Characterisation of Corrosion Products on Iron in Contact With Hot Water Available to Purchase

The corrosion of galvanised sheets of carbon steel in contact with hot water in two household systems was investigated by means of metallographic techniques, X‐ray diffraction analysis and trasmission Mössbauer spectroscopy. The corrosion process gave rise to localised attack of the inner wall of the steel sheets, with formation of tubercules of reaction products in zones where the protective effect of the zinc coating vanished, probably for an excessive increase in the heating temperature leading zinc to become cathodic to iron. Significant differences were found in the phase composition of the corrosion products depending on the in‐service life of the steel component. After ∼1 year of exposure to hot water, siderite and lepidocrocite were found to be the prevailing corrosion products, formed together with lower amounts of akaganeite, mixed Zn‐Fe carbonate and hydrozincite. After about a double exposure time to hot water, the corrosion products were mainly constituted by magnetite, siderite and lepidocrocite, together with lower amounts of goethite, akaganeite, Zn‐Fe carbonate and hydrozincite. A complementary use of X‐ray diffraction and Mössbauer techniques proved to be determining for a satisfactory identification of the corrosion products.