Molybdenum

Category: transition metal Atomic number: 42 Colour: silvery white Melting point: 2,623°C (4,753°F) Boiling point: 4,639°C (8,382°F) First identified: 1781

For an element that most people know very little about, molybdenum is surprisingly crucial to human life. In plants and animals, there is a wide range of enzymes, one of which is nitrogenase. This is found in bacteria that live in the roots of plants such as beans. They absorb nitrogen from the air and emit ammonia: a key part of the process of ‘nitrogen fixing’, whereby nitrogen is converted into a form that humans and animals can digest. We rely on that nitrogen to manufacture proteins in our body. So, we simply couldn’t survive without trace elements of molybdenum in the environment.

The element is also integral to the production of ‘moly steel’, an alloy of steel with molybdenum added to it. In the First World War, the earliest British tanks to be deployed on the Western Front were armour plated with three-inch manganese steel plates, which couldn’t withstand direct hits. They were replaced with molybdenum steel plating, which was only one inch thick (so lighter) but proved to be far more effective. Moly steel is also used in high-grade construction, such as skyscrapers and bridges.

The name of the element comes from the Greek molybdos, meaning ‘lead’: it doesn’t occur naturally in its pure form and its main ore, molybdenite, was often mistaken for either a lead ore or graphite, which it closely resembles. Carl Wilhelm Scheele realized in 1778 that it was neither lead nor graphite. His friend Peter Jacob Hjelm successfully followed up on his work and isolated the element, a shiny, silvery metal, in 1781, using a method that looks like alchemical magic: he ground up some carbon with molybdic acid, then made a paste of this with linseed oil. When this was heated until it became red-hot, the metal emerged from the mixture.

Molybdenum is used today in tiny amounts in electric heater filaments, missiles and protective boiler coatings, and as a catalyst for refining petroleum. Molybdenum sulphides are also the main ingredient in lubricants that are heat-resistant at higher temperatures than petroleum-based oils such as WD-40.