Iron(III) oxide


This article is about a red-colored oxide of iron. For other uses, see Red Iron.























































































Iron(III) oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron(II) oxide (FeO), which is rare; and iron(II,III) oxide (Fe3O4), which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main source of iron for the steel industry. Fe2O3 is 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.[citation needed]




Contents





  • 1 Structure

    • 1.1 Alpha phase


    • 1.2 Gamma phase


    • 1.3 Other phases



  • 2 Hydrated iron(III) oxides


  • 3 Reactions


  • 4 Preparation


  • 5 Uses

    • 5.1 Iron industry


    • 5.2 Polishing


    • 5.3 Pigment


    • 5.4 Magnetic recording


    • 5.5 Photocatalysis


    • 5.6 Medicine



  • 6 See also


  • 7 References


  • 8 External links




Structure


Fe2O3 can be obtained in various polymorphs. In the main ones, α and γ, iron adopts octahedral coordination geometry. That is, each Fe center is bound to six oxygen ligands.



Alpha phase


α-Fe2O3 has the rhombohedral, corundum (α-Al2O3) 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.[9] 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-Fe2O3 has a 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,[10] although ultrafine particles smaller than 10 nanometers are superparamagnetic. It can be prepared by thermal dehydratation of gamma iron(III) oxide-hydroxide. Another method involves the careful oxidation of iron(II,III) oxide (Fe3O4).[10] 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), metastable, and at temperatures above 500 °C (930 °F) 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 500 and 750 °C (930 and 1,380 °F). Can also be prepared by oxidation of iron in an electric arc or by sol-gel precipitation from iron(III) nitrate.[citation needed] Additionally at high pressure an amorphous form is claimed.[6] Recent research has revealed epsilon iron(III) oxide in ancient Chinese Jian ceramic glazes, which may provide insight into ways to produce that form in the lab.[11]



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)3, but Fe2O3·H2O (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 rusticles, and the orange goethite, which occurs internally in rusticles.
When Fe2O3·H2O is heated, it loses its water of hydration. Further heating at 1670 K converts Fe2O3 to black Fe3O4 (FeIIFeIII2O4), which is known as the mineral magnetite.
Fe(O)OH is soluble in acids, giving [Fe(H2O)6]3+. In concentrated aqueous alkali, Fe2O3 gives [Fe(OH)6]3−.[10]



Reactions


The most important reaction is its carbothermal reduction, which gives iron used in steel-making:


Fe2O3 + 3 CO → 2 Fe + 3 CO2

Another redox reaction is the extremely exothermic thermite reaction with aluminium.[12]


2 Al + Fe2O3 → 2 Fe + Al2O3

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 °C produces magnetite, a black magnetic material that contains both Fe(III) and Fe(II):[13]


3 Fe2O3 + H2 → 2 Fe3O4 + H2O

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


Heating iron(III) oxides with other metal oxides or carbonates yields materials known as ferrates (ferrate (III)):[13]


ZnO + Fe2O3 → Zn(FeO2)2


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 O2 + 2 H2O → 4 FeO(OH)

The resulting hydrated iron(III) oxide, written here as Fe(O)OH, dehydrates around 200 °C.[13][14]


2 FeO(OH) → Fe2O3 + H2O


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.[14]



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 jewelry and lenses, and historically as a 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 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 compound" are often applied to a leather strop to assist in getting a razor edge on knives, straight razors, or any other edged tool.



Pigment


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Two different colors at different hydrate phase (α = red, β = yellow) of iron(III) oxide hydrate;[3] they are useful as pigments.


Iron(III) oxide is also used as a pigment, under names "Pigment Brown 6", "Pigment Brown 7", and "Pigment Red 101".[15] Some of them, e.g. Pigment Red 101 and Pigment Brown 6, are approved by the US Food and Drug Administration (FDA) for use in cosmetics. Iron oxides are used as pigments in dental composites alongside titanium oxides.[16]


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



Magnetic recording


Iron(III) oxide was the most common magnetic particle used in all types of 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). Its use in computer disks was superseded by cobalt alloy, enabling thinner magnetic films with higher storage density.[17]



Photocatalysis


α-Fe2O3 has been studied as a photoanode for solar water oxidation.[18] However, its efficacy is limited by a short diffusion length (2-4 nm) of photo-excited charge carriers[19] and subsequent fast recombination, requiring a large overpotential to drive the reaction.[20] Research has been focused on improving the water oxidation performance of Fe2O3 using nanostructuring,[18] surface functionalization,[21] or by employing alternate crystal phases such as β-Fe2O3.[22]



