Estimation of activation energies from differential thermal analysis curves

Abstract

An average activation energy Δ E‡ of 31.7 ± 10.0 kcal/mole was calculated from exothermic peaks of urea nitrate differential thermal analysis (DTA) curves using the Murray and White equation and various other reaction rate equations developed by the authors. An average enthalpy of activation, Δ H‡ of 30.8 ±9.7 kcal/mole was calculated from the same results. The values of Δ E‡ and Δ H‡ differed by a fraction of a kcal/mole indicating that Δ E‡ <Δ H‡ cannot be differentiated experimentally in our study. Application of the Kissinger method of calculating Δ E‡ and Δ H‡ produced respectively 21.6 ±7.9 and 20.7 ±8.0 kcal/mole, which are quite low. The values of Δ E‡ and Δ H‡ calculated thermogravimetrically were 28.1, ± 1.1 kcal/mole and 27.6 ± 1.2 kcal/mole which are close to those obtained from the Murray and White approach and the authors' approach to treatment of the DTA data. These results illustrate the pronounced effect of self heating on calculation of activation energies. The Kissinger method of calculating the reaction order developed for endothermic DTA peaks produced good results when applied to the present DTA study.