Search Results

You are looking at 81 - 90 of 206 items for :

  • "non-isothermal kinetics" x
  • Refine by Access: All Content x
Clear All

Abstract  

A model describing the roles of bound and unbound vacancies is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. This is an alternative treatment of a previous approach. The model has been applied to the differential scanning calorimetry (DSC) curves of Cu-5 at.% Zn quenched from different temperatures. An expression to calculate the activation energy for migration of solute-vacancy complexes was also developed which make use of DSC trace data. A value of 89.120.32 kJ mol-1 was obtained for the above alloy. The relative contribution of bound and unbound vacancies to partition of effective activation energy corresponding to the ordering process as influenced by quenching temperature was also assessed.

Restricted access

Abstract  

The condensation approximation (CA) and numerical regularization procedure (RP) methods used to solve a Fredholm integral equation of the first kind describing the adsorption equilibria on a heterogeneous solid surface under isothermal conditions have been adopted in the present study to evaluate desorption energy distributions from temperature-programmed desorption (TPD) spectra. From comparisons of the computational results obtained by means of these methods on the basis of simulated TPD spectra, it follows that the CA gives stable solutions for wide desorption energy distributions and it can be used successfully for calculations from wide and clear resolved peaks in the TPD spectra. The use of the RP is more advantageous for acquisition of the distributions from closely related narrow peaks in the TPD spectra.

Restricted access

Abstract  

In the present work a comparative kinetic study was performed on the thermal behavior of three antioxidants of IRGANOX-type (L101, L109 and L115) in dynamic air atmosphere under non-isothermal conditions. The TG-DTG data were obtained at heating rates of 5, 7, 10 and 15 K min−1. The kinetic parameters were obtained by processing these data with strategies corresponding to Flynn-Wall-Ozava (FWO), Friedman (FR), Budrugeac-Segal (BS) and non-parametric kinetic (NPK) methods. The thermal degradation by all the three compounds take place in melted state, so that any kinetic models regarding the decomposition of solids are inapplicable. Only with the NPK method it was possible a separation between the two functions of the reaction rate. For the temperature dependence, f(T), an Arrhenius-type model was searched; for the conversion dependence, the Ŝestak-Berggren equation was suggested in order to discriminate between physical (m) and chemical (n or p) steps of a complex thermodegradation process.

Restricted access

Abstract  

The kinetics of thermal decomposition of Ca(H2PO4)2H2O under non-isothermal conditions was studied. The TG/DTG curves were obtained at five heating rates: 5, 7, 10, 12 and 20 K min–1. The kinetic analysis was performed by means of three methods: Friedman, Budrugeac–Segal and NPK by Sempere and Nomen. An important dependence of the activation energy vs. the conversion degree was observed and also a compensation effect. The decomposition consists of water loss and is due to the elimination of crystallization water and an intermolecular condensation, respectively.

Restricted access

Abstract  

Kinetics of thermal decomposition of three structurally similar complexes Co2Cu(C2O4)3 (R-diam)2, where R is ethyl, 1,2-propyl or 1,3-propyl, was studied under non-isothermal conditions and nitrogen dynamic atmosphere at heating rates of 5, 7, 10, 12 and 15 K min−1. For data processing the Flynn-Wall-Ozawa and a modified non-parametric kinetic methods were used. By both methods the activation energy are in the range of 97–102 kJ mol−1. The formal kinetic is r=kα(1−α)2. Also a compensation effect between lnA and E was evidenced. The kinetic analysis lead to the conclusion of an identic decomposition mechanism by a single step process.

Restricted access

Kinetic analysis of thermogravimetric data

XXX. Thermal decomposition of some Reinecke salt like complexes

Journal of Thermal Analysis and Calorimetry
Authors: J. Zsakó, I. Ganescu, Cs. Várhelyi, and L. Chirigiu

Thermal decomposition of 6 complexes of the type AH[Cr(NCS)4 (am)2]· nH2O is studied with derivatograph. The formation of Cr(NCS)3 as a labile intermediate is presumed. For some decomposition stages kinetic parameters are derived. The kinetic compensation effect is discussed.

Restricted access

Abstract  

A new procedure for the prediction of the isothermal behaviour of the solid-gas system from non-isothermal data is suggested. It bypasses the use of various approximations of the temperature integral that ground the integral methods of prediction. The procedure was checked for: (1) simulated data corresponding to a first order reaction; (2) experimental data obtained in the isothermal and non-isothermal decompositions of ammonium perchlorate. For the simulated data, a very good agreement between calculated isotherms and those evaluated by means of the suggested procedure was obtained. A satisfactory agreement (errors in time evaluation corresponding to a given degradation lower than 18%, for 0.10a0.37 and lower than 10% for 0.37a0.70) was obtained for the experimental data corresponding to the decomposition of ammonium perchlorate. In this last case, the mentioned differences between experimental and calculated data can be due both to the inherent errors in the evaluation of the decomposition isotherms and to the dependence of the activation energy on the conversion degree.

Restricted access

Abstract  

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 estimation.

Restricted access

Abstract  

Recently, Órfão obtained two simple equations for the estimation of the relative error in the activation energy calculated by the integral methods [2]. In this short communication, the validity of the equations has been evaluated by comparing the results calculated by the equations with the results calculated by the equation from theoretical derivation without introducing any assumption.

Restricted access

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.

Restricted access