Molybdenum minerals have long been known, but the element was "discovered" (in the sense of differentiating it as a new entity from minerals salts of other metals) in 1778 by Carl Wilhelm Scheele who thought that he was observing lead while studying a sample of molybdenite. Named from the Greek word "molybdos, which actually means lead, Scheele notice an apparent visual similarity, which upon further analysis, proved to be incorrect. His studies led him to conclude that the ore sample did not contain lead, but a new element, which he named a molybdenum after the mineral molybdenite.
Originally molybdenum history was confused with graphite and lead ore, and was not prepared till 1782 by Hjelm in the impure state. Molybdenum history does not occur native, and is obtained mainly from molybdenite (MoS2). Other minor commercial ores of molybdenum are powellite (Ca(MoW)O4) and wulfenite (PbMoO4). It may also be recovered from copper and tungsten operations as a by-product. After the initial isolation of molybdenum in 1782, a commercial application for molybdenum was not identified until the early 1900's.
The metal is prepared from the powder made by the hydrogen reduction of purified molybdic trioxide or ammonium molybdate. Molybdenum metal is silvery-white, and very hard. However, it is softer and more ductile than tungsten and is readily worked or drawn into very fine wire. It cannot be hardened by heat treatment, only by working. It exhibits a high elastic modulus and a very high melting point. Above temperatures of 760°C (1400°F) molybdenum metal forms an oxide that evaporates as it is formed and its resistance to corrosion is high. It has a low thermal expansion and its heat conductivity is twice that of iron. It is one of the few metals that has some resistance to hydrofluoric acid.
Industrial and Military applications required stronger steels with greater resistance to corrosion and damage. The First World War saw the demand for molybdenum rise dramatically as alloyed steels used for transportation and armor plating increased with the war effort. It was found that molybdenum could impart an impact resistance similar to tungsten when alloyed with steel, with less weight. Demand for molybdenum initiated an intensive search for new sources to insure a reliable supply. This led to the discovery of the enormous Climax deposit in Colorado, which began production in 1918. In addition to primary molybdenum mines, molybdenum is also recovered as a byproduct of copper and tungsten mining operations. The metal is produced from purified ammonium molybdate or molybdic trioxide powder through hydrogen reduction at high temperatures.In its elemental form, Molybdenum is a silvery-white metallic element. Its symbol in the periodic table is Mo and its atomic number is 42. Though molybdenum is chemically stable, it will react with acids.
In 1768, the Swedish scientist Carl Wilhelm Scheele determined that molybdenite was a sulfide compound of an as-yet unidentified element, by decomposing it in hot nitric acid and heating the product in air to yield a white oxide powder. In 1782, at Scheele's suggestion, Peter Jacob Hjelm chemically reduced the oxide with carbon, obtaining a dark metal powder that he named 'molybdenum.'
Molybdenum history remained mainly a laboratory curiosity until late in the 19th century, when technology for the extraction of commercial quantities became practical. Experiments with steel demonstrated that molybdenum could effectively replace tungsten in many steel alloys. This change brought weight benefits, since the atomic weight of tungsten is nearly twice that of molybdenum. In 1891, the French company Schneider & Co. first used molybdenum as an alloying element in armour plate steel.
Demand for alloy steels during World War I caused tungsten demand to soar, severely straining its supply. The tungsten shortage accelerated molybdenum substitution in many hard and impact-resistant tungsten steels. This increase in molybdenum demand spurred an intensive search for new sources of supply, culminating with the development of the massive Climax deposit in Colorado, USA and its startup in 1918.
After the war, reductions in alloy steel demand triggered intense research efforts to develop new civilian applications for molybdenum, and a number of new low-alloy molybdenum automotive steels were soon tested and accepted. In the 1930s, researchers determined the proper temperature ranges to forge and heat-treat molybdenum-bearing high-speed steels, a breakthrough that opened large new markets to molybdenum. Researchers eventually developed a full understanding of how molybdenum imparts its many cost-effective benefits as an alloying element to steels and other systems.
By the end of the 1930s, molybdenum was a widely accepted technical material. The conclusion of World War II in 1945 once again brought increased research investment to develop new civilian applications, and the post-war reconstruction of the world provided additional markets for molybdenum-containing structural steels. Steels and cast iron still comprise the single biggest market segment, but molybdenum history has also proven to be invaluable in superalloys, nickel base alloys, lubricants, chemicals, electronics and many other applications.
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