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


  • Chalcanthum


References




  1. ^ abcd "SDS of Iron(III) oxide" (PDF). KJLC. England: Kurt J Lesker Company Ltd. 2012-01-05. Retrieved 2014-07-12..mw-parser-output cite.citationfont-style:inherit.mw-parser-output .citation qquotes:"""""""'""'".mw-parser-output .citation .cs1-lock-free abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/6/65/Lock-green.svg/9px-Lock-green.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .citation .cs1-lock-limited a,.mw-parser-output .citation .cs1-lock-registration abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/d/d6/Lock-gray-alt-2.svg/9px-Lock-gray-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .citation .cs1-lock-subscription abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/a/aa/Lock-red-alt-2.svg/9px-Lock-red-alt-2.svg.png")no-repeat;background-position:right .1em center.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registrationcolor:#555.mw-parser-output .cs1-subscription span,.mw-parser-output .cs1-registration spanborder-bottom:1px dotted;cursor:help.mw-parser-output .cs1-ws-icon abackground:url("//upload.wikimedia.org/wikipedia/commons/thumb/4/4c/Wikisource-logo.svg/12px-Wikisource-logo.svg.png")no-repeat;background-position:right .1em center.mw-parser-output code.cs1-codecolor:inherit;background:inherit;border:inherit;padding:inherit.mw-parser-output .cs1-hidden-errordisplay:none;font-size:100%.mw-parser-output .cs1-visible-errorfont-size:100%.mw-parser-output .cs1-maintdisplay:none;color:#33aa33;margin-left:0.3em.mw-parser-output .cs1-subscription,.mw-parser-output .cs1-registration,.mw-parser-output .cs1-formatfont-size:95%.mw-parser-output .cs1-kern-left,.mw-parser-output .cs1-kern-wl-leftpadding-left:0.2em.mw-parser-output .cs1-kern-right,.mw-parser-output .cs1-kern-wl-rightpadding-right:0.2em


  2. ^ abcdefg Lide, David R., ed. (2009). CRC Handbook of Chemistry and Physics (90th ed.). Boca Raton, Florida: CRC Press. ISBN 978-1-4200-9084-0.


  3. ^ abc Comey, Arthur Messinger; Hahn, Dorothy A. (February 1921). A Dictionary of Chemical Solubilities: Inorganic (2nd ed.). New York: The MacMillan Company. p. 433.


  4. ^ Fakouri 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. ISSN 0360-3199.


  5. ^ abcd Ling, Yichuan; Wheeler, Damon A.; Zhang, Jin Zhong; Li, Yat (2013). Zhai, Tianyou; Yao, Jiannian, eds. One-Dimensional Nanostructures: Principles and Applications. John Wiley & Sons, Inc. Hoboken, New Jersey: John Wiley & Sons, Inc. p. 167. ISBN 978-1-118-07191-5.


  6. ^ abcd Vujtek, Milan; Zboril, Radek; Kubinek, Roman; Mashlan, Miroslav. "Ultrafine Particles of Iron(III) Oxides by View of AFM – Novel Route for Study of Polymorphism in Nano-world" (PDF). Univerzity Palackého. Czech. Retrieved 2014-07-12.


  7. ^ abc Sigma-Aldrich Co., Iron(III) oxide. Retrieved on 2014-07-12.


  8. ^ abc NIOSH Pocket Guide to Chemical Hazards. "#0344". National Institute for Occupational Safety and Health (NIOSH).


  9. ^ Greedan, J. E. (1994). "Magnetic oxides". In King, R. Bruce. Encyclopedia of Inorganic chemistry. New York: John Wiley & Sons. ISBN 978-0-471-93620-6.


  10. ^ abc .Housecroft, Catherine E.; Sharpe, Alan G. (2008). "Chapter 22: d-block metal chemistry: the first row elements". Inorganic Chemistry (3rd ed.). Pearson. p. 716. ISBN 978-0-13-175553-6.


  11. ^ 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


  12. ^ Adlam; Price (1945). Higher School Certificate Inorganic Chemistry. Leslie Slater Price.


  13. ^ abc Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY. Vol. 1. p. 1661.


  14. ^ ab Greenwood, N. N.; Earnshaw, A. (1997). Chemistry of the Element (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 978-0-7506-3365-9.


  15. ^ Paint and Surface Coatings: Theory and Practice. William Andrew Inc. 1999. ISBN 978-1-884207-73-0.


  16. ^ Banerjee, Avijit (2011). Pickard's Manual of Operative Dentistry. United States: Oxford University Press Inc., New York. p. 89. ISBN 978-0-19-957915-0.


