Abstract
Autoradiography has been used to investigate the distribution of inhibitive anions on the surfaces of mild steel and high purity iron which had been in contact with 14C-labelled solutions of sodium azelate. Regions of intense uptake of the anion, corresponding to sites of incipient breakdown of the air-formed oxide at which local anodes are produced, have been found to be more extensive at positions overlying grain boundaries in the metal than elsewhere. This enhanced reactivity of the grain boundary regions has been shown to be independent of gross impurity segregation effects involving the precipitation of cementite or other second phase particles at the boundaries. It is thought to depend on discontinuity in the epitaxial growth of oxide at grain boundaries in the substrate metal.
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