Chromium Cr

Discovery

In the eighteenth century a striking orange-red mineral from the Beryozovsky mines in the Urals, known as Siberian red lead, attracted the attention of European chemists. It is now called crocoite, lead chromate.

In 1797 the French chemist Louis-Nicolas Vauquelin treated the mineral with acid and obtained a new oxide. The following year, 1798, he heated it with charcoal and isolated the metal itself. He also detected chromium in rubies and emeralds, explaining their colours. Around the same time Martin Heinrich Klaproth and Tobias Lowitz independently studied the mineral.

Chromium found its first big market in pigments during the nineteenth century, and in the twentieth century stainless steel, invented in the 1910s, and electroplating turned it into a major industrial metal.

Origin of the name

The name comes from the Greek chroma, meaning colour, because chromium compounds display so many vivid colours: yellow chromates, orange dichromates, green chromium oxide and more. The symbol is Cr.

Main uses

• Stainless steel: steel containing at least about 10.5 percent chromium forms a self-healing oxide film that prevents rust. This is by far the largest use of chromium.
• Plating: a thin chromium coating gives taps, car trim and tools a bright, hard, corrosion-resistant finish.
• Superalloys: nickel–chromium alloys withstand high temperatures in jet engines and heating elements.
• Leather: chromium(III) salts are widely used to tan leather.
• Pigments and refractories: chromium oxide green is a stable pigment, and chromite bricks line furnaces.

Isotopes

Chromium has four stable isotopes: chromium-50, chromium-52 (about 84 percent), chromium-53 and chromium-54. Variations in chromium-53, produced by the decay of manganese-53, help date the formation of meteorites in the early solar system. The radioactive chromium-51, with a half-life of about 28 days, has been used in medicine to label red blood cells and measure their lifespan and volume.

In everyday life

Chromium's safety depends strongly on its chemical form. Chromium(III), found in foods such as whole grains and broccoli, is generally considered a trace nutrient involved in glucose metabolism, though its exact role is debated. Chromium(VI) compounds, used in some industrial processes, are toxic and carcinogenic when inhaled or ingested, and their use is tightly regulated.

Stainless steel cutlery, sinks and cookware are the most familiar chromium products in the home.