ironIIoxo

Iron(II) oxide, commonly called ferrous oxide, is a binary oxide of iron with the chemical formula FeO. In nature it occurs as the mineral wüstite and is best described as a non-stoichiometric solid, often written as Fe1−xO, with iron vacancies and lattice defects. It adopts a rock-salt crystal structure and is typically a black or dark brown powder.

FeO is stable only under reducing conditions or at high temperatures; in air it readily oxidizes to iron(II,III) oxide (Fe3O4) or iron(III) oxide (Fe2O3). In industrial and geological settings, FeO can be produced transiently during the direct reduction of iron oxides and is commonly formed by reducing Fe2O3 with carbon monoxide or hydrogen at elevated temperatures. It can also be generated in laboratory preparations by controlled reduction of iron(III) salts or oxides under carefully maintained atmospheres.

Physical properties of FeO include a high melting point (around 1370–1400 °C) and a density near 5.7 g/cm3. It is insoluble in water and exhibits magnetic order that is temperature-dependent: it is antiferromagnetic below about 198 K and behaves as a paramagnet at higher temperatures. The compound is chemically reactive with acids, yielding iron(II) salts and water.

Applications of FeO are mostly as a chemical intermediate and research material rather than a primary industrial product. It serves as a precursor to ferrites and other iron oxides and is of interest in studies of non-stoichiometry, magnetism, and catalysis. Safety considerations are modest; as a fine iron oxide, it may pose inhalation hazards in powder form, and handling should follow standard inorganic oxide precautions.