Formation of rust during the corrosion of steel in water and (NH4>2S04 solutions was monitored at 20 °C up to 3 months and at 90 °C up to 3 days. All corrosion products were analyzed by X-ray diffraction and Fourier transform IR spectroscopy. Four oxide phases, lepidocrocite (y-FeOOH), goethite (a-FeOOH), magnetite (Fe3C>4) and hematite (a-Fe203), were found in the corrosion products. Their distribution or absence of some oxide phases in corrosion products were strongly dependent on the experimental conditions. The strong influence of (NH4>2S04 electrolyte on the phase composition of the rust was explained by the cumulative effect of two aggressive ions, NH4 and SO4. Possible pathways for the formation of iron oxide phases in the rust were discussed
