Short-range and Middle-range Ordering

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Ferrous Fe(II) ions and ferric Fe(III) ions dissolved in aqueous solution are precipitated as polycations during corrosion of metallic iron, by which corrosion products are formed. In these processes, iron oxyhydroxides and oxides with complicated structure are formed. In this work, the EXAFS and quantitative X-ray diffraction methods were systematically used for characterizing influences of foreign ions on the short range and middle range ordering of their iron compounds. In addition to these experiments, reaction conditions of the aqueous solution were also analyzed using electrochemical potential and pH measurements, in order to clarifying the formation conditions of these iron compounds. In this works, green rust containing ferrous ions was specially synthesized, which was oxidized to iron oxyhydroxides and oxides under controlled conditions such as temperature. The results showed that the transformation from green rust to different iron oxides and oxyhydroxides strongly depend on reaction conditions such as temperature rate and pH of aqueous solution. In addition, X-ray anomalous scattering measurement of solid particles was carried out in order to investigate an influence of foreign cations such as manganese on the structure of iron oxides. This result indicated that manganese was almost equally distributed to different sites in the spinel structure of magnetite. Furthermore, the short range and middle range ordering the atomic arrangements of iron oxyhydroxides, which were oxidized with foreign anions was also characterized. Foreign ions like silicate ions were considered to be incorporated into the solid particles during structural changes of GR, by which the structure was distorted. As a result, foreign anions are likely to induce the distortion of the atomic arrangement by their incorporation, and this appears to cause not only the morphological changes and also properties of particles such as ion selectivity.