iron oxide

{{Short description|Class of chemical compounds composed of iron and oxygen}}

An iron oxide is a chemical compound composed of iron and oxygen. Several iron oxides are recognized. Often they are non-stoichiometric. Ferric oxyhydroxides are a related class of compounds, perhaps the best known of which is rust.{{cite book

| last = Cornell.

| first = RM.

|author2=Schwertmann, U

| title = The iron oxides: structure, properties, reactions, occurrences and

| year = 2003

| publisher = Wiley VCH

| isbn = 978-3-527-30274-1

}}

Iron oxides and oxyhydroxides are widespread in nature and play an important role in many geological and biological processes. They are used as iron ores, pigments, catalysts, and in thermite, and occur in hemoglobin. 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 has E number E172.

==Stoichiometries==

File:IronOxidePigmentUSGOV.jpg

File:Red and green iron oxides.jpg

Iron oxides feature as ferrous (Fe(II)) or ferric (Fe(III)) or both. They adopt octahedral or tetrahedral coordination geometry. Only a few oxides are significant at the earth's surface, particularly wüstite, magnetite, and hematite.

Oxides of Fe^II
FeO: iron(II) oxide, wüstite
Mixed oxides of Fe^II and Fe^III
Fe₃O₄: Iron(II,III) oxide, magnetite
Fe₄O₅{{cite journal|title=Discovery of the recoverable high-pressure iron oxide Fe4O5|date=Oct 2011 | doi=10.1073/pnas.1107573108 |pmid=21969537 | volume=108|issue=42|journal=Proceedings of the National Academy of Sciences|pages=17281–17285|bibcode=2011PNAS..10817281L|pmc=3198347|last1=Lavina |first1=B. |last2=Dera |first2=P. |last3=Kim |first3=E. |last4=Meng |first4=Y. |last5=Downs |first5=R. T. |last6=Weck |first6=P. F. |last7=Sutton |first7=S. R. |last8=Zhao |first8=Y. |doi-access=free }}
Fe₅O₆{{cite journal|title = Synthesis of Fe5O6|journal = Science Advances|volume = 1|issue = 5|pages = e1400260|doi = 10.1126/sciadv.1400260|pmid = 26601196|year = 2015|last1 = Lavina|first1 = Barbara|last2 = Meng|first2 = Yue|pmc = 4640612}}
Fe₅O₇{{cite journal| title = Structural complexity of simple Fe2O3 at high pressures and temperatures| journal = Nature Communications| volume = 7| pages = 10661| doi = 10.1038/ncomms10661| pmid = 26864300| pmc = 4753252| year = 2016| last1 = Bykova| first1 = E.| last2 = Dubrovinsky| first2 = L.| last3 = Dubrovinskaia| first3 = N.| last4 = Bykov| first4 = M.| last5 = McCammon| first5 = C.| last6 = Ovsyannikov| first6 = S. V.| last7 = Liermann| first7 = H. -P.| last8 = Kupenko| first8 = I.| last9 = Chumakov| first9 = A. I.| last10 = Rüffer| first10 = R.| last11 = Hanfland| first11 = M.| last12 = Prakapenka| first12 = V.| bibcode = 2016NatCo...710661B}}
Fe₂₅O₃₂
Fe₁₃O₁₉{{cite journal| title = The crystal structures of Mg2Fe2C4O13, with tetrahedrally coordinated carbon, and Fe13O19, synthesized at deep mantle conditions| journal = American Mineralogist| volume = 100| issue = 8–9| pages = 2001–2004| doi = 10.2138/am-2015-5369| year = 2015| last1 = Merlini| first1 = Marco| last2 = Hanfland| first2 = Michael| last3 = Salamat| first3 = Ashkan| last4 = Petitgirard| first4 = Sylvain| last5 = Müller| first5 = Harald| bibcode = 2015AmMin.100.2001M| s2cid = 54496448}}
Oxides of Fe^III
Fe₂O₃: iron(III) oxide
α-Fe₂O₃: alpha phase, hematite
β-Fe₂O₃: beta phase
γ-Fe₂O₃: gamma phase, maghemite
ε-Fe₂O₃: epsilon phase

Thermal expansion

class="wikitable"

!Iron oxide

! CTE (× 10⁻⁶ °C⁻¹)

Fe₂O₃

|14.9{{Cite journal|last1=Fakouri Hasanabadi|first1=M.|last2=Kokabi|first2=A.H.|last3=Nemati|first3=A.|last4=Zinatlou Ajabshir|first4=S.|date=February 2017|title=Interactions near the triple-phase boundaries metal/glass/air in planar solid oxide fuel cells|journal=International Journal of Hydrogen Energy|volume=42|issue=8|pages=5306–5314|doi=10.1016/j.ijhydene.2017.01.065|issn=0360-3199}}

