Chemical Fact Sheet
Molybdenum
| Chemical Abstract Number (CAS #) | 7439-98-7 |
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| Synonyms | MCHVL-;TSM1- |
| Analytical Methods | 200.7 - 200.8 - 6010 - 6020 |
| Molecular Formula | Mo |
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Synopsis
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Molybdenum - (Gr. molybdos lead), Mo; at. wt. 95.94(1); at. no. 42; m.p. 2623 deg C; b.p. 4639 deg C; sp. gr. 10.22 (20 deg C); valence 2, 3, 4?, 5?, or 6. Before Scheele recognized molybdenite as a distinct ore of a new element in 1778, it was confused with graphite and lead ore. The metal was prepared in an impure form in 1782 by Hjelm. Molybdenum does not occur native, but is obtained principally from molybdenite (MoS2). Wulfenite (PbMoO4) and Powellite (Ca(MoW)O4) are also minor commercial ores. Molybdenum is also recovered as a by-product of copperand tungsten mining operations. The metal is prepared from the powder made by the hydrogen reduction of purified molybdic trioxide or ammonium molybdate. The metal is silvery white, very hard, but is softer and more ductile than tungsten. It has a high elastic modulus, and only tungsten and tantalum, of the more readily available metals, have higher melting points. It is a valuable alloying agent, as it contributes to the hardenability and toughness of quenched and tempered steels. It also improves the strength of steel at high temperatures. It is used in certain nickel-based alloys, such as the "Hastelloys (R)" which are heat-resistant and corrosion-resistant to chemical solutions. Molybdenum oxidizes at elevated temperatures. The metal has found recent application as electrodes for electrically heated glass furnaces and forehearths. The metal is also used in nuclear energy applications and for missile and aircraft parts. Molybdenum is valuable as a catalyst in the refining of petroleum. It has found application as a filament material in electronic and electrical applications. Molybdenum is an essential trace element in plant nutrition. Some lands are barren for lack of this element in the soil. Molybdenum sulfide is useful as a lubricant, especially at high temperatures where oils would decompose. Almost all ultra-high strength steels with minimum yield points up to 300,000 psi(lb/sq. in.) contain molybdenum in amounts from 0.25 to 8%. Natural molybdenum contains seven isotopes. Twenty three other isotopes and isomers are known, all of which are radioactive. Molybdenum metal costs about $1/g (99.999% purity). Commercial molybdenum metal (99.9%) costs about $200/kg. |
| Use | Resistance elements for electric furnaces; electric & electronic components; wear resistant coatings for machine & engine parts; electrodes for glass industry; machine tool accessories (eg, boring bars, grinding quills) Manufacture special steels for tools, boiler plate, rifle barrels, propeller shafts ( as ferromolybdenum); in electrical contacts, spark plugs X-Ray tubes, filaments, screens & grids for radio tubes; prodn of tungsten; in glass-to-metal seals; nonferrous alloys; in colloidal form as lubricant additive Nuclear energy applications; missile & aircraft parts; catalyst in refining of petroleum In pigments for paints, lacquers, ink, rubber, & leather; in fertilizers for microbial fixation of nitrogen Catalyst in prodn of ammonia Electron transport agent The primary use of molybdenum is as a steel alloy. As such it is utilized in the arms industry, in aeronautical engineering, and in the automobile industry. |
| Consumption Patterns | End use applications: Machinery, 35%; oil and gas industry, 20%; transportation, 15%; chemicals, 15%; electrical, 10%; and other, 5% (1986) End use applications: Machinery, 35%; oil and gas industry, 10%; transportation, 15%; chemicals, 10%; electrical, 15%; and other, 15% (1988) |
| Apparent Color | Dark-gray or black powder with metallic luster or coherent mass of silver white color; body centered cubic structure |
| Boiling Point | About 4825 deg C |
| Melting Point | 2622 deg C |
| Molecular Weight | 95.94 |
| Density | 10.28 |
| Sensitivity Data | Fume from arcing molybdenum metal causes respiratory irritation in animals. |
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Chemical and Physical Properties |
