Metalloxids

Metalloxids, or metal oxides, are inorganic compounds composed of oxygen and one or more metal elements. Their general formula is not fixed; binary oxides have the formula MxOy, and mixed or doped oxides extend this family. They occur widely in minerals and are synthesized industrially by direct oxidation of metals, calcination of metal carbonates or hydroxides, or precipitation of metal salts followed by heat treatment.

Structure and properties: Most metal oxides form ionic solids with a lattice of metal cations and oxide anions. The resulting properties span a wide range: many oxides are high-melting, hard insulators (alumina, magnesia), while others are semiconductors (tin oxide, zinc oxide, titanium dioxide) and some act as electrical conductors in thin films. Structures vary from rock-salt (NaCl-type) for simple oxides to corundum, rutile, perovskite, spinel, and layered frameworks. Oxide surfaces exhibit basic to amphoteric behavior: basic oxides react with acids to give salts; amphoteric oxides such as Al2O3 and ZnO react with both acids and bases.

Applications: Metal oxides are essential in ceramics, pigments and catalysts. TiO2 and V2O5 are used in catalysis and photocatalysis; Fe2O3 and TiO2 are common pigments; Al2O3 and ZrO2 are structural ceramics and refractories. In electronics and sensors, ZnO and SnO2 serve as wide-bandgap semiconductors; some oxides form perovskites used in solar cells. Oxides also play a major role in energy storage and conversion, for example lithium metal oxides in rechargeable batteries and oxide catalysts in fuel cells.

Safety and environment: Some metal oxides pose inhalation hazards; certain oxides containing Cr(VI) or other toxic metals are restricted. Overall, metal oxides are stable and diverse in use.