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A potentiodynamic and SEM study of the behaviour of iron in pH 8.9‐11.0 phosphate solutions

A potentiodynamic and SEM study of the behaviour of iron in pH 8.9‐11.0 phosphate solutions The behaviour of iron electrodes immersed in pH 8.9‐11.0 Na 2 HPO 4 solutions was studied by potentiodynamic measurements (cyclic voltammetry) and scanning electron microscopy (SEM). The influence of proton and phosphate content, scan rate, anodic switching potential and other devised potential/time perturbation regimes were evaluated in order to obtain an understanding of the reactions involved during the passivation process. The oxidation‐reduction peaks were analysed using a thermodynamic approach. It was possible to reveal the most important reactions coming about on the electrode surface, which comprise, initially, the formation of Fe 3 (PO 4 ) 2 and Fe(OH) 2 at ca. −0.8 V/SCE. Subsequently, these ferrous species are further oxidized to γ‐FeOOH at ca. −0.36 V/SCE, the latter being transformed into Fe 2 O 3 in the passive region. Depending on the pH value (11.0) and scan rate (slow), Fe 3 O 4 is clearly present as an intermediate oxide structure between the ferrous and ferric species mentioned earlier. In addition, scan rate was discovered to play a remarkable influence on the surface morphology observed during the SEM examinations. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Anti-Corrosion Methods and Materials Emerald Publishing

A potentiodynamic and SEM study of the behaviour of iron in pH 8.9‐11.0 phosphate solutions

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Publisher
Emerald Publishing
Copyright
Copyright © 2004 Emerald Group Publishing Limited. All rights reserved.
ISSN
0003-5599
DOI
10.1108/00035590410533138
Publisher site
See Article on Publisher Site

Abstract

The behaviour of iron electrodes immersed in pH 8.9‐11.0 Na 2 HPO 4 solutions was studied by potentiodynamic measurements (cyclic voltammetry) and scanning electron microscopy (SEM). The influence of proton and phosphate content, scan rate, anodic switching potential and other devised potential/time perturbation regimes were evaluated in order to obtain an understanding of the reactions involved during the passivation process. The oxidation‐reduction peaks were analysed using a thermodynamic approach. It was possible to reveal the most important reactions coming about on the electrode surface, which comprise, initially, the formation of Fe 3 (PO 4 ) 2 and Fe(OH) 2 at ca. −0.8 V/SCE. Subsequently, these ferrous species are further oxidized to γ‐FeOOH at ca. −0.36 V/SCE, the latter being transformed into Fe 2 O 3 in the passive region. Depending on the pH value (11.0) and scan rate (slow), Fe 3 O 4 is clearly present as an intermediate oxide structure between the ferrous and ferric species mentioned earlier. In addition, scan rate was discovered to play a remarkable influence on the surface morphology observed during the SEM examinations.

Journal

Anti-Corrosion Methods and MaterialsEmerald Publishing

Published: Jun 1, 2004

Keywords: Passivation; Iron; Electrodes

References