Antimony discontinued. Antimony is resistant to attack by acids. Four allotropes of antimony are known: a stable metallic form and three metastable forms (explosive, black and yellow). Elemental antimony is a brittle, silver-white shiny metalloid. When slowly cooled, molten antimony crystallizes in a trigonal cell, isomorphic with the gray allotrope of arsenic. A rare explosive form of antimony can be formed from the electrolysis of antimony trichloride. When scratched with a sharp implement, an exothermic reaction occurs and white fumes are given off as metallic antimony forms; when rubbed with a pestle in a mortar, a strong detonation occurs. Black antimony
Application of silicon-germanium thermoelectrics in space exploration Application of silicon-germanium thermoelectrics in space exploration Silicon-germanium (SiGe) thermoelectrics have been used for converting heat into power in spacecraft designed for deep-space NASA missions since 1976. This material is used in the radioisotope thermoelectric generators (RTGs) that power "Voyager 1", "Voyager 2", "Galileo", "Ulysses", "Cassini", and "New Horizons" spacecraft. SiGe thermoelectric material converts enough radiated heat into electrical power to fully meet the power demands of each spacecraft. The properties of the material and the remaining components of the RTG contribute towards the efficiency of this thermoelectric conversion. Heavily doped semiconductors, such as silicon-germanium (SiGe) thermoelectric couples (also called