Isothermal measurement:
Isothermal measurement suffers from the disadvantage of being rather time consuming. There is also hardness in bringing the sample and apparatus to the needed temperature without a few decomposition of the sample having already taken place. One way of prevent this problem is to change a rate controlling variable during the course of measurement. A meaningful method is temperature jump TGA. The rate of decomposition could then be measured either side of the modification in temperature and the activation energy determined from Eq. (10.11).
Ea = R ln [ (dm/dt)T1/ dm/dt T2] [ 1/T1-1/T2]
where (dm/dt) T1 and (dm/dt) T2 are the rate of mass loss at T1 and T2 either side of temperature jump. A study of kinetics using data from conventional increasing temperature TGA have been proposed through several scientists but the most popular method is elaborates through Ozawa and Flynn and Wall, that has been incorporated within American Society of Testing Materials standard methods. In this method, fundamentally separate measurements are carried out at variant linear heating rate and temperature at that a set of percentage mass loss occurs. Those are then plotted as function of heating rate (dT/dt) and the activation energy determined through an iterative process. We frequent suppose, without appropriate justification, which decomposition reaction are first order processes as in Eq. 10.12.
(dα/ dt) = k(1- α)