Composition and morphology of corrosion products formed on galvanised steel exposed to a swimming pool atmosphere

Abstract

This paper reports a study of the composition and morphology of the corrosion products formed on galvanised steel specimens exposed to a swimming pool atmosphere. Two thicknesses of hot dip zinc coatings were investigated measuring 1·8 and 180 µm, respectively. Specimens were analysed throughout a 12 month exposure period and a reaction sequence identified using the techniques of X-ray diffraction, X-ray photoelectron spectroscopy, and SEM/EDX. The main phases determined were: zincite (ZnO), simonkolleite (Zn₅(OH)₈Cl₂. H₂O), hydrated zinc hydroxychlorosulphate (Zn₄Cl₂(OH)₄SO₄. 5H₂O), and hydrated sodium zinc hydroxychlorosulphate (NaZn₄Cl(OH)₆SO₄. 6H₂O). Amarantite (FeSO₄(OH). 3H₂O) was found only on the specimens with the thinner zinc coating through which iron diffusion from the bulk steel could occur.

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