Diffusion effect on the anodic reactions of tungsten


Anik M., Cansizoglu T., Cevik S.

International Symposium on Surface Oxide Films held at the 204th Electrochemical-Society Meeting, Florida, United States Of America, 12 - 17 October 2003, vol.2003, pp.227-240 identifier

  • Publication Type: Conference Paper / Full Text
  • Volume: 2003
  • City: Florida
  • Country: United States Of America
  • Page Numbers: pp.227-240
  • Eskisehir Osmangazi University Affiliated: Yes

Abstract

Potentiodynamic and potentiostatic polarizations, and rotating disk electrode technique were used to study the influence of diffusion on the anodic reactions of tungsten (W) in a broad pH range (similar to0.3 - 13.5) in H3PO4 buffered solutions, The anodic current was controlled totally by the kinetics of H+-assisted dissolution below pH 1 (Region A). At around pH 2.5 (Region B), in addition to the kinetics of H2O-assisted dissolution, specimen rotation was effective on the current. This observation was attributed mainly to the physical damage to an oxide phase by hydrodynamic effects and partly to the diffusion of surface H2WO4(aq) species. The anodic current was under mixed control of the kinetics of OH- -assisted dissolution and slow diffusion of surface WO42- ion in between pH 4 and 7 (Region C). The kinetics of H2WO4(S) solubilization and slow diffusion of surface WO42- ion were observed to influence the anodic current in between pH 7.5 and 11.5 (Region D). In highly alkaline solutions (pH > 12; Region E), however, W anodic current was controlled totally by slow diffusion of bulk OH- ions to the electrode surface.