View source for Iron(II,III) oxide

{{Use dmy dates|date=December 2025}}
{{cs1 config|name-list-style=vanc|display-authors=6}}
{{chembox
| Name           = 
| ImageFile      = Fe3O4.JPG
| ImageFile2     = 
| ImageSize      = 
| IUPACName      = iron(II) diiron(III) oxide<ref>{{nist |name=Iron(ii) diiron(iii) oxide |id=B8022203 |accessdate=2024-12-22}}</ref>
| OtherNames     = ferrous ferric oxide, ferrosoferric oxide, iron(II,III) oxide, magnetite, black iron oxide, lodestone, rust, Mars black, Pigment Black 11
| SystematicName = 
| Section1       = {{Chembox Identifiers
| ChemSpiderID = 17215625
| UNII = XM0M87F357
| InChI = 1/3Fe.4O/rFe3O4/c1-4-2-6-3(5-1)7-2
| InChIKey = SZVJSHCCFOBDDC-QXRQKJBKAR
| StdInChI = 1S/3Fe.4O
| StdInChIKey = SZVJSHCCFOBDDC-UHFFFAOYSA-N
| CASNo = 1317-61-9
| PubChem = 16211978
| ChEBI = 50821
| ChEMBL = 1201867
| SMILES = O1[Fe]2O[Fe]O[Fe]1O2
}}
| Section2       = {{Chembox Properties
| Formula = Fe<sub>3</sub>O<sub>4</sub><br />
FeO·Fe<sub>2</sub>O<sub>3</sub>
| MolarMass = 231.533 g/mol
| Appearance = solid black powder
| Density = 5 g/cm<sup>3</sup>
| MeltingPtC = 1597
| BoilingPtC = 2623<ref>[http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=1002&context=cas-lehighreview-vol-15 Magnetite (Fe3O4): Properties, Synthesis, and Applications] {{Webarchive|url=https://web.archive.org/web/20170720012739/http://preserve.lehigh.edu/cgi/viewcontent.cgi?article=1002&context=cas-lehighreview-vol-15 |date=2017-07-20 }} Lee Blaney, Lehigh Review 15, 33-81 (2007). See Appendix A, p.77</ref>
| Solubility = 
| RefractIndex = 2.42<ref>Pradyot Patnaik. ''Handbook of Inorganic Chemicals''. McGraw-Hill, 2002, {{ISBN|0-07-049439-8}}</ref>
}}
| Section3       = {{Chembox Hazards
| MainHazards = 
| FlashPt = 
| AutoignitionPt = 
| NFPA-H = 0
| NFPA-F = 0
| NFPA-R = 1
| NFPA-S = OX
 }}
|Section4={{Chembox Thermochemistry
| DeltaHf = −1120.89&nbsp;kJ·mol<sup>−1</sup><ref>{{Cite journal|url=https://webbook.nist.gov/cgi/cbook.cgi?ID=C1309382&Units=SI&Mask=2|title=NIST-JANAF Themochemical Tables | edition = Fourth |year=1998|pages=1–1951| vauthors = Chase MW |journal=NIST }}</ref>
}}
| Section5       = 
| Section6       = 
}}

'''Iron(II,III) oxide''', or black iron oxide, is the chemical compound with formula Fe<sub>3</sub>O<sub>4</sub>. 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]] (Fe<sub>2</sub>O<sub>3</sub>) which also occurs naturally as the mineral [[hematite]]. 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>. This iron oxide is encountered in the laboratory as a black powder. It exhibits permanent magnetism and is [[Ferrimagnetism|ferrimagnetic]], but is sometimes incorrectly described as [[Ferromagnetism|ferromagnetic]].<ref name = "Greenwood">{{Greenwood&Earnshaw }}</ref> Its most extensive use is as a black pigment (see: [[Mars Black (pigment)|Mars Black]]). For this purpose, it is synthesized 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">{{cite book | vauthors = Cornell RM, Schwertmann U | date = 2007 | title = The Iron Oxides: Structure, Properties, Reactions, Occurrences and Uses | publisher = Wiley-VCH | isbn = 978-3-527-60644-3 }}</ref>

==Preparation==
Heated iron metal interacts with steam to form iron oxide and hydrogen gas.

