Abstract
The original intention of the work was to study the decomposition of certain chromium(III) complexes, by thermogravimetric analysis and other methods, and to use the thermogravimetric data in the evaluation of kinetic parameters for the various decomposition stages. In view, however, of the somewhat confused state of knowledge in this field, the work developed into a detailed examination of the determination of kinetic parameters from thermogravimetric data. The existing methods were compared, and were found to be limited in application to systems of known or assumed order of reaction or did not give reliable values. Various new approaches using the rate equation dalpha/dt = k(1-alpha)[n] and the Arrhenius expression were developed and initially tested on the three stages of the decomposition of calcium oxalate monohydrate. On closer examination these stages proved to be poor standard reactions. The sublimation of some organic compounds, relevant to some work on platinum amine complexes, was used as standard zero-order reactions. The better of the seven developed approaches were investigated in some detail and the results compared with those from isothermal studies. Further, the influence of procedural details such as heating rate, environmental atmosphere and weight of sample were investigated. The possibility of studying the variation of the kinetic parameters throughout the course of the reaction was investigated. Wherever possible the parameters obtained in the present work were compared with those in the literature from isothermal and thermogravimetric studies. Some general conclusions regarding the conditions, under which meaningful kinetic parameters could be evaluated from thermogravimetric data, are stated.