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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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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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Some transition metal nitrate complexes with hexamethylenetetramine

Part LV. Preparation, X-ray crystallography and thermal decomposition

Journal of Thermal Analysis and Calorimetry
Authors: G. Singh, B. Baranwal, I. Kapoor, D. Kumar, C. Singh, and R. Fröhlich

Abstract  

Three hexamethylenetetramine (HMTA) metal nitrate complexes such as [M(H2O)4(H2O-HMTA)2](NO3)·4H2O (where M=Co, Ni and Zn) have been prepared and characterized by X-ray crystallography. Their thermal decomposition have been studied by using dynamic, isothermal thermogravimery (TG) and differential thermal analysis (DTA). Kinetics of thermal decomposition was undertaken by applying model-fitting as well as isoconversional methods. The possible pathways of thermolysis have also been proposed. Ignition delay measurements have been carried out to investigate the response of these complexes under condition of rapid heating.

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The thermal behavior under isothermal conditions of some ammonia nitrate, ammonia phosphates and calcium phosphates mixtures with added micronutrients was studied. In order to establish the variation of activation energy (E) vs. conversion (α), the TG data were interpolated with spline functions, followed by numeric derivation. Using the so determined reaction rate the Friedman differential-isoconversional method was applied. A dependence of the activation energy vs. conversion was observed, meaning a many-step reaction. Therefore a procedure based on the compensation effect (and suggested by Budrugeac and Segal) was applied.

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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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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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Journal of Thermal Analysis and Calorimetry
Authors: G. Vázquez, F. López-Suevos, J. González-Alvarez, and G. Antorrena

Summary  

Phenol-urea-formaldehyde-tannin (PUFT) adhesives have been prepared by copolymerization at room temperature of pine bark tannins with phenol-urea-formaldehyde (PUF) prepolymers prepared under varying operating conditions. Differential scanning calorimetry (DSC) and dynamic mechanical analysis (DMA) have been used to analyse the curing of prepolymers and adhesives. DSC curves were obtained at three different heating rates and, by means of the Model Free Kinetics isoconversional method, chemical conversion vs. time at a given temperature was obtained. Mechanical conversion was calculated from DMA storage modulus data for those adhesives which gave the best results for plywood and MDF boards.

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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  

Kinetics of a thermal dechlorination and oxidation of gadolinium oxychloride (GdOCl) originating from a molten salt process was investigated under various oxygen partial pressures by using a non-isothermal thermogravimetric (TG) analysis. The results of isoconversional analysis of the TG data suggests that the dechlorination and oxidation of GdOCl follows a single step reaction and the observed activation energy was determined as 137.7�4.1 kJ mol−1. The kinetic rate equation was derived for a conversion of the GdOCl with a linear-contacting boundary reaction model. The power dependency for oxygen and the pre-exponential factor was determined as 0.306 and 1.012 s−1 Pa−0.306, respectively.

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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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