:<chem>3Fe + 4H2O->Fe3O4 + 4H2 </chem>

Under [[Hypoxia (environmental)|anaerobic]] conditions, [[Iron(II) hydroxide|ferrous hydroxide]] (Fe(OH)<sub>2</sub>) can be oxidized by water to form magnetite and molecular [[hydrogen]]. This process is described by the [[Schikorr reaction]]:
:<chem>\underset{ferrous\ hydroxide}{3Fe(OH)2} -> \underset{magnetite}{Fe3O4} + \underset{hydrogen}{H2} + \underset{water}{2H2O}</chem>
This works because crystalline magnetite (Fe<sub>3</sub>O<sub>4</sub>) is thermodynamically more stable than amorphous ferrous hydroxide (Fe(OH)<sub>2</sub> ).<ref>{{cite journal | vauthors = Ma M, Zhang Y, Guo Z, Gu N | title = Facile synthesis of ultrathin magnetic iron oxide nanoplates by Schikorr reaction | journal = Nanoscale Research Letters | volume = 8 | issue = 1 | page = 16 | date = January 2013 | pmid = 23294626 | pmc = 3598988 | doi = 10.1186/1556-276X-8-16 | bibcode = 2013NRL.....8...16M | doi-access = free }}</ref>

The [[Massart method]] of preparation of magnetite as a [[ferrofluid]], is convenient in the laboratory: mix [[iron(II) chloride]] and [[iron(III) chloride]] in the presence of [[sodium hydroxide]].<ref>{{cite journal| vauthors = Massart R |title=Preparation of aqueous magnetic liquids in alkaline and acidic media|journal=IEEE Transactions on Magnetics|date=1981|volume=17|issue=2|pages=1247–1248|doi=10.1109/TMAG.1981.1061188|bibcode=1981ITM....17.1247M}}</ref>

A more efficient method of preparing magnetite without troublesome residues of sodium, is to use ammonia to promote chemical co-precipitation from the iron chlorides: first mix solutions of 0.1 M FeCl<sub>3</sub>·6H<sub>2</sub>O and FeCl<sub>2</sub>·4H<sub>2</sub>O with vigorous stirring at about 2000 rpm. The molar ratio of the FeCl<sub>3</sub>:FeCl<sub>2</sub> should be about 2:1. Heat the mix to 70&nbsp;°C, then raise the speed of stirring to about 7500 rpm and quickly add a solution of NH<sub>4</sub>OH (10 volume %). A dark precipitate of nanoparticles of magnetite forms immediately.<ref>{{cite journal| vauthors = Keshavarz S, Xu Y, Hrdy S, Lemley C, Mewes T, Bao Y |title=Relaxation of Polymer Coated Fe<sub>3</sub>O<sub>4</sub> Magnetic Nanoparticles in Aqueous Solution|journal=IEEE Transactions on Magnetics|date=2010|volume=46|issue=6|pages=1541–1543|doi=10.1109/TMAG.2010.2040588|s2cid=35129018}}</ref>

In both methods, the precipitation reaction relies on rapid transformation of acidic iron ions into the spinel iron oxide structure at pH 10 or higher.

