KINETICS OF THE THERMAL-OXIDATION OF TANT ALUM IN OXYGEN-WATER VAPOR MIXTURES

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