Iron(II,III) oxide 1309936 225779369 2008-07-15T10:44:08Z 203.87.201.158 {{Chembox new | ImageFile = | ImageSize = | IUPACName = iron(II) diiron(III) oxide | OtherNames = ferrous ferric oxide, ferroso ferric oxide, iron(II,III) oxide, magnetite, black iron oxide, lodestone, rust | Section1 = {{Chembox Identifiers | CASNo = 1317-61-9 <br />1309-38-2 | PubChem = | SMILES = }} | Section2 = {{Chembox Properties | Formula = Fe<sub>3</sub>O<sub>4</sub> | MolarMass = 231.533 g/mol | Appearance = black powder | Density = 5.17 g/cm3 | MeltingPt = | BoilingPt = | Solubility = }} | Section3 = {{Chembox Hazards | MainHazards = | FlashPt = | Autoignition = }} }} '''Iron(II,III) oxide''' is the chemical compound with formula Fe<sub>3</sub>O<sub>4</sub>. It is one of a number of [[iron oxides]]. It is found in nature as the mineral [[magnetite]]. It contains both Fe<sup>2+</sup> and Fe<sup>3+</sup> ions and is sometimes formulated as FeO.Fe<sub>2</sub>O<sub>3</sub>. It is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is [[ferrimagnetic]], but is sometimes incorrectly described as [[ferromagnetic]].<ref name = "Greenwood">{{Greenwood&Earnshaw}}</ref> Its most extensive use is as a black pigment which is synthesised rather than being extracted from the naturally occurring mineral as the particle size and shape can be varied by the method of production.<ref name = "Cornell">Rochelle M. Cornell, Udo Schwertmann 2007 ''The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses'' Wiley-VCH ISBN 3527606440</ref> ==Preparation== Pigment quality Fe<sub>3</sub>O<sub>4</sub>, so called synthetic magnetite, can be prepared using processes that utilise industrial wastes, scrap iron or solutions containing iron salts (e.g. those produced as by-products in industrial processes such as the acid treatment ([[pickling (metal)|pickling]]) of steel): *Oxidation of Fe metal in the Laux process where [[nitrobenzene]] is reacted with iron metal using FeCl<sub>2</sub> as a catalyst to produce [[aniline]]<ref name = "Cornell"/> : :C<sub>6</sub>H<sub>5</sub>NO<sub>2</sub> + 9Fe + 2H<sub>2</sub>O → C<sub>6</sub>H<sub>5</sub>NH<sub>2</sub> + Fe<sub>3</sub>O<sub>4</sub> *Oxidation of Fe<sup>II</sup> compounds, e.g. the precipitation of iron(II) salts as hydroxides followed by oxidation by aeration where careful control of the pH determines the oxide produced.<ref name = "Cornell"/> Reduction of Fe<sub>2</sub>O<sub>3</sub> with hydrogen<ref>US patent 2596954, 1947, Process for reduction of iron ore to magnetiteHeath T.D.</ref><ref> Kinetics of reduction of iron oxides by H2 Part I: Low temperature reduction of hematite, A. Pineau, N. Kanari, I. Gaballah, Thermochimica Acta, 447, 1, 1 (2006), 89-100 doi:10.1016/j.tca.2005.10.004</ref>: :3Fe<sub>2</sub>O<sub>3</sub> + H<sub>2</sub> → 2Fe<sub>3</sub>O<sub>4</sub> +H<sub>2</sub>O Reduction of Fe<sub>2</sub>O<sub>3</sub> with CO<ref>The effects of nucleation and growth on the reduction of Fe<sub>2</sub>O<sub>3</sub> to Fe<sub>3</sub>O<sub>4</sub> Hayes P. C., Grieveson P Metallurgical and Materials Transactions B (1981), 12, 2, 319-326,{{doi| 10.1007/BF02654465}}</ref>: :3Fe<sub>2</sub>O<sub>3</sub> + CO → 2Fe<sub>3</sub>O<sub>4</sub> + CO<sub>2</sub> Production of nano-particles can be performed chemically by taking for example mixtures of Fe<sup>II</sup> and Fe<sup>III</sup> salts and mixing them with alkali to precipitate colloidal Fe<sub>3</sub>O<sub>4</sub>. The reaction conditions are critical to the process and determine the particle size.<ref>Arthur T. Hubbard (2002) ''Encyclopedia of Surface and Colloid Science'' CRC Press, ISBN 0824707966</ref> ==Reactions== Reduction of magnetite ore by [[carbon monoxide|CO]] in a [[blast furnace]] is used to produce iron as part of steel production process<ref name = "Greenwood"/>: :Fe<sub>3</sub>O<sub>4</sub> + 4CO → 3Fe + 4CO<sub>2</sub> Controlled oxidation of Fe<sub>3</sub>O<sub>4</sub> is used to produce brown pigment quality [[iron(III)oxide|γ-Fe<sub>2</sub>O<sub>3</sub>]] ([[maghemite]])<ref name = "Buxbaum">Gunter Buxbaum, Gerhard Pfaff (2005) ''Industrial Inorganic Pigments'' 3d edition Wiley-VCH ISBN 3527303634</ref>: :2Fe<sub>3</sub>O<sub>4</sub> + ½ O<sub>2</sub> → 3(γ-Fe<sub>2</sub>O<sub>3</sub>) More vigorous calcining, (roasting in air), gives red pigment quality [[iron(III) oxide|α-Fe<sub>2</sub>O<sub>3</sub>]] ([[hematite]])<ref name = "Buxbaum"/>: :2Fe<sub>3</sub>O<sub>4</sub> + ½ O<sub>2</sub> → 3(α-Fe<sub>2</sub>O<sub>3</sub>) ==Structure== Fe<sub>3</sub>O<sub>4</sub> has a cubic inverse [[spinel]] structure which consists of a cubic close packed array of oxide ions where all of the Fe<sup>2+</sup> ions occupy half of the octahedral sites and the Fe<sup>3+</sup> are split evenly across the remaining octahedral sites and the tetrahedral sites.