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Model-free kinetics
Staying free of multiplying entities without necessity
Abstract
The paper presents the model-free kinetic approach in the context of the traditional kinetic description based on the kinetic triplet, A, E, and f(α) or g(α). A physical meaning and interpretability of the triplet are considered. It is argued that the experimental values of f(α) or g(α) and A are unlikely to be interpretable in the respective terms of the reaction mechanism and of the vibrational frequency of the activated complex. The traditional kinetic description needs these values for making kinetic predictions. Interpretations are most readily accomplished for the experimental value of E that generally is a function of the activation energies of the individual steps of a condensed phase process. Model-free kinetic analysis produces a dependence of E on α that is sufficient for accomplishing theoretical interpretations and kinetic predictions. Although model-free description does not need the values of A and f(α) or g(α), the methods of their estimating are discussed.
from room temperature up to 900 °C, at a heating rate of 5, 10, and 20 °C min −1 . The model-free kinetics proposed by Vyazovkin and co-workers [ 11 , 12 ] was used to evaluate the kinetic parameters of surfactants decomposition from the optimized
Abstract
The evaporation of octanoic (caprylic) acid was investigated by means of thermogravimetric analysis (temperature range: 300–600 K) under a nitrogen dynamic atmosphere (heating rates: 0.16, 0.31, 0.63, 1.25, 2.5, 5 and 10 K min−1). Kinetic plots for a zero-order process were constructed based on the Arrhenius equation. The activation energy for the evaporation process was calculated via both the Arrhenius plot and Vyazovkin’s isoconversional model-free method.
Abstract
The degradation kinetics of polycarbonate with flame retardant additive was investigated by means of thermogravimetric analysis. The samples were heated from 30 to 900C in nitrogen atmosphere, with three different heating rates: 5, 10 and 20C min–1. The Vyazovkin model-free kinetics method was applied to calculate the activation energy (E a) of the degradation process as a function of conversion and temperature. The results indicated that the polycarbonate without flame retardant additive starts to loose mass slightly over 380C and the polycarbonate with flame retardant additive, slightly over 390C (with heating rate of 5C min–1). The activation energy for flame retardant polycarbonate and normal polycarbonate were 190 and 165 kJ mol–1, respectively.
Abstract
The effect of both formaldehyde content and catalyst type used in the synthesis of several resole type phenolic resins has been studied by using differential scanning calorimetry. In this study Kissinger-Akahira-Sunose (KAS), Ozawa-Flynn-Wall (OFW) and Friedman model-free kinetics are applied in order to correlate the dynamic cure behaviour with the mentioned synthesis variables. Strong upward dependency of activation energy on conversion has been detected in all cases up to a maximum value. Lower the formaldehyde content fewer changes in activation energy have been detected, revealing a more homogeneous polymerization. As formaldehyde content increases, stronger variations of energy values have been observed and the maximum value is shifted to lower conversions. By comparing triethylamine and sodium hydroxide catalysts similar behaviour has been observed, with higher energy values and shifting of the maximum in the latter. Friedman approach has been resulted in more convenient and accurate for the energy values determination and KAS method seems useful for the dynamic cure prediction of that type of thermoset.
. The objective of this study is to study the thermal degradation of the ligand groups with the metallic ions of the system using the Flynn and Wall and “Model-free kinetics” methods and evaluate the results in order to establish the activation energy as
). Initial mass was defined as the mass at ambient temperature and final mass by the DTG (derived thermogravimetric) curve. This study used model-free kinetics to determine pyrolysis kinetic parameters of the reaction. In this method, the kinetic
. In this case, to obtain reliable and consistent kinetic information about the overall process, the model-free kinetics was applied based on the Vyazovkin theory. This theory is based on an isoconversional computational technique that calculates the
