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Friday, 11 February 2011 21:16

Osmium

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Gunnar Nordberg

Occurrence and Uses

Osmium (Os) is found almost exclusively in osmiridium, a natural alloy consisting of osmium and iridium, and in all platinum ores. The major ore deposits are located in the Urals, Canada and Colombia, with less important ores in Australia and in Alaska, California and Oregon in the United States.

Osmium alloys readily with the other platinum metals and with iron, cobalt and nickel. It also forms brittle intermetallic compounds with tin and zinc. One of the distinctive features of osmium is the ease with which it forms osmium tetroxide (OsO4). Osmium powder always has the characteristic odour of its tetroxide because even at normal temperatures it oxidizes in air to OsO4, even if only to a slight degree. The tetroxide is extremely volatile and has an unpleasant odour, from which the name of the element was derived (osme=odour). It is a powerful oxidizer and is easily converted to osmium dioxide (OsO2) or even to metallic osmium. With alkalis it forms unstable compounds such as OsO4·2KOH. When heated, osmium readily forms osmium disulphide (OsS2). The fluorides OsF4, OsF6 and OsF8 are also formed. Various chlorides are formed when osmium is treated with chlorine at high temperatures. With carbon monoxide, it forms carbonyls. It also forms a number of compounds with the complex anion containing osmium, as for example ammonium osmium hexachloride ((NH4)2OsCl6).

Osmium is used as a catalyst in the synthesis of ammonia and in the hydrogenation of organic compounds. As an alloy with indium it is used for the manufacture of compass needles and fine machine bearings. It is found in the parts of watch and lock mechanisms and in fountain pen points. Osmium tetroxide, sometimes incorrectly termed osmic acid, is used as an oxidizing agent, particularly for converting olefins to glycols. The chloro-osmiates are used in place of gold salts in photography.

Hazards

The metal is innocuous, but persons engaged in its production are exposed to the effects of vapours from acids and chlorine. Osmium tetroxide vapours are poisonous and extremely irritating to the eyes even at low concentrations, causing weeping and conjunctivitis, and to the upper respiratory system, causing bronchitis, bronchial spasms and difficulty in breathing, which may last for several hours. Longer exposure can result in damage to the cornea, blindness, disturbances of the digestive system and inflammatory disorders of the lungs and kidneys. Upon contact, it discolours the skin green or black and causes dermatitis and ulceration.

Safety and Health Measures

During the production of osmium, local exhaust ventilation should be provided and the apparatus should be sealed if gaseous chlorine is used. An enclosed ventilated area or hood is necessary in order to control the release of osmium tetroxide vapours into the work environment and prevent eye and respiratory irritation. Exposed workers should wear protective clothing, hand protection, gas-tight chemical safety eye protection and appropriate respiratory protective equipment. Containers must be stored in naturally ventilated premises. The vapour has a pronounced and nauseating odour which should serve as a warning of toxic concentration in the air, and personnel should leave the polluted area immediately. Determination in air and blood is possible by colourimetry of the complex with thiourea.

 

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More in this category: « Niobium Palladium »

Contents

Preface
Part I. The Body
Part II. Health Care
Part III. Management & Policy
Part IV. Tools and Approaches
Part V. Psychosocial and Organizational Factors
Part VI. General Hazards
Part VII. The Environment
Part VIII. Accidents and Safety Management
Part IX. Chemicals
Using, Storing and Transporting Chemicals
Minerals and Agricultural Chemicals
Metals: Chemical Properties and Toxicity
Resources
Part X. Industries Based on Biological Resources
Part XI. Industries Based on Natural Resources
Part XII. Chemical Industries
Part XIII. Manufacturing Industries
Part XIV. Textile and Apparel Industries
Part XV. Transport Industries
Part XVI. Construction
Part XVII. Services and Trade
Part XVIII. Guides

Metals: Chemical Properties and Toxicity Additional Resources

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Metals: Chemical Properties and Toxicity References

Agency for Toxic Substances and Disease Registry (ATSDR). 1995. Case Studies in Environmental Medicine: Lead Toxicity. Atlanta: ATSDR.

Brief, RS, JW Blanchard, RA Scala, and JH Blacker. 1971. Metal carbonyls in the petroleum industry. Arch Environ Health 23:373–384.

International Agency for Research on Cancer (IARC). 1990. Chromium, Nickel and Welding. Lyon: IARC.

National Institute for Occupational Safety and Health (NIOSH). 1994. NIOSH Pocket Guide to Chemical Hazards. DHHS (NIOSH) Publication No. 94-116. Cincinnati, OH: NIOSH.

Rendall, REG, JI Phillips and KA Renton. 1994. Death following exposure to fine particulate nickel from a metal arc process. Ann Occup Hyg 38:921–930.

Sunderman, FW, Jr., and A Oskarsson,. 1991. Nickel. In Metals and their compounds in the environment, edited by E Merian, Weinheim, Germany: VCH Verlag.

Sunderman, FW, Jr., A Aitio, LO Morgan, and T Norseth. 1986. Biological monitoring of nickel. Tox Ind Health 2:17–78.

United Nations Committee of Experts on the Transport of Dangerous Goods. 1995. Recommendations on the Transport of Dangerous Goods, 9th edition. New York: United Nations.