Sintering kinetics of submicron sized cobalt powder

The paper details the results of sintering kinetics studies on submicron sized fine cobalt metal powders prepared through oxalate decomposition route using both conventional sintering method as well as stepwise isothermal dilatometry (SID) technique. Powder preparation and processing parameters such as decomposition temperature, compaction pressure and sintering atmosphere, etc. were optimized to achieve highest sintered density with lowest activation energy through conventional sintering. Role of submicron sized powder and surface contamination layers on initial shrinkage was explained towards early shrinkage of cobalt compacts by dilatometric analysis. Measured step isothermal shrinkage data were analyzed by Makipirtti–Meng method. The shrinkage data were found to fit well with the rate equation proposed in this method and its validity was established for the metallic systems also. Kinetic parameters were evaluated and sintering was found to occur through three major mechanisms operative successively, which are grain boundary diffusion, lattice diffusion and plastic/viscous flow with the energy of activation as 135, 234 and 373 kJ/mol, respectively. The results were well supported by microstructural analysis of sintered specimens.