Application of the third-law methodology to investigation of decomposition kinetics

The most important results obtained since the first application (in 2002) of the third-law methodology to kinetic studies of decomposition reactions are considered. The third-law method has been significantly improved and extended to powdered and melted materials. The use of the average values of molar entropy greatly simplified its application to materials with unknown product composition and/or unknown thermodynamic parameters. The order of magnitude higher precision and low susceptibility of the third-law method to the self-cooling compared with the Arrhenius-plots method, guarantees measurement of the E parameter with the error less than 2%. A significant reduction of experimental time and a possibility of simple evaluation of self-cooling are the additional advantages of this method. The application of the third-law method to decomposition studies permitted to support the basic assumptions underlying the physical approach to interpretation of decomposition kinetics. A good fit of experiment to theory for the ratio of the initial decomposition temperature to the E parameter, the peculiarities of carbonate decomposition in CO2 and regularities of solid and melted nitrate decomposition are in complete agreement with the mechanism of dissociative evaporation and consumption of a part tau of the condensation energy by reactant. It has become possible to evaluate the tau parameter a priori on the basis of thermodynamic features of the low-volatility product. From comparison of the E parameters with the molar enthalpies of the implied reactions, the decomposition mechanisms of 40 different reactants are identified. Some peculiarities in evolution of gaseous products in atomic and molecular forms are interpreted in accordance with the crystal symmetry of reactants. The earlier theoretical evaluations of the self-cooling effect, which can reach in high vacuum several ten degrees, are supported experimentally. (C) 2004 Elsevier B.V. All rights reserved.