pH-dependent anodic reaction behavior of tungsten in acidic phosphate solutions


Anik M.

ELECTROCHIMICA ACTA, cilt.54, sa.15, ss.3943-3951, 2009 (SCI-Expanded) identifier identifier

  • Yayın Türü: Makale / Tam Makale
  • Cilt numarası: 54 Sayı: 15
  • Basım Tarihi: 2009
  • Doi Numarası: 10.1016/j.electacta.2009.02.014
  • Dergi Adı: ELECTROCHIMICA ACTA
  • Derginin Tarandığı İndeksler: Science Citation Index Expanded (SCI-EXPANDED), Scopus
  • Sayfa Sayıları: ss.3943-3951
  • Anahtar Kelimeler: Tungsten, Phosphate solution, Polarization, EIS, pzc, ELECTROCHEMICAL IMPEDANCE SPECTROSCOPY, WO3 ELECTRODES, KINETICS, DISSOLUTION, OXIDATION, GROWTH, FILMS
  • Eskişehir Osmangazi Üniversitesi Adresli: Evet

Özet

Potentiodynamic and potentiostatic polarization experiments, and the electrochemical impedance spectroscopy technique were used to study the pH dependent anodic behavior of tungsten (W) in acidic phosphate solution. At very low pH values (pH < 2.6) the dissolution of tungsten was W-assisted and as the pzc (pH 2.6) was approached H(2)O-assisted dissolution became main dissolution pathway. Above pH 2.6, however, tungsten dissolution was CH-assisted. The thickness and dielectric properties of the W-oxide barrier layer were observed almost pH independent at corrosion potential. The oxygen vacancy transport across the oxide film caused a capacitive response at very acidic solutions (pH <= 3.5) and as the dissolution rate increased (pH > 4.5) the capacitive response turned into the inductive one due to the accelerating effect of negative surface charge in Tafel region. The inductive response in the tungsten impedance spectra shifted to a very low frequency range as the tungsten dissolution rate decreased in the pseudo-plateau and potential independent regions. Fitting of the tungsten impedance data according to the surface charge approach showed that the resistance to the defect migration increased as the pzc was approached and the film capacitance decreased above pH 3.5 due to the accelerated formation rate of the non-protective loosely bound hydrated layer on the metal oxide surface. (C) 2009 Elsevier Ltd. All rights reserved.