Decomposition of Fe complexes

Morris et al. (1991) obtained hematite of very small particle size ( 10 nm), termed nanophase by slow thermal decomposition in air of tri-Ee -acetato-hy-droxy-nitrate. XRD shows only two broad lines as in a 2-line ferrihydrite, but the magnetic hyperfine field at 4.2 K of 50.4 T appears to be more in agreement with poorly crystalline hematite. Well-crystalline hematite and Al-hematite were produced by decomposing Ee-Al-oxinates at 700 °C (da Costa et al. 2001). 

A characteristic of the iron oxide system is the variety of possible interconversions between the different phases. Under the appropriate conditions, almost every iron oxide can be converted into at least two others. Under oxic conditions, goethite and hematite are thermodynamically the most stable compounds in this system and are, therefore, the end members of many transformation routes. The transformations which take place between the iron oxides are summarized in Table 14.1. These interconversions have an important role in corrosion processes and in processes occurring in various natural environments including rocks, soils, lakes and biota. In the latter environments, they often modify the availability and environmental impact of adsorbed or occluded elements, for example, heavy metals. Interconversions are also utilized in industry, e.g. in the blast furnace and in pigment production, and in laboratory syntheses. 

The second type of transformation, the reconstructive transformation involves dis-solution/reprecipitation the initial phase breaks down completely (dissolves) and the new phase precipitates from solution (for a review see Blesa Matijevic, 1989). There is, therefore, no structural relationship between the precursor and the product. In contrast to the solid-state transformation, the reconstructive process is 

The Iron Oxides Structure, Properties, Reactions, Occurences and Uses. R. M. Cornell, U. Schwertmann Copyright 2003 WILEY-VCH Verlag GmbH Co. KGaA,Weinheim ISBN 3-527-30274-3 

Precursor Product Type oftranrformation Preferred medium 

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