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Iron oxide
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<h2 id="stoichiometries">Stoichiometries</h2> <p>Iron oxides feature as <a href="/facts/Ferrous/AGImjWqq">ferrous</a> (<a href="/facts/Iron(II)/TCxvdjfW">Fe(II)</a>) or <a href="/facts/Iron(III)/TMrSskIt">ferric</a> (<a href="/facts/Iron(III)/TMrSskIt">Fe(III)</a>) or both. They adopt <a href="/facts/Octahedral_molecular_geometry/bNXLVvks">octahedral</a> or <a href="/facts/Tetrahedral_molecular_geometry/583AL1sP">tetrahedral coordination geometry</a>. Only a few oxides are significant at the earth's surface, particularly wüstite, magnetite, and hematite. </p> <ul><li>Oxides of FeII <ul><li>FeO: <a href="/facts/Iron(II)_oxide/H9V7S3MG">iron(II) oxide</a>, <a href="/facts/W%25C3%25BCstite/8Dd4dGP6">wüstite</a></li></ul></li> <li>Mixed oxides of FeII and FeIII <ul><li>Fe3O4: <a href="/facts/Iron(II%2cIII)_oxide/8VzDaSxu">Iron(II,III) oxide</a>, <a href="/facts/Magnetite/SVxoGUs2">magnetite</a></li> <li>Fe4O5<a class="footnote-ref" id="fnref:2" href="#fn:2"><sup>2</sup></a></li> <li>Fe5O6<a class="footnote-ref" id="fnref:3" href="#fn:3"><sup>3</sup></a></li> <li>Fe5O7<a class="footnote-ref" id="fnref:4" href="#fn:4"><sup>4</sup></a></li> <li>Fe25O32<a class="footnote-ref" id="fnref:5" href="#fn:5"><sup>5</sup></a></li> <li>Fe13O19<a class="footnote-ref" id="fnref:6" href="#fn:6"><sup>6</sup></a></li></ul></li> <li>Oxides of FeIII <ul><li>Fe2O3: <a href="/facts/Iron(III)_oxide/vam0XoC5">iron(III) oxide</a> <ul><li>α-Fe2O3: <a href="/facts/Iron(III)_oxide/vam0XoC5">alpha phase</a>, <a href="/facts/Hematite/716YBzGr">hematite</a></li> <li>β-Fe2O3: <a href="/facts/Iron(III)_oxide/vam0XoC5">beta phase</a></li> <li>γ-Fe2O3: <a href="/facts/Iron(III)_oxide/vam0XoC5">gamma phase</a>, <a href="/facts/Maghemite/wl4s9Ucg">maghemite</a></li> <li>ε-Fe2O3: <a href="/facts/Iron(III)_oxide/vam0XoC5">epsilon phase</a></li></ul></li></ul></li></ul> <h2 id="thermal-expansion">Thermal expansion</h2> <table><tbody><tr><th>Iron oxide</th><th><a href="/facts/Thermal_expansion/BP2vjX0N">CTE</a> (× 10−6 °C−1)</th></tr><tr><td>Fe2O3</td><td>14.9<a class="footnote-ref" id="fnref:7" href="#fn:7"><sup>7</sup></a></td></tr><tr><td>Fe3O4</td><td>>9.2<a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a></td></tr><tr><td>FeO</td><td>12.1<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a></td></tr></tbody></table> <h2 id="oxide-hydroxides">Oxide-hydroxides</h2> <p class="note">Main article: <a href="/facts/Iron(III)_oxide-hydroxide/YpW6aAAS">iron(III) oxide-hydroxide</a></p> <ul><li><a href="/facts/Goethite/6uHDbPae">goethite</a> (α-FeOOH)</li> <li><a href="/facts/Akagan%25C3%25A9ite/67xmPD9N">akaganéite</a> (β-FeOOH)</li> <li><a href="/facts/Lepidocrocite/XUcLhV1c">lepidocrocite</a> (γ-FeOOH)</li> <li><a href="/facts/Feroxyhyte/9EoUzAw2">feroxyhyte</a> (δ-FeOOH)</li> <li><a href="/facts/Ferrihydrite/sswCdIIx">ferrihydrite</a> (Fe5HO8 · 4 H2O approx., or 5 Fe2O3 · 9 H2O, better recast as FeOOH · 0.4 H2O)</li> <li>high-pressure pyrite-structured FeOOH.<a class="footnote-ref" id="fnref:10" href="#fn:10"><sup>10</sup></a> Once <a href="/facts/Dehydration_reaction/dTAxlyRX">dehydration</a> is triggered, this phase may form FeO2H<i>x</i> (0 < <i>x</i> < 1).<a class="footnote-ref" id="fnref:11" href="#fn:11"><sup>11</sup></a></li> <li><a href="/facts/Green_rust/nGtySEbh">green rust</a> (FeIII<i>x</i>FeII<i>y</i>OH3<i>x</i> + <i>y</i> − <i>z</i> (A−)<i>z</i> where A− is Cl− or 0.5 SO2−4)</li></ul> <h2 id="reactions">Reactions</h2> <p>In <a href="/facts/Blast_furnace/DJzUB2EG">blast furnaces</a> and related factories, iron oxides are converted to the metal. Typical <a href="/facts/Reducing_agent/CtfSGVXC">reducing agents</a> are various forms of carbon. A representative reaction starts with ferric oxide:<a class="footnote-ref" id="fnref:12" href="#fn:12"><sup>12</sup></a> </p> 2 Fe2O3 + 3 C → 4 Fe + 3 CO2 <h3>In nature</h3> <p>Iron is stored in many organisms in the form of <a href="/facts/Ferritin/w7G85xJg">ferritin</a>, which is a ferrous oxide encased in a solubilizing protein sheath.