View source for Ferric oxide

:''This page is about a red-colored oxide of iron. For other uses, see [[red iron]].''
{{chembox new
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 464185021
| Name = Iron(III) oxide
| ImageFile = Ferric oxide Chembox.png

| ImageSize = 200px
| ImageName = Haematite unit cell
| IUPACName = Iron(III) oxide
| OtherNames = Ferric oxide, [[Hematite]], Ferric iron, Red iron oxide, Rouge, [[Maghemite]], Colcothar, Iron sesquioxide, [[Rust]], [[Ochre]]
| Section1 = {{Chembox Identifiers
| CASNo = 1309-37-1
| CASNo_Ref = {{cascite|correct|CAS}}
| ChemSpiderID_Ref = {{chemspidercite|changed|chemspider}}
| ChemSpiderID = 14147
| UNII = 1K09F3G675
| UNII_Ref = {{fdacite|correct|FDA}}
| ChEBI = 50819
| ChEBI_Ref = {{ebicite|correct|EBI}}
| SMILES = O1[Fe]2O[Fe]1O2
| PubChem = 518696
| PubChem_Ref = {{pubchemcite}}
| RTECS = NO7400000
| KEGG = C19424
| KEGG_Ref = {{keggcite|changed|kegg}}
| InChI = 1/2Fe.3O/rFe2O3/c3-1-4-2(3)5-1
| InChIKey = JEIPFZHSYJVQDO-ZVGCCQCPAC
| StdInChI_Ref = {{stdinchicite|correct|inchi}}
| StdInChI = 1S/2Fe.3O
| StdInChIKey_Ref = {{stdinchicite|correct|inchi}}
| StdInChIKey = JEIPFZHSYJVQDO-UHFFFAOYSA-N
| EC-number = 215-168-2
  }}
| Section2 = {{Chembox Properties
| Fe=2|O=3
| Appearance = Red-brown solid
| Odor = Odorless
| Density = 5.242 g/cm<sup>3</sup><ref name=leker>{{cite web|url = http://www.lesker.com/msds/pdfs/cd72f997d54d3bc42d09a34d6bdca56ebf2ea7fd3a31f08843ec5bd413.pdf|title = SDS of Iron(III) oxide|date = 2012-01-05|publisher = Kurt J Lesker Company Ltd.|place = England|accessdate = 2014-07-12|website = http://www.lesker.com}}</ref>
| MeltingPtC = 1539-1565
| Melting_ref = <ref name=crc>{{CRC90}}</ref><br> decomposes<ref name=leker /><br> {{convert|105|C|F K}}<br> β-dihydrate, decomposes<br> {{convert|150|C|F K}}<br> β-monohydrate, decomposes<br> {{convert|50|C|F K}}<br> α-dihydrate, decomposes<br> {{convert|92|C|F K}}<br> α-monohydrate, decomposes<ref name=doc00>{{cite book|page = 433|title = A Dictionary of Chemical Solubilities: Inorganic|edition = 2nd|first = Arthur Messinger|last = Comey|first2 = Dorothy A.|last2 = Hahn|place = New York|publisher = The MacMillan Company|date = 1921-02}}</ref>
| Solubility = Insoluble
| SolubleOther = Soluble in diluted [[acid]]s,<ref name=crc /> [[sugar]] solution<br> Trihydrate slighty soluble in aq. [[tartaric acid]], [[citric acid]], [[acetic acid|CH<sub>3</sub>COOH]]<ref name=doc00 />
  }}
| Section3 = {{Chembox Structure