Participates in biochemical redox reactions such as nitrogen fixation Specific heat: 5.68 cal/g-atom/deg Heat of fusion: 6.6 kcal/g-atom Oxidized to trioxide @ red heat; slowly oxidized by steam; not attacked by water, dilute acids or concn hydrochloric acid; attacked by fluorine @ ordinary temp, by chlorine or bromine @ a red heat Very hard but softer & more ductile than tungsten; high elastic modulus Atomic number: 42; Valences: 2, 3, 4, 5, 6; Naturally occurring isotopes: 98 (23.75%), 96 (16.5%), 92 (15.86%), 95 (15.7%), 100 (9.62%), 97 (9.45%), 94 (9.12%) Inert in hydrogen; resistant to acid attack by hydrogen fluoride. Prepn: L Northcott, molybdenum (Academic Press, NY, 1956) 222 PP; Hein, Herzog, in Handbook of Preparative Inorganic Chem Vol. 2, G Braver, Ed (Academic Press, NY 2nd ed, 1965), PP 1401-1402. It (molybdenum) is not easily oxidized by air or water @ ordinary temp & has poor oxidn resistance @ higher temp. When heated above 400 deg C it yeilds a highly volatile trioxide (MOO3) and above 700 deg C oxidn becomes so severe that its use is pssible only if it is protected by a covering layer of an oxidn-resistant metal, an alloy or deposition of silicon. Reacts at elevated temp with sulfur, carbon, nitrogen, and the halogens except iodine. Reacts with nitric acid, hot concn sulfuric acid, fused potassium chlorate or nitrate. |
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Environmental Impact |
Indust exposures related to prodn & fabrication of molybdenum products are exposures to dusts & fume of molybdenum, its oxides & sulfides chiefly from electric furnace or other high temp treatment. Spraying of molybdenum may provide hazard; and loss of molybdenum catalysts to the air adds to the metal burden of contaminated atmospheres. Common operations in which exposure to soluble molybdenum compounds may occur are: liberation during rolling of hot billets in processing molybdenum steel; for use as electrodes; during welding operations; use as chemical reagent for lab analyses; in petroleum refining and chemical processing; as an intermediate in the manufacture of corrosion inhibitors; use as coloring agents for enamels and ceramic glazes; agricultural chemicals; use in electroplating process; use in formulation of corrosion inhibitors for aqueous systems; pigments for paints, lacquers, and coloring animal fibers and hair; use in enamel processes for adherence of vitreous coatings to ceramics and metal; use in leather and skin tanning; use as chlorination catalysts; in fire retardant resins; as a brazing flux and as an intermediate for organo metallic compunds; use in photography; ion exchange processes and formulation of plastics and adhesives; as a catalyst in desulfurization of gasoline, use as a reagent for determination of phosphorus and lead. |
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Environmental Fate |
Primary ore bodies in the Western Hemisphere contain about 0.2-0.4% molybdenum and give a recovery of 2 to 4 kg per metric ton of ore. Does not occur native, but obtained principally from molybdenite (molybdenum disulfide) wulfenite lead (molybdate) & powellite are also minor commercial ores. Occurrence in earth's crust: 1-2 mg/kg, world mean of soils around 2 mg/kg. Molybdenum occurs as iron molybdates in nature. Global mobilization: by weathering: 6x106 kg Molybdenum (Mo)/year; by rivers: 19x106 kg Mo/year; by mining: 76x106 kg Mo/year; by combustion (oil and coal): 0.8x106 kg Mo/year. Terrestrial plants can contain enough Mo to be toxic to animals but still grow normally, adding lime to soil increases Mo availability. The total body burden is: 9.3 mg amount in skeleton: 5 mg amount in liver: 2 mg kidney: 0.9-3.1 mg Mo/kg liver: 1.3-5.8 Mg mo/kg muscle: 0.018 mg Mo/kg bone: 0.7 mg Mo/kg hair: 0.06-0.2 mg Mo/kg nail: 0.15-16 mg Mo/kg whole blood: 0.001 mg Mo/kg. |
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Disposal |
At the time of review, criteria for land treatment or burial (sanitary landfill) disposal practices are subject to significant revision. Prior to implementing land disposal of waste residue (including waste sludge), consult with environmental regulatory agencies for guidance on acceptable disposal practices. The following wastewater treatment technologies have been investigated for molybdenum: Chemical precipitation. |
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Atmosphere |
In ambient air in urban areas, molybdenum ranged from 0.01 to 0.03 ug/cu m and in non urban areas it varied between 0.001 and 0.0032 ug/cu m. |
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