Iron(II,III) oxide, also known as ferrous ferric oxide, black iron oxide, or mineral magnetiteis an iron oxide with the chemical formula Fe3O4.
Magnitite can be calcinated in air to yield iron(III) oxide:
- 2Fe3O4 + ½ O2 → 3 Fe2O3
Iron(II,III) oxide is a black compound, insoluble in water. It is ferrimagnetic and an electrical conductor.
Black iron oxide is available as pigment in pottery shops and can be cheaply purchased.
There are several ways to prepare magnetite. One method involves the reduction of nitrobenzene with iron and water, in the presence of iron(II) chloride, process that reduces the nitrobenzene to aniline. It can also be done by precipitating iron(II) salts as hydroxides, then carefully oxidizing the resulting iron(II) hydroxide at controlled pH.
Black iron oxide can also be prepared by oxidizing iron(II) hydroxide with water, in an oxygen-free medium.
- 3 Fe(OH)2 → Fe3O4 + H2 + 2 H2O
This process is known as Schikorr reaction.
Another method of producing this oxide is burning iron wire in oxygen.
- 3 Fe + 2 O2 → Fe3O4
This reaction may also give other iron oxides.
Black iron oxide is not particularly toxic, unless large amounts are consumed. Inhalation of finely powdered magnetite may lead to lung conditions.
It should be stored in closed containers, away from acidic vapors.
As iron(II,III) oxide occurs naturally, it is not harmful to the environment and can be useful as an iron supplement for soil.