Matter & Energy


Matter is composed of atoms or groups of atoms called molecules. The arrangement of particles in a material depends on the physical state of the substance. In a solid, particles form a compact structure that resists flow. Particles in a liquid have more energy than those in a solid. They can flow past one another, but they remain close. Particles in a gas have the most energy. They move rapidly and are separated from one another by relatively large distances.

Manganese

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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.

PROPERTIES AND OCCURRENCE

Manganese was first distinguished as an element in 1774 by the Swedish chemist Johan Gottlieb Gahn. Manganese metal corrodes in moist air and dissolves in acid. Manganese melts at about 1245° C (about 2271° F), boils at about 1962° C (about 3564° F), and has a specific gravity of 7.2; the atomic weight of manganese is 54.938.

Pure manganese is obtained by igniting pyrolusite (manganese dioxide) with aluminum powder or by electrolyzing manganese sulfate. The metal does not occur in the free state, except in meteors, but is widely distributed over the world in the form of ores, such as rhodochrosite, franklinite, psilomelane, and manganite. It ranks about 12th in abundance among elements in the earth's crust. The principal ore of manganese is pyrolusite.

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.

Manganese commonly forms compounds in which its valence is 2, 3, 4, 6, or 7. Manganese dioxide 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, 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 are dark purple crystals, formed by the oxidation of acidified manganese salts, which are used as oxidizers and disinfectants.