Iron oxides, surface structures

Ranke, W. Weiss, W. (1999) Structure and reactivity of iron oxide surfaces. Faraday Discuss. 114 363-380... 

The outstanding virtue of zinc-rich paints is simplicity in application. No special equipment is required and the operation can, of course, be carried out on site, large or small structures being equally suitable for treatment. While there is some evidence that the zinc-rich paints will reduce iron oxides remaining on the steel surface, proper surface preparation is as important here as with traditional paints if the best results are to be achieved. The main use of zinc-rich paints is to protect structural steel-work, ships hulls, and vulnerable parts of car bodies, and to repair damage to other zinc coatings. 

The effect of oxidation pretreatment and oxidative reaction on the graphitic structure of all CNF or CNF based catalysts has been studied by XRD and HRTEM. From the diffraction patterns as shown in Fig. 2(a), it can be observed the subsequent treatment do not affect the integrity of graphite-like structure. TEM examination on the tested K(0.5)-Fe(5)/CNF catalysts as presented in Fig.2(b), also indicates that the graphitic structure of CNF is still intact. The XRD and TEM results are in agreement with TGA profiles of fi-esh and tested catalyst there is no obviously different stability in the carbon dioxide atmosphere (profiles are not shown). Moreover, TEM image as shown in Fig. 2(b) indicates that the iron oxide particle deposited on the surface of carbon nanofibcr are mostly less than less than 10 nm. 

The physical origin of this structural flexibility of the FeO overlayer is still unclear, the more so since no clear trend is observable in the sequence of lattice parameters of the coincidence structures. The FeO(l 11) phase forming up to coverages of 2-3 ML is clearly stabilized by the interactions with the Pt substrate since FeO is thermodynamically metastable with respect to the higher iron oxides [106,114], FeO has the rock salt structure and the (111) plane yields a polar surface with a high surface energy [115], which requires stabilization by internal reconstruction or external compensation. The structural relaxation observed in the form of the reduced Fe—O... 

Direct Photolysis of Surface-Located Inner Coordination Sphere Complexes. In the presence of a strong metal binding ligand, the underlying central metal ion in the surface layer of a metal oxide can exchange its structural OH" ions for the ligand. Thus, the association of citrate with an iron oxyhydroxide surface may be represented ... 

Hydrated iron oxides can adsorb heavy metals. These adsorption properties arise from the presence of structural hydroxyl groups on their surface, which exhibit amphoterism (56) ... 

In contrast, the reddish-brown jerrihydrite (often wrongly termed amorphous iron oxide or hydrous ferric oxide (HFO) ) is widespread in surface environments. It was first described by Chukhrov et al. in 1973. Unlike the other iron oxides it exists exclusively as nano-crystals and unless stabilized in some way, transforms with time into the more stable iron oxides. Ferrihydrite is, thus, an important precursor of more stable and better crystalline Fe oxides. Structurally ferrihydrite consists of hep anions and is a mixture of defect-free, and defective structural units.The composition, especially with respect to OH and H2O, seems to be variable. A preliminary formula, often used, is FesOgH H2O. 

The oxide surface has structural and functional groups (sites) which interact with gaseous and soluble species and also with the surfaces of other oxides and bacterial cells. The number of available sites per unit mass of oxide depends upon the nature of the oxide and its specific surface area. The specific surface area influences the reactivity of the oxide particularly its dissolution and dehydroxylation behaviour, interaction with sorbents, phase transformations and also, thermodynamic stability. In addition, specific surface area and also porosity are crucial factors for determining the activity of iron oxide catalysts. 

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