Effect of pH on the anodic behavior of tungsten

Potentiodynamic and potentiostatic polarization, and the rotating disk electrode technique, were used to study the anodic behavior of tungsten (W) in a broad pH range (0.5-13.5) in H sub 3 PO sub 4 /KOH buffered solution. Surface oxides were found to play a prominent role in the anodic oxidation and...

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Bibliographic Details
Published in:Journal of the Electrochemical Society 2002-06, Vol.149 (6), p.B224-B233
Main Authors: ANIK, M, OSSEO-ASARE, K
Format: Article
Language:English
Subjects:
Applied sciences
Corrosion
Corrosion mechanisms
Exact sciences and technology
Metals. Metallurgy
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Summary:Potentiodynamic and potentiostatic polarization, and the rotating disk electrode technique, were used to study the anodic behavior of tungsten (W) in a broad pH range (0.5-13.5) in H sub 3 PO sub 4 /KOH buffered solution. Surface oxides were found to play a prominent role in the anodic oxidation and dissolution of tungsten. Five distinct pH regimes and the corresponding reaction mechanisms were identified. Below pH 1 (region A) H exp + -assisted dissolution was the main dissolution pathway. As the pH increased, the role of H exp + diminished and at pH 2.6 (region B), which was identified as the point of zero charge (pzc) of the surface tungsten oxide, dissolution was mainly H sub 2 O-assisted. The dissolution was observed to be OH exp - -assisted above the pzc. The reaction order for OH exp - was one between pH 4.5 and 6.5 (region C). The reaction order became zero at pH 8 (region D). This observation was attributed to the pH-independent dissolution of the hydrated oxide phase. Above pH 10, OH exp - dependence of the anodic current commenced and at around pH 12.5 (region E) the reaction order for OH exp - became one.
ISSN:0013-4651
1945-7111
DOI:10.1149/1.1471544