Iron(III) oxide
Iron(III) oxide, also known as ferric oxide or rust, is an inorganic compound with the chemical formula Fe2O3. It is one of several iron oxides, the most common being FeO (iron(II) oxide) and Fe3O4 (iron(II,III) oxide or magnetite). Iron(III) oxide is a red to reddish-brown solid and is the main component of rust, the reddish coating formed when iron or steel is exposed to oxygen and moisture.
Properties:
- Chemical Formula: Fe2O3
- Molar Mass: 159.69 g/mol
- Appearance: Red to reddish-brown solid (powder or crystalline)
- Melting Point: 1,565 °C (2,849 °F; 1,838 K)
- Boiling Point: Decomposes
- Density: 5.24 g/cm³
- Solubility: Insoluble in water, slightly soluble in acids.
Forms (Polymorphs):
Iron(III) oxide exists in several polymorphs, including:
- α-Fe2O3 (Hematite): The most common and thermodynamically stable form. It has a rhombohedral crystal structure and exhibits weak ferromagnetism. Hematite is a significant iron ore.
- γ-Fe2O3 (Maghemite): A metastable polymorph with a spinel structure. It is ferrimagnetic and used in magnetic recording media.
- β-Fe2O3: A less common polymorph that is metastable and transforms to hematite at high temperatures.
- ε-Fe2O3: Exhibiting very strong coercive field.
Occurrence and Production:
Iron(III) oxide occurs naturally as the mineral hematite. It is also produced industrially through various processes, including:
- Thermal decomposition of iron compounds: For example, heating iron(II) sulfate (FeSO4).
- Precipitation from iron solutions: By adding a base to a solution containing iron(III) ions.
- Oxidation of iron metal: Through controlled rusting.
Uses:
Iron(III) oxide has a wide range of applications, including:
- Pigment: Used as a pigment in paints, coatings, plastics, and ceramics, providing a red, brown, or yellow color depending on the particle size and hydration state. It is also used as a pigment in cosmetics.
- Iron Ore: The primary ore used in the production of iron and steel.
- Catalyst: Used as a catalyst in various chemical reactions.
- Magnetic Recording Media: Maghemite (γ-Fe2O3) is used in magnetic tapes and disks.
- Polishing Compound: Used as a polishing compound for metals and glass.
- Thermite: A component of thermite, a pyrotechnic composition used in welding, cutting, and incendiary devices.
Safety:
Iron(III) oxide is generally considered non-toxic, but inhalation of fine dust may cause irritation of the respiratory tract. Prolonged exposure to high concentrations of dust may lead to pneumoconiosis (siderosis).