Fe₃O₄

|>9.2

FeO

|12.1

Oxide-hydroxides

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.{{Cite journal|last1=Nishi|first1=Masayuki|last2=Kuwayama|first2=Yasuhiro|last3=Tsuchiya|first3=Jun|last4=Tsuchiya|first4=Taku|date=2017|title=The pyrite-type high-pressure form of FeOOH|url=https://www.nature.com/articles/nature22823|journal=Nature|language=en|volume=547|issue=7662|pages=205–208|doi=10.1038/nature22823|pmid=28678774|bibcode=2017Natur.547..205N |s2cid=205257075|issn=1476-4687|url-access=subscription}} Once dehydration is triggered, this phase may form FeO₂H_x (0 < x < 1).{{cite journal|last1=Hu|first1=Qingyang|last2=Kim|first2=Duckyoung|last3=Liu|first3=Jin|last4=Meng|first4=Yue|last5=Liuxiang|first5=Yang|last6=Zhang|first6=Dongzhou|last7=Mao|first7=Wendy L.|author-link7=Wendy Mao|last8=Mao|first8=Ho-kwang|year=2017|title=Dehydrogenation of goethite in Earth's deep lower mantle|journal=Proceedings of the National Academy of Sciences|volume=114|issue=7|pages=1498–1501|doi=10.1073/pnas.1620644114|pmc=5320987|pmid=28143928|bibcode=2017PNAS..114.1498H |doi-access=free}}
green rust (Fe{{sup sub|III|x}}Fe{{sup sub|II|y}}OH_{3x + y − z} (A⁻)_z where A⁻ is Cl⁻ or 0.5 {{chem2|SO4(2-)}})

Reactions

In blast furnaces and related factories, iron oxides are converted to the metal. Typical reducing agents are various forms of carbon. A representative reaction starts with ferric oxide:{{Greenwood&Earnshaw2nd|page=1072}}

:{{chem2|2 Fe2O3 + 3 C -> 4 Fe + 3 CO2}}

=In nature =

Iron is stored in many organisms in the form of ferritin, which is a ferrous oxide encased in a solubilizing protein sheath.{{cite journal|doi=10.1021/cr5004908|title=Unity in the Biochemistry of the Iron-Storage Proteins Ferritin and Bacterioferritin |year=2015 |last1=Honarmand Ebrahimi |first1=Kourosh |last2=Hagedoorn |first2=Peter-Leon |last3=Hagen |first3=Wilfred R. |journal=Chemical Reviews |volume=115 |issue=1 |pages=295–326 |pmid=25418839 |doi-access=free }}

Species of bacteria, including Shewanella oneidensis, Geobacter sulfurreducens and Geobacter metallireducens, use iron oxides as terminal electron acceptors.{{cite journal|last1=Bretschger|first1=O.|last2=Obraztsova|first2=A.|last3=Sturm|first3=C. A.|last4=Chang|first4=I. S.|last5=Gorby|first5=Y. A.|last6=Reed|first6=S. B.|last7=Culley|first7=D. E.|last8=Reardon|first8=C. L.|last9=Barua|first9=S.|last10=Romine|first10=M. F.|last11=Zhou|first11=J.|last12=Beliaev|first12=A. S.|last13=Bouhenni|first13=R.|last14=Saffarini|first14=D.|last15=Mansfeld|first15=F.|last16=Kim|first16=B.-H.|last17=Fredrickson|first17=J. K.|last18=Nealson|first18=K. H.|title=Current Production and Metal Oxide Reduction by Shewanella oneidensis MR-1 Wild Type and Mutants|journal=Applied and Environmental Microbiology|date=20 July 2007|volume=73|issue=21|pages=7003–7012|doi=10.1128/AEM.01087-07|pmid=17644630|pmc=2223255|bibcode=2007ApEnM..73.7003B }}

Uses

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 important pigments, coming in a variety of colors (black, red, yellow). Among their many advantages, they are inexpensive, strongly colored, and nontoxic.{{Ullmann|doi=10.1002/14356007.n20_n02|title=Pigments, Inorganic, 3. Colored Pigments |year=2009 |last1=Buxbaum |first1=Gunter |last2=Printzen |first2=Helmut |last3=Mansmann |first3=Manfred |last4=Räde |first4=Dieter |last5=Trenczek |first5=Gerhard |last6=Wilhelm |first6=Volker |last7=Schwarz |first7=Stefanie |last8=Wienand |first8=Henning |last9=Adel |first9=Jörg |last10=Adrian |first10=Gerhard |last11=Brandt |first11=Karl |last12=Cork |first12=William B. |last13=Winkeler |first13=Heinrich |last14=Mayer |first14=Wielfried |last15=Schneider |first15=Klaus |isbn=978-3527306732 }}

Magnetite is a component of magnetic recording tapes.

References

External links

[https://web.archive.org/web/20171118055115/http://www.nano-oxides.com/pdf/Fe2O3_Brochure.pdf Information from 4thNano-Oxides, Inc. on Fe₂O₃.]
[http://chemed.chem.purdue.edu/demos/demosheets/12.3.html The Iron One-Pot Reaction]
[http://minerals.usgs.gov/minerals/pubs/commodity/iron_oxide/ Iron Oxide Pigments Statistics and Information]
[https://www.cdc.gov/niosh/npg/npgd0344.html CDC – NIOSH Pocket Guide to Chemical Hazards]

Category:Iron compounds

Category:Iron oxide pigments

Category:Transition metal oxides