vanadium (vənāˈdēəm) [key], metallic chemical element; symbol V; at. no. 23; at. wt. 50.9415; m.p. about 1,890°C; b.p. 3,380°C; sp. gr. about 6 at 20°C; valence +2, +3, +4, or +5. Vanadium is a soft, ductile, silver-grey metal. It is the element above niobium in Group 5 of the periodic table. In its properties it resembles chromium. It is corrosion resistant at normal temperatures, but oxidizes above 660°C. It resists attack by hydrochloric and sulfuric acids, saltwater, or alkalies. Vanadium forms numerous compounds, including vanadates and complex organic compounds. Vanadium pentoxide, V2O5, is commercially important. Vanadium is not found uncombined in nature but occurs widely distributed in minerals. Important ores include carnotite, patronite, roscoelite, and vanadinite. In the United States vanadium ores are mined in Arizona, Colorado, and Utah; other sources are Peru and Africa. Vanadium is recovered from these ores largely as the pentoxide; the pentoxide is also recovered during phosphorus production in Idaho and from certain crude oils and petroleum ashes. The principal use of vanadium is in alloys, especially with steel. In tool and spring steels it is a powerful alloying agent; a small amount (less than 1%) adds strength, toughness, and heat resistance. It is usually added in the form of ferrovanadium, a vanadium-iron alloy. Vanadium compounds, especially the pentoxide, are used in the ceramics, glass, and dye industries, and are important as catalysts in the chemical industry. Although high-purity vanadium metal can be produced by chemical reduction of the trichloride, most commercial production of the metal is by calcium reduction of the pentoxide. Vanadium was discovered in 1801 by A. M. del Rio, who called it erythronium; however, it was mistaken for impure chromium. The element was rediscovered and named in 1830 by N. G. Sefström, a Swedish chemist. It was first isolated in 1867 by H. E. Roscoe.