EQCM Study of Anodic Film Growth on Valve Metals

Abstract

A comparative study of anodic film growth on niobium, zirconium, and tungsten in was performed using the rotating electrochemical quartz crystal microbalance (EQCM). Potential sweep as well as potential step and hold experiments were performed in the range between open circuit and 8 Significant differences in the mass transients between the three metals were observed. During the formation of anodic films on niobium and zirconium, the dissolution was negligible and the fraction of the current serving for film growth was always close to unity. On tungsten, anodic dissolution in combination with film growth led to a growth fraction that diminished with time. The results obtained by the double potential step technique were compared with numerical simulations based on models considering either high field conduction or an interface reaction as limiting the kinetics of film growth. The growth of anodic films on niobium and zirconium was found limited by high field conduction, whereas film growth on tungsten was interface controlled. Film growth on tungsten was accompanied by important anodic dissolution, while dissolution of niobium and zirconium was negligible. © 2004 The Electrochemical Society. All rights reserved.