Manganese - chemistry.

Manganese - chemistry. I INTRODUCTION Manganese, symbol Mn, silvery white, brittle metallic element used principally in making alloys. Manganese is one of the transition elements of the periodic table (see Periodic Law). The atomic number of manganese is 25. II PROPERTIES AND OCCURRENCE Manganese was first isolated in 1774 by the Swedish chemist Johan Gottlieb Gahn. Manganese metal corrodes in moist air and dissolves in acid. The element melts at 1245°C (2271°F), boils at 2061°C (3742°F), and has a specific gravity of 7.4. Its atomic weight is 54.938. Manganese does not occur in the free state, except in meteors, but is widely distributed over the world in the form of ores, such as pyrolusite, rhodochrosite, franklinite, psilomelane, and manganite. The principal ore is pyrolusite. The element's name comes from the Latin word magnes, "magnet" and was chosen because pyrolusite is magnetic. Manganese ranks about 12th in abundance among elements in Earth's crust. Ukraine, Georgia, and South Africa are important producers of manganese. III USES Manganese is used principally in the form of alloys with iron, obtained by treating pyrolusite in a blast furnace with iron ore and carbon. The most important of these alloys, which are used in steelmaking, are ferromanganese, containing about 78 percent manganese, and spiegeleisen, containing from 12 to 33 percent manganese. Small amounts of manganese are added to steel as a deoxidizer; large amounts are used to produce a very tough alloy, resistant to wear. Safes, for example, are made of manganese steel containing about 12 percent manganese. Nonferrous manganese alloys include manganese bronze (composed of manganese, copper, tin, and zinc), which resists corrosion from seawater and is used for propeller blades on boats and torpedoes, and manganin (containing manganese, copper, and nickel), used in the form of wire for accurate electrical measurements because its electrical conductivity does not vary appreciably with temperature. See also Iron and Steel Manufacture. Manganese commonly forms compounds in which its valence is 2, 3, 4, 6, or 7. Manganese dioxide (MnO2) occurs natively as pyrolusite and is prepared artificially by heating manganese nitrate; it is used in dry-cell batteries as a depolarizer, in paint and varnish oils, for coloring glass and ceramics, and in preparing chlorine and iodine. Manganese sulfate (MnSO4), a pink crystalline solid, is prepared by the action of sulfuric acid on manganese dioxide and is used in dyeing cotton. Sodium and potassium permanganate (NaMnO4 and KMnO4) are dark purple crystals, formed by the oxidation of acidified manganese salts, which are used as oxidizers and disinfectants. Microsoft ® Encarta ® 2009. © 1993-2008 Microsoft Corporation. All rights reserved.