Simultaneous carburisation and oxidation of niobium in the presence of carbon monoxide

During reaction with CO, niobium was observed to carburise and oxidise simultaneously, with NbC, NbO and NbO forming as intermediate products before complete conversion to NbC. It was shown that the reason for such a complex reaction path was the fact that during the carburising reactions enough CO is produced to oxidise the metal. Oxidation takes place by the inward diffusion of CO through cracks and pores to the metal surface. After depletion of Nb, NbC and NbO, the monocarbide continues to grow on NbO. The reaction NbO + 4CO = NbC + 3CO is extremely slow and is controlled by chemical kinetics