Potentiostatic Oxide Growth Kinetics on Ni-Cr and Co-Cr Alloys: Potential and pH Dependences

Ahmed Y. Musa, Mehran Behazin, Jungsook Clara Wren

Research output: Contribution to journalArticle

8 Citations (Scopus)

Abstract

Oxide growth kinetics on the Ni-Cr-Fe alloy Inconel 600 and the Co-Cr alloy Stellite 6 under potentiostatic polarization have been investigated by current measurements augmented by ex-situ surface analyses. The results reveal a mechanism for metal oxidation and oxide formation that is common to both alloys. The reaction thermodynamics for the oxidation of a metal determine whether a certain metal oxidation can or cannot occur. However, the metal oxidation proceeds via two competing pathways, oxide formation and metal ion dissolution. At pH 10.6 where the solubilities of Fe<sup>II</sup>, Ni<sup>II</sup> or Co<sup>II</sup> species are near their minima, oxide formation is favoured over metal ion dissolution. As the oxide grows, the rate of metal oxidation decreases with time due to an increase in the electrochemical potential barrier. The oxide formation occurs sequentially; the conversion of the preformed Cr<inf>2</inf>O<inf>3</inf> film to chromite (FeCr<inf>2</inf>O<inf>4</inf> or CoCr<inf>2</inf>O<inf>4</inf>) proceeds before the next layers of Fe<inf>3</inf>O<inf>4</inf>/NiFe<inf>2</inf>O<inf>4</inf> and NiO/Ni(OH)<inf>2</inf> grow on Inconel 600, or CoO/Co(OH)<inf>2</inf> grows on Stellite 6. The effect of a different E<inf>APP</inf> is to limit the oxidation sequence. The pH does not directly affect the driving force for metal oxidation but it strongly influences the relative rates of oxide formation and metal dissolution, thereby affecting metal oxidation kinetics.

Original languageEnglish
Pages (from-to)185-197
Number of pages13
JournalElectrochimica Acta
Volume162
DOIs
Publication statusPublished - 20 Apr 2015
Externally publishedYes

Fingerprint

Growth kinetics
Oxides
Metals
Oxidation
Stellite
Dissolution
Metal ions
Chromite
Electric current measurement
Solubility
Thermodynamics
Polarization

Keywords

  • Co-Cr alloy
  • Metal oxidation kinetics
  • Ni-Cr-Fe alloy
  • Oxide growth kinetics
  • Potentiostatic polarization

ASJC Scopus subject areas

  • Electrochemistry
  • Chemical Engineering(all)

Cite this

Potentiostatic Oxide Growth Kinetics on Ni-Cr and Co-Cr Alloys : Potential and pH Dependences. / Musa, Ahmed Y.; Behazin, Mehran; Wren, Jungsook Clara.

In: Electrochimica Acta, Vol. 162, 20.04.2015, p. 185-197.

Research output: Contribution to journalArticle

Musa, Ahmed Y. ; Behazin, Mehran ; Wren, Jungsook Clara. / Potentiostatic Oxide Growth Kinetics on Ni-Cr and Co-Cr Alloys : Potential and pH Dependences. In: Electrochimica Acta. 2015 ; Vol. 162. pp. 185-197.
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