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Abstract  

The thermal behaviour of chitosan was studied by means of thermogravimetry, mass spectrometry and infrared spectrometry. Kinetic parameters were obtained by advanced kinetic evaluation (differential isoconversional analysis) from DSC curves, in non-isothermal conditions, at several heating rates, between 5 and 30°C min−1. The results showed that the decomposition of chitosan does not follow a single mechanism because both the activation energy and the pre-exponential factor are not constant during the course of the reaction. A comparison with the results obtained by applying different conventional calculating methods is also shown.

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Abstract  

A modified isoconversional method is applied to perform the kinetic analysis of non-isothermal processes. The solidification process of a polyethylene glycol with a mean molecular of 4000 (PEG 4000) was here analyzed. It was stated that the Avrami model provides a good description of the solidification process. Temperature-cooling rate-transformation diagrams were constructed and there was a good agreement between experimental data and the calculated T-CR-T curves. Moreover, morphological qualitative analysis has been performed by means of scanning electron microscopy.

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Abstract  

Two glasses, the first one with the composition of Li2O·2SiO2 and the second one with the addition of CaO, P2O5 and CaF2 in the stoichiometric ratio corresponding to fluoroapatite were prepared and their tendency to crystallize has been studied by non-isothermal DTA analysis. The values of kinetic parameters calculated using the isoconversional integral method have been used to determine the temperature dependencies of both the length of isothermal induction period and the length of overall isothermal crystallization for both glasses. The estimated dependencies indicate that the glass containing CaO, P2O5 and CaF2 has a lower thermal stability.

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Abstract  

The kinetic parameters (reaction order, n, activation energy, E, pre-exponential factor, A, constant rate, k) for the dehydration step due to elimination of osmotic water and hydrogen-bounded water with the carboxylic groups, and for the anhydrifying step owing to the dehydration of two neighboring (-COOH) groups, were determined under non-isothermal conditions for some carboxylic resins with acrylic-divinylbenzene (DVB) matrix. The kinetic parameters were evaluated by means of isoconversional methods from (TG/DTG) thermal analysis data. The results show a dependence of the apparent kinetic parameters on the cross-linking degree, granulation, gel/macroporous matrix nature, exchange capacity and heating rate.

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Abstract  

The non-isothermal kinetics of precipitation of an Al-12.6 mass% Mg alloy for different heating rates were studied using thermal expansion techniques. The structural changes associated with the precipitation of the and b phases were identified. The conversion degree of each phase was associated with the area under the derivative curve of the thermal expansion with respect to temperature. Using the Kissinger relation and an iso-conversional method we calculated the apparent activation energies associated with formation of the precipitated phases. We report an increasing dependence of the activation energy on the conversion degree, the values obtained being within the range reported in the literature.

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Abstract  

Transformation diagrams are one of the most reliable ways to predict the thermal behavior of the materials. In this work, the crystallization process of several metallic glasses and polymer materials was analyzed and two isoconversional methods are applied to perform kinetic analysis of non-isothermal heating/cooling and isothermal processes. Moreover, the diagrams were constructed from modeling experimental data without the knowledge of the kinetic model. There was a good agreement between experimental data and the calculated curves, which verifies the reliability of the method and the validity of the rate constant model description.

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Abstract  

A new temperature function, derived from the observed dependence of the isoconversional temperature on heating rate, is suggested. Using the new function, extrapolation of the accelerated thermooxidative tests has been performed for 26 experimental data sets. The data cover a wide range of materials from polyolefins and other polymers to biodiesel, edible oils and dried milk. It has been found that the extrapolation from high-temperature data to ambient temperature provides estimations corresponding with experience. Coefficients of variability of the adjustable parameters occurring in the new function are low so enabling to make trustworthy stability predictions.

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Abstract  

Non-isothermal decomposition of iron (III)-diclofenac anhydrous salt was investigated by thermogravimetry (TG) under different conditions in opened and closed α-alumina pans under nitrogen atmosphere. To estimate the activation energy of decomposition, the Capela and Ribeiro isoconversional method was applied. The results show that due to the lid cover different activation energies were obtained. From these curves a tendency can be seen where the plots maintain the same profile for closed lids and almost run parallel to each other. Independently of the different experimental conditions no remarkably different results have been obtained.

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Abstract  

The crystallization mechanism of the glass-ceramics obtained from Romanian (Şanoviţa) basalt in the presence of 3 and 5% CaF2 as nucleation agent has been investigated under non-isothermal conditions using DTA technique. The activation energies of the crystallization processes were calculated using the Kissinger-Akahira-Sunose, Ozawa-Flynn-Wall, Starink and Tang isoconversional methods. The monotonous decreases in the activation energy (E a) with the crystallized fraction (α) confirms the complex mechanism of the glass-ceramics crystallization process. It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the studied glass-ceramics crystallization process.

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Summary Non-isothermal thermogravimetric data were used to evaluate the Arrhenius parameters (activation energy and the pre-exponential factor) of the combustion of two carbonaceous materials, selected as diesel soot surrogates. The paper reports on the application of model-free isoconversional methods (Flynn-Wall-Ozawa and Kissinger methods) for evaluating the activation energy of the combustion process. On the other hand, by means of the compensation relation between E and lnA, which was established by the model-dependent Coats-Redfern method, the value of the pre-exponential factor was estimated from the known value of the model-independent activation energy.

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