Anodic and air oxidation of niobium studied by ion beam analysis with implanted Xe marker

Xe marker implantation and backscattering analysis were used to study the growth mechanism of anodic oxides on niobium. In 5 wt% aqueous ammonium citrate solution, analysis of the Xe marker movement demonstrated that the oxide was formed mainly within the existing oxide through the transport of both niobium cations and oxygen anions from each side when the anodic oxidation was carried out with a constant current density of 1.0 mA cm(-2) and a limiting oxidation potential from 60 to 100 V. During anodization, the transport numbers of niobium increased with the elevation of potential. The air oxidation behavior of niobium and the profile of Xe ions at the temperature of 200-500 degrees C were also studied. The growth law of niobium oxide was obtained and no movement of the peak position of Xe ions was observed when the temperature was below 350 degrees C.