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Molybdenum

physical science Maturity 7-9 Next article →

Molybdenum is a silvery-grey transition metal with the atomic number 42. It is a highly significant element because of its unique physical and chemical properties. It possesses the sixth-highest melting point of all naturally occurring elements. Only tantalum, osmium, rhenium, tungsten, and carbon can withstand higher temperatures. This extreme heat resistance makes it vital for many industrial uses. It also plays a critical role in biology as an essential element for all higher eukaryotes, including humans.

Molly Hill molybdenite
Molly Hill molybdenite

The metal is rarely found alone in nature. Instead, it usually exists in oxidized states within various minerals. The most important commercial source is a mineral called molybdenite, which is molybdenum disulfide (MoS2). To extract the metal, the ore undergoes a process called roasting. In this step, the molybdenite is heated in air to produce molybdenum trioxide (MoO3). This trioxide is a volatile substance at high temperatures. It serves as the precursor for almost all other molybdenum compounds and alloys.

Molybdenum world production
Molybdenum world production

Molybdenum is famous for its ability to form hard, stable carbides when mixed with other metals. Because of this, about 80% of the world's production is used to create steel alloys. These include high-strength alloys and superalloys used in demanding environments. The metal also has one of the lowest coefficients of thermal expansion among commercial metals. This means it does not change size much when the temperature shifts. It is also used as a pigment and a catalyst in various industrial applications, accounting for about 14% of its use.

Plate of Molybdenum Copper
Plate of Molybdenum Copper

In the world of biology, molybdenum acts as a vital component in many enzymes. There are at least 50 known molybdenum-bearing enzymes in bacteria, plants, and animals. These enzymes are essential for biological nitrogen fixation. This is the process where bacteria use catalysts to break the chemical bonds in atmospheric molecular nitrogen. Most of these nitrogenase enzymes contain an iron–molybdenum cofactor, known as FeMoco. This cofactor is believed to contain either Mo(III) or Mo(IV). In other enzymes, molybdenum is complexed with a molecule called molybdopterin.

Phosphotungstate-3D-polyhedra
Phosphotungstate-3D-polyhedra

The history of molybdenum involves a long period of confusion. For centuries, its ore, molybdenite, was often mistaken for graphite or lead. The name itself comes from the Ancient Greek word for lead. In 1754, Bengt Andersson Qvist determined that molybdenite was not lead. In 1778, the Swedish chemist Carl Wilhelm Scheele proved it was a distinct new element. Three years later, in 1781, Peter Jacob Hjelm successfully isolated the metal using carbon and linseed oil. For a long time, the metal was difficult to use because it was hard to extract and often became brittle in alloys.

Industrial use of molybdenum changed significantly during the 20th century. In 1906, William D. Coolidge patented a way to make the metal ductile. This allowed it to be used as heating elements in furnaces and as supports in light bulbs. During World War I, the demand for the metal spiked. It was used in armor plating and as a substitute for tungsten in high-speed steels. For example, British tanks were upgraded from manganese steel to lighter, more maneuverable molybdenum steel. During World War II, it again served as a strategic substitute for tungsten in various steel alloys.

Molybdenum also has important roles in nuclear science and medicine. In nuclear fuel, molybdenum acts as a redox buffer in the spent fuel matrix. It is a common fission product, with a fission yield of 6.1%. It helps control the chemistry of the fuel by affecting oxygen fugacity. In medicine, the isotope molybdenum-99 is very important. It is a parent radioisotope that decays into technetium-99m. This daughter isotope is a short-lived gamma-emitter used widely in medical imaging applications.

Phosphotungstate-3D-polyhedra
Phosphotungstate-3D-polyhedra

Even in space, molybdenum is present. The Soviet Luna 24 mission discovered a tiny molybdenum-bearing grain on the Moon. This grain was found in a fragment from the Mare Crisium region. On Earth, molybdenum is the 54th most abundant element in the crust. It is also the 25th most abundant element in the oceans. Today, major producers include China, the United States, and Chile. These nations provide much of the metal used to build the modern, high-strength world.

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File:Phosphotungstate-3D-polyhedra.png
Phosphotungstate-3D-polyhedra.png
File:Molly Hill molybdenite.JPG
Molly Hill molybdenite.JPG
File:Molybdenum world production.svg
Molybdenum world production.svg
File:Plate of Molybdenum Copper .jpg
Plate of Molybdenum Copper .jpg
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