<br /> Both [[iron(II) oxide|FeO]] and [[iron(III) oxide|γ-Fe<sub>2</sub>O<sub>3</sub>]] have a similar cubic close packed array of oxide ions and this accounts for the ready interchangeability between the three compounds on oxidation and reduction as these reactions entail a relatively small change to the overall structure.<ref name ="Greenwood"/> Fe<sub>3</sub>O<sub>4</sub> samples can be non-stoichiometric.<ref name ="Greenwood"/><br /> The [[ferrimagnetism]] of Fe<sub>3</sub>O<sub>4</sub> arises because the electron spins of the Fe<sup>II</sup> and Fe<sup>III</sup> ions in the octahedral sites are coupled and the spins of the Fe<sup>III</sup> ions in the tetrahedral sites are coupled but anti-parallel to the former. The net effect is that the magnetic contributions of both sets are not balanced and there is a permanent magnetism.<ref name = "Greenwood"/> ==Properties== Fe<sub>3</sub>O<sub>4</sub> is [[ferrimagnetic]] with a [[Curie point|Curie temperature]] of 858 K. There is a phase transition at 120K, the so-called '''Verwey transition''' where there is a discontinuity in the structure, conductivity and magnetic properties.<ref>Electronic Conduction of Magnetite (Fe<sub>3</sub>O<sub>4</sub>) and its Transition Point at Low Temperatures, Verwey E. J. W., nature 144, 327-328 (1939) {{doi|10.1038/144327b0}}</ref> This effect has been extensively investigated and whilst various explanations have been proposed, it does not appear to be fully understood.<ref>The Verwey transition - a topical review Walz F. J. Phys.:Condens. Matter (2002) 14, 285-340 {{doi|10.1088/0953-8984/14/12/203}}</ref><br /> Fe<sub>3</sub>O<sub>4</sub> is a an electrical conductor with a conductivity is significantly higher (X 10<sup>6</sup>) than [[iron(III) oxide|Fe<sub>2</sub>O<sub>3</sub>]], and this is ascribed to electron exchange between the Fe<sup>II</sup> and Fe<sup>III</sup> centres.<ref name = "Greenwood"/> ==Uses== Fe<sub>3</sub>O<sub>4</sub> is used as a black pigment and is known as '''C.I pigment black 11''' (C.I. No.77499).<ref name = "Buxbaum"/><br /> Fe<sub>3</sub>O<sub>4</sub> is used as a catalyst in the [[Haber process]] and in the [[water gas shift reaction]].<ref name = "Lee">Sunggyu Lee (2006) Encyclopedia of Chemical Processing CRC Press ISBN 0824755634</ref> The latter uses an HTS (high temperature shift catalyst) of iron oxide stabilised by chromium oxide.<ref name = "Lee"/> This iron-chrome catalyst is reduced at reactor start up to generate Fe<sub>3</sub>O<sub>4</sub> from α-Fe<sub>2</sub>O<sub>3</sub> and Cr<sub>2</sub>O<sub>3</sub> to CrO<sub>3</sub>.<ref name = "Lee"/><br /> Nano particles of Fe<sub>3</sub>O<sub>4</sub> are used as contrast agents in [[Magnetic resonance imaging|MRI scanning]] <ref>Synthesis of Iron Oxide Nanoparticles Used as MRI Contrast Agents: A Parametric Study, Babes L, Denizot B, Tanguy G, Le Jeune J.J., Jallet P. Journal of Colloid and Interface Science, 212,2, (1999), 474-482, {{doi|10.1006/jcis.1998.6053}}</ref> ==Biological Occurrence== Magnetite has been found as nano-crystals in [[magnetotactic bacteria]] (42-45 μm)<ref name = "Cornell"/> and in homing pigeon beak tissue<ref>Superparamagnetic Magnetite in the Upper Beak Tissue of Homing Pigeons Hanzlik M., Heunemann C., Holtkamp-Rötzler E., Winklhofer M., Petersen N., Fleissner G. BioMetals, (2000), 13, 4, 325-331 {doi|10.1023/A:1009214526685}}</ref> ==References== {{reflist}} [[Category:Oxides]] [[Category:Iron compounds]] [[Category:Iron oxide pigments]] [[Category:Mixed valence compounds]] [[zh:四氧化三铁]]