Zone-refined iron corrodes at the same rate whether cold-worked or annealed. Cold-working of iron containing 0.007-0.15% carbon increases the corrosion rate in 0.12N HC1 (pH = 1.01), the rate increasing still more after heat treating the iron at 77~176 for 2 hr. Cold-working of iron containing 0.01-0.02% nitrogen increases the corrosion rate only after heat treatment at 77~176Two maxima in the rate appear for heat treated N alloys but only

1975). aJ zL A. Foroulis and M. J. Thubrikar, Werksto~e Korrosion, 2S, 350 (1979). ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-03-24 to IP ) unless CC License in place (see abstract). ecsdl.org/site/terms_use address. Redistribution subject to ECS terms of use (see 169.230.243.252 Downloaded on 2015-03-24 to IP

The kinetics of passivity breakdown and nucleation of pitting of preanodized aluminum by chloride ions has been investigated using aluminum supporting oxide films of reasonably well‐known thickness and structure. The kinetics of passivity breakdown at the steady‐state, critical pitting potential is influenced by chloride ion concentration, temperature, and oxide film thickness; it was found to be independent of solution pH in the range 5–10. It is postulated that passivity breakdown and nucleation of pitting at the critical pitting potential occurs by a process of Cl− adsorption (assisted by the field at the oxide‐solution interface) on the hydrated oxide surface and formation of a soluble, basic chloride salt with the lattice cation which readily goes in solution. This process of localized dissolution of the hydrated oxide film via formation of a soluble, basic, aluminum chloride salt once initiated is likely to continue in an “autocatalytic” fashion until the oxide is locally “penetrated” and dissolution of the substrate metal begins.

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The critical pitting potential of oxide covered aluminum electrodes in aqueous chloride solutions has been investigated as a function of chloride ion concentration, temperature, solution pH and oxide film thickness. The steady state critical pitting potential decreases with chloride ion concentration and increasing solution temperature. Solution pH in the range 5 to 9 has no effect on the breakdown potential. The role of the oxide film thickness is to slightly increase the critical potential for passivity breakdown and intiation of pitting. It is postulated that at the critical pitting potential, passivity breakdown occurs by a process of field assisted Cl adsorption on the hydrated oxide surface and formation of a soluble basic chloride salt with a lattice cation which readily goes in solution. This process of localized dissolution of the hydrated oxide film via formation of a soluble basic aluminum chloride salt, once initiated, is likely to continue in an “autocatalytic” fashion until the oxide is locally “penetrated” and dissolution of the substrate metal begins.