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Atomic Number: 42
Atomic Symbol: Mo
Atomic Weight: 95.94
Electron Configuration: [Kr]5s14d5
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®"
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 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/in2) contain molybdenum in amounts
from 0.25 to 8%.
Sources: CRC Handbook of Chemistry and
Physics and the American Chemical Society.
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