Abstract
Mild steel exposed first to certain acid vapours and subsequently to condensation has been shown to develop black, horn-shaped corrosion products. Hydrochloric acid was the most effective initiator, growth rates up to 3 mm per day being observed. The corrosion products were identified as magnetite (Fe3O4), their formation being explained by an electrochemical mechanism involvig the intermediate production of ferrous hydroxide and hydrated ferric oxide. The underlying metal was pitted to a maximum depth of 60 μm. Corniform corrosion has been observed in emulsion paint containers and on steel exposed to the thermal decomposition of chlorinated polymers.
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