Oxidation of niobium sheets at high temperature

This work shows the role of oxygen pressure on growth kinetics, morphology, phase composition and texture of oxide scale in the oxidation of niobium sheets at 900 degrees C. The particular morphology observed at low pressure shows the existence of competition between edge and surface growth mechanisms. Pressure and conversion rate influence the nature of preferential orientations of the Nb2O5 oxide layer: a [110] fibre axis is stabilized at high pressure but, at low pressure, the higher is the conversion rate, the more evident is this fibre axis, This behaviour is observed not only after cooling but also in situ. At high pressure, the evolution is not only temporal but also spatial: with increasing distance from the metal/oxide interface, a gradual transition from more oriented to randomly oriented layer is observed.