The course of the transformation of synthetic γ‐FeOOH (lepidocrocite) samples, prepared by different methods was investigated and the effect of a preliminary heat treatment of the initial material on the product phase composition and morphology studied. Both the goethite‐tohematite ratio and the particle size of the products depend on the preparation method and on the preliminary heat treatment of the initial lepidocrocite. The results are discussed in terms of the dissolution of the less stable lepidocrocite followed by the crystallization of the more stable phases α‐FeOOH and α‐Fe2O3 from the solution. The final product phase composition and the particle size are affected considerably by a presence of goethite and/or hematite germs in the initial γ‐FeOOH.

Bei der Umwandlung von verschiedenen synthetischen γ‐FeOOH‐ Proben in FeSO4‐Lösungen hängen die Gehalte der Endprodukte an α‐FeOOH und α‐Fe2O3 sowie deren Partikelgrößen vom Präparationsweg der Ausgangslepidocrocite ab.

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Amorphous FeIII hydroxides prepared at pH = 6 differ from analogous precipitates obtained in alkaline media in that they have an increased content of anions bound in their structures, and crystallize less readily both in dry thermal treatment and under hydrothermal conditions. The shapes of DTA curves obtained for freshly prepared gels and for products of ageing in mother liquor are discussed, and the effect of the anions present on the course of thermal decomposition is assessed.