Chromium, a silvery-white metallic element. It was named from the Greek word chroma, meaning color, because of the variety of colors of chromium compounds. It is an important constituent of alloy steels and has many other industrial uses. Chromium has a bright sheen and takes a high polish. Because it does not tarnish or corrode easily, it is a valuable plating for other metals.
The most important use of chromium is in the steel industry. Stainless steels are alloys containing approximately 10 to 25 per cent chromium, making them resistant to corrosion. Chrome steel, or chromium steel, is a hard steel containing about one per cent chromium. Much of the chrome trim on automobiles is chromium-plated steel, but stainless steels and aluminum are also used for that purpose. Chromite, an oxide of iron and chromium, is used to make refractory bricks for high-temperature furnaces. Stellite, an alloy consisting primarily of cobalt, chromium, and tungsten, is used in high-speed cutting tools. Nichrome, an alloy of nickel, iron, and chromium, is used for electric heating coils.
Many pigments, including chrome yellow, chrome green, chrome red, and chrome orange, are made from chromium compounds. They are used in staining glass, in glazing porcelain, and as paint pigments. Chromium compounds are also used in tanning leather, dyeing textiles, preserving wood, and treating metals for manufacture.
The chief ore of chromium is chromite. Leading producers of chromite are South Africa, Kazakhstan, India, Albania, Turkey, Zimbabwe, and Finland. Chromium was discovered in 1797 by Louis Vauquelin, a French chemist.
Symbol: Cr. Atomic number: 24. Atomic weight: 51.996. Specific gravity: 7.19. Melting point: 3,375 F. (1,857 C.). Boiling point: 4,842 F. (2,672 C.). Chromium has four stable isotopes: Cr-50, Cr-52, Cr-53, and Cr-54. Chromium belongs to Group VI-B of the Periodic Table and may have a valence of +2, 3, or 6.