On the change of the activation energy with conversion degree and heating rate for the non-isothermal dehydration of CaC2O4·H2O

Int J of Chemical Kinetics

2001

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140

Isoconversional methods, those using only one curve α = α(T ) (α is the conversion degree and T is the temperature), and invariant kinetic parameter method were applied to estimate the kinetic parameters from the following nonisothermal data: (1) simulated TG curves for a single reaction; (2) TG curves for thermal degradation of PVC; and (3) TG curves for the dehydration of CaC 2 O 4 ·H 2 O. The results obtained by applying various methods for the same system are compared and discussed. Finally, a procedure of kinetic analysis is suggested. Its application could lead to kinetic parameter values that can be used to predict either α = α(t) curves for other heating rates or α = α(T ) curves for isothermal conditions.

Section: Tg Curves Obtained For the Dehydration Of Cac 2 O 4 ·H 2 Osupporting

confidence: 66%

Some methodological problems concerning nonisothermal kinetic analysis of heterogeneous solid–gas reactions

Budrugeac

Int J of Chemical Kinetics

2001

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140

“…That is the reason why we expect that under such conditions inequalities (11) should be fulfilled. But, as it is well known for many thermal decompositions and thermooxidative degradations of solids, the activation energy changes with the degree of conversion [20][21][22][23]. For these cases a compensation relationship has been evidenced between the activation energy and the preexponential factor:…”

Section: On the Isoconversional Methods For Estimating The Activationmentioning

confidence: 97%

“…Thermogravimetric data from [21] for heating rates of 0.987; 2.353; 4.988 and 9.573 K min -1 were used. The activation energies were estimated by means of the Flynn-Wall-Ozawa and the Friedman methods using values of the degree of conversion in the range 0.20-0.55.…”

Section: Dehydration Of Calcium Oxalate Monohydratementioning

confidence: 99%

Some problems concerning the evaluation of non-isothermal kinetic parameters

Budrugeac¹,

Petre

Journal of Thermal Analysis

1996

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“…The TG curves corresponding to the dehydration of CaC 2 O 4 ·H 2 O at the heating rates of 0.987; 2.353; 4.988 and 9.573 K min -1 were reported in a previous paper [21]. Using isoconversional differential methods, it was shown [5] that the activation energy decreases from 130 kJ mol -1 (for α=0.1) to 63 kJ mol -1 (for α=0.9).…”

Section: Dehydration Of Calcium Oxalate Monohydratementioning

confidence: 83%

On the use of Diefallah’s composite integral method for the non-isothermal kinetic analysis of heterogeneous solid-gas reactions

Budrugeac¹,

2005

J Therm Anal Calorim

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The paper contains an analysis of the used of Diefallah's composite integral method of kinetic parameters evaluation. It is shown that the application of this method should be preceded by the application of an isoconversional method through which the dependence of the activation energy, E, on the conversion degree, α, should be established. If E depends on α, Diefallah's composite integral method leads to erroneous results. If E does not depend on α, the true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC 2 O 4 ·H 2 O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).