Iron hydroxide oxide

Deposits contained organic acids formed by oxidation of rolling oils. Up to 40% by weight of the lumps shown in Fig. 4.27A and B was iron oxides, hydroxides, and organic-acid iron salts. Acidic species concentrated in the deposits. 

Internal surfaces of all tubes were severely attacked (Fig. 4.29). A brown deposit layer consisting of magnetite, iron oxide hydroxide, and silica covered all surfaces. Deposition was thicker and more tenacious along the bottom of tubes. These deposits had a distinct greenish-blue cast caused by copper corrosion products beneath the deposit. Underlying corrosion products were ruby-red cuprous oxide crystals (Fig. 4.29). Areas not covered with deposits suffered only superficial attack, but below deposits wastage was severe. 

Hence, in the absence of a redox system in solution the anodic reaction of FeS2 yields iron oxide/hydroxide and water-soluble sulfate ions. The compound does not undergo non-oxidative dissolution. 

Landsat imagery was downloaded from the GloVis viewer (http //glovis.usgs.gov/). The data were atmospherically and geometrically corrected. Band ratios were used to map the presence of iron oxides, hydroxides, and hydrous minerals, possibly associated with porphyry-style hydrothermally altered and mineralized rocks. 

Almost all the iron oxides, hydroxides and oxide hydroxides are crystalline. The degree of structural order and the crystal size are, however, variable and depend on the conditions under which the crystals were formed. All Fe oxides display a range of crystallinities except for ferrihydrite and schwertmannite which are poorly crystalline. 

Table 2.2 summarizes basic crystallographic data for the iron oxides. Iron oxides, hydroxides and oxide hydroxides consist of arrays of Fe ions and 0 or OH ions. As the anions are much larger than the cations (the radius of the 0 ion is 0.14 nm, whereas those of Fe and Fe" are 0.065 and 0.082 nm, respectively), the arrangement of anions governs the crystal structure and the ease of topological interconversion between different iron oxides. Table 2.3 lists the atomic coordinates of the iron oxides. 

Tab. 2.4 Dependence of Fe-Fe distances in iron oxide hydroxide on type of octahedral linkage (Adapted from Manceau Combes,1988 with permission)...

The high pressure form of FeOOH is more compact than any other iron oxide hydroxide, hence it has a higher than usual Neel temperature of 470 K. At room temperature, high pressure FeOOH is antiferromagnetic with a collinear spin arrangement parallel to the c-axis (Fernet et al., 1973). High-pressure FeOOH is completely miscible with CrOOH. Substitution with Cr reduces T to the extent that with 80%... 

Kgo is the solubility product. It applies to iron oxides, hydroxides and oxide hydroxides. 

A common feature of the dehydroxylation of all iron oxide hydroxides is the initial development of microporosity due to the expulsion of water. This is followed, at higher temperatures, by the coalescence of these micropores to mesopores (see Chap. 5). Pore formation is accompanied by a rise in sample surface area. At temperatures higher than ca. 600 °C, the product sinters and the surface area drops considerably. During dehydroxylation, hydroxo-bonds are replaced by oxo-bonds and face sharing between octahedra (absent in the FeOOH structures see Chap. 2) develops and leads to a denser structure. As only one half of the interstices are filled with cations, some movement of Fe atoms during the transformation is required to achieve the two thirds occupancy found in hematite. 

Lauwiner, M. Rys, P. Wissmann, J. (1998) Reduction of aromatic nitro compounds with hydrogene hydrate in the presence of an iron oxide hydroxide catalyst. I. The reduction of monosubstituted nitrobenyenes with hydrazine hydrate in the presence of ferrihydrite. 

Geckeis, H. Rabung, T. 2002. Solid-water interface reactions of polyvalent metal ions at iron oxide-hydroxide surfaces. In Hubbard, A. (ed) Encyclopedia of Surface and Colloid Science. Dekker Inc., 4737-4748. 

Phosphates, molybdates, and (at high pH) silicates act as anodic inhibitors much as do alkalis, except that the iron oxides/hydroxides formed on anodic sites then contain some PO43-, M0O42-, or Si044- ( basic iron phosphates, etc.). These inhibitors require the presence of 02 to produce basic iron(III) phosphate, molybdate, or silicate films, whereas oxidizing anions such as chromates and nitrites oxidize Fe2+ (aq) rapidly to insoluble iron(III) oxides on anodic sites. Dianodic inhibitors combine complementary inhibition mechanisms for example, sodium triphosphate may be used with sodium chromate, or sodium molybdate with NaN02. 

Dissolution in iron(III) chloride solutions [2.17], the resulting iron(II) salt is oxidized with air to give iron oxide hydroxides and iron(III) salts... 

Oxidation with air in the presence of electrolytes. Various iron oxide or iron oxide hydroxide phases are formed depending on the electrolyte used Possible electrolytes include iron(II) chloride solutions [2.18], ammonium chloride [2.19], or ammonium carbonate-carbonic acid [2.20]... 

Naturally occurring iron oxides and iron oxide hydroxides were used as pigments in prehistoric times (Altamira cave paintings) [3.2]. They were also used as coloring materials by the Egyptians, Greeks, and ancient Romans. 

Goethite is the colored component of yellow ocher a weathering product mainly of siderite, sulfidic ores, and feldspar. It occurs in workable amounts mainly in the Republic of South Africa and France. The Fe2Oa content gives an indication of the iron oxide hydroxide content of the ocher, and is ca. 20% in the French deposits and ca. 55% in the South African. 

Precipitation Processes. In principle, all iron oxide hydroxide phases can be prepared from aqueous solutions of iron salts (see Table 23). However, precipitation with alkali produces neutral salts (e.g., Na2S04, NaCl) as byproducts which enter the wastewater. 

The process can be accelerated by operating at 150 °C under pressure this technique also improves pigment quality [3.19]. Rapid heating of a suspension of iron oxide hydroxide with the necessary quantity of Fe(OH)2 to ca. 90 °C also produces black iron oxide of pigment quality [3.20], [3.21],... 

Production. Metallic iron pigments are commercially produced by the reduction of acicular (needle-shaped) iron compounds [5.30], As in the production of magnetic iron oxide pigments, the starting materials are iron oxide hydroxides (see Section 3.1.1) or iron oxalates, which are reduced to iron in a stream of hydrogen either directly or via oxidic intermediates. 

Ferrous corrosion products do not have a biocidal effect however, iron corrosion tends to form a much more extensive and encapsulating matrix. This corrosion matrix, which is principally formed of iron oxides, hydroxides, and soil minerals, will encapsulate any organic materials. This usually takes the form of a negative cast (Keepax 1975), provided that the primary layer of corrosion product has been laid down prior to any extensive degradation of the organic material, then fine surface detail will be preserved in the corrosion cast. Because the iron corrosion will not inhibit degradation... 

Figure 31.37. Structure of Ferritin. (A) Twenty-four ferritin polypeptides form a nearly spherical shell. (B) A cut-away view reveals the core that stores iron as an iron oxide-hydroxide complex.

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