Iron(II) oxide

Iron(II) oxide, or wüstite, is an inorganic compound with the formula FeO, containing iron in the +2 oxidation state. Its crystal structure is related to rock salt, and its actual composition is often slightly iron-deficient.

Iron: A metallic chemical element with symbol Fe and atomic number 26. Iron supplies the metal ions whose +2 state defines FeO.
Wüstite nonstoichiometry: The iron deficiency and charge-compensating defects found in wüstite, commonly written Fe₁₋ₓO. Most wüstite departs from the ideal one-to-one FeO formula.
Blast furnace: A tall industrial furnace that produces molten iron by reducing iron ore with carbon-rich fuel. FeO occurs during the sequence of iron-ore reduction inside the furnace.
Wüstite: A naturally occurring, iron-deficient iron oxide with a rock-salt-related structure, commonly approximated by FeO. Wüstite is the mineral name most closely associated with iron(II) oxide.
Oxygen: A chemical element with symbol O and atomic number 8, commonly forming oxide ions in solids. Oxygen forms the oxide sublattice in FeO.
Iron vacancy: A point defect formed when an iron atom is absent from its expected site in a crystal lattice. Iron vacancies are central to wüstite’s iron-deficient composition.
Direct reduced iron: Iron produced from ore in the solid state by reducing gases or carbon, without melting the ore. FeO is one oxide stage that must be reduced to make metallic iron.
Iron–oxygen phase diagram: A diagram showing stable phases and phase boundaries as iron–oxygen composition and temperature vary. It places wüstite’s stability among other iron oxides and metallic iron.
Oxidation state: A bookkeeping value representing an atom’s assigned charge in a compound under specified bonding conventions. The +2 oxidation state distinguishes FeO from iron oxides containing Fe(III).
Point defect: A localized imperfection in a crystal, such as a vacancy, interstitial atom, or substitutional impurity. Wüstite’s composition and charge balance arise from interacting lattice defects.

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