Diffusion Effect on the Anodic Reactions of Tungsten

Authors : Mustafa ANIK, Tuba CANSIZOĞLU and Sinem ÇEVİK

Pages : 425-440

View : 22 | Download : 11

Publication Date : 0000-00-00

Article Type : Research Paper

Abstract :Potentiodynamic and potentiostatic polarizations, and a rotating disk electrode technique were used to study the influence of diffusion on the anodic reactions of tungsten insert ignore into journalissuearticles values(W); in a broad pH range insert ignore into journalissuearticles values(\sim 0.3--13.5); in H3PO4 buffered solutions. The anodic current was controlled totally by the kinetics of H+ -assisted dissolution below pH 1 insert ignore into journalissuearticles values(Region A);. At around pH 2.5 insert ignore into journalissuearticles values(Region B);, in addition to the kinetics of H2O-assisted 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 H2WO4insert ignore into journalissuearticles values(aq); species. The anodic current was under the mixed control of the kinetics of OH--assisted dissolution and slow diffusion of surface WO42- ions between pH 4 and 7 insert ignore into journalissuearticles values(Region C);. The kinetics of the H2WO4insert ignore into journalissuearticles values(s); solubilization and slow diffusion of surface WO42- ions were observed to influence the anodic current between pH 7.5 and 11.5 insert ignore into journalissuearticles values(Region D);. In highly alkaline solutions insert ignore into journalissuearticles values(pH > 12; Region E);, however, W anodic current was controlled totally by the slow diffusion of bulk OH- ions to the electrode surface.
Keywords : Tungsten, Anodic Reactions, Diffusion