| CrystalStruct = [[Rhombohedral]], [[pearson symbol|hR30]] (α-form)<ref name=odnpa>{{cite book|page = 167|url = http://books.google.com/books?id=sY-0IGwimWkC&pg=PA167|title = One-Dimensional Nanostructures: Principles and Applications|editor-first = Tianyou|editor-last =  Zhai|editor-first2 = Jiannian|editor-last2 = Yao|publisher = John Wiley & Sons, Inc.|year = 2013|place = Hoboken, New Jersey|isbn = 978-1-118-07191-5|website = http://www.wiley.com|first1 = Yichuan|last1 = Ling|first2 = Damon A.|last2 = Wheeler|first3 = Jin Zhong|last3 = Zhang|first4 = Yat|last4 = Li}}</ref><br> [[cubic crystal system|Cubic]] bixbyite, cI80 (β-form)<br> Cubic spinel (γ-form)<br> [[orthorhombic crystal system|Orthorhombic]] (ε-form)<ref name="atmilab" />
| SpaceGroup = R3c, No. 161 (α-form)<ref name=odnpa /><br> Ia{{overline|3}}, No. 206 (β-form)<br> Pna2<sub>1</sub>, No. 33 (ε-form)<ref name="atmilab" />
| PointGroup = 3m (α-form)<ref name=odnpa /><br> 2/m {{overline|3}} (β-form)<br> mm2 (ε-form)<ref name="atmilab" />
| Coordination = [[octahedral molecular geometry|Octahedral]] (Fe<sup>3+</sup>, α-form, β-form)<ref name=odnpa />
  }}
| Section4 = {{Chembox Thermochemistry
| DeltaHf = −824.2 kJ/mol<ref name=crc />
| DeltaGf = −742.2 kJ/mol<ref name=crc />
| Entropy = 87.4 J/mol·K<ref name=crc />
| HeatCapacity = 103.9 J/mol·K<ref name=crc />
  }}
| Section7 = {{Chembox Hazards
| GHSPictograms = {{GHS07}}<ref name="sigma">{{Sigma-Aldrich|id=529311|name=Iron(III) oxide|accessdate=2014-07-12}}</ref>
| GHSSignalWord = Warning
| HPhrases = {{H-phrases|315|319|335}}<ref name="sigma" />
| PPhrases = {{P-phrases|261|305+351+338}}<ref name="sigma" />
| SPhrases = {{S26}}
| RPhrases = {{R36/37/38}}
| EUClass = {{Hazchem Xi}}
| NFPA-H = 0
| NFPA-F = 0
| NFPA-R = 0
| NFPA_Ref = <ref name=leker />
| TLV-TWA = 5&nbsp;mg/m<sup>3</sup><ref name=crc />
| LD50 = 10 g/kg (rats, oral)<ref name=leker />
| PEL = TWA 10 mg/m<sup>3</sup><ref name=PGCH>{{PGCH|0344}}</ref>
| IDLH = 2500 mg/m<sup>3</sup><ref name=PGCH/>
| REL = TWA 5 mg/m<sup>3</sup><ref name=PGCH/> 
  }}
| Section8 = {{Chembox Related
| OtherAnions = [[Iron(III) fluoride]]
| OtherCations = [[Manganese(III) oxide]]<br> [[Cobalt(III) oxide]]
| OtherFunctn = [[Iron(II) oxide]]<br> [[Iron(II,III) oxide]]
| Function = [[iron oxides]]
  }}
}}
__NOTOC__
{{SI}}
{{CMG}}
== Overview ==
'''Iron(III) oxide''' or '''ferric oxide''' is the [[inorganic compound]] with the formula Fe<sub>2</sub>O<sub>3</sub>. It is one of the three main [[oxide]]s of [[iron]], the other two being [[iron(II) oxide]] (FeO), which is rare, and [[iron(II,III) oxide]] (Fe<sub>3</sub>O<sub>4</sub>), which also occurs naturally as the mineral [[magnetite]]. As the mineral known as [[hematite]], Fe<sub>2</sub>O<sub>3</sub> is the main source of iron for the steel industry. Fe<sub>2</sub>O<sub>3</sub> is [[ferromagnetism|ferromagnetic]], dark red, and readily attacked by acids. Iron(III) oxide is often called [[rust]], and to some extent this label is useful, because rust shares several properties and has a similar composition. To a chemist, rust is considered an ill-defined material, described as ''hydrated'' ferric oxide.

