Phase transformations of iron oxides, oxohydroxides, and hydrous oxides in aqueous media

Abstract

The available information regarding the pathways of processes leading to precipitation of iron (hydrous) oxides in aqueous salt solutions is reviewed. The importance of the early hydrolysis stages in determining the nature and the morphology of the solid phases is discussed. In the second part, the phase transformation between various oxides and oxohydroxides in aqueous suspensions is described with emphasis on mechanistic considerations. Such phase transformations may proceed under milder conditions (e.g., at lower temperatures) by a dissolution-recrystallization mechanism than in dry powders, which can also influence the morphology and the size of the resulting particles. A proper control of experimental parameters has resulted in a number of well defined colloidal iron (hydrous) oxides with respect to their composition, structure, morphology, and size.