Arsenic and Arsenic Alloys

Abstract

AbstractArsenic, although often referred to as a metal, is classified chemically as a nonmetal or metalloid and belongs to Group 15 (VA) of the Periodic Table (as does antimony). The principal valences of arsenic are\documentclass{article}\pagestyle{empty}\begin{document}${+3}$\end{document},\documentclass{article}\pagestyle{empty}\begin{document}${+5}$\end{document}, and\documentclass{article}\pagestyle{empty}\begin{document}${-3}$\end{document}. Only one stable isotope of arsenic having mass 75 (100% natural abundance) has been observed. Metallic arsenic is stable in dry air, but when exposed to humid air the surface oxidizes, giving a superficial golden bronze tarnish that turns black upon further exposure. The amorphous form is more stable to atmospheric oxidation. Upon heating in air, both forms sublime and the vapor oxidizes to arsenic trioxide, As2O3. Elemental arsenic combines with many metals to form arsenides. Arsenic is widely distributed about the earth and has a terrestrial abundance of approximately 5 g/t. The most important commercial source of arsenic, however, is as a by‐product from the treatment of copper, lead, cobalt, and gold ores. Arsenic metal is also offered in high (ranging from 99.99% to in excess of\documentclass{article}\usepackage{amssymb}\pagestyle{empty}\begin{document}${99.999{\%}+}$\end{document}) purity form for semiconductor applications. The predominant use of arsenic in the United States is in the manufacture of chemicals. During the 1980s, the market for arsenic chemicals had shifted from cotton farming, where its use is now restricted because of environmental considerations, to wood preservatives for the protection of lumber and other wood products. Arsenic trioxide is the basic commodity of commerce from which a number of important chemicals are manufactured. Trace quantities of arsenic are added to lead–antimony grid alloys used in lead–acid batteries. Phosphorized deoxidized arsenical copper (alloy 142) is used for heat exchangers and condenser tubes. The toxicity of arsenic ranges from very low to extremely high depending on the chemical state. Metallic arsenic and arsenious sulfide, As2S3, have low toxicity. Arsine is extremely toxic. The toxicity of other organic and inorganic arsenic compounds varies. Arsenic is classified as a carcinogen by the International Agency for Research on Cancer (IARC). The handling of arsenic in the work‐place should be in compliance with the U.S. Occupational Safety and Health Administration (OSHA) regulations. Precautions should be taken to avoid accidental generation of arsine gas. Disposal of arsenical products should be in compliance with Federal and local government environmental regulations.