Properties of Iron Oxides

Physical, chemical and mineralogical properties of the iron oxides can be variable. Aluminium (Al(III)) may substitute isomorphically for Fe(III) due to very similar ionic radii (Fe(III) 0.73 A Al(III) 0.61 A) and the same valence. Norrish and 

Taylor (1961) fonnd a maximum of one-third mole percent A1 substitution for Fe within goethite and a maximum of one-sixth substitution was determined for hematite in soils (Schwertmaim et al. 1979). As a product of terrestrial weathering magnetites usually contain minor amounts of Ti(IV) (ionic radius 0.69 A) as a substitution for Fe which is then called titano-magnetite. In contrast, bio-mineralized magnetite is a pure iron oxide. Different colors of iron oxides / oxyhy-droxide are immediately apparent in nature. This holds true for different pure iron oxides, for different grain sizes of one oxide (e.g. goethite) as well as for distinct substitutions for Fe, e.g. by Mn or Cr (Schwertmann and Cornell 1991). The color of synthetic minerals and natural sediment can be quantitatively determined by reflectance spectroscopy (e.g. Morris et al. 1985). 

In the presence of water the surface of an iron oxide is completely hydroxylated which can be understood as a two-step reaction which is shown schematically in Fig. 7.11. 

As iron oxides / oxyhydroxide have a very high affinity for the adsorption of anions as well as cations under natural conditions the early diagenetic reactivity of iron is often of great significance for the behavior of compounds such as trace metals, phosphate and organic acids. The adsorption on iron oxides is caused by the 

As the complexation of cations causes a release of H and anions compete with surface bound hydroxyl groups (Tigand exchange ) the adsorption is strongly pH-dependant (see above). As a result, anions are preferably adsorbed at lower pH-values whereas cations are primarily adsorbed at higher pH values (Fig. 7.12). 

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Sohn B.H., Cohen R.E., and Papaefthymiou G.C., Magnetic properties of iron oxide nanoclusters within microdomains of block copolymers, J. Magn. Magn. Mater., 182, 216, 1998. 

The magnetic properties of iron oxides can be determined using Mossbauer spectroscopy, neutron powder diffraction and magnetometry (see Chap. 7). The characteristic parameters are the magnetic moment, the permeability, the saturation magnetization, the magnetic anisotropy constants and the Bhf (Tab. 6.2). 

Anand, R.R. Gilkes, R.J. (1987) Variations in the properties of iron oxides within individual specimens of lateritic duricmst. Aust. J. Soil Res. 25 287-302... 

Diakonov, I. Khodakovsky I. Schott, J. Sergeeva, E. (1994) Thermodynamic properties of iron oxides and hydroxides. I. Surface and bulk thermodynamic properties of goethite (a-FeOOH) up to 500 K. Fur. J. Min. 6 967-983... 

Pourbaix, M. (1974) Applications of electrochemistry in corrosion science and in practice. Corrosion Sci. 14 25-82 Prasad, J. Murray, E. Kelber, J.A. (1993) site selective chemistry of S, Cl and H2O at the iron oxide surface. Surface Sci. 289 10-18 Prasetyo, B.H. Gilkes, R.J. (1994) Properties of iron oxides from red soils derived from volcanic tuff in West Java. Aust. J. Soil Res. 32 781-794... 

Schwertmann, U. Latham, M. (1986) Properties of iron oxides in some New Caledonien soils. Geoderma 39 105-123... 

Schwertmann, U. Carlson, L. Murad, E. (1987) Properties of iron oxides in two Finnish lakes in relation to the environment of their formation. Clays Clay Min. 35 297-304 Schwertmann, U. Fechter, H. Taylor, R.M. Stanjek, H. (1995b) A lecture and demonstration for students on iron oxide formation. In Eggleton, R.A. Churchman, J. (eds.) Proc. 10 Int. Clay Conf. Adelaide, Australia, 1993 11-14... 

Lamrani, M.A. Regragui, M. Erguig H. (2006) Physicochemical, optical and electrochemical properties of iron oxide thin films prepared by spray pyrolysis. Appl Surf Sci 253 1823-1829... 

In addition to the usual chemical characterization, the properties of iron oxides vary sensitively with oxidation state, and it is commonly necessary to control the partial pressure of oxygen during preparation and during measurement at elevated temperatures. 

In addition to X-ray and neutron-diffraction structural characterization, the physical properties of iron oxides have been studied by a wide variety of techniques. Most common are conventional transport, optical, dielectric, calorimetric and magnetic measurements. In addition, NMR and Mossbauer are widely used. 

Fig. 5.13 Particle size and properties of iron oxide pigments based on a a-Fe203 [5.101].

Huang, P. M., and Wang, M. K. (1997). Formation chemistry and selected surface properties of iron oxides. La. Advances in GeoEcology Soil and Environments, ed. Auerswald,... 

Additionally, St is an aquifer specific property that is related to the amount, species, and surface properties of iron oxides in the aquifer. Hence, the influence of spatial chemical heterogeneity is apparent. When iron oxide compositions in the samples, even from the same site, are different, different isotherms will result. Therefore, isotherms that does not specify these conditions can vary significantly. 

Liu, C., Huang, PM., 1999a. Properties of iron oxides formed at various citrate concentrations. In Kodama, K., Mermut, A.R., Torrance, J.K., (Eds.), Clays for Our Future. The Proceedings of the 11th International Clay Conference, Ottawa, Canada. The International Association for the Study of Clays. Ottawa, Canada, pp. 513-522. 

M. Pregelj, P. Umek, B. Drolc, B. Jancar, Z. Jaglicic, R. Dominko, and D. Arcon, Synthesis, structure, and magnetic properties of iron-oxide nanowires, J. Mater. Res., 21,2955-2962 (2006). 

Table I. Selected electronic properties of iron oxides...

J. Chatteijee, Y. Haik, C.J. Chen, Size dependent magnetic properties of iron oxide nanopaiticles. J. Magn. Magn. Mater. 257, 113-118 (2003)... 

J. Azadmanjiri, P. Hojati-Talemi, G. P. Simon, K. Suzuki, C. Selomulya, Synthesis and Electromagnetic Interference Shielding Properties of Iron Oxide/Polypyrrole Nanocomposites. Polym. Eng. Sci. 2011,51,247-253. 

Choi WI, Kim JY, Heo SU, Jeong YY, Kim YH, Tae G (2012) The effect of mechanical properties of iron oxide nanoparticle-loaded functional nano-carrier on tumor targeting and imaging. J Control Release 162 267-275... 

Benjelloun, D., Bonnet, J.P., Doumerc, J.P., Launay, J.C., Onillon, M., Hagenmuller, P. Anisotropy of the electrical-properties of iron-oxide alpha-Fe203. Mater. Chem. Phys. 10, 503 (1984)... 

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