Method according to Flynn and Wall

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  

The frequency (pre-exponential) factor A is then calculated based upon the assumption of reaction order of unity (n = 1) by the method of Zsako and Zsako [3-23]  

C = empirical approximation whose value depends upon E 

The values of E and A are used to calculate the other kinetic parameters such as specific rate constant (reaction constant) k and half life time with the help of equations 3-7 and 3-8  

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

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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... 

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