APPLICATION OF VARIOUS METHODS OF NONISOTHERMAL KINETIC-ANALYSIS TO MAGNESIUM-HYDROXIDE DECOMPOSITION

In the present study the determination of the mechanism of the thermal decomposition of magnesium hydroxide from thermogravimetric experiments is attempted. For this purpose nonisothermal kinetic analysis of the dynamic experimental data is applied, using different methods, which are based on the best linearization of a functional form of the Arrhenius equation. The experiments were carried out under nonisothermal conditions in a thermogravimetric analyzer with nitrogen atmosphere, at five different heating rates, i.e., 3, 8, 15, 20, and 35 deg/min. The nonisothermal methods used for the kinetic analysis of the experimental data were the Coats-Redfern method, the Romero et al., the improved Coats-Redfern method, the differential method, the differential by Jerez et al., and a method using the heating rate as a variable. Applying each of these methods, the kinetic parameters and, in most cases, the form of the conversion function (kinetic model) which governs the dehydroxylation process of Mg(OH)2 were determined. From the comparative study of the results of the above methods and using criteria about the credibility of each method, it was concluded that the kinetic model which represents the mechanism of the dehydroxylation of magnesium hydroxide, is that corresponding to the two dimensions nucleation with a reference value of activation energy 117.67 kJ/mol. (C) 1993 John Wiley & Sons, Inc.