Controlling the formation of magnetite nanoparticles presents challenges: the reactions and phase transformations necessary for the creation of the magnetite spinel structure are complex.<ref>{{cite journal | vauthors = Jolivet JP, Chanéac C, Tronc E | title = Iron oxide chemistry. From molecular clusters to extended solid networks | journal = Chemical Communications | issue = 5 | pages = 481–7 | date = March 2004 | pmid = 14973569 | doi = 10.1039/B304532N }}</ref> The subject is of practical importance because magnetite particles are of interest in bioscience applications such as [[magnetic resonance imaging]] (MRI), in which iron oxide magnetite nanoparticles potentially present a non-toxic alternative to the gadolinium-based [[contrast agents]] currently in use. However, difficulties in controlling the formation of the particles, still frustrate the preparation of superparamagnetic magnetite particles, that is to say: magnetite nanoparticles with a coercivity of 0 A/m, meaning that they completely lose their permanent magnetisation in the absence of an external magnetic field. The smallest values currently reported for nanosized magnetite particles is ''Hc'' = 8.5 A m<sup>−1</sup>,<ref>{{cite journal| vauthors = Ström V, Olsson RT, Rao KV |title=Real-time monitoring of the evolution of magnetism during precipitation of superparamagnetic nanoparticles for bioscience applications|journal=Journal of Materials Chemistry|date=2010|volume=20|issue=20|page=4168|doi=10.1039/C0JM00043D}}</ref> whereas the largest reported magnetization value is 87 Am<sup>2</sup> kg<sup>−1</sup> for synthetic magnetite.<ref>{{cite journal| vauthors = Fang M, Ström V, Olsson RT, Belova L, Rao KV |title=Rapid mixing: A route to synthesize magnetite nanoparticles with high moment|journal=Applied Physics Letters |date=2011 |volume=99 |issue=22 |page=222501 |doi=10.1063/1.3662965 |bibcode=2011ApPhL..99v2501F }}</ref><ref>{{cite journal | vauthors = Fang M, Ström V, Olsson RT, Belova L, Rao KV | title = Particle size and magnetic properties dependence on growth temperature for rapid mixed co-precipitated magnetite nanoparticles | journal = Nanotechnology | volume = 23 | issue = 14 | article-number = 145601 | date = April 2012 | pmid = 22433909 | doi = 10.1088/0957-4484/23/14/145601 | bibcode = 2012Nanot..23n5601F | s2cid = 34153665 }}</ref>

Pigment quality Fe<sub>3</sub>O<sub>4</sub>, so called synthetic magnetite, can be prepared using processes that use 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 (metal)|pickling]]) of steel):

*Oxidation of Fe metal in the Laux process where [[nitrobenzene]] is treated 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> + 3 Fe + 2 H<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>{{cite patent | country = US | number = 2596954 | gdate = 13 May 1952 | title = Process for reduction of iron ore to magnetite | inventor = Heath TD | assign1 = Dorr Company }}</ref><ref>{{cite journal | title = Kinetics of reduction of iron oxides by H2 Part I: Low temperature reduction of hematite | vauthors = Pineau A, Kanari N, Gaballah I | journal = Thermochimica Acta | volume = 447 | issue = 1 | pages = 89–100 | year = 2006 | 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>{{cite journal | title = 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> | vauthors = Hayes PC, Grieveson P | journal = Metallurgical and Materials Transactions B | year = 1981 | volume = 12 | issue = 2 | pages = 319–326 | doi = 10.1007/BF02654465|bibcode=1981MTB....12..319H |s2cid=94274056 }}</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|0-8247-0796-6}}</ref>

[[Iron(II) carbonate]] can also be thermally decomposed into Iron(II,III):<ref>{{Cite web |title=FeCO3 = Fe3O4 + CO2 + CO {{!}} The thermal decomposition of iron(II) carbonate |url=https://chemiday.com/en/reaction/3-1-0-5222 |access-date=2022-10-14 |website=chemiday.com}}</ref>

: {{Chem2|3FeCO3 → Fe3O4 + 2CO2 + CO}}

==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"/>
:<chem>{Fe3O4} + 4CO -> {3Fe} + 4CO2</chem>
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|3-527-30363-4}}</ref>
:<math chem>\ce{\underbrace{2Fe3O4}_{magnetite} + {1/2O2} ->}\ {\color{Brown}\ce{\underbrace{3(\gamma-Fe2O3)}_{maghemite}}}</math>
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"/>
:<math chem>\ce{\underbrace{2Fe3O4}_{magnetite} + {1/2O2} ->}\ {\color{BrickRed}\ce{\underbrace{3(\alpha-Fe2O3)}_{hematite}}}</math>

== Structure ==
Fe<sub>3</sub>O<sub>4</sub> has a cubic inverse [[spinel group]] 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.

