheptane (VI).
Authors:H. Mothé Filho, M. Gonçalves, and C. Mothé
Thermal degradation of granite and marble industry reject (GMIR), a red clay (RC)and their composites were studied by non-isothermal
thermogravimetry (TG/DTG) in nitrogen atmosphere, differential thermal analysis (DTA) and derivative thermogravimetry(DTG)
in air atmosphere. Measurements were made in the temperature range of 25–1000,25–1200 and 25–1400C. The kinetic parameters
were determined by Flynn–Wall and Kissinger's methods. The results indicate the absent dominance of one mechanism of reaction,
and the composites show smaller values of kinetic parameters than GMIR or RC.
Thermal decomposition processes of selected chemicals used as food preservatives such as sodium formate, sodium propionate,
sodium nitrates(V and III) and sodium sulphate(IV) were examined by the derivatographic method. Based on the curves obtained,
the number of decomposition stages and characteristic temperatures of these compounds have been found. Mass decrements calculated
from TG curves ranged from 28.9% for sodium formate to 77.8% for sodium nitrate(V), while sodium sulphate showed a mass increment
of 5.6%. Kinetic parameters such as activation energy (Ea ), frequency factor (A ) and reaction order (n ) were calculated from TG, DTG and T curves. Sodium formate shows the highest values of Ea and A which amount to 171.7 kJ mol–1 and 5.8⋅1014 s–1 , respectively, while the lowest ones, Ea =28.2 kJ mol–1 and A =3.65⋅102 s–1 belong to sodium nitrate(V).
Due to the complex character of the thermal degradation of polymers as a solid-gas chain reaction, an unequivocal kinetic
characteirzation is possible only for stationary states of both radical concentration and reaction mechanism. These conditions
are hardly realizable in non-isothermal thermogravimetry. Additional the weight losses are depedent on the volatility of the
reaction products. That is not always certain in polymer degradation. As a consequence the deduced ‘kinetic parameters’ are
not unequivocal. They are conversion and heating rate dependent and may be influenced by sample shape and size. Thus the ‘kinetic
parameters’ are in fact from the point of view of mathematics the fitting parameters of a ‘rate equation’ like relation, specific
for the used reaction conditions only. From the point of view of chemical kinetics they are neither attributable to a determined
reaction mechanism nor can they be used for predictions.
A graphic method is proposed to determine all of the kinetic parameters in Wigner-Polanyi equation of desorption. A desorption rate curve from a single temperature-programmed desorption experiment is required by this method to determine the order of reaction (n), the activation energy (Ed) and the pre-exponential factor (v) of the equation. The proposed method has been applied to the oxygen desorption from PdO/Al2O3 samples prepared by impregnating γ-Al2O3 with H2PdCl4 solution used as examples. From the graphic method, the values ofn=2, andv=1.37±0.80×109 s−1 were successfully determined for the desorption. The value ofEd depended on the dispersion of palladium (D) on PdO/Al2O3 samples, and was expressed by the equation:Ed=175+174D kJ·mol−1. This graphic method is a direct and time-saving technique, on comparing with other methods suggested in the literature, for analysis of data from temperature-programmed desorption of simple desorption processes.
In this work, a kinetic study on the thermal degradation of carbon fibre reinforced epoxy is presented. The degradation is
investigated by means of dynamic thermogravimetric analysis (TG) in air and inert atmosphere at heating rates from 0.5 to
20C min−1 . Curves obtained by TG in air are quite different from those obtained in nitrogen. A three-step loss is observed during
dynamic TG in air while mass loss proceeded as a two step process in nitrogen at fast heating rate. To elucidate this difference,
a kinetic analysis is carried on. A kinetic model described by the Kissinger method or by the Ozawa method gives the kinetic
parameters of the composite decomposition. Apparent activation energy calculated by Kissinger method in oxidative atmosphere
for each step is between 40–50 kJ mol−1 upper than Ea calculated in inert atmosphere.
The thermo-oxidative degradation illustrated by Ozawa method shows a stable apparent activation energy (Ea ≈130 kJ mol−1 ) even though the thermal degradation in nitrogen flow presents a maximum Ea for 15% mass loss (Ea ≈60 kJ mol−1 ).
Authors:Michelle G. Mothé, Leni F. M. Leite, and Cheila G. Mothé
predictions, especially due to the combination of factors such as heat transfer, mass transfer phenomena, chemical reactions, and thermal stability [ 3 , 6 , 7 ]. Knowledge of kineticparameters as activation energy and pre-exponential factor would help
Authors:O. N. Nikulicheva, V. P. Fadeeva, and V. A. Logvinenko
The paper reports the calculation of kinetic parameters (activation energy, pre-exponent and reaction order) of thermodegradation of some phenol stabilizers. For this purpose, a software package for IBM-compatible personal computers is proposed. The first calculation of kinetic parameters (E, Z, n) was carried out for these compounds. The package can be applied for kinetic calculations on the thermodegradation of other substances.
Authors:Sonia de Almeida, Giseli Bernabé, Marisa S. Crespi, Clóvis A. Ribeiro, and Evaneide Nascimento Lima
, independently from the kinetic model reaction f (α).
The kineticparameters E (kJ mol −1 ) and A (s −1 ) can be determined by the Flynn–Wall–Ozawa isoconversional method [ 12 , 13 ].
A , β , and R are pre-exponential factor
Using the thermal decomposition of [Co(NH3)6]2(C2O4)3·4H2O as a basis, the paper presents results which show how computed values of kinetic parameters are influenced by experimental
conditions (ambient atmosphere, sample mass, linear heating rate) when using the non-isothermal methods and the Coats-Redfern
(CR) modified equation. It also illustrates the influence of the experimental methods i.e. non-isothermal and isothermal (conventional)
methods and also a quasiisothermal-isobaric one which can be recognised as equivalent to Constant Rate Thermal Analysis (CRTA).
The results obtained have confirmed the significant influence of the experimental parameters as well as that of the experimental
method used on the estimated values of kinetic parameters. The correlation between activation energy (E) and sample mass (m) or heating rate (β) is generally of a linear nature:E=a+bx