Iron(III) oxide

Iron(III) oxide

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 (Jmol)	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	518696
RTECS number	NO7400000
UNII	1K09F3G675 Y
InChI InChI=1S/2Fe.3O Y[inchi] Key: JEIPFZHSYJVQDO-UHFFFAOYSA-N Y[inchi] InChI=1/2Fe.3O/rFe2O3/c3-1-4-2(3)5-1 Key: JEIPFZHSYJVQDO-ZVGCCQCPAC
SMILES O1[Fe]2O[Fe]1O2
Properties
Chemical formula	Fe2O3
Molar mass	159.69 g·mol−1
Appearance	Red-brown solid
Odor	Odorless
Density	5.242 g/cm3
Melting point	1,539–1,565 °C (2,802–2,849 °F; 1,812–1,838 K) decomposes 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
Solubility in water	Insoluble
Solubility	Soluble in diluted acids,sugar solution Trihydrate slightly soluble in aq. tartaric acid, citric acid, CH3COOH
Magnetic susceptibility (χ)	+3586.0·10−6 cm3/mol
Structure
Crystal structure	Rhombohedral, hR30 (α-form) Cubic bixbyite, cI80 (β-form) Cubic spinel (γ-form) Orthorhombic (ε-form)
Space group	R3c, No. 161 (α-form) Ia3, No. 206 (β-form) Pna21, No. 33 (ε-form)
Point group	3m (α-form) 2/m 3 (β-form) mm2 (ε-form)
Coordination geometry	Octahedral (Fe3+, α-form, β-form)
Thermochemistry
Specific heat capacity (C)	103.9 J/mol·K
Std molar entropy (So298)	87.4 J/mol·K
Std enthalpy of formation (ΔfHo298)	−824.2 kJ/mol
Gibbs free energy (ΔfG˚)	−742.2 kJ/mol
Hazards
GHS pictograms
GHS signal word	Warning
GHS hazard statements	H315, H319, H335
GHS precautionary statements	P261, P305+351+338
EU classification (DSD)	Xi
R-phrases	R36/37/38
S-phrases	S26
NFPA 704	0 0 0
Threshold limit value	5 mg/m3 (TWA)
Lethal dose or concentration (LD, LC):
LD50 (median dose)	10 g/kg (rats, oral)
US health exposure limits (NIOSH):
PEL (Permissible)	TWA 10 mg/m3
REL (Recommended)	TWA 5 mg/m3
IDLH (Immediate danger)	2500 mg/m3
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).
N  (what is YN ?)
Infobox references

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 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.

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.

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. 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.