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Iron oxide

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Electrochemically oxidized iron (rust)

Iron oxidesarechemical compoundscomposed ofironandoxygen.Several ironoxidesare recognized. Often they arenon-stoichiometric.Ferric oxyhydroxidesare a related class of compounds, perhaps the best known of which isrust.[1]

Iron oxides and oxyhydroxides are widespread in nature and play an important role in many geological and biological processes. They are used asiron ores,pigments,catalysts,and inthermite,and occur inhemoglobin.Iron oxides are inexpensive and durable pigments in paints, coatings and colored concretes. Colors commonly available are in the "earthy"end of the yellow/orange/red/brown/black range. When used as a food coloring, it hasE numberE172.

Stoichiometries

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Iron oxide pigment. The brown color indicates that iron is at the oxidation state +3.
Green and reddish brown stains on a limestone core sample, respectively corresponding to oxides/hydroxides of Fe2+and Fe3+.

Iron oxides feature asferrous(Fe(II)) orferric(Fe(III)) or both. They adoptoctahedralortetrahedral coordination geometry.Only a few oxides are significant at the earth's surface, particularly wüstite, magnetite, and hematite.

Thermal expansion

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Iron oxide CTE(× 10−6°C−1)
Fe2O3 14.9[6]
Fe3O4 >9.2[6]
FeO 12.1[6]

Oxide-hydroxides

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Main article:iron(III) oxide-hydroxide
  • goethite(α-FeOOH)
  • akaganéite(β-FeOOH)
  • lepidocrocite(γ-FeOOH)
  • feroxyhyte(δ-FeOOH)
  • ferrihydrite(Fe5HO8· 4 H2O approx., or 5 Fe2O3· 9 H2O, better recast as FeOOH · 0.4 H2O)
  • high-pressure pyrite-structured FeOOH.[7]Oncedehydrationis triggered, this phase may form FeO2Hx(0 <x< 1).[8]
  • green rust(FeIII
    x    FeII
    y    OH3x+y−z(A−)zwhere A−is Cl−or 0.5SO2−4)

Reactions

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Inblast furnacesand related factories, iron oxides are converted to the metal. Typicalreducing agentsare various forms of carbon. A representative reaction starts with ferric oxide:[9]

2 Fe2O3+ 3 C → 4 Fe + 3 CO2

In nature

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Iron is stored in many organisms in the form offerritin,which is a ferrous oxide encased in a solubilizing protein sheath.[10]

Species ofbacteria,includingShewanella oneidensis,Geobacter sulfurreducensandGeobacter metallireducens,use iron oxides asterminal electron acceptors.[11]

Uses

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Almost all iron ores are oxides, so in that sense these materials are important precursors to iron metal and its many alloys.

Iron oxides are importantpigments,coming in a variety of colors (black, red, yellow). Among their many advantages, they are inexpensive, strongly colored, and nontoxic.[12]

Magnetiteis a component of magnetic recording tapes.

