A kinetic study of the thermal decomposition of iron(III) oxide-hydroxides .3. Shape control and thermal decomposition of alpha-FeO(OH)

The shape control of crystalline particles of alpha-FeO(OH) was performed through growth treatment in an aqueous medium and subsequent hydrothermal treatment. The samples were subjected to a thermogravimetric (TG) study. The different TG curves obtained for the samples before and after the hydrothermal treatment were explained in connection with the existence of an irregular outer surface layer on the samples before the hydrothermal treatment. The overall decomposition kinetics of the samples after hydrothermal treatment were determined by analyzing the TG curves at different heating rates, An apparent activation energy of approx. 140 kJ mol(-1) was obtained in the restricted range of fractional reaction 0.4 less than or equal to alpha less than or equal to 0.95, irrespective of the samples, The appropriate kinetic model functions changed from nucleation growth to reaction interface shrinkage with increasing particle size, The correspondence of the overall kinetics obtained from the thermoanalytical method with the physico-geometry of the reaction is discussed briefly.