Molybdenum

Most molybdenum today comes from the mineral ore molybdenite (molybdenum disulfide, MoS₂). But prior to 1778, molybdenite was often confused with graphite (a form of carbon) and the lead ore, galena (lead sulfide, PbS). In fact, the element's name comes from the Greek word molybdos, meaning lead, and molybdenite was often used like graphite. It was a darkening agent like pencil “lead” and a dry lubricant like powdered graphite.

In 1778, Carl Wilhelm Sheele, a Swedish chemist, determined that molybdenite was neither graphite nor lead sulfide. He suggested it contained a new element and named it molybdenum, after the ore. Sheele then handed his research off to Peter Jacob Hjelm, who found a way to isolate molybdenum in 1781.

Molybdenum metal is shiny, silver-white, and very hard. It has one of the highest melting points among readily available metals. It is very resistant to being stretched or compressed and is less likely to expand with heat.

About 80% of commercially available molybdenum is used in alloys. Its high melting point, resistance to oxidizing except at high temperatures, lack of elasticity, and lack of thermal expansion (swelling with heat) make it ideal for strengthening other metals. It is particularly valuable for alloying with steel to increase strength, hardness, and resistance to corrosion. Most high-strength steels contain up to 8 percent molybdenum. It also makes valuable heat- and corrosion-resistant nickel alloys. Molybdenum alloys are used in engine parts, power tools, heating elements, and electrodes. Alloying with molybdenum also improves electrical conductivity.

Molybdenum disulfide powder is still used as a dry lubricant, just as it was hundreds of years ago. It can withstand high temperatures that would break down oil-based lubricants. Other uses for molybdenum include catalysts and pigments.

Though rare—58th in abundance in the earth’s crust—molybdenum is found in concentrated pockets, which increases its availability. It is mostly obtained from molybdenite ore. Wulfenite and Powellite are minor commercial sources. Molybdenum is also recovered as a byproduct of copper and tungsten mining operations.

Getting molybdenum metal out of molybdenite is a complex, multi-step chemical process. The process involves oxidizing (replacing the sulfide with oxide), treating and extracting with ammonia, and reacting with hydrogen gas to displace the oxide. Multiple heating steps are needed along the way. Once isolated, it is sold as a gray powder.