Slow and forced hydrolyses of Fe(III)-salts in aqueous solutions were extensively investigated because of the importance of these reactions in natural aquatic or sediment systems and living systems on one side, and chemical syntheses and technology (corrosion problems) on the other. The hydrolyses of Fe(III)-salts in aqueous solutions are often used as models with a view to better understanding the mechanism of hydrolyses of metal cations. The kinetics, the phase composition of the precipitates, as well as the size and morphology of particles depend on experimental parameters such as temperature, pH, concentration of Fe³⁺ salts, the nature of the anion present, or some other «foreign» substance, for example surfactants. In the present work we have focused on the process of forced hydrolysis of Fe³⁺ ions in a perchlorate-containing aqueous solution. Forced hydrolyses were conducted at 90 or 160 ^oC. The influence of the concentration of Fe(ClO₄)₃, HClO₄, NaClO₄ as well as selected surfactants, were investigated. The precipitates, as the solid products of Fe³⁺ ion hydrolysis, were analysed with XRD, Mössbauer, FT-IR and FE-SEM, and EDS techniques. Hematite (a-Fe₂O₃) was the principal product of hydrolysis of solutions at 90 ^oC. However, very small amounts of goethite (a-FeOOH) were found in the precipitates. FT-IR spectroscopy in particular was found to be very sensitive to small amounts of goethite present. Hematite was found as a single phase in the precipitates obtained at 160 ^oC. However, the size and morphology of hematite particles obtained at this temperature depended on the absence/presence of HClO₄. The presence of SDS or AOT drastically changed the phase composition and microstructure of the precipitates. Hollow goethite particles were formed by the aggregation mechanism.

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