molybdène

Molybdæne, known in English as molybdenum, is a chemical element with the symbol Mo and atomic number 42. It is a transition metal in group 6 and is typically found only in minerals rather than as a native metal. The element is named after the Greek molubdos, meaning lead, reflecting its resemblance to lead ore.

The most important ore is molybdenite (MoS2). Other minerals include powellite (CaMoO4) and wulfenite (PbMoO4). Molybdæne commonly occurs in porphyry copper deposits, where it is recovered as a byproduct of copper mining.

Properties of molybdene include a silvery-grey appearance, a very high melting point of about 2,623°C, and a density around 10.2 g/cm3. It is hard and ductile and exhibits good strength and stability at elevated temperatures. Its crystal structure at room temperature is body-centered cubic.

Chemically, the most common oxidation state is +6, as in molybdate (MoO4)2−, and MoS2 serves as a well-known solid lubricant. Molybdæne is widely used as an alloying element in steel and other alloys to improve strength, hardness, creep resistance, and high-temperature performance. It also plays a role in catalysts, notably hydrodesulfurization catalysts where MoS2 on alumina or silica supports is promoted by cobalt or nickel. Molybdenum compounds are used in various chemical processes and in the glass industry.

Biologically, molybdæne is an essential trace element for many organisms, required for enzymes such as xanthine oxidase and nitrate reductase. In humans, deficiency is rare and typically linked to specific medical or dietary conditions; exposure to certain compounds can be toxic.

Historically, the element was isolated in the late 18th century and named for the Greek word meaning lead.