  17. ^ S.N. Piramanayagam, J. Appl. Phys. 102, 011301 (2007).


  18. ^ ab Kay, A., Cesar, I. and Grätzel, M., J. Am. Chem. Soc. 2006, 128, 15714-15721


  19. ^ Kennedy, J.H. and Frese, K.W., J. Electrochem. Soc. 1978, 125, 709-714


  20. ^ Le Formal, F. et al., J. Am. Chem. Soc. 2014, 136, 2564-2574


  21. ^ Zhong, D.K. and Gamelin, D.R., J. Am. Chem. Soc. 2010, 132, 4202-4207


  22. ^ Emery, J.D. et al., ACS Appl. Mater. Interfaces 2014, 6, 21894-21900




External links


Iron(III) oxide

Haematite unit cell

Sample of iron(III) oxide

Pourbaix Diagram of aqueous Iron
Names

IUPAC name
Iron(III) oxide

Other names
ferric oxide, hematite, ferric iron, red iron oxide, rouge, maghemite, colcothar, iron sesquioxide, rust, ochre

Identifiers

CAS Number



  • 1309-37-1 ☑Y


3D model (JSmol)


  • Interactive image


ChEBI


  • CHEBI:50819 ☑Y


ChemSpider


  • 14147 ☒N


ECHA InfoCard

100.013.790

EC Number
215-168-2

E number
E172(ii) (colours)

Gmelin Reference

11092

KEGG


  • C19424 ☒N



PubChem CID


  • 518696


RTECS number
NO7400000

UNII


  • 1K09F3G675 ☑Y





Properties

Chemical formula


Fe2O3

Molar mass

7002159687000000000♠159.687 g·mol−1
Appearance
Red-brown solid

Odor
Odorless

Density
5.242 g/cm3[1]

Melting point
 1,539–1,565 °C (2,802–2,849 °F; 1,812–1,838 K)[2]
decomposes[1]
105 °C (221 °F; 378 K)
β-dihydrate, decomposes
150 °C (302 °F; 423 K)
β-monohydrate, decomposes
50 °C (122 °F; 323 K)
α-dihydrate, decomposes
92 °C (198 °F; 365 K)
α-monohydrate, decomposes[3]

Solubility in water

Insoluble

Solubility
Soluble in diluted acids,[2]sugar solution
Trihydrate slightly soluble in aq. tartaric acid, citric acid, CH3COOH[3]


Magnetic susceptibility (χ)

+3586.0·10−6 cm3/mol
Structure

Crystal structure


Rhombohedral, hR30 (α-form)[5]
Cubic bixbyite, cI80 (β-form)
Cubic spinel (γ-form)
Orthorhombic (ε-form)[6]

Space group

R3c, No. 161 (α-form)[5]
Ia3, No. 206 (β-form)
Pna21, No. 33 (ε-form)[6]

Point group

3m (α-form)[5]
2/m 3 (β-form)
mm2 (ε-form)[6]

Coordination geometry


Octahedral (Fe3+, α-form, β-form)[5]
Thermochemistry


Heat capacity (C)

103.9 J/mol·K[2]


Std molar
entropy (So298)

87.4 J/mol·K[2]


Std enthalpy of
formation (ΔfHo298)

−824.2 kJ/mol[2]


Gibbs free energy (ΔfG˚)

−742.2 kJ/mol[2]
Hazards

GHS pictograms

The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)[7]

GHS signal word
Warning

GHS hazard statements


H315, H319, H335[7]

GHS precautionary statements


P261, P305+351+338[7]

NFPA 704


[1]



Flammability code 0: Will not burn. E.g., waterHealth code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chlorideReactivity code 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g., calciumSpecial hazard OX: Oxidizer. E.g., potassium perchlorateNFPA 704 four-colored diamond

0


0


1

OX





Threshold limit value

5 mg/m3[2] (TWA)
Lethal dose or concentration (LD, LC):


LD50 (median dose)

10 g/kg (rats, oral)[1]
US health exposure limits (NIOSH):


PEL (Permissible)

TWA 10 mg/m3[8]


REL (Recommended)

TWA 5 mg/m3[8]


IDLH (Immediate danger)

2500 mg/m3[8]
Related compounds

Other anions


Iron(III) fluoride

Other cations


Manganese(III) oxide
Cobalt(III) oxide

Related iron oxides


Iron(II) oxide
Iron(II,III) oxide

Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).


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Infobox references




  • NIOSH Pocket Guide to Chemical Hazards









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