<a class="footnote-ref" id="fnref:13" href="#fn:13"><sup>13</sup></a> </p><p>Species of <a href="/facts/Dissimilatory_metal-reducing_bacteria/plClNQ01">bacteria</a>, including <i><a href="/facts/Shewanella_oneidensis/CwWRA5PM">Shewanella oneidensis</a></i>, <i><a href="/facts/Geobacter_sulfurreducens/HFUUdElR">Geobacter sulfurreducens</a></i> and <i><a href="/facts/Geobacter_metallireducens/U2sl8LQT">Geobacter metallireducens</a></i>, use iron oxides as <a href="/facts/Electron_acceptor/sRvhMXqH">terminal electron acceptors</a>.<a class="footnote-ref" id="fnref:14" href="#fn:14"><sup>14</sup></a> </p> <h2 id="uses">Uses</h2> <p>Almost all iron ores are oxides, so in that sense these materials are important precursors to iron metal and its many alloys. </p><p>Iron oxides are important <a href="/facts/Pigment/I3clCYkF">pigments</a>, coming in a variety of colors (black, red, yellow). Among their many advantages, they are inexpensive, strongly colored, and nontoxic.<a class="footnote-ref" id="fnref:15" href="#fn:15"><sup>15</sup></a> </p><p><a href="/facts/Magnetite/SVxoGUs2">Magnetite</a> is a component of magnetic recording tapes. </p> <h2 id="see-also">See also</h2> <ul><li><a href="/facts/Great_Oxidation_Event/LmTyM8jT">Great Oxidation Event</a></li> <li><a href="/facts/Iron_cycle/xDhevRaI">Iron cycle</a></li> <li><a href="/facts/Iron_oxide_nanoparticle/8NXDS1fG">Iron oxide nanoparticle</a></li> <li><a href="/facts/Limonite/KCPspvHH">Limonite</a></li> <li><a href="/facts/List_of_inorganic_pigments/8Q9HC7AT">List of inorganic pigments</a></li> <li><a href="/facts/Iron(II)_hydroxide/hCohGhDJ">Iron(II) hydroxide</a></li></ul> <h2 id="external-links">External links</h2> Wikimedia Commons has media related to Iron oxides. <ul><li><a href="https://web.archive.org/web/20171118055115/http://www.nano-oxides.com/pdf/Fe2O3_Brochure.pdf">Information from 4thNano-Oxides, Inc. on Fe2O3.</a></li> <li><a href="http://chemed.chem.purdue.edu/demos/demosheets/12.3.html">The Iron One-Pot Reaction</a></li> <li><a href="https://minerals.usgs.gov/minerals/pubs/commodity/iron_oxide/">Iron Oxide Pigments Statistics and Information</a></li> <li><a href="https://www.cdc.gov/niosh/npg/npgd0344.html">CDC – NIOSH Pocket Guide to Chemical Hazards</a></li></ul> <h2 id="references">References</h2> <ol> <li id="fn:1"><p>Cornell., RM.; Schwertmann, U (2003). The iron oxides: structure, properties, reactions, occurrences and. Wiley VCH. ISBN 978-3-527-30274-1. <a href="978-3-527-30274-1" target="_blank">978-3-527-30274-1</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li> <li id="fn:2"><p>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. PMC 3198347. PMID 21969537. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3198347" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3198347</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li> <li id="fn:3"><p>Lavina, Barbara; Meng, Yue (2015). "Synthesis of Fe5O6". Science Advances. 1 (5): e1400260. doi:10.1126/sciadv.1400260. PMC 4640612. PMID 26601196. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4640612" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4640612</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li> <li id="fn:4"><p>Bykova, 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. PMC 4753252. PMID 26864300. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753252" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753252</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li> <li id="fn:5"><p>Bykova, 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. PMC 4753252. PMID 26864300. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753252" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4753252</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li> <li id="fn:6"><p>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. 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