chromium

Chromium is a chemical element with the symbol Cr and atomic number 24. It is a hard, steely-grey transition metal known for its high melting point, good strength, and, most notably, exceptional resistance to corrosion due to a stable oxide film that forms on its surface.

In nature, chromium occurs primarily in chromite ore (FeCr2O4). Major producers include South Africa, Kazakhstan, India, Turkey, and Russia. Commercial chromium is obtained by mining chromite and refining it through smelting and reduction to produce metallic chromium, which is then used directly or alloyed and processed for various applications.

Chromium exhibits several oxidation states, with Cr(III) and Cr(VI) being the most important in compounds. Cr(III) compounds are relatively stable and are considered essential trace elements in many organisms, implicated in metabolic processes. Cr(VI) compounds are highly toxic and carcinogenic, requiring careful handling and strict regulatory controls.

The principal uses of chromium are as an alloying element in stainless steels, where chromium imparts corrosion resistance and strength (often 10–20% Cr). It is also used in electroplating to improve wear and corrosion resistance, and in various pigments and catalysts. Chromium salts are employed in leather tanning and in some chemical syntheses.

Safety and environmental concerns surround chromium chemistry, particularly for Cr(VI) compounds, which pose health risks upon exposure. Managing occupational exposure and preventing environmental release are central considerations in chromium production and use.