Kinetic Parameters from Thermogravimetric Data

Abstract

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.

Synthesis, characterization and thermal decomposition kinetics of a bio-based transparent nylon 10I/10T

“…(7) at different conversion values [35]. By substituting the ln(1-2 RT/E )→0, the following equation can be obtained [36]: …”

Evaluation of Kinetic Parameters and Thermal Stability of Melt-Quenched BixSe100-xAlloys (x ≤7.5 at%) by Non-Isothermal Thermogravimetric Analysis

“…Improving resolution of non-isothermal TG measurements and separating possible thermal processes can be realized via long experimental runs at slow heating rates (2°C/min~30°C/ min), so the time at any T must be long enough to permit completeness of a kinetic reaction, by reducing sample's size (5~30 mg), hence minimizing temperature gradients and inhomogeneities across it, and by choosing a suitable purge gas during TG measurements. As regards to kinetic analysis of experimental thermoanalytical data, two main approaches are realized: the modelfree and model-based analysis methods, both demand a set of accurate isothermal or non-isothermal measurements at different conditions, such as the sample's temperature T and the heating rate β (Abdel- Rahim et al, 2008;Abu ElOyoun, 2000;Achar et al, 1966;Atmani, 1988;Brown, 2004;Coat & Redfern, 1964;Flynn & Wall, 1966;Jones et al, 1975;Keattch & Dollimore, 1975;Marini et al, 1979;Moharram & Abu El-Oyoun, 2000;Moukhina, 2012;Ozawa, 1965;Ptáček et al, 2010;Šesták, 1984;Sharp & Wentworth, 1969;Sharp et al, 1966). The model-based kinetic (discrimination) analysis solves an equation (Eq.)…”

“…(2) can be used to construct a curve of dα[T(t)]/dT-T(t) by numerical differentiation of the α[T(t)]-T(t) data. Model-based (discrimination) kinetic analysis methods include the differential-form method of ABS and integral-form method proposed by CR (Coat & Redfern, 1964), which was amended by Marini et al (1979) to extend its applicability to a broader range of α(t) or α[T(t)] values. We shall give the key algebraic formulas of these model-based CR and ABS methods, which can be employed to analyze non-isothermal TG/DTG curves at a constant heating rate β=dT/dt using the model function…”

“…n for few values of the reaction order (n=0, 1/2, 2/3, and 1) (Marini et al, 1979;Sharp & Wentworth, 1969). Having the conversion curves or the dα(T)/dT-T data, calculated from non-isothermal TG curve at a constant β using a kinetic…”

“…, where γ is a numerical constant, depends on the kinetic reaction mechanism, the model-based differential-form ABS analysis method has the form Marini et al, 1979)…”