==Structure==
Fe<sub>2</sub>O<sub>3</sub> can be obtained in various [[polymorphism (materials science)|polymorph]]s. In the main ones, α and γ, iron adopts octahedral coordination geometry. That is, each Fe center is bound to six oxygen [[ligand]]s.

===Alpha phase===
α-Fe<sub>2</sub>O<sub>3</sub> has the [[rhombohedral]], [[aluminium oxide|corundum]] (α-Al<sub>2</sub>O<sub>3</sub>) structure and is the most common form. It occurs naturally as the mineral [[hematite]] which is mined as the main [[ore]] of iron. It is [[antiferromagnetic]] below ~260 K ([[Morin transition]] temperature), and exhibits weak [[ferromagnetism]] between 260 K and the [[Néel temperature]], 950 K.<ref>{{cite book |first=J. E. |last=Greedon |year=1994 |chapter=Magnetic oxides |title=Encyclopedia of Inorganic chemistry |editor-first=R. Bruce |editor-last=King |publisher=John Wiley & Sons |location=New York |isbn=0-471-93620-0 }}</ref> It is easy to prepare using both [[thermal decomposition]] and precipitation in the liquid phase. Its magnetic properties are dependent on many factors, e.g. pressure, particle size, and magnetic field intensity.

===Gamma phase===
γ-Fe<sub>2</sub>O<sub>3</sub> has a [[cubic crystal system|cubic]] structure. It is metastable and converted from the alpha phase at high temperatures. It occurs naturally as the mineral [[maghemite]]. It is [[ferromagnetic]] and finds application in recording tapes,<ref name="InorgChem"/> although [[ultrafine particles]] smaller than 10 nanometers are [[superparamagnetic]]. It can be prepared by thermal dehydratation of gamma [[iron(III) oxide-hydroxide]], careful oxidation of [[iron(II,III) oxide]]. Another method involves the careful oxidation of Fe<sub>3</sub>O<sub>4</sub>.<ref name="InorgChem"/> The ultrafine particles can be prepared by thermal decomposition of [[iron(III) oxalate]].

===Other phases===
Several other phases have been identified or claimed. The β-phase is cubic body centered (space group Ia3), [[metastability in molecules|metastable]], and at temperatures above {{convert|500|°C|°F|-1|abbr=on|lk=off}} converts to alpha phase. It can be prepared by reduction of hematite by carbon, [[pyrolysis]] of [[iron(III) chloride]] solution, or thermal decomposition of [[iron(III) sulfate]]. The epsilon phase is rhombic, and shows properties intermediate between alpha and gamma, and may have useful magnetic properties. Preparation of the pure epsilon phase has proven very challenging due to contamination with alpha and gamma phases. Material with a high proportion of epsilon phase can be prepared by thermal transformation of the gamma phase. This phase is also metastable, transforming to the alpha phase at between {{convert|500|and|750|°C|°F|-1|abbr=on|lk=off}}. Can also be prepared by oxidation of iron in an [[electric arc]] or by [[sol-gel]] precipitation from [[iron(III) nitrate]].{{Citation needed|date=July 2011}} Additionally at high pressure an [[amorphous]] form is claimed.<ref name="atmilab">{{cite web|url = http://atmilab.upol.cz/texty/ultrafine02.pdf|accessdate = 2014-07-12|title = Ultraﬁne Particles of Iron(III) Oxides by View of AFM – Novel
Route for Study of Polymorphism in Nano-world|first = Milan|last = Vujtek|first2 = Radek|last2 = Zboril|first3 = Roman|last3 = Kubinek|first4 = Miroslav|last4 = Mashlan|place = Czech|website = http://atmilab.upol.cz}}</ref> Recent research has revealed epsilon iron(III) oxide in ancient Chinese [[Chinese_ceramics#Jian_tea_wares|Jian ceramic]] glazes, which may provide insight into ways to produce that form in the lab. <ref>{{Learning from the past: Rare ε-Fe2O3 in the ancient black-glazed Jian (Tenmoku) wares Catherine Dejoie, Philippe Sciau, Weidong Li, Laure Noé, Apurva Mehta, Kai Chen, Hongjie Luo, Martin Kunz,Nobumichi Tamura & Zhi Liu Scientific Reports 4, Article number: 4941 doi:10.1038/srep04941 Received 20 February 2014 Accepted 15 April 2014 Published 13 May 2014}}</ref>

