Zairyo-to-Kankyo
Online ISSN : 1881-9664
Print ISSN : 0917-0480
ISSN-L : 0917-0480
Effects of Rust Layers on the Corrosion of Metals
Norio Sato
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1999 Volume 48 Issue 4 Pages 182-189

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Abstract

Anodic metal dissolution produces hydrated metal salts concentrated at the anode interface and modifies the ion transport in the interfacial diffusion layer to be anion-selective or cation-selective. The anion-selective diffusion layer formed with monovalent chloride or hydroxide contributes to the formation of a chloride film and leads to either the chloride-film-induced passivation if the chloride is insoluble (e.g. Ag/AgCl) or the transition from the active state to the polishing state dissolution if the chloride is soluble (e.g. Fe/FeCl2). The cation-selective diffusion layer formed with multivalent phosphate or sulfate ions leads to the formation of an oxide film, and thereby to the oxide-film-induced passivation of metal anode (e.g. Ni/NiO). Generally, rust layers are anion-selective in acidic solutions and cation-selective in basic solutions. Adsorption of multivalent oxoanions often changes the rust layer from an anion-selective to a cation-selective layer. The anion-selective rust layer accelerates the localized corrosion of metals; whereas, the cation-selective rust layer inhibits the localized corrosion. The bipolar rust ion-selective layer suppresses the anodic metal dissolution and leads to metal passivation. The cathodic oxygen reduction is allowed to proceed on p-type rust layers but is inhibited on n-type rust layers.

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© Japan Society of Corrosion Engineering
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