Praseodymium Pr

Discovery

In 1841 Carl Gustaf Mosander separated another substance from lanthanum oxide and called it didymium, "twin", because it always accompanied lanthanum. For more than forty years didymium was treated as a single element.

As spectroscopy advanced, however, it became clear that didymium's spectrum varied slightly from sample to sample. In 1885 the Austrian chemist Carl Auer von Welsbach performed hundreds of fractional crystallisations of didymium ammonium nitrate and succeeded in splitting it into a green salt and a pink salt.

He named the element of the green salt praseodymium and that of the pink salt neodymium. Reasonably pure praseodymium metal was not produced until the twentieth century.

Origin of the name

The name combines the Greek prasios, "leek-green", with didymos, "twin", meaning "green twin", after the colour of its salts. The symbol is Pr.

Main uses

• Permanent magnets: part of the neodymium in neodymium magnets is often replaced with praseodymium, and the NdPr mixture is a key raw material for electric vehicle motors and wind turbine generators.
• Protective eyewear: didymium glass, containing praseodymium and neodymium, filters the intense yellow sodium light given off by hot glass, protecting glassblowers and welders.
• Colouring: praseodymium-doped zircon makes a bright yellow ceramic glaze, and in glass it gives a light green tint.
• Alloys: added to magnesium, it produces high-strength alloys for aircraft engine parts.
• Optics: it is a dopant in some fibre amplifiers and lasers.

Isotopes

Praseodymium has only one stable isotope, praseodymium-141. Radioactive praseodymium-143 (half-life about 13.6 days) and praseodymium-144 (about 17 minutes) are fission products; praseodymium-144 forms when cerium-144 decays.

In everyday life

Praseodymium is extracted with other rare earths from bastnäsite and monazite and is often produced and traded mixed with neodymium. China accounts for a large share of mining and refining.

The metal slowly oxidises in air, so it is stored under oil or inert gas. Its toxicity is low, but the metal powder ignites easily. The growth of electric vehicles and wind power has made it an element of strategic importance.