==Hydrated iron(III) oxides==
Several hydrates of Iron(III) oxide exists.
When alkali is added to solutions of soluble Fe(III) salts, a red-brown gelatinous precipitate forms. This is ''not'' Fe(OH)<sub>3</sub>, but Fe<sub>2</sub>O<sub>3</sub>·H<sub>2</sub>O (also written as Fe(O)OH).
Several forms of the hydrated oxide of Fe(III) exist as well. The red ''lepidocrocite'' γ-Fe(O)OH, occurs on the outside of [[rusticle]]s, and the orange ''goethite'', which occurs internally in [[rusticle]]s.
When Fe<sub>2</sub>O<sub>3</sub>·H<sub>2</sub>O is heated, it loses its water of hydration. Further heating at 1670 K converts Fe<sub>2</sub>O<sub>3</sub> to black Fe<sub>3</sub>O<sub>4</sub> (Fe<sup>II</sup>Fe<sup>III</sup><sub>2</sub>O<sub>4</sub>), which is known as the mineral ''[[magnetite]]''.
Fe(O)OH is soluble in acids, giving [Fe(OH<sub>2</sub>)<sub>6</sub>]<sup>3+</sup>. In concentrated aqueous alkali, Fe<sub>2</sub>O<sub>3</sub> gives [Fe(OH)<sub>6</sub>]<sup>3−</sup>.<ref name="InorgChem">.{{cite book|title = Inorganic Chemistry, 3rd Edition|chapter = Chapter 22: ''d''-block metal chemistry: the first row elements|first = Catherine E.|last = Housecroft|first2 = Alan G.|last2 = Sharpe|publisher = Pearson|year = 2008|isbn = 978-0-13-175553-6|page = 716}}</ref>

==Reactions==
The most important reaction is its [[carbothermal reduction]], which gives iron used in steel-making:
: Fe<sub>2</sub>O<sub>3</sub> + 3 CO → 2 Fe + 3 CO<sub>2</sub>

Another redox reaction is the extremely [[exothermic]] [[thermite]] reaction with [[aluminium]].<ref>{{cite book |last=Adlam |first= |last2=Price |first2= |title=Higher School Certificate Inorganic Chemistry |location= |publisher=Leslie Slater Price |year=1945 }}</ref>
: 2 [[aluminium|Al]] + Fe<sub>2</sub>O<sub>3</sub> → 2 Fe + [[alumina|Al<sub>2</sub>O<sub>3</sub>]]

This process is used to weld thick metals such as rails of train tracks by using a ceramic container to funnel the molten iron in between two sections of rail. Thermite is also used in weapons and making small-scale cast-iron sculptures and tools.

Partial reduction with hydrogen at about 400&nbsp;°C gives [[magnetite]], a black magnetic material that contains both Fe(III) and Fe(II):<ref name=Brauer/>
:3 Fe<sub>2</sub>O<sub>3</sub> + H<sub>2</sub> → 2 Fe<sub>3</sub>O<sub>4</sub> + H<sub>2</sub>O

Iron(III) oxide is insoluble in water but dissolves readily in strong acid, e.g. hydrochloric and [[sulfuric acid]]s. It also dissolves well in solutions of the chelating agents such as [[EDTA]] and [[oxalic acid]].

Heating iron(III) oxides with other metal oxides or carbonates yields materials known as [[ferrate]]s:<ref name=Brauer/>
: ZnO + Fe<sub>2</sub>O<sub>3</sub> → Zn(FeO<sub>2</sub>)<sub>2</sub>

==Preparation==
Iron(III) oxide is a product of the oxidation of iron. It can be prepared in the laboratory by electrolyzing a solution of sodium bicarbonate, an inert electrolyte, with an iron anode:
:4 Fe + 3 O<sub>2</sub> + 2 H<sub>2</sub>O → 4 FeO(OH)

The resulting hydrated iron(III) oxide, written here as Fe(O)OH, dehydrates around 200 °C.<ref name=Brauer>Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1661.</ref><ref name=Ullmann/>
:2 FeO(OH) → Fe<sub>2</sub>O<sub>3</sub> + H<sub>2</sub>O

It can also be prepared by the thermal decomposition of iron(III) hydroxide under temperature above 200&nbsp;°C.
:2 Fe(OH)<sub>3</sub> → Fe<sub>2</sub>O<sub>3</sub> + 3H<sub>2</sub>O

