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Flynn and Wall method

The Flynn and Wall method [3-21,3-22] uses the thermogravimetric curves to calculate the activation energy E and the frequency (pre-exponential) factor A of the Arrhenius equation. In this approach the TGA curve of the analysed material is recorded from at least three test runs at heating rates P between 1 and 20 K/min. The corresponding temperatures of selected constant conversion levels are determined for each test run (Fig. 3-51). The measured values of temperature and heating rate are then used to compute the activation energy E using the method of successive approximations ... [Pg.72]

The Flynn and Wall method is well-suited to demonstrate the dependence of activation energy and frequency (pre-exponential) factor upon the conversion level. [Pg.73]

The Raw Data Plot of the ASTM E 698-79 method shows whether the correct maximum temperatures have been obtained by selection of the limits. For the Flynn and Wall method there is a control whether the desired points of inflexion of the TGA curves are marked correctly. In the McCarty and Green program a Raw Data plot has no significance. [Pg.481]

The application of thermoanalytical methods to the investigation of the kinetics of pyrolysis and oxidation processes of heavy petroleum components representing multi-component systems proved to be successful. Whereas the ASTM E 698-79 and the Flynn and Wall methods can be applied relatively uncritically, the interpretation of the data from the McCarty and Green method requires a solid knowledge of the thermal and oxidative behavior of the samples. The attempt to use the evaluation according to Borchardt and Daniels proved not to be successful for pyrolysis nor for oxidation reactions. Most of the... [Pg.482]

DSC instruments can be used as well as thermobalances. The use of a Simultaneous Thermal Analyzer (TGA/DSC or TGS/DTA) makes sense only if the software permits evaluation of the DSC (DTA) data using the ASTM E 698-79 method, and evaluation of thermogravimetric data by the Flynn and Wall method. Otherwise using a cheaper instrument will be just as good. [Pg.483]

Flynn and Wall method. The evaluation according to Flynn and Wall applies measured conversion levels whereas the Ozawa correction of the ASTM E 698-79 incorporated in the DuPont software is based on an empirical function of the dependence of activation energy upon conversion level. [Pg.484]

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. [Pg.402]

The methods according to ASTM E 689-79, and to Borchardt and Daniels apply data from DSC or DTA test runs, whereas the methods according to Flynn and Wall, and to McCarty and Green are based upon the use of data fi om thermogravimetty. For the... [Pg.68]

In the evaluation of a decomposition experiment on calcium oxalate monohydrate, the temperatures of the onset and offset points of each of the three consecutive reactions were used as integration limits. The results are shown in Fig. 3-65. These data diverge considerably from those calculated using the Flynn and Wall or the ASTM E 698-79 methods (Table 3-20). Considerable differences in the data are also reported in the literature. Freeman and Caroll 73-34/ reported the following data found by thermogravimetry ... [Pg.94]

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... [Pg.284]

The decomposition kinetic analysis of the mass loss curves was carried out using standard TGA kinetics software that is based on the Flynn-Wall method (Flynn and Wall 1966a,b) and described in Section 3.5.5. In this technique a plot of the logarithm of the heating rate (log q) against the reciprocal of the absolute temperature [see. Eq. (3.23)] was made where the conversion or mass loss equaled 4%, 5.5%, 8%, 12%, 18% and 26%. From the slope of this plot (Fig. 3.32) the activation energy for decomposition E) was calculated from Eq. (3.32), which is based on Eq. (3.23) ... [Pg.299]

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. [Pg.966]

Flynn, J.A. and Wall, L.A. (1966) A quick and direct method for the determination of activation energy from thermogravimetric data. Polymer Letters, 4, 323-8. [Pg.308]

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. [Pg.31]

The calculation of the activation energy is based on multiple scan methods where several measurements at different heating rates are needed, i.e. the iso-conversion methods the Ozawa-Flynn-Wall method, the Kissinger-Akahira-Sunose method and the expanded Friedman method. The first two are described in Section 3.3.1. The expanded Friedman method is expressed in the form... [Pg.57]

Usually the TG curve should be determined at a slow heating rate, and E was estimated for low conversion (say mass loss 5%) by using the Ozawa-Flynn-Wall method. If we assume t( = 20 000h, Tf equals the thermal index of the material. With the use of higher temperatures, the shorter is the lifetime, as shown in Figure 5.1. [Pg.131]


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See also in sourсe #XX -- [ Pg.118 ]




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Flynn

Method according to Flynn and Wall

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