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"/>

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"/>

In the molten state, experimentally constrained models show that the iron ions are coordinated to 5 oxygen ions on average.<ref name="ShiFeOx2020">{{cite journal | vauthors = Shi C, Alderman OL, Tamalonis A, Weber R, You J, Benmore CJ |title=Redox-structure dependence of molten iron oxides |journal=Communications Materials |date=2020 |volume=1 |issue=1 |page=80 |doi=10.1038/s43246-020-00080-4 |bibcode=2020CoMat...1...80S |s2cid=226248368 |ref=ShiFeOx2020|doi-access=free }}</ref> There is a distribution of coordination sites in the liquid state, with the majority of both Fe<sup>II</sup> and Fe<sup>III</sup> being 5-coordinated to oxygen and minority populations of both 4- and 6-fold coordinated iron.

==Properties==
[[File:Magnetite.jpg|thumb|240px|Sample of [[magnetite]], naturally occurring Fe<sub>3</sub>O<sub>4</sub>.]]

Fe<sub>3</sub>O<sub>4</sub> is [[ferrimagnetic]] with a [[Curie point|Curie temperature]] of {{Convert|858|K|C}}. There is a phase transition at {{Convert|120|K|C}}, called [[Verwey transition]] where there is a discontinuity in the structure, conductivity and magnetic properties.<ref>{{cite journal |title = Electronic Conduction of Magnetite (Fe<sub>3</sub>O<sub>4</sub>) and its Transition Point at Low Temperatures | vauthors = Verwey EJ |journal = [[Nature (journal)|Nature]] |volume = 144 |pages = 327–328 (1939) |doi = 10.1038/144327b0 |year = 1939 | issue=3642|bibcode = 1939Natur.144..327V |s2cid = 41925681 }}</ref> This effect has been extensively investigated and whilst various explanations have been proposed, it does not appear to be fully understood.<ref>{{cite journal| vauthors = Walz F |title=The Verwey transition - a topical review |journal=Journal of Physics: Condensed Matter |date=2002 |volume=14 |issue=12 |pages=R285–R340 |doi=10.1088/0953-8984/14/12/203|s2cid=250773238 }}</ref>

While it has much higher [[electrical resistivity]] than iron metal (96.1 nΩ m), Fe<sub>3</sub>O<sub>4</sub>'s electrical resistivity (0.3 mΩ m <ref>{{cite journal| vauthors = Itai R |title=Electrical resistivity of Magnetite anodes |journal=Journal of the Electrochemical Society |date=1971 |volume=118 |issue=10 |page=1709 |doi=10.1149/1.2407817 |bibcode=1971JElS..118.1709I |url=http://www.chlorates.exrockets.com/magnetite/jes1971.html|url-access=subscription }}</ref>) is significantly lower than that of [[iron(III) oxide|Fe<sub>2</sub>O<sub>3</sub>]] (approx kΩ m). This is ascribed to electron exchange between the Fe<sup>II</sup> and Fe<sup>III</sup> centres in Fe<sub>3</sub>O<sub>4</sub>.<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) or [[Mars Black (pigment)|Mars Black]].<ref name = "Buxbaum"/>

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|0-8247-5563-4}}</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"/>

