Journal of Thermal Analysis, Vol. 41 (1994) 357-385 In celebration of the 60 th birthday of Dr. Andrew K. Galwey KINETICS OF THE THERMAL DEHYDRATIONS AND DECOMPOSITIONS OF SOME MIXED METAL OXALATES A. Coetzee, M. E. Brown*, D. J. Eve and C. A. Strydom 1 Chemistry Department, Rhodes University, Grahamstown 6140, South Africa ] . . . . . . Chenustry Department, Umverslty of Pretona, Pretona 0002, South Africa Abstract "Both isothermal and programmed temperature experiments have been used to obtain kinetic parameters for the dehydrations and the decompositions in nitrogen of the mixed metal oxalates: FeCu(ox)2-3H20, CoCu(ox)2.3H20 and NiCu(ox)2-3.5H20, [ox = C204]. Results are compared with those reported for the thermal decompositions of the individual metal oxalates, Cuox, Coox.2H20, Niox.2H20 and Feox-2H20. X-ray photoelectron spectroscopy (XPS) was also used to examine the individual and the mixed oxalates. Dehydrations of the mixed oxalates were mainly deceleratory processes with activation ener-' gies (80 to 90 kJ-mol-1), similar to those reported for the individual hydrated oxalates. Tempera- ture ranges for dehydration were broadly similar for all the hydrates studied here (130 to 180~ Decompositions of the mixed oxalates were all complex endothermic processes with no obvi- ous resemblance to the exothermic reaction of Cuox, or the reactions of physical mixtures of the corresponding individual oxalates. The order of decreasing stability, as indicated by the temperature ranges giving comparable decomposition rates, was NiCu(ox)2 > CoCu(ox)2 > FeCu(ox)2, which also corresponds to the or- der of increasing covalency of the Cu-O bonds as shown by XPS. Keywords: decomposition, dehydration, DSC, EGA kinetics, mixed metal oxalates, TG, TM Introduction The thermal decompositions of metal oxalates have been studied extensively and various mechanisms of decomposition have been proposed [ 1]. * To whom correspondence should be addressed John Wiley & Sons, Limited, Chichester Akaddmiai Kiad6, Budapest