Chromated

Chromated describes a material or surface that has been treated with chromate-containing compounds, or that contains chromate species such as the chromate anion CrO4^2−. In chemistry and materials science, chromated items may involve pigments, catalysts, or additives where chromate ligands are present. In metal finishing, chromate conversion coatings are widely used to improve corrosion resistance and paint adhesion on metals.

Chromate conversion coatings are formed by applying a solution containing chromium compounds to metal surfaces such as aluminum, zinc, magnesium, and steel. The coating is a thin film of chromium oxide or hydroxide with incorporated chromate species, which enhances corrosion protection and primer adhesion. On aluminum, commercial processes like Alodine or Iridite yield protective coatings that range in color from yellow to olive-drab, depending on the chemistry and substrate. Similar coatings on zinc and magnesium follow the same principles, while on steel they provide a baseline for protective primers. The resulting films are typically very thin, often measured in micrometers.

Health and regulatory aspects: Chromium(VI) compounds are toxic and carcinogenic, leading to strict regulations in many countries. Consequently, the industry has increasingly adopted chromium(III)-based conversion coatings or non-chromate alternatives to reduce environmental and health risks, although chromium(VI) coatings remain in use in certain aerospace, military, and automotive applications under controlled conditions.

Other uses: The term can also apply to materials containing chromate ions, and historically to chromated wood preservatives such as chromated copper arsenate (CCA). Modern practices have largely moved away from these formulations due to safety concerns.