indium

indium (ĭn`dēəm), a metallic chemical element; symbol In; at. no. 49; at. wt. 114.82; m.p. 156.6°C;; b.p. about 2,080°C;; sp. gr. 7.31 at 20°C;; valence +1, +2, or +3. Indium is a soft, malleable, ductile, lustrous, silver-white metallic element; it crystallizes in a face-centered tetragonal structure. Its properties are similar to those of gallium, the element directly above it in Group 13 of the periodic table. Like gallium, it remains in the liquid state over a wide range of temperatures. It wets glass and can be used to form a mirror surface that is more corrosion-resistant than, and reflects as well as, one of silver. It is also used in low-melting fusible alloys and as a protective plating for bearings and other metal surfaces. Although indium resists oxidation at room temperature, when heated above its melting point it ignites and burns with a violet flame; the oxide that is formed is used in glassmaking to give a yellow color. Indium reacts readily with the halogens and (when warm) with other nonmetals, e.g., phosphorus, selenium, and sulfur. It has trivalent compounds that are similar to those of gallium and aluminum. Indium salts color the Bunsen flame a deep blue-violet. Indium phosphide, arsenide, and antimonide are semiconductor materials used in photocells, thermistors, and rectifiers. Indium is found in very low concentrations in many ores and minerals; it was first found in zinc blende and is produced commercially as a byproduct of the smelting of zinc. Indium was discovered in 1863 by Ferdinand Reich and H. T. Richter, using spectroscopic analysis; it was named for a brilliant indigo line in its spectrum.

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indium

Metallic chemical element, chemical symbol In, atomic number 49. Of a brilliant, silvery-white lustre, it is so soft that it can be scratched with a fingernail. Its most common isotope, indium-115, is very weakly radioactive, with a half-life measured in billions of years. Like tin, the pure metal emits a high-pitched “cry” when bent, and, like gallium, molten indium wets glass and other surfaces, which makes it valuable for producing seals between glass, metals, quartz, ceramics, and marble. The metal is used in coating high-performance engine bearings and is an ingredient in low-melting-point alloys for sprinkler heads, fire-door links, and fusible plugs. In various combinations with elements such as gallium, phosphorus, and arsenic, it forms compounds having semiconductor properties useful in electronics, including solid-state light-emitting devices. Transparent electrodes made from an oxide of indium and tin are widely employed in liquid crystal displays.

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A natural element that, combined with tin, is widely used as a transparent wire. Indium-tin-oxide (ITO) electrodes are attached to the glass plates that sandwich the liquid crystals in LCD displays. When energized, an electric field is created that causes the liquid crystal molecules to rotate in that location. Indium is not mined directly, rather it is extracted from the refuse when zinc and other materials are refined. See LCD.