Overview
Molybdenum is a chemical element with the symbol Mo and atomic number 42. It is a transition metal notable for a silvery-gray appearance, high mechanical strength and exceptional stability at elevated temperatures. The element is commonly discussed in materials science, metallurgy and biology for its role in alloying, catalysis and in small amounts as an essential nutrient.
Characteristics and occurrence
Molybdenum has physical and chemical properties that make it useful where durability and heat resistance are required. In nature the element is not often found as a free metal; instead it occurs in several minerals. The most important ore is molybdenite, a sulfide mineral, from which the metal is commercially extracted. Many commercial deposits are mined as a primary resource or recovered as a byproduct of copper mining.
Extraction and production
Commercial production typically begins with the flotation concentration of molybdenite, followed by roasting and chemical processing to obtain molybdenum oxides and then the metal. The metal is produced by reduction of oxides or by more complex hydrometallurgical and pyrometallurgical techniques. Refined molybdenum is then used to alloy steels and produce specialty components that exploit its high melting point and resistance to corrosion.
Uses and applications
Major uses of molybdenum include alloying with steel to improve strength and toughness, and production of high-performance parts for engines, turbines and industrial equipment. It is also valued as a catalyst in petroleum refining and chemical synthesis, and as a solid lubricant in the form of molybdenum disulfide. In electronics and special alloys, molybdenum provides thermal stability and conductivity that are important in vacuum and semiconductor applications.
Biological role and safety
Although needed only in trace amounts, molybdenum is an essential micronutrient for many organisms. It forms part of several enzymes (molybdoenzymes) involved in nitrogen, sulfur and carbon cycles in plants and animals. Like many metals, molybdenum compounds can be toxic at high concentrations, so occupational and environmental controls are used in processing and handling.
History, name and notable facts
The name derives from the Greek word meaning "leadlike," reflecting early confusion between its ores and lead minerals; the Greek root is reflected in historical accounts of the element. The pure metal was isolated in the late 18th century, and since then its industrial importance has grown with the development of modern alloys and high-temperature engineering. Molybdenum has a number of isotopes and is studied both for its material properties and its role in biological systems.