Temperature Dependence of Tafel Slope in the Formation of Very Thin Anodic Oxide Films on Niobium

Abstract

A kinetic study was made of the formation of very thin anodic oxide films on niobium at constant current over the temperature range −10° to 70°C. Formation voltages were limited to the range below the oxygen evolution potential to eliminate possible interaction of an electronic component of the current with the measured formation field. It was found that the measured temperature dependence of Tafel slope agreed with that predicted by the theory of Mott and Cabrera. Using this theory, a zero field interfacial barrier height of 1.19 ev and barrier half‐width of 2.40Aå were obtained. Values of the differential formation field are reported at current densities of 1000, 100, 10, and 1 µa/cm² at ten degree intervals over the temperature range studied.