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|Section2= |Section3= }} Iron(II,III) oxide is the chemical compound with formula Fe3O4. It occurs in nature as the mineral magnetite. It is one of a number of iron oxides, the others being iron(II) oxide (FeO), which is rare, and iron(III) oxide (Fe2O3) also known as hematite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙ Fe2O3. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is ferrimagnetic, but is sometimes incorrectly described as ferromagnetic. 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.〔Rochelle M. Cornell, Udo Schwertmann 2007 ''The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses'' Wiley-VCH ISBN 3-527-60644-0〕 ==Preparation== Under anaerobic conditions, ferrous hydroxide (Fe(OH)2) can be oxidized by water to form magnetite and molecular hydrogen. This process is described by the Schikorr reaction: :''3 Fe(OH)2 → Fe3O4 + H2 + 2 H2O'' :''ferrous hydroxide → magnetite + hydrogen + water'' The well-crystallized magnetite (Fe3O4) is thermodynamically more stable than the ferrous hydroxide (Fe(OH)2 ). Magnetite can be prepared in the laboratory as a ferrofluid in the Massart method by mixing iron(II) chloride and iron(III) chloride in the presence of sodium hydroxide.〔Massart, R., Preparation of aqueous magnetic liquids in alkaline and acidic media, ''IEEE transactions on magnetics'', 17, 2, 1981. 1247–1248〕 Magnetite can also be prepared by the chemical co-precipitation in presence of ammonia, which consist in a mixture of a solution 0.1 M of FeCl3·6H2O and FeCl2·4H2O with mechanic agitation of about 2000 rpm. The molar ratio of FeCl3:FeCl2 can be 2:1; heating this solution at 70 °C, and immediately the speed is elevated to 7500 rpm and adding quickly a solution of NH4OH (10 volume %), immediately a dark precipitate will be formed, which consists of nanoparticles of magnetite.〔Keshavarz, Sahar, Yaolin Xu, Spencer Hrdy, Clay Lemley, Tim Mewes, and Yuping Bao. ("Relaxation of Polymer Coated Magnetic Nanoparticles in Aqueous Solution" ), IEEE Transactions on Magnetics, Volume: 46, Issue: 6 pp. 1541-43, June 2010, Tuscaloosa. Retrieved on 3 September 2012.〕 In both cases, the precipitation reaction rely on a quick transformation of acidic hydrolyzed iron ions into the spinel iron oxide structure, by hydrolysis at elevated pH values (above ca. 10). Considerable efforts has been devoted towards controlling the particle formation process of magnetite nanoparticles due to the challenging and complex chemistry reactions involved in the phase transformations prior to the formation of the magnetite spinel structure.〔Jean-Pierre Jolivet, Corinne Chanéac and Elisabeth Tronc, Iron oxide chemistry. From molecular clusters to extended solid networks,''Chem. Commun.'', 2004, 5, 481-483〕 Magnetite particles are of interests in bioscience applications such as in magnetic resonance imaging (MRI) since iron oxide magnetite nanoparticles represent a non-toxic alternative to currently employed gadolinium-based contrast agents. However, due to lack of control over the specific transformations involved in the formation of the particles, truly superparamagnetic particles have not yet been prepared from magnetite, i.e. magnetite nanoparticles that completely lose their permanent magnetic characteristic in the absence of an external magnetic field (which by definition show a coercivity of 0 A/m). The smallest values currently reported for nanosized magnetite particles is ''Hc'' = 8.5 A m−1,〔Valter Ström, Richard T. Olsson, K. V. Rao, Real-time monitoring of the evolution of magnetism during precipitation of superparamagnetic nanoparticles for bioscience applications, ''J. Mater. Chem.'', 2010, 20, 4168-4175〕 whereas the largest reported magnetization value is 87 Am2 kg−1 for synthetic magnetite.〔Mei Fang, Valter Ström, Richard T. Olsson, Lyubov Belova, K. V. Rao, Rapid mixing: A route to synthesize magnetite nanoparticles with high moment, ''Appl. Phys. Lett.'' 99, 222501 (2011)〕〔Mei Fang, Valter Ström, Richard T. Olsson, Lyubov Belova, K. V. Rao, Particle size and magnetic properties dependence on growth temperature for rapid mixed co-precipitated magnetite nanoparticles, ''Nanotechnology'', 2012, 23, 14, 145601〕 Pigment quality Fe3O4, 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 vat treatment (pickling) of steel): *Oxidation of Fe metal in the Laux process where nitrobenzene is treated with iron metal using FeCl2 as a catalyst to produce aniline:〔 :C6H5NO2 + 3 Fe + 2 H2O → C6H5NH2 + Fe3O4 *Oxidation of FeII 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.〔 Reduction of Fe2O3 with hydrogen:〔US patent 2596954, 1947, Process for reduction of iron ore to magnetiteHeath T.D.〕 :3Fe2O3 + H2 → 2Fe3O4 +H2O Reduction of Fe2O3 with CO: :3Fe2O3 + CO → 2Fe3O4 + CO2 Production of nano-particles can be performed chemically by taking for example mixtures of FeII and FeIII salts and mixing them with alkali to precipitate colloidal Fe3O4. The reaction conditions are critical to the process and determine the particle size.〔Arthur T. Hubbard (2002) ''Encyclopedia of Surface and Colloid Science'' CRC Press, ISBN 0-8247-0796-6〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Iron(II,III) oxide」の詳細全文を読む スポンサード リンク
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