In the nature, the molybdenum mainly exists in the form of molybdenite (MoS2). Natural molybdenite is a soft black mineral. Although molybdenite has been applied in ancient times, molybdenite, lead, galena and graphite are too similar to distinguish. “Molybdos” in Greece refers to the lead. Before the late 18th century, both molybdos and lead in the European market were sold under the name of molybadenite (ancient Greece).
In 1779, Scheler (a famous Swedish chemist, one of the discoverers of oxygen) pointed out that lead or graphite and molybadenite are two completely different substances. He found that nitric acid had no effect on graphite, but reacted with molybadenite, then obtaining a white powder; this powder can separate out a salt after the crystallization by boiling together with the alkaline solution. He believed that this white powder is a metal oxide (which is actually a molybdenum oxide); it did not obtain metals after mixing with the charcoal by heating to high temperatures, but obtained the original molybadenite when heated with the sulfur.
In 1782, Scheler’s friend, a Swedish mine owner Elmer mixed the charcoal processed by linseed oil with molybdic acid and burned the mixture in an airtight container, separating out the metal from molybadenite named molybdenum, with element symbol as Mo. It was recognized by the famous Swedish chemist Berzelius who had discovered cerium, selenium, silicon, tantalum, thorium and other elements.
Molybdenum metal gives off a golden light when it burns in air; molybdenum ions in different oxidation states have different colors. It is not until 1893 when the molybdenum was discovered for more than 100 years later that M.Mathison melted a mixture of carbon and molybdenum trioxide in the furnace, and obtained cast metal with 92% to 96% molybdenum for the first time.
Molybdenum was found over 200 years, but it has been exploited and used on a large scale in the century, especially in recent decades. Molybdenum and molybdenum alloys are versatile, because they have many features such as high strength, low thermal expansion coefficient, excellent thermal conductivity and electrical conductivity, improvement of the wear resistance of thin coatings as well as higher corrosion resistance to the molten glass, molten salt and molten metal.
Molybdenum is primarily used in the areas of alloy steel, stainless steel, tool steel and cast iron, and production in these areas determines the demand for molybdenum. Adding molybdenum powder to the stainless steel can improve the corrosion resistance of steel. Adding molybdenum to the cast iron can improve the strength and wear resistance of iron. Nickel-base superalloys containing 18% of molybdenum, with high melting point, low density and low thermal expansion coefficient, used in the manufacture of a variety of high-temperature components in the aviation and aerospace field. Molybdenum metal is widely used in the tubes, transistors, rectifiers and other electronic devices. Pure molybdenum wire is used for high-temperature furnaces, electrical discharge machining and wire electrical discharge machining. Molybdenum plates are used to manufacture radio equipments and X-ray equipments. Molybdenum’s applications in other alloy areas and the chemical industry are also expanding. Adding molybdenum to the alloy steel can not only improve the elastic limit and corrosion resistance of the materials, but also maintain permanent magnetism. MoO3 Nanopowder and molybdate are excellent catalysts in the chemical and petroleum industries.
Molybdenum disulfide is an important lubricant for the aerospace and mechanical industries. In addition, as its unique property resistant to sulfur can catalyze the hydrogenation of carbon monoxide to produce alcohols under certain conditions, molybdenum disulfide is a promising chemical catalyst. Molybdenum metal is also gradually used in nuclear power, new energy and other fields.
Molybdenum is one of the trace elements required by plants, and plants can not survive without it. Molybdenum can be used as trace element fertilizers in agriculture. All kinds of human tissues contain molybdenum, with total content of 9mg for an adult and the highest content in liver and kidney. Molybdenum-99 is one of molybdenum radioisotopes, for the preparation of technetium-99 in the hospital. Technetium-99 is a radioactive isotope, used for the angiography of internal organs after patients taking it. For the use of molybdenum-99, it is usually absorbed by the alumina powder stored in a relatively small container. Technetium-99 generates when molybdenum-99 decays.
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