Moessbauer studies of the corrosion products of cast iron in aqueous ammonium nitrate solution

The corrosion products of cast iron in 45​% NH4NO3 soln. at different temps. were studied using mainly Moessbauer spectroscopy. ferrihydrite [39473-​89-​7] (Fe5HO8.4H2O) or 5Fe2O3.9H2O [12259-​21-​1] is found with γ-​FeOOH in the initial stages of the reaction at room temp. At a later stage, partial dissoln. of γ-​FeOOH takes place and magnetite is pptd. Above 80° either Fe3-​xO4 or Fe5HO8.4H2O or α-​Fe2O3 is formed as the major product depending on the ratio of the reactants