Authors:W. Yan, C. Ma, J. Wu, W. Zhang, and D. Jang
Crystal of the complex Ni2L (ClO4)2 was obtained by reaction of Ni(ClO4)2 and macrocyclic ligand H2L, where L2– is the dinucleating macrocycle with two 2,6-di(aminomethyl)-4-methyl phenolate entities combined by the same two lateral chains, –(CH2)2–NH–(CH2)2–, at the amino nitrogens. The thermal decomposition processes of the title complex were studied in a dynamic atmosphere of dry argon using TG-DTG. The kinetic analysis of the first and second thermal decomposition steps were performed via the TG-DTG curves, and the kinetic parameters were obtained from analysis of the TG-DTG curves with integral and differential methods. The most probable kinetic function was suggested by comparison of the kinetic parameters.
A differential method is proposed which uses local heating rates to evaluate non-isothermal kinetic parameters. The method
allows to study the influence of the deviation of the true heating rate with respect to the programmed one on the values of
the kinetic parameters. For application, the kinetic parameters of the following solid-gas decomposition reaction were evaluated:
[Ni(NH3)6]Br2(s)→[Ni(NH3)2]Br2(s)+4NH3(g). The results obtained revealed significant differences between the values of the non-isothermal kinetic parameters obtained
by using local heating rates and those obtained by using the programmed heating rate. It was also demonstrated that the kinetic
equation which makes use of the local heating rates permits a better description of the experimental (α, t) data than the
kinetic equation which uses the programmed constant heating rate.
Three rational fraction approximations for the temperature integral have been proposed using the pattern search method. The
validity of the new approximations has been tested by some numerical analyses. Compared with several published approximating
formulas, the new approximations is more accurate than all approximations except the approximations proposed by Senum and
Yang in the range of 5≤E/RT≤100. For low values of E/RT, the new approximations are superior to Senum-Yang approximations as solutions of the temperature integral.
Authors:C. Păcurariu, R. Lazău, I. Lazău, R. Ianoş, and T. Vlase
The influence of the specific surface area on the crystallization processes of two silica gels with different specific surface
areas has been investigated in non-isothermal conditions using DTA technique. The activation energies of the crystallization
processes were calculated using four isoconversional methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink and Tang.
It has been established that, the decrease of the surface area from S=252.62 m2 g−1, in the case of sample GS2, to S=2.52 m2 g−1, in the case of sample GS1, has determined a slight increase of the activation energy of the crystallization process of the
gels. Regardless of the isoconversional method used, the activation energy (Eα) decreases monotonously with the crystallized fraction (α), which confirms the complex mechanism of gels crystallization.
It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the crystallization processes of the studied silica
Authors:C. Ribeiro, W. de Souza, Marisa Crespi, J. Gomes Neto, and F. Fertonani
Tungsten carbide, WC, has shown dissimilar thermal behavior when it is heated on changeable heating rate and flow of oxidant
atmosphere. The oxidation of WC to WO3 tends to be in a single and slow kinetic step on slow heating rate and/or low flux of air. Kinetic parameters, on non-isothermal
condition, could be evaluated to the oxidation of WC to heating rate below 15°C min−1 or low flow of air (10 mL min−1). The reaction is governed by nucleation and growth at 5 to 10°C min−1 then the tendency is to be autocatalytic, JMA and SB, respectively.
Authors:T. Vlase, Gabriela Vlase, Dorina Modra, and N. Doca
Thermal behavior of four food
dyes, i.e. tartrazine, crysoine, azorubine and amarant was studied under non-isothermal
conditions, in dynamic air atmosphere and at heating rates of 5, 10, 15 and
20C min–1. The TG data were correlated
to the FTIR spectra of each sample, before and after the thermal decomposition.
Kinetic study by processing the TG data was performed. The main conclusion
of this study is that the non-parametric kinetic method allows a separation
of the steps of a complex process and that the values of the activation energy
obtained by this method agree satisfactory with that of Flynn–Wall–Ozawa
Authors:M. Badea, R. Olar, E. Cristurean, D. Marinescu, M. Brezeanu, C. Calina-Soradi, and E. Segal
Data concerning the thermal behaviour of four heteropolynuclear compounds with the general formula [CuML(CH3COO)3] whereM=Ni(II), Zn(II), Mn(II) and Co(II); LH=2-amino-5-mercapto-1,2,3-thiadiazole were obtained. For the kinetically workable decomposition steps the values of the kinetic
parameters were estimated.
There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no ‘best' method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations . Here we propose a method for extractingE from non-isothermal data, that promises general validity.
The adsorption of n -butane on extruded cylindrical activated carbon grains is studied providing two kinds of information: the influence of the
temperature and the hydrocarbon partial pressure on the adsorption dynamics (kinetic study) and on the adsorption capacities
(thermodynamic study). The thermodynamic aspect could be interpreted by a Langmuir model. From a kinetic point of view, we
have experimentally proved that strong temperature variations occur inside the particles during the adsorption. In this paper,
a kinetic model including both mass and heat transfer phenomena is proposed. Good agreement is found between the kinetic model
predictions and the experimental mass and temperature variations inside the grain during the hydrocarbon adsorption.
A differential isoconversional non-linear procedure for evaluating activation energy from non-isothermal data is suggested.
This procedure was applied to model reactions (simulations) and to the dehydration of CaC2O4⋅H2O. The results were compared with those obtained by other isoconversional methods.