Kinetic Analysis Of Non-isothermal Data Research Articles

Kinetic and Thermodynamic Analyses of Co-Pyrolysis of Nylon-Polyethylene Pouch Wastes.

In this study, thermogravimetric measurements of nylon-6/polyethylene double-layer pouch wastes were conducted in N2 under a constant heating-rate mode, and the multiple heating-rate results were analyzed in terms of degradation features and specific temperatures. Experimental results show that the waste pyrolysis involves one reaction stage, and all specific parameters appear to increase with the heating rate. Kinetic analysis of non-isothermal data was thoroughly performed using various isoconversional model-free methods for the calculations of the activation energy, resulting in 143~215 kJ/mol over the whole pyrolysis process. By means of the model-fitting method, the reaction mechanism model g(α) and pre-exponential factor lnk0 are concurrently determined with the aid of the linear compensation effect. With such methodology proposed, the Avrami-Erofeev kinetic model A3/2 of g(α) = [-ln(1 - α)]2/3 is found to be the most appropriate mechanism function for describing the pyrolysis of the nylon-6/polyethylene waste along with lnk0 of 23.14 to 34.26 min-1. With the Arrhenius parameters thus obtained, the predictions were made and performed very satisfactorily to correlate experimental results. Additionally, the service life and thermodynamic parameters over the entire pyrolysis process were also estimated.

Kinetic analysis of the phase transformation from α- to β-copper phthalocyanine: A case study for sequential and parametric Rietveld refinements

The solid-state phase transformation from α- to β-copper phthalocyanine, using isothermal data obtained at T=250 °C and nonisothermal data obtained in the temperature range of 30 °C≤T≤330 °C with a constant heating rate of 1.67 °/min, was investigated by sequential and parametric full quantitative Rietveld analyses. Results obtained in this study show that the parametric Rietveld refinement technique is most suitable and applicable for kinetic studies of isothermal powder diffraction data. On the other hand, the sequential Rietveld refinement technique can give reliable results for the kinetic analysis of nonisothermal data. The main advantages of the parametric Rietveld refinement over the sequential Rietveld refinement are increased robustness against outliers, low weight fractions, and noisy data and an increase in computational speed.

Critical study of the isoconversional methods of kinetic analysis

A critical study of the use of isoconversional methods for the kinetic analysis of non-isothermal data corresponding to processes with either a real or an apparent variation of the activation energy, E, with the reacted fraction, α, has been carried out using for the first time simulated curves. It has been shown that the activation energies obtained from model-free methods are independent of the heating rate. However, the activation energy shows a very strong dependence of the range of heating rates used for simulating the curves if the apparent change of E with α is caused by overlapping processes with different individual activation energies. This criterion perhaps could be used for determining if a real dependence between E and α is really occurring.

Crystallization of supercooled liquid of selenium: The comparison of kinetic analysis of both isothermal and non-isothermal DSC data

Isothermal crystallization of supercooled melt of selenium was studied in a wide temperature range by means of differential scanning calorimetry (DSC). Isothermal crystallization of selenium was described by Johnson–Mehl–Avrami (JMA) model, the JMA kinetic exponent was found to be ∼3.5. The activation energy of isothermal crystallization was determined E a = 83 kJ/mol. The non-isothermal crystallization of selenium was also studied and the results of kinetic analysis of non-isothermal data were compared with results obtained from isothermal measurements. The applicability of currently used method of kinetic analysis of non-isothermal data is discussed.

Some methodological problems concerning the kinetic analysis of non-isothermal data for thermal and thermo-oxidative degradation of polymers and polymeric materials

The procedures used in some very recent works for evaluation of the kinetic parameters from non-isothermal data corresponding to thermal and thermo-oxidative degradation of polymers and polymeric materials are critically analysed. It is pointed out that only the use of a set of conversion degree vs. temperature curves recorded at different heating rates can give reliable information on the degradation mechanism and in some suitable cases, can lead to the true kinetic parameters. A general algorithm for evaluation of the kinetic parameters from the non-isothermal data is suggested. The application of this algorithm for a set of simulated non-isothermal data has been shown that when the activation energy is independent of the conversion, the invariant kinetic parameters method associated with the criterion of independence of kinetic parameters on the heating rate is recommended for evaluation of the kinetic triplet (activation energy, pre-exponential factor, conversion function).

