Chemical Fact Sheet
Tantalum
| Chemical Abstract Number (CAS #) | 7440-25-7 |
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| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 |
| Molecular Formula | Ta |
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Synopsis
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Tantalum - (Gr. Tantalos, mythological character, father of Niobe), Ta; at wt. 180.9479(1); at. no. 73; m.p. 3017 deg C; b.p. 5458 +/- 100 deg C; sp. gr. 16.654; valence 2?, 3, 4?, or 5. Discovered in 1802 by Ekeberg, but many chemists thought niobium and tantalum were identical elements until Rose, in 1844, and Marignac, in 1866 showed that niobic and tantalic acids were two different acids. The early investigators only isolated the impure metal. The first relatively pure ductile tantalum was produced by von Bolton in 1903. Tantalum occurs principally in the mineral columbite-tantalite (Fe, Mn)(Nb, Ta)2O6. Tantalum ores are found in Australia, Brazil, Mozambique, Thailand, Portugal, Nigeria, Zaire, and Canada. Separation of tantalum from niobium requires several complicated steps. Several methods are used to commercially produce the element, including electrolysis of molten potassium fluorotantalate, reduction of potassium fluorotantalate with sodium, or reacting tantalum carbide with tantalum oxide. Thirty four isotopes and isomers of tantalum are known to exist. Natural tantalum contains two isotopes, one of which is radioactive with a very long half-life. Tantalum is a gray, heavy, and very hard metal. When pure, it is ductile and can be drawn into fine wire, which is used as a filament for evaporating metals such as aluminum. Tantalum is almost completely immune to chemical attack at temperatures below 150 deg C, and is attacked only by hydrofluoric acid, acidic solutions containing the fluoride ion, and free sulfur trioxide. Alkalis attack it only slowly. At high temperatures, tantalum becomes much more reactive. The element has a melting point exceeded only by tungsten and rhenium. Tantalum is used to make a variety of alloys with desirable properties such as high melting point, high strength, good ductility, etc. Scientists at Los Alamos have produced a tantalum carbide graphite composite material, which is said to be one of the hardest materials ever made. The compound has a melting point of 3738 deg C. Tantalum has good "gettering" ability at high temperatures, and tantalum oxide films are stable and have good rectifying and dielectric properties. Tantalum is used to make electrolytic capacitors and vacuum furnace parts, which account for about 60% of its use. The metal is also widely used to fabricate chemical process equipment, nuclear reactors, and aircraft and missile parts. Tantalum is completely immune to body liquids and is a nonirritating metal. It has, therefore, found wide use in making surgical appliances. Tantalum oxide is used to make special glass with high index of refraction for camera lenses. The metal has many other uses. The price of (99.9%) tantalum is about $900/kg. The metal of 99.995% purity sells for about $2/g. |
| Use | In rectifiers, esp for railway signals; in electrolysis capacitors; in mfr of radio & power tubes In alloys, with tungsten for filaments & grid wires; In cutting tools; in mfr of spinnerets in rayon industry In chem industry for acid-proff equipment; In rubber industry as catalyst in synthesis of butadiene In surgical & prosthetic appliances In analytical weights & pen points Used in vacuum furnace parts, nuclear reactors, used to fabricate aircraft parts, missle parts Used in paint 7 dye industry, in glass & ceramic industry Sheets in surgical repair of bones, muscles, nerve tissue Tantalum oxide is used to make special glass with high index of refraction for camera lenses Electronic circuitry; Thin-film components; High-speed tools Tantalum powder can be used for assessment of upper qirway obstruction. |
| Apparent Color | Gray metal; cubic or powder; black powder; steel-blue colored metal when unpolished; nearly platinum color when polished |
| Boiling Point | 5425 +/- 100 deg C |
| Melting Point | 2996 deg C |
| Molecular Weight | 180.948 |
| Density | 16.654; 14.401 (powder) |
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Chemical and Physical Properties |
Atomic number: 73; Valence: 5 also 4, 3, & 2; Very hard, dense, malleable, ductile metal Readily drawn in fine wires; specific heat @ 0 deg C: 0.036 cal/g; Electrical resistivity @ 18 deg C: 12.4 microhms-cm Slowly attacked by fused alkalies At high temp absorbs several hundred times its volume of hydrogen; combines with nitrogen, with carbon Metal in inert Has good "gettering" ability @ high temp Ta is inert toward most gases below 200 deg C but absorbs hydrogen gas It becomes brittle on contact with dilute hydrofluoric acid (AQ), or when deposited cathodically in electrolysis Ta wire heated to incandesence is converted to the oxide Fluorine gas attaches ir @ room temp; chlorine gas @ 250 deg C, & bromine @ 3000 deg C; Ta is inert to iodine below red heat Very resistant to chemical attack; not attacked by acids other than hydrofluoric; not attacked by AQ alkalies Tensile strength of drawn wire may be as high as 130,000 psi; expansion coefficient 8X10-6 over range 20-1500 deg C Natural isotopes: 181 (99.9877%); 180 (0.0123%); (Half-life greater than 10+12 yr) |
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Environmental Impact |
CLINICAL STUDIES MADE ON 22 RUSSIAN CHEM WORKERS & WELDERS HANDLING BOTH TA & NIOBIUM SHOWED LITTLE EVIDENCE OF POISONING APART FROM RADIOLOGIC SIGNS OF EARLY PULMONARY FIBROSIS &, IN 1 OR 2 CASES, CHRONIC ATROPHIC RHINITIS. SOME INDUSTRIAL SKIN INJURIES FROM TANTALUM HAVE BEEN REPORTED. HOWEVER, SYSTEMIC INDUST POISONING IS APPARENTLY NOT KNOWN. THE WORKING OF TANTALUM METAL PRESENTS THE HAZARDS OF BURNS, ELECTRIC SHOCK, & EYE & TRAUMATIC INJURIES. REFINING PROCESSES INVOLVES TOXIC & HAZARDOUS CHEMICALS SUCH AS HYDROGEN FLUORIDE, SODIUM & ORGANIC SOLVENTS. HOW RELEVANT THE TOXICITY EVIDENCE OBTAINED FROM SOLID METAL SURFACES IS TO THAT OF FINELY DIVIDED TA METAL POWDER IS CERTAINLY QUESTIONABLE. CERTAINLY ONE WOULD EXPECT TANTALUM METAL FUME TO HAVE A DIFFERENT ORDER OF TOXICITY THAN THE MORE COARSELY DIVIDED DUSTS. |
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Environmental Fate |
Occurs almost invariably along with niobium. Found in the minerals columbite, tantalite & microlite. Obtained from ores tantalite or columbite mixed oxides of iton, manganese, niobium & tnatalum. Considered as rare element earth's crust contains about 0.003% of niobium & tantalum together. |
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