Flynn-Wall-Ozawa kinetic method

PEN/CNT nanocomposites induced by the incorporation of the CNT may be explained by the function of the CNT as an effective physieal barrier to retard the thermal degradation of volatile components and to prevent the diffusion out of the deeomposed polymeric molecules in the PEN/CNT nanocomposites [145, 146], Based on the Flynn-Wall-Ozawa analysis, it can be deduced that the Ea values of the PEN/CNT nanocomposites calculated from Flyim-Wall-Ozawa method exhibited good reliance on describing the thermal degradation kinetics of their nanocomposites, which was confirmed by the fact that the values of the correlation coefficient (r2) were greater than 0.99. 

To evaluate the apparent activation energy, the isoconversional methods are use as suitable analysis procedures. These methods are based on the assumption that at a constant extent of conversion degree (a), the decomposition rate da/dt is a function only of the temperature. In methods developed by Friedman and Flynn-Wall-Ozawa, linear functions are obtained from which slopes the apparent activation energy at constant conversion a is achieved. In the free kinetic method set by Kissinger is calculated from the slope of the linear function takes into consideration the relationship between the heating rate and peak temperature of the first-derivative thermogravimetric curve [97]. 

Where a is the extent of decomposition, Z is a pre-exponential factor, E is the activation energy, R the universal gas constant (8.3154 Jmol K 0> and f(a) depends on the decomposition mechanisms. E, Z, and a) are commonly called the kinetic triplet [28]. There are different kinds of methods to obtain the kinetic triplet reported in the scientific literatme among which are those reported by Flynn-Wall-Ozawa [29], Friedman [30], Kissinger [21], or Coats-Redfem [31], with different proposed equations presented to solve Eq. (7.1). 

Similar to studies reported by Litwinienko and co-workers discussed above, a recent report (Dunn, 2006b) demonstrated that non-isothermal (conventional) DSC, static mode P-DSC and dynamic mode P-DSC may be employed to study kinetics of the oxidation of SME. OT results obtained at ambient pressure for DSC and P = 2000kPa for P-DSC and with varying p = 1-20 °C/ min were analyzed by the Ozawa-Flynn-Wall method to calculate activation energies and rate constants. This work concluded that rates of the oxidation reaction could be calculated at any temperature based on accurate measurement of kinetic parameters from analysis of non-isothermal dynamic mode P-DSC scans. 

C. Popescu (1996). Integral method to analyze the kinetics of heterogeneous reactions under non-isothermal conditions A variant on the Ozawa-Flynn-Wall method. Thermochimica Acta 285 (2) 309-323. 

Kinetic model of Ozawa—Flynn—Wall method... 

Reaction kinetics from DSC, DTA or TGA, have been used to examine the stability of a limited number of pharmaceutical materials. Various models have been used including the Power Law, Avarami-Erofeev and Prout-Tomkins models [72]. These methods are also based on the Kissinger [73], ASTME 698 [74] or Ozawa [75] methods [8]. Most frequently, they have been applied to the dehydration of various materials such as theophylline monohydrate [76], phenobarbitone monohydrate or hemihydrate [77], phenylbutazone [78], oxazepam [23] and trazodone tetrahydrate [79]. The uses are limited for pharmaceutical systems, not least because dehydration is particle size dependent. Thermal analysis, especially DSC, DTA and TG, has been used outside the pharmaceutical area in the prediction of reaction kinetics as described elsewhere in this handbook. Methods used include those by Borchart and Daniels [80], Kissinger [73], Freeman and Carroll [81] and Flynn and Wall [82]. Although these techniques are well established and, if used properly, can give pertinent information, their use in pharmaceutical arenas is restricted to dehydration and decomposition. 

The kinetics of thermal degradation have generally been studied using isothermal and nonisothermal methods. In earlier literature, isothermal methods were mostly employed for the study of the kinetics of solid-state reactions. During the past three decades, however, nonisothermal methods, for example, the Doyle method [17, 18], Freeman and Carroll method [19], Coats and Redfem method [24], Ozawa method [20], Flynn and Wall method [21, 22], Friedman method [25], and Kissinger method [26], have received more attention. 

Kinetic analyses of multiple nonisothermal, also referred to as multiple heating rate, runs are most commonly performed by using the methods of Friedman, Ozawa, and Flynn and Wall. However, application of the Kissinger method (Kissinger 1957) is discouraged because the method yields a single value of... 

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