Effect of pH on the anodic behavior of tungsten

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Abstract

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 H3PO4/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+-assisted dissolution was the main dissolution pathway. As the pH increased, the role of H+ 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 H2O-assisted. The dissolution was observed to be OH--assisted above the pzc. The reaction order for OH- 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- dependence of the anodic current commenced and at around pH 12.5 (region E) the reaction order for OH- became one.

Original languageEnglish (US)
Pages (from-to)B224-B233
JournalJournal of the Electrochemical Society
Volume149
Issue number6
DOIs
StatePublished - Jun 1 2002

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Renewable Energy, Sustainability and the Environment
  • Surfaces, Coatings and Films
  • Electrochemistry
  • Materials Chemistry

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