Monitoring of the gas phase composition: A prerequisite for unravelling the mechanism of decomposition of solids - Thermal decomposition of cobalt oxalate dihydrate

The complexity of the processes occurring during cobalt oxalate dihydrate ( COD) decomposition indicates that an interpretation of the mechanism based only on the TG curve is of little value. Mass change alone does not allow d eeper insight into all of the potential primary and secondary reactions tha t could occur. The observed mass changes (TG) and thermal effects (DTA/DSC) are a superposition of several phenomena and thus do not necessarily refle ct COD decomposition alone. Investigation of the mechanism of decomposition requires the application of different simultaneous techniques that allow t he qualitative and quantitative determination of the composition of the gas eous products. Composition of the solid and gaseous products of COD decomposition and heat s of dehydration and oxalate decomposition were determined for inert, oxidi zing and hydrogen-containing atmospheres. Contrary to previous suggestions about the mechanism of cobalt oxalate decomposition, the solid product form ed during decomposition in helium contains not only metallic Co-met, but al so a substantial amount of CoO (ca 13 mol%). In all atmospheres, the compos ition of the primary solid and gaseous products changes as a result of seco ndary gas-solid and gas-gas reactions, catalyzed by freshly formed Co-met. The course of the following reactions has been investigated under steady-st ate and transient conditions characteristic for COD decomposition: water ga s shift, Fischer-Tropsch, CO disproportionation, CoO reduction by CO and H- 2, Co-met oxidation under rich and lean oxygen conditions.