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Non-isothermal model-free predictions

Application to the formation of yttria from yttrium trifluoroacetate

Journal of Thermal Analysis and Calorimetry
Authors: Hichem Eloussifi, Jordi Farjas, Pere Roura, and Mohamed Dammak

deposition, and thermal treatment to remove the organic species and to crystallize the material. Thermal treatment can be optimized by setting up a temperature program that involves isothermal stages to slow down the reaction at the critical steps and non-isothermal

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Abstract  

The authors present the results concerning the thermal behaviour of three polynuclear coordination compounds of Nd(III) and Co(II) or Fe(III) with triptophan. For the dehydration steps the values of the non-isothermal kinetic parameters have been determined.

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Abstract  

Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances. TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability, compatibility, polymorphism, kinetic analysis, phase transitions etc.). The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process. The results are further used to predict the system’s behaviour in various circumstances. A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric kinetics. In the model-fitting methods the kinetic triplets (f(α), A and E a) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition. The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation energies on the extent of conversion. It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous work. The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as well as a different strategy of experimental data processing.

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The thermal decomposition of Eu2(BA)6(bipy)2 (BA=C2H5N 2, benzoate; bipy=C10H8N2, 2,2'-bipyridine)and its kinetics were studied under the non-isothermal condition by TG-DTG, IR and SEM methods. The kinetic parameters were obtained from analysis of the TG-DTG curves by the Achar method, the Madhusudanan-Krishnan-Ninan (MKN) method, the Ozawa method and the Kissinger method. The most probable mechanism function was suggested by comparing the kinetic parameters. The kinetic equation for the first stage can be expressed as: dα/dt=Aexp(–E/RT)3(1–α)2/3.

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Two methods for estimating the critical temperature (T b) of thermal explosion for the highly nitrated nitrocellulose (HNNC) are derived from the Semenov's thermal explosion theory and two non-isothermal kinetic equations, d/dt=Af()e–E/RT and d/dt=Af()[1+E/(RT)(1–T o/T)]e–E/RT, using reasonable hypotheses. We can easily obtain the values of the thermal decomposition activation energy (E), the onset temperature (T e) and the initial temperature (T o) at which DSC curve deviates from the baseline of the non-isothermal DSC curve of HNNC, and then calculate the critical temperature (T b) of thermal explosion by the two derived formulae. The results obtained with the two methods for HNNC are in agreement to each other.

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Pyrolysis of petroleum refinery sludge has received global acclamation as a clean conversion technique for providing solution of sludge disposal as well as efficient resource utilization. This communication reports the kinetics study of pyrolysis of petroleum refinery sludge. Experiments were carried out by means of thermogravimetric analysis at different heating rates of 5, 10 and 20�C min−1. The pyrolytic reaction is significant in the temperature range of 200–350�C and analysis and evaluation of kinetic parameters is done in the 100–500�C region of non-isothermal TG curves obtained in nitrogen atmosphere. The activation energy is calculated by iso-conversional method, then other kinetic parameters are determined by considering single reaction and two reaction global kinetic model. Two-reaction model is found to fit satisfactorily the experimental results.

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Abstract  

Data on the thermal stability of organic materials such as diaminofurazan (DAF) and diaminoglyoxime (DAG) was required in order to obtain safety information for handling, storage and use. These compounds have been shown to be a useful intermediate for the preparation of energetic compounds. In the present study, the thermal stability of the DAF and DAG was determined by differential scanning calorimetery (DSC) and simultaneous thermogravimetery-differential thermal analysis (TG-DTA) techniques. The results of TG analysis revealed that the main thermal degradation for the DAF and DAG occurs in the temperature ranges of 230–275°C and 180–230°C, respectively. On the other hand, the TG-DTA analysis of compounds indicates that DAF melts (at about 182°C) before it decomposes. However, the thermal decomposition of the DAG started simultaneously with its melting. The influence of the heating rate (5, 10, 15 and 20°C min−1) on the DSC behaviour of the compounds was verified. The results showed that, as the heating rate was increased, decomposition temperatures of the compounds were increased. Also, the kinetic parameters such as activation energy and frequency factor for the compounds were obtained from the DSC data by non-isothermal methods proposed by ASTM E698 and Ozawa. Based on the values of activation energy obtained by ASTM and Ozawa methods, the following order in the thermal stability was noticed: DAF>DAG.

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Journal of Thermal Analysis and Calorimetry
Authors: Rogério L. Pagano, Verônica M. A. Calado, Frederico W. Tavares, and Evaristo C. Biscaia

Introduction A cure kinetic study of polymeric resin can be carried out in a calorimeter analysis, operating by two models: isothermal and non-isothermal. A way to estimate the kinetic parameters using any experimental data is

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Journal of Thermal Analysis and Calorimetry
Authors: Seied Mahdi Pourmortazavi, Mehdi Rahimi-Nasrabadi, Iraj Kohsari, and Seiedeh Somayyeh Hajimirsadeghi

parameters corresponding to the thermal decomposition of NTO are still unclear. On the other hand, there is no report on the prediction of thermal decomposition parameters of NTO via non-isothermal methods using DSC data under various heating rates. Thus, in

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The thermal decomposition of the mixed-ligand complex of iron(III) with 2-[(o-hydroxy benzylidene)amino] phenol and pyridine-[Fe2O(OC6H4CH=NC6H4O)2(C5H5N)4]·2H2O and its non-isothermal kinetics were studied by TG and DTG techniques. The non-isothermal kinetic data were analyzed and the kinetic parameters for the first and second steps of the thermal decomposition were evaluated by two different methods, the Achar and Coats-Redfern methods. Steps 1 and 2 are both second-order chemical reactions. Their kinetic equations can be expressed as: dα/dt=Ae−E/RT(1-α)2

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