Saturday, April 3, 2021

Rare Earth Metals

Scientists and engineers disagree on exactly which element should be included in a list of the rare earths, but they generally include the fifteen lanthanide elements, plus scandium and yttrium. This includes atomic number 57 through 71, as well as 39 (yttrium) and 21 (scandium).

Despite their name, the rare earths aren't actually rare with respect to abundance in the Earth's crust. The exception is promethium, a radioactive metal.

China holds about 70% of the world’s known rare earth reserves, making it the dominator in this market. But now, under President Joe Biden’s administration, the Department of Energy has planned to make rare earth metals a priority among the domestic supply chain. Rare earth elements are crucial to Biden’s ambitious climate and technology policy. These metals are used in electric vehicle production, battery, renewable energy systems and technology manufacturing.

Rare earth metals include all the 15 elements in the lanthanoid group of the periodic table plus scandium and yttrium. 

Rare Earth Uses
In general, the rare earths are used in alloys, for their special optical properties, and in electronics. Some specific uses of elements include:
  • Scandium: Use to make light alloys for the aerospace industry, as a radioactive tracer, and in lamps
  • Yttrium: Used in yttrium aluminum garnet (YAG) lasers, as a red phosphor, in superconductors, in fluorescent tubes, in LEDs, and as a cancer treatment
  • Lanthanum: Use to make high refractive index glass, camera lenses, and catalysts
  • Cerium: Use to impart a yellow color to glass, as a catalyst, as a polishing powder, and to make flints
  • Praseodymium: Used in lasers, arc lighting, magnets, flint steel, and as a glass colorant
  • Neodymium: Used to impart violet color to glass and ceramics, in lasers, magnets, capacitors, and electric motors
  • Promethium: Used in luminous paint and nuclear batteries
  • Samarium: Used in lasers, rare earth magnets, masers, nuclear reactor control rods
  • Europium: Used to prepare red and blue phosphors, in lasers, in fluorescent lamps, and as an NMR relaxant
  • Gadolinium: Used in lasers, x-ray tubes, computer memory, high refractive index glass, NMR relaxation, neutron capture, MRI contrast
  • Terbium: Use in green phosphors, magnets, lasers, fluorescent lamps, magnetostrictive alloys, and sonar systems
  • Dysprosium: Used in hard drive disks, magnetostrictive alloys, lasers, and magnets
  • Holmium: Use in lasers, magnets, and calibration of spectrophotometers
  • Erbium: Used in vanadium steel, infrared lasers, and fiber optics
  • Thulium: Used in lasers, metal halide lamps, and portable x-ray machines
  • Ytterbium: Used in infrared lasers, stainless steel, and nuclear medicine
  • Lutetium: Used in positron emission tomography (PET) scans, high refractive index glass, catalysts, and LEDs

Rare earth elements were originally thought to be rare, however it is now known that many of them are actually fairly abundant, with cerium being the 25th most abundant material in the Earth’s crust. What makes rare earths harder to come by is their geochemical tendency to co-exist in very small amounts attached to common ores and elements. It is for this reason that they are generally produced as by-products from other mined ores. 

These elements became popular when it was discovered that they could help greatly reduce the size of those brick-sized old cell phones. Since then, they’ve been implemented in all sorts of new technology and have also become important in the creation of powerful rare earth magnets.

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