Overview of the Element Praeseodymium


Chemical Symbol: Pr

Atomic Number: 59

Atomic Mass: 140.90765 amu (atomic mass units)

Melting Point: 935.0 C (1208.15 K, 1715.0 F)

Boiling Point: 3127.0 C (3400.15 K, 5660.6 F)

Number of Protons/Electrons: 59

Number of Neutrons: 82

Classification: Rare Earth Metal

Crystal Structure: Hexagonal

Density @ 293 K: 6.77 grams per cubic centimeter

Color: Silver

Praseodymium is a rare earth element of the lanthanide or lanthanoid series. It was discovered by the German chemist Carl F. Auer von Welsbach in the year 1885. He separated praseodymium and another rare earth element – neodymium from a substance called dydimium. The dydimium had in turn been extracted from the mineral Samarskite which is a source ore of many of the naturally occuring rare earth elements. Praseodymiums’ name comes from the Greek words “prasios” meaning green and “didymos” which means twin.

The silvery colored element oxidizes in air leaving a green powder coating the surface of the metal. To prevent this oxidization it is recommended that pure praseodymium be sealed in plastic or stored under liquid paraffin or petroleum. The pure metal is soft, malleable and ductile.

Praseodymium has one naturally occurring isotopes this being Praseodymium-141 which is stable. A number of man made isotopes have also been produced and there are currently thirty eight recognized isotopes with mass numbers ranging from 121 to 159.

Praseodymium has never been found as a pure metal in nature instead it is found as part of a mineral ore. The first relatively pure sample of the element was prepared in 1931. The metal is extracted from the mineral sand monazite and from bastnasite ore using ion exchange and solvent extraction methods. These ores also contain the highly radioactive element thorium so extreme care must be taken in the extraction process.

There are a number of uses for praseodymium.

* It can be combined with the element neodymium to give a yellow/green color to glass.

* When incorporated with zircon it is used to provide a yellow-orange ceramic glaze known as “Praseodymium yellow”.

* Along with a number of other rare earth elements it is used in carbon-arc lighting for the motion picture industry.

* It is found as part of dydimium glass which is used in the production of welder safety goggles and masks.

* Praseodymium is one of the elements making up the rare earth metal alloy, misch metal, which is used to make the flints in cigarette lighters.

* Another major use is as an alloying agent with Magnesium to produce high strength metals suitable for use in the production of aircraft engines.

Praseodymium has no proven biological role but some researchers believe it may stimulate metabolism. As the toxicity of the element has not yet been fully studied industrial exposure to the pure element should be minimized.

The Los Alamos National Laboratory Chemistry Division http://periodic.lanl.gov/elements/59.html

The National Nuclear Data Center http://www.nndc.bnl.gov/