Chromia

Chromia is a common name for chromium(III) oxide, with the chemical formula Cr2O3, and it also refers to related materials in chemistry, geology, and industry. In chemistry, chromia denotes the oxide Cr2O3, a hard, green solid that is thermally stable and chemically resistant. It occurs naturally as the mineral eskolaite, Cr2O3, a rare oxide mineral named after Finnish geologist Kaj Eskola. Eskolaite is found in certain ultramafic and metamorphic rocks and typically occurs only in trace amounts within rock matrices.

Chromia has a corundum-like, hexagonal crystal structure. It is insoluble in water and is only slowly attacked by strong acids, with Cr3+ as the common oxidation state under ambient conditions. The oxide can form protective scales on chromium-containing alloys at high temperatures, contributing to oxidation resistance in harsh environments.

Industrial uses include its role as a pigment, known as chromia green, used in paints, ceramics, and glass due to its stability and distinct green coloration. It is also employed as a pigment in glazes and as a colorant in specialty glasses. In metallurgy and catalysis, chromia serves as a component of protective oxide layers on alloys and as a support material in chromia-alumina catalysts used in various hydrocarbon processing reactions.

Safety and regulatory notes reflect the broader chromium chemistry: many chromium compounds, particularly those in the hexavalent state (Cr(VI)), are hazardous, while Cr2O3 and Cr(III) pigments are generally less toxic but still require standard occupational hygiene controls.

See also: chromium oxide, eskolaite, chromite, chromium pigments.