Thermoanalytical study of the cure characteristics of a main-chain liquid crystalline oligoester: Model-free approach to kinetic analysis of non-isothermal data

The curing behavior of a liquid crystalline oligoester (LCO), based on 4,4′-diacetoxybiphenyl and sebacic acid in presence of a mixture 75:25 of diglycidyl terephthalate and triglycidyl trimellitic acid ester (D&TGE), as a curing agent, was studied by non-isothermal differential scanning calorimetry (DSC). The analysis of non-isothermal data was carried out using the model-free isoconversional method. Activation energy as a function of extent of conversion, α, have been calculated by the Friedman technique. It shows a constant value of 95.5 ± 2.5 kJ/mol, in the 0.27 < α < 0.68 range. The activation energy, out of the above-mentioned interval, is strongly dependent on the degree of extent of the curing reaction. The y( α) and z( α) plots, which were obtained through transformation of DSC data, are not completely identical at a variety of heating rates. It indicates that the kinetic process dose not follow a single-step curing reaction model and a multi-step process controls it during curing. To approve the non-isothermal analysis result, we carried out further, depolarizing transmittance measurements and optical microscopy observations on the stoichiometric mixture of LCO/D&TGE during curing, at various heating rates. The results of these experiments exhibit that the kinetic process of the investigated system is strongly influenced by altering the mesomorphism features of the sample.

KINETIC ANALYSIS OF NON-ISOTHERMAL DSC DATA Computer-aided test of its applicability

The applicability of the kinetic analysis of data obtained by non-isothermal differential scanning calorimetry (DSC) is discussed. The Johnson-Mehl-Avrami (JMA) model was used for the computer simulation of DSC traces subsequently analysed by common methods of kinetic analysis of non-isothermal data. For the temperature-independent kinetic exponent n of the JMA equation, the kinetic analysis was shown to provide correct results, e.g. a correct kinetic model and apparent activation energy. On the other hand, for the temperature-dependent kinetic exponent, there is a great possibility of erroneous determination of the correct kinetic model and apparent activation energy, especially at higher heating rates. Since the temperature dependence of n cannot be determined on the basis of non-isothermal DSC experiments, conclusions must be drawn with appropriate caution.

A simple method of kinetic model discrimination. Part 1. Analysis of differential non-isothermal data

The applicability and relevance of the Freeman and Carroll (FC) method in the kinetic analysis of non-isothermal data are discussed. It was found that the apparent kinetic parameters obtained by the modified FC method allow the kinetic model to be discriminated. A simple, quick method of kinetic model determination is proposed and verified for theoretically calculated thermal analysis data.

Computer kinetic analysis of thermoanalytical data

A program has been worked out to provide kinetic analysis of non-isothermal data. To evaluate the kinetic parameters the main procedure uses the integral method of exponential multipliers (IMEM). TG and DTA curves have been recorded with a Setaram TAG 24S24 thermoanalyser. The program has been tested for dehydration of CaC 2O 4·H 2O. Also it has been applied to the kinetic study of copper oxidation with barium peroxide and oxygen thermodesorption in YBa 2Cu 3O 6.9±0.1 superconductor.

Applicability of the master plots in kinetic analysis of non-isothermal data

The ability to determine the actual reaction mechanism (RM) of solid state processes from a single non-isothermal curve was analysed and discussed. Owing to the correlation of all kinetic parameters the RM cannot be ascertained without the knowledge of activation energy. However, if the activation energy is known a simple and precise method for the determination of RM can be proposed. The method was used to analyse the experimental data of the thermal decomposition of magnesium carbonate in vacuum. It was found that the reaction follows the R3 mechanism which is in very good agreement with the results of isothermal experiments.

Modification of the hancock and sharp “lnln method” in order to perform the kinetic analysis of non-isothermal data

Modification of the hancock and sharp “lnln method” in order to perform the kinetic analysis of non-isothermal data