Structural properties magnetite

Crucial to the understanding of metal-substituted magnetite and their properties is the determination of the site occupancy of the metals. The structure of magnetite is very well known. It is a cubic, inverse spinel with one quarter of the tetrahedral (Tj) and one half of the octahedral (0 j) sites filled by Fe. The formula for magnetite is (Fe )[Fe Fe ]04 where Fe ... 

The sensitive dependence of the electrical and magnetic properties of spinel-type compounds on composition, temperature, and detailed cation arrangement has proved a powerful incentive for the extensive study of these compounds in connection with the solid-state electronics industry. Perhaps the best-known examples are the ferrites, including the extraordinary compound magnetite Fc304 (p. 1080) which has an inverse spinel structure (Fe )t[Fe Fe ]o04. 

Gallagher, KJ. Feifknecht,W. Marmweiler, U. (1968) Mechanism of oxidation of magnetite to Y-Fe20j. Nature 217 1118-1121 Gallias, J.L. (1998) Microstructure of the interfacial transition zone around corroded reinforcements. In Katz, A. Benier, M. Alexander, M. Arliguie, G. (eds.) The interfadal transition zone in cementitions composites. E.F.N. Spon, London, 171-178 Galvez, N. Barron,V. Torrent, J. (1999) Preparation and properties of hematite with structural phosphorus. Clays Clay Miner. 47 375-385... 

Unfortunately, any attempt to reduce ferric oxide results in the formation of magnetite as a distinct separate phase, and there is no solubility of this spinel in the corundum structure ( 5, 6). Thus, all the properties reported above for were... 

It can be readily understood that the structure of the oxide, from which the reduced catalyst is prepared, plays an important role for the properties of the catalyst. This dependence has been proved experimentally by the influence which the rate of cooling of the oxides of a given catalyst composition shows upon the catalytic properties of the reduced catalyst. This effect can be interpreted by considering that in the reduced catalyst the promoters are distributed all over the surface and that it is, of course, highly important how they are distributed. This distribution cannot be independent of the way in which the promoters are present in the oxidic state, whether in solid solution in the magnetite, as separate crystals or as amorphous glassy layers. 

Vig. 4.32. Molecular-orbital/band models to illustrate the electronic structures of chromite, ulvospinel, and magnetite and based on MS-SCF-iV a calculations on FeO, , FeO ", TiO ,, FeO/ , FeO/, and CrOf clusters. The double arrows labeled (a) through (g) refer to electronic transitions giving rise to optical properties (after Vaughan and Tossell, 1978). 

Special experimental investigations of the properties, particulars of structure, and variations as a function of time, temperature and pressure have not been made so far for the iron cherts. However, the main components of such sediments—iron hydroxide and silica—have been rather well studied, and some data which are of interest to understanding the diagenetic processes are considered in this section. For the other components—magnetite, siderite, and sulfides—the very limited experimental data were examined in our previous work (Mel nik, 1972b). 

Magnetite, Fes04, is the outstanding example of this class of semi-conductor. De Boer and Verwey (7) first proposed the interpretation of its properties and Verwey and his co-workers (8) have studied the structural problem with some success. They deduce from their studies of related spinels that, at ordinary temperature, F O has all the Fe + ions and half the Fe + ions distributed statistically over one kind of cation position (octahedral) in the unit cell. The remaining Fe + are localized in tetrahedral sites. Ihe ease of electron transfer from Fe + to Fe ions is responsible for the... 

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. 

Electrodialyzed Magnetite from Toda Properties Structure confirmed by XRD [1281]. 

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