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Potentiodynamic and potentiostatic polarizations, and a rotating disk electrode technique were used to study the influence of diffusion on the anodic reactions of tungsten (W) in a broad pH range (∼0.3-13.5) 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 H2Oassisted dissolution, specimen rotation had an effect 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 the mixed control of the kinetics of OH −assisted dissolution and slow diffusion of surface WO 2− 4 ions between pH 4 and 7 (Region C). The kinetics of the H2WO4(s) solubilization and slow diffusion of surface WO 2− 4 ions were observed to influence the anodic current 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 the slow diffusion of bulk OH − ions to the electrode surface.

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