Properties of potentiostatic passive films grown on iron electrodes immersed in weak‐alkaline phosphate solutions

Abstract

Purpose

This paper aims to study the growth and properties of potentiostatic passive films formed on iron electrodes immersed in pH 8.9‐11.0 phosphate solutions.

Design/methodology/approach

First, passive films were grown potentiostatically on pure iron electrodes under different experimental conditions (namely the Na₂HPO₄ concentration, time and potential of polarization, solution pH and temperature). Subsequently, the properties of the resulting passive layer were evaluated by electrochemical measurements (open circuit potential and potentiodynamic polarization measurements) and scanning electron microscopy.

Findings

The formation of passive films on iron electrodes immersed in weak‐alkaline phosphate solutions was found to occur in three main steps, being the Na₂HPO₄ concentration a very important parameter to promote reduction of iron dissolution. Films with protective properties could be obtained within at least 30 s of polarization at +0.50 V/SCE. The effect of the polarization potential was interpreted according to previous potentiodynamic data and the influences of solution pH and temperature follow thermodynamic laws.

Research limitations/implications

In‐situ surface analytical techniques such as extended X‐ray absorption fine structure (EXAFS) and elipsometry coupled to electrochemical measurements can elucidate more information on the film growth process, and in turn on resulting properties.

Originality/value

This contribution provides useful insights into the potentiostatic behaviour of iron in alkaline phosphate solutions.

Citation

Giacomelli, C., Giacomelli, F.C., Bortolluzzi, R.L. and Spinelli, A. (2006), "Properties of potentiostatic passive films grown on iron electrodes immersed in weak‐alkaline phosphate solutions", Anti-Corrosion Methods and Materials, Vol. 53 No. 4, pp. 232-239. https://doi.org/10.1108/00035590610678938