KINETICS OF THE THERMAL-OXIDATION OF TANTALUM IN OXYGEN-WATER VAPOR MIXTURES

The thermal oxidation of tantalum was studied between 450 and 600 degrees C in pure oxygen, pure water vapour or oxygen-water vapour mixtures. In these three atmospheres, Ta2O5 was observed to be the major product, with a porous stratified morphology. Oxidation kinetics are linear after a short parabolic regime followed by a breakaway period, with rates depending on the atmosphere. Pressure influences were recorded at 520 degrees C and showed that the reaction of adsorbed species were always rate-limiting. In the oxygen-water vapour mixtures, an additionnal slow process of dissociative oxygen adsorption was shown to take place, leading to a peculiar shape of the rate of reaction/water vapour pressure curve.