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Friday, 11 February 2011 21:44

Tantalum

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Gunnar Nordberg

Occurrence and Uses

Tantalum (Ta) is obtained from the ores tantalite and columbite, which are mixed oxides of iron, manganese, niobium and tantalum. Although they are considered rare elements, the earth’s crust contains about 0.003% of niobium and tantalum together, which are similar chemically and usually occur in combination.

The chief use of tantalum is in the production of electric capacitators. Tantalum powder is compacted, sintered and subjected to anodic oxidation. The film of oxide on the surface serves as an insulator, and upon introduction of an electrolyte solution, a high-performance capacitator is obtained. Structurally, tantalum is used where its high melting point, high density and resistance to acids are advantageous. The metal is employed widely in the chemical industry. Tantalum has also been used in rectifiers for railway signals, in surgery for suture wire and for bone repair, in vacuum tubes, furnaces, cutting tools, prosthetic appliances, fibre spinnerets and in laboratory ware.

Tantalum carbide is used as an abrasive. Tantalum oxide finds use in the manufacture of special glass with a high index of refraction for camera lenses.

Hazards

Metallic tantalum powder presents a fire and explosion hazard, although not as serious as that of other metals (zirconium, titanium and so on). The working of tantalum metal presents the hazards of burns, electric shock, and eye and traumatic injuries. Refining processes involve toxic and hazardous chemicals such as hydrogen fluoride, sodium and organic solvents.

Toxicity. The systemic toxicity of tantalum oxide, as well as that of metallic tantalum, is low, which is probably due to its poor solubility. It does, however, represent a skin, eye and respiratory hazard. In alloys with other metals such as cobalt, tungsten and niobium, tantalum has been attributed an aetiological role in hard-metal pneumoconiosis and in skin affections caused by hard-metal dust. Tantalum hydroxide was found to be not highly toxic to chick embryos, and the oxide was non-toxic to rats by intraperitoneal injection. Tantalum chloride, however, had an LD50 of 38 mg/kg (as Ta) while the complex salt K2TaF7 was about one-fourth as toxic.

Safety and Health Measures

In most operations, general ventilation can maintain the concentration of the dust of tantalum and its compounds below the threshold limit value. Open flames, arcs and sparks should be avoided in areas where tantalum powder is handled. If workers are regularly exposed to dust concentrations approaching the threshold limit level, periodic medical examinations, with emphasis on pulmonary function, are advisable. For operations involving fluorides of tantalum, as well as hydrogen fluoride, the precautions applicable to these compounds should be observed.

Tantalum bromide (TaBr5), tantalum chloride (TaCl5) and tantalum fluoride (TaF5) should be kept in tightly stoppered bottles which are plainly labelled and stored in a cool, ventilated place, away from compounds which are affected by acids or acid fumes. Personnel involved should be cautioned about their hazards.

 

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More in this category: « Silver Tellurium »

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
Metals: Chemical Properties and Toxicity
Resources
Minerals and Agricultural Chemicals
Using, Storing and Transporting Chemicals
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.