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The corrosion behavior of pure iron in diluted (inhibiting) and moderately concentrated (aggressive) polyphos-phate solutions has been re-examined in the light of the results of surface analyses of iron samples by means of x-ray photoeleetron spectroscopy. The passive film responsible for the anodic control of the corrosion of iron in diluted (NaPO3)x solutions appears much like an air-formed oxide film with, in addition, some inclusions of iron phosphate. The photoelectron spectra of iron samples exposed to (NaPO3)x/CaC12 solutions suggest the reversion of polyphos-pharos to orthophosphates as being an essential step in the formation of the protective film. A possible mechanism of the growth of such a film, composed of a mixture of calcium and iron orthophosphates, is proposed. Among various inorganic ions acting as corrosion inhibitors of iron or steel, polyphosphates (metaphos-phates) possess a rather unique property of being effective when added in small amounts to even con-centrated chloride solutions (1-3). However, the ef-fectiveness of polyphosphates depends to a large extent on the simultaneous presence in the solution
Koudelka et al. (Tue,) studied this question.