Molybdenum
Molybdenum is a silvery white metalelement denoted by the atomic symbol, Mo. Its atomic number is 42 and it has an atomic weight of 95.94. It melts at a higher temperature than all but two other readily available metals ( tungsten and tantalum); its melting point, 4753.443° F (2623° C), is the sixth highest of all the elements. Most molybdenum comes from an ore called molybdenite, which is a compound of molybdenum and sulfur (MoS2).
Before the 1770s, scientists confused molybdenite with other substances such as lead ore and graphite. Then in 1778, Carl Scheele recognized that molybdenite was a distinct ore of a new element. However, molybdenum was not isolated until 1782, when Swedish mineralogist Peter Jacob Hjelm (1746-1813) prepared the silvery-white metal in an impure form. Hjelm was a friend of Scheele's, and it was Scheele's suggestions that led Hjelm to isolate not only molybdenum, but also manganese.
In addition to molybdenite, molybdenum is found in smaller quantities in other mineral ores. Some molybdenum is also recovered as a by-product of copper and tungsten mining. The world's leading producer of molybdenum is the United States, where Colorado produces the greatest amount. Several other countries, including Canada, some of the former Soviet republics, Chile, and China, also produce molybdenum.
In nature, the metal occurs only in compounds with other elements, not by itself. Molybdenum has seven natural, stable isotopes. As a trace element, molybdenum is found in nearly all plant and animal tissues, and it is essential to plant nutrition. Some soils are barren because they lack traces of molybdenum.
Molybdenum is an important industrial material. Some industrial processes require metal equipment that can withstand extremely high temperatures (up to 2000 ° F, or 1100° C). For this reason, manufacturers often mix ordinary metals with refractory metals, which have very high melting points, to make superalloys designed for high-temperature processes. Molybdenum is one of the most valuable refractory metals used for this purpose.
Besides melting at a very high temperature, molybdenum is very hard and conducts heat well. It is often added to steel and iron to make the metals stronger, harder, and more resistant to corrosion. Molybdenum is also a constituent of some nickel-based alloys such as the Hastelloys, which are resistant to heat and corrosion. Although molybdenum is slightly softer than tungsten, it is also more ductile, making it useful for certain types of equipment. Molybdenum wire, for example, is used as a filament material in metallurgical and electronic applications. Certain molybdenum compounds are used as lubricants in greases and oils, and as adhesive agents in enamel coating materials. Other applications of molybdenum include use in nuclear power generation, as a catalyst for refining petroleum, and as a building material for aircraft parts.
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