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Isoconversional analysis of solid-state transformations

A critical review. Part III. Isothermal and non isothermal predictions

Journal of Thermal Analysis and Calorimetry
Authors: J. Farjas and P. Roura

Introduction Kinetic methods are routinely employed to determine the kinetic parameters of solid-state transformations from thermal analysis experiments. In particular, there are isoconversional methods which are model-free, i

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Isoconversional analysis of solid state transformations

A critical review. Part II. Complex transformations

Journal of Thermal Analysis and Calorimetry
Authors: J. Farjas and P. Roura

Introduction The second part of this review is devoted to the analysis of complex transformations. In particular, we will describe the use of the isoconversional methods introduced in the first part of this review (Part I [ 1

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Abstract

A nonlinear algorithm has been suggested to increase the accuracy of evaluating the activation energy by the integral isoconversional method. A minor modification of the algorithm has made it possible to adapt the isoconversional method for an arbitrary variation of the temperature. This advanced isoconversional method allows for trustworthy estimates of the activation energy when the thermal effect of a reaction makes the temperature of a sample deviate from a prescribed heating program.

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literature. These methods are generally based on either the isokinetic hypothesis or the isoconversional principle and they can be accordingly classified as (1) isokinetic methods where rate of reaction is considered to be the same throughout the temperature

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Isoconversional vs. Model fitting methods

A case study of crystallization kinetics of a Fe-based metallic glass

Journal of Thermal Analysis and Calorimetry
Authors: A. Pratap, T. Lilly Shanker Rao, K. Lad, and Heena Dhurandhar

Abstract  

The crystallization of metallic glasses has been studied quite extensively using differential scanning calorimetry (DSC) technique. Most methods rely on isokinetic hypothesis for the kinetic analysis of crystallization for which the choice of a reliable model is very important. Due to inherent uncertainty in the determination of kinetic parameters, the model-free isoconversional analytical techniques were proposed. However, these isoconversional methods are scarcely used for metallic glasses. In the present work, the crystallization kinetics of Fe67Co18B14Si1 metallic glass through both isoconversional and isokinetic methods has been investigated and attention has been focused on the relative applicability of the two methods.

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Introduction Iso-conversional methods are used for non-isothermal analysis, in which the transformation rate at a constant extent of conversion is only a function of temperature as suggested by Vyazovkin et al. [ 1 – 4 ] and

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, α ) with extent of conversion (isoconversional method) [ 12 – 14 , 24 – 29 ] and temperature (non-parametric kinetics method) [ 30 , 31 ]. Further, Arrhenius parameters evaluated using model-free techniques facilitate modeling of a degradation

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(activation energy, pre-exponential factor, and conversion function) of each degradation step is one important target of kinetic investigations. Many kinetic analysis methods have been developed, among which isoconversional methods have been widely used [ 1

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method, which can not detect the complex nature of the solid-state reaction, has been replaced by multiple scan method at different heating rates using iso-conversional and iso-temperature calculation procedures [ 12 – 14 ]. Among the iso-conversional

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found to be, respectively, as 63.5 and 38.7 kJ mol −1 . The isoconversional method [ 34 – 37 ] is known to permit estimation of the apparent activation energy; independent of the model, corresponding to extent of conversion of the sample. This

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