Electrochemical polarization and passivation of nanostructured iron in acid solution

Abstract

Purpose

The purpose of this paper is to demonstrate the effect of grain‐size reduction on the stability of passive films formed on pure iron. Possible mechanisms capable of their improvement are discussed.

Design/methodology/approach

Nanocrystalline iron was produced by pulse electrodeposition using a citric acid bath. The grain size of the nanocrystalline surface was analyzed by X‐ray diffractometry and atomic force microscopy. The tests were carried out in 95‐97 percent H₂SO₄ aqueous solution. The stability of the passive films was investigated using Tafel polarization curves and electrochemical impedance spectroscopy measurements.

Findings

The corrosion resistance of Fe in concentrated sulfuric acid solution increased as the grain size decreased from microcrystalline to nanocrystalline. The decreased passive current density of nanocrystalline Fe may be due to the more rapid formation of continuous passive films at surface crystalline defects, compared with coarse‐grained Fe structures.

Originality/value

The behavior of passive film growth and corrosion is considered in terms of excess free energy caused by the nanocrystalline surface.

Citation

Afshari, V. and Dehghanian, C. (2010), "Electrochemical polarization and passivation of nanostructured iron in acid solution", Anti-Corrosion Methods and Materials, Vol. 57 No. 3, pp. 142-147. https://doi.org/10.1108/00035591011040100