Kinetic analysis of thermogravimetric data

Zsakó, J.; Arz, H. E.

doi:10.1007/bf01911785

Cited by 112 publications

(35 citation statements)

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“…Many examples are known, particularly for reversible, endothermic dissociations, amongst which the thermal breakdown of calcium carbonate has probably been studied most exhaustively. The kinetic characteristics of this reaction are highly sensitive to experimental conditions, resulting in exceptionally large variations in the measured, or apparent, values of the Arrhenius parameters: compensation behavior is observed [13,14]. Searcy and coworkers [15,16] have concluded that, to obtain reliable rate measurements for the chemical steps in this dissociation process, the pressure of carbon dioxide product present must be below 1% of its equilibrium value.…”

Section: Type 2h Kces: Varied Experimental Conditions Constant Reactionmentioning

confidence: 96%

Compensation effects and compensation defects in kinetic and mechanistic interpretations of heterogeneous chemical reactions

Galwey

Mortimer

2006

Int J of Chemical Kinetics

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A case is presented for kinetic compensation effects (KCEs) reported for sets of heterogeneous rate processes to be classified. Because many of these KCEs do not conform to the ideal of isokinetic behavior, a quantitative method for describing the degree of compensation (κ) is introduced. In the case of solid-promoted catalytic reactions, it is suggested that (unlike simple homogeneous reactions) the effective concentrations and dispositions of surface intermediates can vary with temperature. Thus, the rate constants vary differently with temperature for the individual reactions of a set and, thereby, influence apparent magnitudes of the measured Arrhenius parameters. As a consequence, compensation is observed for sets of chemically related reactions occurring within a common temperature interval. KCEs are thus linked to mechanistic information and, depending on the magnitude of κ, for identifying shared features of catalytic rate controls. In this respect, the classification of KCEs is useful and can be based on similarities or differences between the reactants, catalysts, or experimental conditions in a given set of measurements. These ideas are demonstrated for selected sets of catalytic reactions. KCEs reported from a range of thermal decompositions of solids are also discussed. It is argued that, for mathematical as well as term definition reasons, compensation in this type

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Section: Type 2h Kces: Varied Experimental Conditions Constant Reactionmentioning

confidence: 96%

Compensation effects and compensation defects in kinetic and mechanistic interpretations of heterogeneous chemical reactions

Galwey

Mortimer

2006

Int J of Chemical Kinetics

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“…Agrawal disputes mainly three reports [3][4][5]. After re-examining their data by plotting In k vs. lIT and finding no isokinetic temperature in these plots, he concludes that these are cases of a "false" CE.…”

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confidence: 88%

“…Chornet and Roy [3] and Zsak6 and Arz [4] have reported kinetic parameters (A and E) derived from non-isothermal experiments; neither they nor Alvarez et al [5] have reported any k values. Agrawal must have calculated his In k values, using the Arrhenius relation (1): from the reported A and E values, which are mutually dependent, and which are derived directly from the original non-isothermal data.…”

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confidence: 97%

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Critical remarks on “On the compensation effect”

Zsakó

Somasekharan

1987

Journal of Thermal Analysis

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A critical assessment of a published paper (by Agrawal) is presented. The procedure proposed and used by Agrawal to distinguish a false compensation effect from a true one is shown not to be COITeCt.In a recent paper, Agrawal [1] proposed some checkpoints for the drawing of conclusions regarding the occurrence of a true or false compensation effect (CE).In the introduction he shows that by applying the Arrhenius equationin the field of heterogeneous kinetics, both A and E have little physical significance. He sees the main cause of this in the lack of a definition for a "mole of solid". It is well known that the application of Eq. (1), valid for homogeneous gas-phase reactions, is an absolutely unjustified extrapolation [2]. Even if the validity of Eq.(1) were proved for certain heterogeneous reactions, the meanings of A and E would be rather obscure, due to the high complexity of the heterogeneous processes involving .solid-state reactions, gas evolution, diffusion, etc. How could the definition of a "mole of solid" help? If the rate constant k actually varies with Tin the way prescribed by Eq. (1), from the experimental data a magnitude can be derived having the dimension of temperature (let us call it the characteristic temperature O), denoted in Eq. (1) by E/R, since it can be transformed into energy per mole by multiplying it by R, or into energy per molecule by multiplying it by the Boltzmann constant. The definition of a mole of solid affects the amount of energy calculated from O, but it cannot clarify the physical meaning of this energy. If a linear relation between In A and Eis observed for a series of related reactions, it is referred to as a CE, formally involving an "isokinetic point", i.e. a temperature

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“…It seems therefore that the neglection as regards the exponential integral adopted by CR (and by other Workers [7] who also proposed "integral" methods) is not generally adequate; this probably can be the reason of the discrepancies existing among literature results obtained by means of "integral" methods [8].…”

Section: B) Dehydration Of Hc00li H20mentioning

confidence: 97%

Kinetic Parameters from Thermogravimetric Data

Marini

Berbenni

Flor

1979

Zeitschrift Für Naturforschung A

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The "differential" method of Achar, Brindley and Sharp (ABS) and the "integral" one of Coats and Redfern (CR) are applied to the dehydration of BaBr2-H20 and HCOOLi-H20 and to the thermal decomposition of Pb(SCN)2, and the kinetic parameters so obtained are compared with those deduced isothermally.The results of the ABS method, at the lowest heating rate (q = 1.2 K min -'), agree well with the isothermal ones, whereas the CR method leads to satisfactory results only for the Pb(SCN)2 thermal decomposition (q = 1.2 K min~*). A possible explanation is given.In a previous work [1] on the nonisothermal dehydration of BaBr2 • 2 H20 we have found that the a (fractional decomposition) vs. t (time) curves, at low and constant heating rates, satisfy the kinetic equations deduced isothermally [2].In this note, two of the methods currently used to exploit nonisothermal TG curves, i. e. the Achar, Brindley and Sharp (ABS) [3] "differential" method and the Coats and Redfern (CR) [4] "integral" method are tested. This is performed by considering three thermal decompositions with very different features (previously or presently studied isothermally in our Institute), i.e. BaBr2H20 dehydration [2], HCOOLi H20 dehydration [5] and Pb(SCN)2 thermal decomposition.The a vs. t curves (with heating rates, q, between 1.2 and 11 K min -1 ) were recorded by using the same apparatus, the same shape, size and amount of sample and the same experimental procedures as employed in the corresponding isothermal studies.Both the ABS and the CR methods are based on the equation where Z is the frequency factor, E the activation energy, and n the order of the reaction.

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Kinetic analysis of thermogravimetric data

Cited by 112 publications

References 13 publications

Compensation effects and compensation defects in kinetic and mechanistic interpretations of heterogeneous chemical reactions

Compensation effects and compensation defects in kinetic and mechanistic interpretations of heterogeneous chemical reactions

Critical remarks on “On the compensation effect”

Kinetic Parameters from Thermogravimetric Data

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