Fémoxid

Fémoxid, or metal oxide, is a compound consisting of metal elements combined with oxygen. They form when metals react with oxygen under suitable conditions and encompass a wide range of stoichiometries and crystal structures. The oxide anion is typically O2− and the metal cation can adopt multiple oxidation states, which leads to non-stoichiometric oxides such as magnetite Fe3O4, where iron exists in mixed valence states.

Most metal oxides are ionic solids with high melting points and are relatively insoluble in water. Their properties vary with composition: many basic oxides (like Fe2O3) react with acids, while some are amphoteric (like Al2O3) and can react with both acids and bases. Common crystal structures include rock-salt, corundum, rutile, and spinel types.

Representative examples are aluminum oxide Al2O3, iron oxides Fe2O3 and Fe3O4, zinc oxide ZnO, titanium dioxide TiO2, copper oxides CuO/Cu2O, nickel oxide NiO, and chromium oxide Cr2O3. Metal oxides have wide-ranging applications: iron oxide pigments for paints; TiO2 as a white pigment and photocatalyst; ZnO and SnO2 in electronics and gas sensors; Al2O3 and MgO in refractories; transition-metal oxides in batteries, such as layered LiCoO2 and LiMn2O4.

Preparation methods include direct oxidation of metals at high temperature, roasting of sulfides or carbonates, precipitation from metal salts followed by calcination, and sol-gel or hydrothermal synthesis.

Safety and handling: many metal-oxide powders pose inhalation hazards; dusts may be irritants or toxic in certain forms. Proper ventilation and protective equipment are advised when handling fine oxides.