Molybdenum
The name molybdenum comes from the Ancient Greek word meaning lead. For centuries, miners confused molybdenite with graphite and galena. They used the black mineral to mark surfaces or as a solid lubricant without knowing its true identity. In 1754 Bengt Andersson Qvist examined a sample of molybdenite. He determined that it did not contain lead and was therefore not galena. Swedish chemist Carl Wilhelm Scheele stated firmly in 1778 that molybdena was neither galena nor graphite. Scheele correctly proposed that molybdena was an ore of a distinct new element. Peter Jacob Hjelm successfully isolated a metal he called molybdenum using carbon and linseed oil in 1781. The pure metal appeared as a silvery-grey substance with a Mohs hardness of 5.5.
For the next century molybdenum had no industrial use. It remained relatively scarce while the pure metal proved difficult to extract. Early steel alloys showed great promise but efforts to manufacture them on a large scale failed. Results were inconsistent and the material suffered from brittleness and recrystallization. William D. Coolidge filed a patent in 1906 for rendering molybdenum ductile. This breakthrough led to applications as a heating element for high-temperature furnaces. Frank E. Elmore developed a froth flotation process in 1913 to recover molybdenite from ores. Flotation remains the primary isolation process today.
Molybdenum possesses the sixth-highest melting point of any naturally occurring element. Only tantalum osmium rhenium tungsten and carbon have higher melting points. Its standard atomic weight is 95.95 g/mol. The element has one of the lowest coefficients of thermal expansion among commercially used metals. Molybdenum does not visibly react with oxygen or water at room temperature. Weak oxidation starts at 450 degrees Celsius while bulk oxidation occurs above 600 degrees Celsius. This reaction results in molybdenum trioxide.
Gaseous molybdenum consists of the diatomic species Mo2. That molecule is a singlet with two unpaired electrons in bonding orbitals. It contains five conventional bonds plus those two unpaired electrons. The result is a sextuple bond. Molybdenum forms chemical compounds in oxidation states ranging from negative four to positive six. Higher oxidation states are more relevant to its terrestrial occurrence and biological roles. Mid-level oxidation states often associate with metal clusters. Very low oxidation states typically appear in organomolybdenum compounds. The chemistry of molybdenum and tungsten show strong similarities.
The world's production of molybdenum reached 250,000 tonnes in 2011. China led global output with 94,000 tonnes followed by the United States at 64,000 tonnes. Chile produced 38,000 tonnes while Peru contributed 18,000 tonnes and Mexico added 12,000 tonnes. Total reserves are estimated at 10 million tonnes concentrated primarily in China the US and Chile. By continent ninety-three percent of world production distributes evenly among North America South America and China.
Molybdenum was valued at approximately thirty thousand dollars per tonne in earlier decades. Prices maintained levels near ten thousand dollars per tonne from 1997 through 2003. A peak price of one hundred three thousand dollars per tonne occurred in June 2005. The London Metal Exchange announced that molybdenum would be traded as a commodity in 2008. The Knaben mine in southern Norway opened in 1885 as the first dedicated molybdenum mine. Large mines in Colorado such as Henderson and Climax yield molybdenite as their primary product. Many porphyry copper deposits like Bingham Canyon Mine produce molybdenum as a byproduct.
About eighty-six percent of molybdenum produced goes into metallurgy applications. Structural steel accounts for thirty-five percent of global use while stainless steel takes twenty-five percent. High-speed steels consume nine percent and cast iron uses six percent. Most high-strength steel alloys contain between 0.25% to 8% molybdenum. More than forty-three thousand tonnes of molybdenum are used each year in these materials.
During World War I demand for molybdenum spiked significantly. It was used both in armor plating and as a substitute for tungsten in high-speed steels. Some British tanks received protection from seven-five millimeter manganese steel plates initially. Those plates proved ineffective against enemy fire. Engineers replaced them with much lighter molybdenum steel plates allowing higher speed and better maneuverability. The Germans also used molybdenum-doped steel for heavy artillery like Big Bertha. Traditional steel melts at the temperatures produced by the propellant of that one-ton shell. TZM alloy resists molten fluoride salts at temperatures above fifteen hundred degrees Celsius.
At least fifty molybdenum-containing enzymes have been identified mostly in bacteria. These enzymes include aldehyde oxidase sulfite oxidase and xanthine oxidase. Molybdenum is an essential element in most organisms. A 2008 research paper speculated that scarcity of molybdenum in Earth's early oceans may have influenced eukaryotic life evolution. Mo-containing enzymes catalyze oxidation and sometimes reduction of certain small molecules. They regulate nitrogen sulfur and carbon processes within living systems.
Nitrogenases are unique among molybdoenzymes because they lack molybdopterin. They use the FeMoco cofactor which has the formula Fe7MoS9C. Nitrogenases catalyze production of ammonia from atmospheric nitrogen. Without molybdenum nitrogen fixation would be greatly reduced. A large part of biosynthesis as we know it would not occur. The human body contains about 0.07 mg of molybdenum per kilogram of body weight. Higher concentrations exist in liver and kidneys while lower levels appear in vertebrae.
The radioactive isotope molybdenum-99 generates technetium-99m for medical imaging applications. Technetium-99m is a short-lived gamma-emitting daughter radioisotope used in various diagnostic procedures. Molybdenum targets produce X-rays in the energy range of seventeen to twenty keV. This energy level proves optimal for imaging soft tissues like breast tissue during mammography. Characteristic X-rays emitted from molybdenum provide high contrast between different types of tissues.
This energy range minimizes radiation dose while maximizing image quality. It allows effective visualization of microcalcifications and other subtle abnormalities in breast tissue. Molybdenum-98 is the most abundant natural isotope comprising 24.14% of molybdenum. Only molybdenum-100 is unstable undergoing double beta decay into ruthenium-100 with half-life 7.07 years. All synthetic isotopes of molybdenum decay into isotopes of niobium technetium or zirconium. The most stable synthetic isotope is 93Mo with half-life 4,839 years.
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Common questions
What is the origin of the name molybdenum?
The name molybdenum comes from the Ancient Greek word meaning lead. For centuries, miners confused molybdenite with graphite and galena before Swedish chemist Carl Wilhelm Scheele stated firmly in 1778 that molybdena was neither galena nor graphite.
When did Peter Jacob Hjelm isolate pure molybdenum metal?
Peter Jacob Hjelm successfully isolated a metal he called molybdenum using carbon and linseed oil in 1781. The pure metal appeared as a silvery-grey substance with a Mohs hardness of 5.5.
Which countries produce the most molybdenum globally?
China led global output with 94,000 tonnes followed by the United States at 64,000 tonnes while Chile produced 38,000 tonnes. Total reserves are estimated at 10 million tonnes concentrated primarily in China the US and Chile.
How does molybdenum function in biological systems?
At least fifty molybdenum-containing enzymes have been identified mostly in bacteria including aldehyde oxidase sulfite oxidase and xanthine oxidase. Molybdenum is an essential element in most organisms where it regulates nitrogen sulfur and carbon processes within living systems.
What medical applications utilize radioactive isotopes of molybdenum?
The radioactive isotope molybdenum-99 generates technetium-99m for medical imaging applications used in various diagnostic procedures. Molybdenum targets produce X-rays in the energy range of seventeen to twenty keV which proves optimal for imaging soft tissues like breast tissue during mammography.