Antimony A chemical element, symbol Sb, atomic number 51. Antimony is not a naturally abundant element; it is occasionally found native, often in isomorphous mixture with arsenic, as allemonite. The symbol Sb is derived from the Latin name stibium.
The element is dimorphic, existing as a yellow, metastable form composed of Sb4 molecules, as in antimony vapor and the structural unit in yellow antimony; and a gray, metallic form, which crystallizes with a layered rhombohedral structure. Antimony differs from normal metals in having a lower electrical conductivity as a solid than as a liquid (as does its congener, bismuth). Metallic antimony is quite brittle, bluish-white with a typical metallic luster, but a flaky appearance. Although stable in air at normal temperatures, it burns brilliantly when heated, with the formation of a white smoke of Sb2O3. Vaporization of the metal gives molecules of Sb4O6, which break down to Sb2O3 above the transition temperature.
Antimony occurs in nature mainly as Sb2S3 (stibnite, antimonite); Sb2O3 (valentinite) occurs as a decomposition product of stibnite. Antimony is commonly found in ores of copper, silver, and lead. The metal antimonides NiSb (breithaupite), NiSbS (ullmannite), and Ag2Sb (dicrasite) also are found naturally.
Antimony is produced either by roasting the sulfide with iron, or by roasting the sulfide and reducing the sublimate of Sb4O6 thus produced with carbon; high-purity antimony is produced by electrolytic refining.
Commercial-grade antimony is used in many alloys (1-20%), especially lead alloys, which are much harder and mechanically stronger than pure lead; batteries, cable sheathing, antifriction bearings, and type metal consume almost half of all the antimony produced. The valuable property of Sn-Sb-Pb alloys, that they expand on cooling from the melt, thus enabling the production of sharp castings, makes them especially useful as type metal.
مقالات قد تفيدك :