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Heteroleptic cadmium(II) complex, potential precursor for semiconducting CDS layers

Thermal stability and non-isothermal decomposition kinetics

Journal of Thermal Analysis and Calorimetry
Authors: Anna Kropidłowska, A. Rotaru, M. Strankowski, Barbara Becker, and E. Segal

Abstract  

Coordination compounds may be used as efficient precursors for fabrication of semiconducting layers. Thermal stability of such a potential precursor — [Cd{SSi(O-tBu)3}(S2CNEt2)]2 — was investigated (tBu means tert-butyl and Et means ethyl). The kinetic study was performed by means of different multi-heating rate methods: isoconversional (Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Friedmann) methods associated with the criterion of the independence of the activation parameters on the heating rate. The kinetic triplet of the non-isothermal decomposition of this Cd(II) complex was established.

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The kinetic and thermal behaviour of the following compounds: R-HN-CO-NH-(CH2)n-C6H4-SO2NH2 where R=3,4-dichlorophenyl, phenyl, cyclohexyl; n=0, 1, 2 were studied by TG and DTA techniques. The compounds decompose in many steps; the last one corresponding to the burning of H2N–S–C6H4–C6H4–S–NH2 occurs with comparable reaction rates.

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Barium(II) tetraphenylborate, Ba(Bph4))2·4H2O was prepared, and its decomposition mechanism was studied by means of TG and DTA. The products of thermal decomposition were examined by means of gas chromatography and chemical methods. A kinetic analysis of the first stage of thermal decomposition was made on the basis of TG and DTG curves and kinetic parameters were obtained from an analysis of the TG and DTG curves using integral and differential methods. The most probable kinetic function was suggested by comparison of kinetic parameters. A mathematical expression was derived for the kinetic compensation effect.

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Abstract  

The crystallization kinetic of the basalt glass ceramic of the oxide composition, (%): SiO2 − 50.82; Al2O3 − 12.05; Fe2O3 − 9.28; CaO − 15.48; MgO − 11.08; Na2O+K2O − 1.14; TiO2 − 0.15, with addition of 10% TiO2 as nucleating agent has been studied using thermal analysis under non-isothermal conditions. In this order, the non-isothermal DTA curves were obtained at different heating rates between 4 and 20°C min−1 in the temperature range of 25–1000°C using a Derivatograph-C (MOM, Hungary). The kinetic parameters of the crystallization process were calculated on the basis of Ozawa-Flynn-Wall, Friedman, Budrugeac-Segal and non-parametric kinetic methods.

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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.

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Abstract  

The thermo-oxidative degradation of poly(vinyl alcohol) (PVA) has been investigated by TG+DTG+DTA simultaneous analysis performed in static air atmosphere, at four heating rates, namely 3, 5, 10 and 15 K min−1. TG, DTG and DTA curves showed that, in the temperature range 25–700°C, four successive processes occur. The first process consisting in the loss of physical adsorbed water is followed by three processes of thermal and/or thermo-oxidative degradations. The processing of the non-isothermal data corresponding to the second process (the first process of thermo-oxidation) was performed by using Netzsch Thermokinetics — A Software Module for Kinetic Analysis. The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that the investigated process is complex one. The mechanism of this process and the corresponding kinetic parameters were determined by Multivariate Non-linear Regression Program and checked for quasi-isothermal experimental data. It was pointed out that the first process of thermo-oxidation of PVA consists in three consecutive steps having Avrami-Erofeev kinetic model. The obtained results can be used for prediction of the thermal lifetime of PVA corresponding to a certain temperature of use and an endpoint criterion.

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Dynamic thermal analysis of solid-state reactions

The ultimate method for data analysis?

Journal of Thermal Analysis and Calorimetry
Authors: Chao-Rui Li and Tong B. Tang

Abstract

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 [1]. Here we propose a method for extractingE from non-isothermal data, that promises general validity.

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Abstract  

The topic of the present work is to study the thermal behavior of phenitoine and pharmaceuticals by means of kinetic parameters determined in non-isothermal conditions. The TG/DTG data were obtained at four heating rates. These data were processed by the following methods: Friedman (FR), Budrugeac-Segal (BS) and the modified non-parametric kinetics (Sempere-Nomen). The main conclusions of the kinetic study are The FR method is versatile, but the values of the kinetic parameters are not certain, especially by multistep processes. The BS method offer a non-variant part of the activation energy, but the kinetic description is only formal. The NPK method is able to discriminate between two or more steps of a complex process. In our case, there are a preponderant process (more than 70% of the explained variance). By the NPK method there is a non-speculative separation of the temperature, respective conversion degree dependence of the reaction rate.

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Abstract  

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.

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Abstract  

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.

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