Iron(III) oxide

Iron(III) oxide
Pure Hematite
General
Other names	Ferric oxide Hematite
Molecular formula	Fe2O3
Molar mass	159.69 g/mol
Appearance	red-brown solid
CAS number	1317-60-8 [1309-37-1] [1309-37-1] (Iron Oxide Red)]
Properties
Density and phase	5.24 g/cm3, solid
Solubility in water	insoluble
Melting point	1565 °C decomp.
Structure
Coordination geometry	?
Crystal structure	?
Thermodynamic data
Std enthalpy of formation ΔfHo298	−825.50 kJ/mol
Standard molar entropy So298	87 J·K−1·mol−1
Hazards
MSDS	External MSDS
EU classification	not listed
Flash point	non-flammable
Supplementary data page
Structure and properties	n, εr, etc.
Thermodynamic data	Phase behaviour Solid, liquid, gas
Spectral data	UV, IR, NMR, MS
Related compounds
Other anions	Iron(II) sulfide
Other cations	Iron(II) oxide Iron(II,III) oxide Ruthenium(IV) oxide Osmium(IV) oxide
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) Infobox disclaimer and references

Iron(III) oxide — also known as ferric oxide, Hematite, red iron oxide, synthetic maghemite, colcothar, or simply rust — is one of several oxide compounds of iron, and has ferromagnetic properties. Its chemical formula is Fe₂O₃.

Different forms

The mineral form of ferric oxide is hematite; it is mined as the main ore of iron.

Iron(III) oxide is often used in magnetic storage, for example in the magnetic layer of floppy disks. These consist of a thin sheet of PET film, coated with iron(III) oxide. The particles can be magnetised to represent binary data. MICR (Magnetic Ink Character Recognition) also uses iron(III) oxide compounds, suspended in an ink which can be read by special scanning hardware.

A very fine powder of ferric oxide is known as jeweller's rouge, red rouge, or simply rouge. It is used to put the final polish on metallic jewellery and lenses, and historically as a cosmetic.

Rouge cuts slower 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.

Uses

Iron(III) oxide is used in the production of pure iron in a blast furnace. Iron(III) oxide is also used in an extremely exothermic reaction called a thermite reaction.

2 Al + Fe₂O₃ → 2 Fe + Al₂O₃

Iron(III) oxide is also used as a pigment, under names Pigment Black 11, Pigment Brown 6, Pigment Brown 7, and Pigment Red 101 (also Iron Oxide Red). Some of them, eg. Pigment Red 101 and Pigment Brown 6, are Food and Drug Administration (FDA)-approved for use in cosmetics.

See also

• Iron oxides
• Iron(II) oxide
• Magnetite (Iron(II,III) oxide)
• Red ochre
• Rust

General references

N. N. Greenwood, A. Earnshaw, Chemistry of the Elements, Pergamon Press, 1984.

External links

• NIOSH Pocket Guide to Chemical Hazards