Iron oxide
Altogether there are 16 known iron oxides (Cornell and Schwertmann, 2003).
These compounds are either oxides (Hematite, Magnetite, Maghemite, β-Fe2O3, ε-Fe2O3, Wüstite), or hydroxides and oxdide-hydroxides (Goethite, Lepidocrocite, Akageneite, Schwertmannite, Feroxyhyte, δ-FeOOH, high pressure FeOOH, Ferrihydrite, Bernalite, Fe(OH)2, green rusts).
Some of these oxides are used in ceramic applications, particularly in glazing. Iron oxides, along with oxides of other metals, provide the colours in some glazes after being fired at a high temperature. They are also used as pigments (see Category:Iron oxide pigments).
Iron oxides
- Iron(II) oxide or ferrous oxide (FeO) The black-coloured powder in particular can cause explosions as it readily ignites.
- Iron(III) oxide or ferric oxide (Fe2O3) known in its natural state as hematite (also 'haematite'), but also purified for use as a coating in magnetic audio and computer media, where it is known as ferric oxide. Also known as rouge. This is the form of iron oxide most commonly seen on corroded iron and steel structures ranging from bridges to automobile bodies, and is extraordinarily destructive.
- Iron(II,III) oxide or ferrous ferric oxide (Fe3O4), better known as the black-coloured mineral magnetite or lodestone also seen on Mars. Also a main source of iron, magnetite is an iron ore. This form of iron oxide tends to occur when iron corrodes underwater, and so is often found inside tanks or below the waterline of ships.
Iron hydroxides
- Iron(II) hydroxide Fe(OH)2. green colour.
- Iron(III) oxide-hydroxide FeO(OH) found as the mineral goethite. Red-brown colour. Also found as the minerals siderogel, limonite and feroxyhyte. There is a variant known as lepidocrocite.
- Iron(III) hydroxide Fe(OH)3. Dark brown.
There are also several other variants.
References
- Cornell, RM and Schwertmann, U. "The Iron oxides: structure, properties, reactions, occurences and uses", Wiley VCH, 2003. ISBN 3527302743