See also

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References

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  1. ^Cornell., RM.; Schwertmann, U (2003).The iron oxides: structure, properties, reactions, occurrences and.Wiley VCH.ISBN978-3-527-30274-1.
  2. ^Lavina, B.; Dera, P.; Kim, E.; Meng, Y.; Downs, R. T.; Weck, P. F.; Sutton, S. R.; Zhao, Y. (Oct 2011)."Discovery of the recoverable high-pressure iron oxide Fe4O5".Proceedings of the National Academy of Sciences.108(42): 17281–17285.Bibcode:2011PNAS..10817281L.doi:10.1073/pnas.1107573108.PMC3198347.PMID21969537.
  3. ^Lavina, Barbara; Meng, Yue (2015)."Synthesis of Fe5O6".Science Advances.1(5): e1400260.doi:10.1126/sciadv.1400260.PMC4640612.PMID26601196.
  4. ^abBykova, E.; Dubrovinsky, L.; Dubrovinskaia, N.; Bykov, M.; McCammon, C.; Ovsyannikov, S. V.; Liermann, H. -P.; Kupenko, I.; Chumakov, A. I.; Rüffer, R.; Hanfland, M.; Prakapenka, V. (2016)."Structural complexity of simple Fe2O3 at high pressures and temperatures".Nature Communications.7:10661.Bibcode:2016NatCo...710661B.doi:10.1038/ncomms10661.PMC4753252.PMID26864300.
  5. ^Merlini, Marco; Hanfland, Michael; Salamat, Ashkan; Petitgirard, Sylvain; Müller, Harald (2015). "The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions".American Mineralogist.100(8–9): 2001–2004.Bibcode:2015AmMin.100.2001M.doi:10.2138/am-2015-5369.S2CID54496448.
  6. ^abcFakouri Hasanabadi, M.; Kokabi, A.H.; Nemati, A.; Zinatlou Ajabshir, S. (February 2017). "Interactions near the triple-phase boundaries metal/glass/air in planar solid oxide fuel cells".International Journal of Hydrogen Energy.42(8): 5306–5314.doi:10.1016/j.ijhydene.2017.01.065.ISSN0360-3199.
  7. ^Nishi, Masayuki; Kuwayama, Yasuhiro; Tsuchiya, Jun; Tsuchiya, Taku (2017)."The pyrite-type high-pressure form of FeOOH".Nature.547(7662): 205–208.Bibcode:2017Natur.547..205N.doi:10.1038/nature22823.ISSN1476-4687.PMID28678774.S2CID205257075.
  8. ^Hu, Qingyang; Kim, Duckyoung; Liu, Jin; Meng, Yue; Liuxiang, Yang; Zhang, Dongzhou;Mao, Wendy L.;Mao, Ho-kwang (2017)."Dehydrogenation of goethite in Earth's deep lower mantle".Proceedings of the National Academy of Sciences.114(7): 1498–1501.Bibcode:2017PNAS..114.1498H.doi:10.1073/pnas.1620644114.PMC5320987.PMID28143928.
  9. ^Greenwood, Norman N.;Earnshaw, Alan (1997).Chemistry of the Elements(2nd ed.).Butterworth-Heinemann.p. 1072.ISBN978-0-08-037941-8.
  10. ^Honarmand Ebrahimi, Kourosh; Hagedoorn, Peter-Leon; Hagen, Wilfred R. (2015)."Unity in the Biochemistry of the Iron-Storage Proteins Ferritin and Bacterioferritin".Chemical Reviews.115(1): 295–326.doi:10.1021/cr5004908.PMID25418839.
  11. ^Bretschger, O.; Obraztsova, A.; Sturm, C. A.; Chang, I. S.; Gorby, Y. A.; Reed, S. B.; Culley, D. E.; Reardon, C. L.; Barua, S.; Romine, M. F.; Zhou, J.; Beliaev, A. S.; Bouhenni, R.; Saffarini, D.; Mansfeld, F.; Kim, B.-H.; Fredrickson, J. K.; Nealson, K. H. (20 July 2007)."Current Production and Metal Oxide Reduction by Shewanella oneidensis MR-1 Wild Type and Mutants".Applied and Environmental Microbiology.73(21): 7003–7012.Bibcode:2007ApEnM..73.7003B.doi:10.1128/AEM.01087-07.PMC2223255.PMID17644630.
  12. ^Buxbaum, Gunter; Printzen, Helmut; Mansmann, Manfred; Räde, Dieter; Trenczek, Gerhard; Wilhelm, Volker; Schwarz, Stefanie; Wienand, Henning; Adel, Jörg; Adrian, Gerhard; Brandt, Karl; Cork, William B.; Winkeler, Heinrich; Mayer, Wielfried; Schneider, Klaus (2009). "Pigments, Inorganic, 3. Colored Pigments".Ullmann's Encyclopedia of Industrial Chemistry.Weinheim: Wiley-VCH.doi:10.1002/14356007.n20_n02.ISBN978-3527306732.
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