=== Medical uses ===
{{Infobox drug
| drug_name         = Ferumoxytol
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<!-- Clinical data -->
| pronounce         = 
| tradename         = Feraheme, Rienso
| Drugs.com         = {{drugs.com|monograph|ferumoxytol}}
| MedlinePlus       = a614023
| DailyMedID        = Ferumoxytol
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| legal_US_comment  = <ref name="Feraheme FDA label">{{cite web | title=Feraheme- ferumoxytol injection | website=DailyMed | date=9 July 2020 | url=https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=32b0e320-a739-11dc-a704-0002a5d5c51b | access-date=14 September 2020}}</ref>
| legal_EU          = Rx-only
| legal_EU_comment  = <ref name="Rienso EPAR">{{cite web | title=Rienso EPAR | website=European Medicines Agency | date=17 September 2018 | url=https://www.ema.europa.eu/en/medicines/human/EPAR/rienso | access-date=14 September 2020}}</ref>
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<!-- Chemical and physical data -->
| IUPAC_name        = iron(2+);iron(3+);oxygen(2-)
| Fe = 3 | O = 4
| SMILES            = [O-2].[O-2].[O-2].[O-2].[Fe+2].[Fe+3].[Fe+3]
| StdInChI          = 1S/3Fe.4O/q+2;2*+3;4*-2
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| StdInChIKey       = WTFXARWRTYJXII-UHFFFAOYSA-N
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Nano particles of Fe<sub>3</sub>O<sub>4</sub> are used as contrast agents in [[Magnetic resonance imaging|MRI scanning]].<ref>{{cite journal | vauthors = Babes L, Denizot B, Tanguy G, Jallet P | title = Synthesis of Iron Oxide Nanoparticles Used as MRI Contrast Agents: A Parametric Study | journal = Journal of Colloid and Interface Science | volume = 212 | issue = 2 | pages = 474–482 | date = April 1999 | pmid = 10092379 | doi = 10.1006/jcis.1998.6053 | bibcode = 1999JCIS..212..474B }}</ref>

Ferumoxytol, sold under the brand names Feraheme and Rienso, is an [[intravenous]] Fe<sub>3</sub>O<sub>4</sub> preparation for treatment of [[anemia]] resulting from [[chronic kidney disease]].<ref name="Feraheme FDA label"/><ref name="Rienso EPAR"/><ref name="schwenk2010">{{cite journal |vauthors=Schwenk MH |title=Ferumoxytol: a new intravenous iron preparation for the treatment of iron deficiency anemia in patients with chronic kidney disease |journal= Pharmacotherapy |volume=30 |issue=1 |pages=70–79 |date=January 2010 |pmid=20030475 |doi=10.1592/phco.30.1.70 |s2cid=7748714 |url=http://www.medscape.com/viewarticle/715178|url-access=subscription }}</ref><ref name="FDA approval">{{cite web |title=Drug Approval Package: Feraheme (Ferumoxytol) Injection NDA #022180 |website=U.S. [[Food and Drug Administration]] (FDA) |url=https://www.accessdata.fda.gov/drugsatfda_docs/nda/2009/022180s000TOC.cfm |access-date=14 September 2020}}<br/>{{cite web | vauthors = Rieves D |date=June 23, 2009 |title=Application Number: 22-180 |publisher=Center for Drug Evaluation and Research |type=Summary Review |url=https://www.accessdata.fda.gov/drugsatfda_docs/nda/2009/022180s000_SumR.pdf}}</ref> Ferumoxytol is manufactured and globally distributed by [[AMAG Pharmaceuticals]].<ref name="Feraheme FDA label"/><ref name="FDA approval"/>

==Biological occurrence==
Magnetite has been found as nano-crystals in [[magnetotactic bacteria]] (42–45&nbsp;nm)<ref name = "Cornell"/> and in the beak tissue of [[homing pigeon]]s.<ref>{{cite journal | vauthors = Hanzlik M, Heunemann C, Holtkamp-Rötzler E, Winklhofer M, Petersen N, Fleissner G | title = Superparamagnetic magnetite in the upper beak tissue of homing pigeons | journal = Biometals | volume = 13 | issue = 4 | pages = 325–31 | date = December 2000 | pmid = 11247039 | doi = 10.1023/A:1009214526685 | s2cid = 39216462 }}</ref>
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== References ==
{{reflist}}

{{Iron compounds}}
{{Oxides}}
{{oxygen compounds}}
{{Portal bar | Medicine}}
{{Authority control}}

[[Category:Iron(II,III) compounds]]
[[Category:Semiconductor materials]]
[[Category:Iron oxide pigments]]
[[Category:Non-stoichiometric compounds]]
[[Category:Excipients]]
[[Category:Multiple Chemboxes|X]]