Initial oxidation of cobalt

The initial oxidation of pure cobalt has been studied by a manometric method in the range 320 to 520° C for 1 to 15 min using purified dry oxygen at 7. 6 cm of mercury. The oxide thickness varies from 400 Å at the lowest to 5000 Å at the highest temperatures. Oxidation follows a direct logarithmic law and is independent of oxygen pressure. A typical Arrhenius plot shows an anomaly at the allotropie change point ( 386° C) of cobalt, although the activation energies of oxidation of both the allotropes are very much the same. The modified model of Uhlig's mechanism on logarithmic oxidation [7] applies in the present case.