Molybdenum
Molybdenum
For filament in electric heaters.
History
(Gr. molybdos, lead) 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 as an impure form in 1782 by Hjelm. Molybdenum does not occur native, but is obtained principally from molybdenite. Wulfenite, and Powellite are also minor commercial ores.
Sources
Molybdenum is also recovered as a by-product of copper and tungsten mining operations. The metal is prepared from the powder made by the hydrogen reduction of purified molybdic trioxide or ammonium molybdate.
Properties
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.
Uses
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 foreheaths. 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 applications as a filament material in electronic and electrical applications. Molybdenum is an
http://pearl1.lanl.gov/periodic/elements/42.html (1 of 2) [3/6/2001 8:38:11 AM]
Molybdenum
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/in.2) contain molybdenum in amounts from 0.25 to 8%.
Isotope
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
http://pearl1.lanl.gov/periodic/elements/42.html (2 of 2) [3/6/2001 8:38:11 AM]
Common Isotopes
Common Isotopes
Last Updated: 8/5/99
http://pearl1.lanl.gov/periodic/commonis.html [3/6/2001 8:38:11 AM]
Mercury
Mercury
For thermometers.
History
(Planet Mercury) Known to ancient Chinese and Hindus; found in Egyptian tombs of 1500 B.C. Mercury is the only common metal liquid at ordinary temperatures. It only rarely occurs free in nature. The chief ore is cinnabar, Spain and Italy produce about 50% of the world's supply of the metal. The commercial unit for handling mercury is the "flask," which weighs 76 lb. The metal is obtained by heating cinnabar in a current of air and by condensing the vapor. It is a heavy, silvery-white metal; a rather poor conductor of heat, as compared with other metals, and a fair conductor of electricity. It easily forms alloys with many metals, such as gold, silver, and tin, which are called amalgams. Its ease in amalgamating with gold is made use of in the recovery of gold from its ores. The most important salts are mercury chloride (corrosive sublimate - a violent poison), mercurous chloride (calomel, occasionally still used in medicine), mercury fulminate, a detonator widely used in explosives, and mercuric sulfide (vermilion, a high-grade paint pigment). Organic mercury compounds are important. It has been found that an electrical discharge causes mercury vapor to combine with neon, argon, krypton, and xenon. These products, held together with van der Waals' forces, correspond to HgNe, HgAr, HgKr, and HgXe. Mercury is a virulent poison and is readily absorbed through the respiratory tract, the gastrointestinal tract, or through unbroken skin. It acts as a cumulative poison and dangerous levels are readily attained in air. Air saturated with mercury vapor at 20C contains a concentration that exceeds the toxic limit many times. The danger increases at higher temperatures. It is therefore important that mercury be handled with care. Containers of mercury should be securely covered and spillage should be avoided. It it is necessary to heat mercury or mercury compounds, it should be done in a well-ventilated hood. Methyl mercury is a dangerous pollutant and is now widely found in water and streams. The triple point of mercury, -38.8344C, is a fixed point on the International Temperature Scale (ITS-90).
Uses
The metal is widely used in laboratory work for making thermometers, barometers, diffusion pumps, and many other instruments. It is used in making mercury-vapor lamps and advertising
http://pearl1.lanl.gov/periodic/elements/80.html (1 of 2) [3/6/2001 8:38:11 AM]
Mercury
signs, etc. and is used in mercury switches and other electronic apparatus. Other uses are in making pesticides, cercury cells for caustic soda and chlorine production, dental preparations, anti-fouling paint, batteries, and catalysts.
Sources: CRC Handbook of Chemistry and Physics and the American Chemical Society.
Last Updated: 12/19/97, CST Information Services Team
http://pearl1.lanl.gov/periodic/elements/80.html (2 of 2) [3/6/2001 8:38:11 AM]