Desorption d'oxydes de niobium a partir de la solution solide niobium-oxygene, sous 3 × 10 −7 Torr A 3 × 10 −5 Torr d'oxygene, entre 1700 K et 2350 K

Abstract

We have studied the desorption of oxygen from homogeneous niobium-oxygen solid solutions under a pressure of 3 × 10 −7 to 3 × 10 −5 Torr of oxygen between 1700 K and 2350 K. The products of this desorption process are NbO and NbO 2, which we have demonstrated are formed by a superficial reaction after chemisorption of molecular oxygen on to two distinct sites. Two models for the process are discussed: in the first, the speeds of desorption are assumed to be a function of the surface coverage. This model suggests that the binding energy of the adsorbed oxygen atoms should vary with the coverage. In the second model the bulk concentration is assumed to be variable. It is shown that at low concentration this model is related theoretically to the first. Good agreement with experiment was found for this model in the steady state throughout the whole homogeneity range of the solid solutions. In the transient state, however, the model only applies to thin samples.