Praseodymium

Praseodymium

Praseodymium is a chemical element that has the symbol Pr and atomic number 59. Praseodymium is a soft, silvery, malleable and ductile metal in the lanthanide group. It is too reactive to be found in native form, and when artificially prepared, it slowly develops a green oxide coating.

The element was named for the color of its primary oxide. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare earth oxide residue he called "didymium" from a residue he called "lantana," in turn separated from cerium salts. In 1885, the Austrian chemist Baron Carl Auer von Welsbach separated didymium into two salts of different colors, which he named praseodymium and neodymium. The name praseodymium comes from the Greek prasios (πράσιος), meaning green, and didymos (δίδυμος), twin.

Like most rare earth elements, praseodymium most readily forms trivalent Pr(III) ions. These are yellow-green in water solution, and various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its use to filter yellow light from light sources.

Occurrence


Praseodymium occurs in small quantities in Earth's crust (9.5 ppm). It is found in the rare earth minerals monazite and bastnäsite, typically comprising about 5% of the lanthanides contained therein, and can be recovered from these minerals by an ion exchange process, or by counter-current solvent extraction. Misch metal, used in making cigarette lighters, historically contained about 5% praseodymium metal.[8]
Praseodymium makes up an average of 8 parts per million of soil's dry weight, though the elements concentration there can be as low as 1 part per million or as high as 15 parts per million. Praseodymium makes up 1 part per trillion of seawater. There is almost no praseodymium in the atmosphere.

Symbol		Pr
Atomic Number		59
Atomic Weight		140.90765
Oxidation States		+3
Electronegativity, Pauling		1.13
State at RT		Solid, Metal
Melting Point, K		1204
Boiling Point, K		3785

Appearance and Characteristics

Harmful effects:

Praseodymium is considered to be moderately toxic.

Characteristics:

• Praseodymium is a soft, malleable, ductile, silvery metal.
• Praseodymium is one of the lanthanide rare earth metals.
• It forms a flaky black oxide coating (Pr6O11) in air. Unlike many metal oxide layers, this one does not protect the metal from further oxidation. The pale green sesquioxide, Pr2O3, is not stable in air. 
• Praseodymium reacts with water to form praseodymium hydroxide plus hydrogen gas.
• Praseodymium usually exists as a trivalent ion, Pr3+, in its compounds. Most of its salts are pale green in color.

Uses of Praseodymium

• Praseodymium is used in high-intensity permanent magnets, which are essential in electric motors and generators used in hybrid cars and wind turbines.
• Praseodymium is used in nickel metal hydride (NiMH) rechargeable batteries for hybrid automobiles. The negative electrode (cathode) in NiMH batteries is a mixture of metal hydrides – typically a rare earth misch metal hydride containing praseodymium, neodymium, lanthanum and cerium.
• The metal is used as an alloying agent with magnesium creating a high-strength metal for aircraft engines.
• Praseodymium is used to make specialized yellow glass goggles for glass blowers and welders.
• Flame lighter flints use misch metal (a rare earth alloy) containing praseodymium to produce sparks by friction.
• Praseodymium salts are used to color glasses and enamels.
• Praseodymium is also used in the core of high-intensity carbon arc lights used by the film industry and in floodlighting.