Maghemite properties

Hematite, wiistite, maghemite and magnetite are semiconductors magnetite displays almost metallic properties. For a compound to be a semiconductor, the essential characteristic is that the separation between the valence band of orbitals and the conduction band is less than 5 eV this condition is met for the above oxides. In a semiconductor the Fermi level (i. e. the level below which all electron energy levels are filled) lies somewhere between the valence band and the conduction band. 

Rheological studies involving Fe oxides appear to be sparse. Most are carried out on acicular crystals, usually maghemite. Details of the method of synthesis or properties of the particles are often lacking. 

The industrial dust deposited in the metropolitan area of Shanghai consisted of high-coercivity (hematite) and low-coercivity (magnetite/maghemite) particles, usually < 10 pm in size. Four different dust sources could be distinguished on the basis of magnetic properties (Shu et al. 2000). Given previously reported links between... 

Taylor, R.M. Schwertmann, U. (1974a) Maghemite in soils and its origin. 1. Properties and observations on soil maghemites. Clay Min. 10 289-298... 

The coercive force of a powder is an extrinsic property, which is influenced by many factors such as size and shape and packing density. Maghemite particles prepared from directly precipitated spindle-type hematite particles showed a tendency of increase in coercive force with decrease in particle size, and increase in their aspect ratios (31). However, a quantitative relationship between the coercive force and size and/or aspect ratio is still not available. 

Property Hematite Maghemite Goethite Akaganeite Lepido- crocite Nontronite Jarosite... 

Stewart, C. (1985) Spectral and other physicochemical properties of submicron powders of hematite (a-Fe203), maghemite (y-Fe203), magnetite (FejO ), goethite (a-FeOOH), and lepidocrocite (y-FeOOH). J. Geophys. Res., 90, 3126-44. 

Diakonov I (1998a) Thermodynamic properties of iron oxides and hydroxides. 111. Surface and bulk thermodynamic properties of lepidocrocite (y-FeOOH) to 500 K. Eur J Mineral 10 31-41 Diakonov I (1998b) Thermodynamic properties of iron oxides and hydroxides. 11. Estimation of the surface and bulk thermodynamic properties of ordered and disordered maghemite (y-Fe203). Eur J Mineral 10 17-29... 

Manganese oxides, which have different structural and surface properties, vary substantially in their ability to promote the precipitation and crystallization of Fe oxides and oxyhydroxides. The Mn(II) dissolved from Mn oxides in the presence of Fe(II) also influences the crystallization of oxidation products of Fe(II). The Fe oxides formed as influenced by Mn oxides and dissolved Mn(II) range from lepidocrocite, goethite, maghemite, dkaganeite, feroxyhyte, magnetite, honessite-like minerals, to noncrystalline Fe oxides. Therefore, Mn oxides deserve close attention in the genesis of Fe oxides. 

Maghemite from Nanotek Properties Structure confirmed by XRD (hematite present as an impurity), BET specific surface area 48.5 mVg, particle diameter 26 nm, TEM image and particle size histogram available [1322]. 

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