Electrochemical and surface study of the oxide growth and conversion on 316L stainless steel
36th Annual CNS-CNA Student Conference - 2012 June 12


Presented at:
36th Annual CNS-CNA Student Conference
2012 June 12
Location:
Saskatoon, Canada
Session Title:
CNS/CNA Student Conference 2012

Authors:
Quintin Knapp (Western University )
Jungsook Clara Wren (Western University )
  

Abstract

The oxide formation and conversion mechanism as a function of potential on 316L stainless steel was investigated under both potentiodynamic and potentiostatic conditions using a range of electrochemical and surface analysis techniques. All of the results were consistent with the expectations arising from electrochemical thermodynamics and competitive metal oxidation kinetics. Four characteristic potential regions were identified for anodic oxidation. In Ox I (E < –0.5 VSCE), the anodic process was limited to the conversion of the pre-existing but defective Cr(III) oxide layer to a chromite-like inner layer followed by growth of a magnetite-like outer layer. In Ox II (–0.5 VSCE < E < –0.1 VSCE), additional oxidation of magnetite to ?-Fe2O3 occurred, providing maximum passivity of the film. At potentials > –0.3 VSCE, the hydrated Fe(II) at the oxide/water interface was oxidized to gamma-FeOOH, with a rate dependent on pH and potential. In Ox III (–0.1 VSCE < E < 0.2 VSCE), oxidation of the maghemite-covered Fe3O4 to gamma-FeOOH led to film fracture, followed by oxidation of the exposed underlying layer. The oxide layer grew via film fracture and repassivation. In Ox IV (0.2 VSCE < E), oxidative dissolution of Cr(III) became important, resulting in a predominantly iron oxide film.

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