MOLYBDENUM

History

Molybdenum 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 copper and tungsten mining operations. The U.S., Canada, Chile, and China produce most of the world’s molybdenum ores. 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? 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. It 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 lb/in.2 contain molybdenum in amounts from 0.25 to 8%. Natural molybdenum contains seven isotopes. Thirty other isotopes and isomers are known, all of which are radioactive. Molybdenum metal costs about $1/g (99.999% purity). Molybdenum metal (99.9%) costs about $160/kg.

Definition

Symbol Mo. A silveryhard metallic transition element;a.n. 42; r.a.m. 95.94; r.d.10.22; m.p. 2617°C; b.p. 4612°C. It is found in molybdenite (MoS₂), themetal being extracted by roasting togive the oxide, followed by reductionwith hydrogen. The element is usedin alloy steels. Molybdenum(IV) sulphide(MoS₂) is used as a lubricant.Chemically, it is unreactive, beingunaffected by most acids. It oxidizesat high temperatures and can be dissolvedin molten alkali to give arange of molybdates and polymolybdates.Molybdenum was discoveredin 1778 by Karl Scheele.