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Ferric oxide

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
1309-37-1 YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:50819 YesY
ChemSpider 14147 N
ECHA InfoCard 100.013.790
EC Number 215-168-2
E number E172(ii) (colours)
11092
KEGG C19424 N
PubChem 518696
RTECS number NO7400000
UNII 1K09F3G675 YesY
Properties
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
Insoluble
Solubility Soluble in diluted acids,sugar solution
Trihydrate slightly soluble in aq. tartaric acid, citric acid, CH3COOH
+3586.0·10−6 cm3/mol
Structure
Rhombohedral, hR30 (α-form)
Cubic bixbyite, cI80 (β-form)
Cubic spinel (γ-form)
Orthorhombic (ε-form)
R3c, No. 161 (α-form)
Ia3, No. 206 (β-form)
Pna21, No. 33 (ε-form)
3m (α-form)
2/m 3 (β-form)
mm2 (ε-form)
Octahedral (Fe3+, α-form, β-form)
Thermochemistry
103.9 J/mol·K
87.4 J/mol·K
−824.2 kJ/mol
−742.2 kJ/mol
Hazards
GHS pictograms The exclamation-mark pictogram in the Globally Harmonized System of Classification and Labelling of Chemicals (GHS)
GHS signal word Warning
H315, H319, H335
P261, P305+351+338
Irritant Xi
R-phrases R36/37/38
S-phrases S26
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
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 YesYN ?)
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.


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