==Uses==
===Iron industry===
The overwhelming application of iron(III) oxide is as the feedstock of the steel and iron industries, e.g. the production of iron, steel, and many alloys.<ref name=Ullmann>{{cite book |last=Greenwood |first=N. N. |last2=Earnshaw |first2=A. |year=1997 |title=Chemistry of the Element |edition=2nd |location=Oxford |publisher=Butterworth-Heinemann |isbn=0-7506-3365-4 }}</ref>

===Polishing===
A very fine powder of ferric oxide is known as "jeweler's rouge", "red rouge", or simply rouge. It is used to put the final polish on metallic [[jewellery|jewelry]] and [[lens (optics)|lenses]], and historically as a [[rouge (cosmetics)|cosmetic]]. Rouge cuts more slowly than some modern polishes, such as [[cerium(IV) oxide]], but is still used in optics fabrication and by jewelers for the superior finish it can produce. When polishing gold, the rouge slightly stains the gold, which contributes to the appearance of the finished piece. Rouge is sold as a powder, paste, laced on polishing cloths, or solid bar (with a [[wax]] or [[petroleum|grease]] binder). Other polishing compounds are also often called "rouge", even when they do not contain iron oxide. Jewelers remove the residual rouge on jewelry by use of [[ultrasonic cleaning]]. Products sold as "[[stropping (blade)|stropping]] compound" are often applied to a [[razor strop|leather strop]] to assist in getting a razor edge on knives, straight razors, or any other edged tool.

===Pigment===
{{multiple image|align = left
|footer = Two different colors at different hydrate phase (α = red, β = yellow) of iron(III) oxide hydrate<ref name=doc00 /> and they are useful as a pigment.
|width1 = 220|image1 = Ferric oxide pigment.png

}}
Iron(III) oxide is also used as a [[pigment]], under names "Pigment Brown 6", "Pigment Brown 7", and "Pigment Red 101".<ref>{{cite book |title=Paint and Surface Coatings: Theory and Practice |location= |publisher=William Andrew Inc. |isbn=1-884207-73-1 }}</ref> Some of them, e.g. Pigment Red 101 and Pigment Brown 6, are [[Food and Drug Administration]] (FDA)-approved for use in cosmetics. Iron oxides are used as pigments in dental composites alongside titanium oxides.<ref>{{cite book|last=Banerjee|first=Avijit|title=Pickard's Manual of Operative Dentistry|year=2011|publisher=Oxford University Press Inc., New York|location=United States|isbn=978-0-19-957915-0|pages=89}}</ref>

Hematite is the characteristic component of the Swedish paint color [[Falu red]].

===Magnetic recording===
Iron(III) oxide was the most common [[magnet]]ic particle used in all types of [[magnetic storage|magnetic storage and recording]] media, including magnetic disks (for data storage) and [[magnetic tape]] (used in audio and video recording as well as data storage).
However, modern magnetic storage media - in particular, the hard disk drives - use more advanced thin film technology, which may consist of a stack of 15 layers or more. <ref>[http://link.aip.org/link?jap/102/011301 S.N. Piramanayagam, J. Appl. Phys. 102, 011301 (2007).]</ref>

===Photocatalyst===
α-Fe<sub>2</sub>O<sub>3</sub> has been studied as a [[photoanode]] for the water-splitting reaction for over 25 years.<ref>Kay, A., Cesar, I. and Gratzel, M, ''Journal of the American Chemical Society'' '''2006''', ''128'', 15714-15721</ref>

===Medicine===
A mixture of zinc oxide with about 0.5% iron(III) oxide is called [[calamine]], which is the active ingredient of calamine lotion.

==See also==
*[[Iron oxides]]

==References==
{{reflist|2}}

==External links==
{{Commons category|Iron(III) oxide}}
*[http://www.cdc.gov/niosh/npg/npgd0344.html NIOSH Pocket Guide to Chemical Hazards]

{{Iron compounds}}
{{Oxides}}
{{Metal metabolism}}
{{Use dmy dates|date=July 2011}}

{{DEFAULTSORT:Iron(Iii) Oxide}}
[[Category:drug]]
[[Category:Iron compounds]]
[[Category:Oxides]]

[[Category:Iron oxide pigments]]
[[Category:Common oxide glass components]]
[[Category:Sesquioxides]]