Iron oxide, amorphous

It has been observed that, in some older power plants designed with precoat filters installed ahead of deep-bed polishers, the deep-bed units were not needed because of effective filtration by the precoats. Where precoat filters are installed, it is sometimes the practice to make use of hydrazine (or hydrazine substitute) to convert amorphous iron oxides to crystalline iron oxides, which enhances filtration. 

The catalytic activity in the CO oxidation should significantly increase due to the gold/oxide interface around the perimeter of nanoparticles [147], therefore, we assumed that this is true regardless of the sequence of gold or FeO c deposition provided that iron oxide is amorphous. When iron oxide is deposited onto Au/Si02/ Si(l 0 0) we call it inverse interface . 

Chao T.T., Zhou L Extraction techniques for selective dissolution of amorphous iron oxides from soils and sediments. Soil Sci Soc Am J 1983 47 225-232. 

The amorphous iron oxide is observed to be considerably more photoactive than the crystalline oxide - presumably as a result of the greater number of surface-located ferric hydroxy chromophores (the BET surface area of the synthesized Y-FeOOH is only 34 m2/g... 

Effects of Flooding and Redox Conditions onfs. I know of no published data on this. Bnt it is likely that the natnre of particle surfaces in intermittently flooded soils wonld restrict snrface mobility. For ions to diffuse freely on the surface there must be a continuous pathway of water molecules over the surface and uniform cation adsorption sites. But in intermittently flooded soils the surface typically contains discontinuous coatings of amorphous iron oxides on other clay minerals, and on flooding reduced iron is to a large extent re-precipitated as amorphons hydroxides and carbonates as discussed above, resulting in much microheterogeneity with adsorption sites with disparate cation affinities. 

Miller, E., Rocheleau, R., Khan, S. 2004. A hybrid multijunction photoelectrode for hydrogen production fabricated with amorphous silicon/germanium and iron oxide thin films. Int J Hydrogen Energy 29 907-914. 

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. 

Iron oxides in soils have in common that they are of extremely small crystal size and/or low crystal order. This, in combination with their low concentration (only tens g kg in most soils) explains why soil iron oxides have escaped identification for a long time in spite of their obvious existence as seen from the soil colour. In the past, therefore, Fe oxides in surface environments have been considered to be amorphous to X-rays and often called limonite , which mineralogically, is an obsolete term. Furthermore, in order to identify the clay minerals in soils properly, Fe oxides are usually removed before X-ray diffraction methods are applied (Alexander et al., 1939 Mehra Jackson, 1960). 

Cornell, R.M. Giovanoli, R. Schneider, W. (1992) The effect of nickel on the conversion of amorphous iron(lll) hydroxide into more crystalline iron oxides in alkaline media. J. Chem. Tech. Biotechnol. 53 73-79 Cornell, R.M. Mann, S. Skamoulis, A.J. 

Trivedi, P. Axe, L. Tyson, T.A. (2001) An analysis of zinc sorption on amorphous versus crystalline iron oxides using XAS. J. Coll. Interf. Sci. 244 221-229... 

Clays Clay Min. 37 273-279 Vempati, R.K. Loeppert, R.H. Dufner, D.C. Cocke, D.L. (1990) X-ray photoelectron spectroscopy as a tool to differentiate siliconbonding state in amorphous iron oxides. Soil Sci. Soc. Am. J. 54 695-698 Vempati, R.K. Morris, R.V. Lauer, H.V Helmke, P.A. (1995) Reflectivity and other physiochemical properties of Mn-substituted goethites and hematites. J. Geophys. Res. 

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