Math Is Fun Forum

Jai Ganesh

Administrator

Registered: 2005-06-28

Posts: 51,439

Praseodymium

Praseodymium

Gist

Praseodymium is a chemical element; it has symbol Pr and atomic number 59. It is the third member of the lanthanide series and is considered one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties.

Praseodymium's primary use is as an alloying agent with magnesium to create high-strength metals that are used in aircraft engines. Praseodymium also makes up about 5% of Misch metal, a material that is used to make flints for lighters.

Summary

Praseodymium is a chemical element; it has symbol Pr and atomic number 59. It is the third member of the lanthanide series and is considered one of the rare-earth metals. It is a soft, silvery, malleable and ductile metal, valued for its magnetic, electrical, chemical, and optical properties. It is too reactive to be found in native form, and pure praseodymium metal slowly develops a green oxide coating when exposed to air.

Praseodymium always occurs naturally together with the other rare-earth metals. It is the sixth-most abundant rare-earth element and fourth-most abundant lanthanide, making up 9.1 parts per million of the Earth's crust, an abundance similar to that of boron. In 1841, Swedish chemist Carl Gustav Mosander extracted a rare-earth oxide residue he called didymium from a residue he called "lanthana", in turn separated from cerium salts. In 1885, the Austrian chemist Carl Auer von Welsbach separated didymium into two elements that gave salts of different colours, which he named praseodymium and neodymium. The name praseodymium comes from the Ancient Greek (prasinos), meaning 'leek-green', and (didymos) 'twin'.

Like most rare-earth elements, praseodymium most readily forms the +3 oxidation state, which is the only stable state in aqueous solution, although the +4 oxidation state is known in some solid compounds and, uniquely among the lanthanides, the +5 oxidation state is attainable at low temperatures. The 0, +1, and +2 oxidation states are rarely found. Aqueous praseodymium ions are yellowish-green, and similarly, praseodymium results in various shades of yellow-green when incorporated into glasses. Many of praseodymium's industrial uses involve its ability to filter yellow light from light sources.

Details

Praseodymium (Pr) is a chemical element, a rare-earth metal of the lanthanide series of the periodic table.

Praseodymium is a moderately soft, ductile, and malleable silvery white metal. It rapidly displaces hydrogen from water in diluted acids (except hydrofluoric acid [HF]) and slowly oxidizes in air, developing a green-yellowish oxide coating with complex and varying stoichiometry that can be expressed using a generic formula PrOx (1.5 ≤ x ≤ 2). The metal is best stored sealed in a plastic covering either in vacuum or in an inert atmosphere. Praseodymium is strongly paramagnetic, and an unstrained single-crystal sample will order antiferromagnetically at 0.03 K (−273.12 °C, or −459.62 °F). However, if praseodymium is strained, it may order at temperatures as high as about 20 K (−253 °C, or −424 °F).

Praseodymium was discovered in didymia, a mixture of several rare-earth oxides. From it, by repeated fractional crystallization of ammonium didymium nitrate, Austrian chemist Carl Auer von Welsbach in 1885 separated salts of the elements praseodymium (the green fraction) and neodymium (the pink fraction). Praseodymium occurs in minerals such as monazite and bastnasite and as one of the products of nuclear fission.

Natural praseodymium is entirely the stable isotope praseodymium-141. Excluding nuclear isomers, a total of 38 radioactive isotopes of praseodymium have been reported. They range in mass from 121 to 159 and have half-lives from 10 milliseconds (praseodymium-121) to 13.57 days (praseodymium-143).

This element is commercially separated and purified by liquid-liquid extraction or ion-exchange techniques. The metal is prepared by electrolysis of fused anhydrous halides or by the metallothermic reduction of the fluoride or chloride with calcium. Praseodymium exists in two allotropic (structural) forms. The α-phase is double close-packed hexagonal with a = 3.6721 Å and c = 11.8326 Å at room temperature. The β-phase is body-centred cubic with a = 4.13 Å at 821 °C (1,510 °F).

Praseodymium is a minor constituent of misch metal, which is used to make lighter flints and as alloying additions to ferrous and nonferrous alloys. The metal is also used as an addition to Nd2Fe14B permanent magnet alloys leading to a reduction of the amount of neodymium required. Praseodymium-stabilized zirconia (ZrO2) is the foundation of synthetic green-coloured gems. A mixture of praseodymium and neodymium is the active component in didymium glass, used for goggles to protect the eyes of glassblowers and welders. Praseodymium compounds are also used to produce light green to yellow colours in ceramics and other glasses.

Praseodymium forms trivalent compounds such as the olive-green oxide Pr2O3, which dissolves readily in acids to yield green trivalent praseodymium salts. The tetravalent blackish purple dioxide PrO2 is known, but the Pr4+ ion is unknown in aqueous solution.

Element Properties

atomic number  :  59
atomic weight  :  140.90765
melting point  :  931 °C (1,708 °F)
boiling point  :  3,520 °C (6,368 °F)
specific gravity  :  6.773 (24 °C, or 75 °F)
oxidation states  :  +3, +4.

Additional Information:

Appearance

A soft, silvery metal.

Uses

Praseodymium is used in a variety of alloys. The high-strength alloy it forms with magnesium is used in aircraft engines. Mischmetal is an alloy containing about 5% praseodymium and is used to make flints for cigarette lighters. Praseodymium is also used in alloys for permanent magnets.

Along with other lanthanide elements, it is used in carbon arc electrodes for studio lighting and projection.

Praseodymium salts are used to colour glasses, enamel and glazes an intense and unusually clean yellow. Praseodymium oxide is a component of didymium glass (along with neodymium). This glass is used in goggles used by welders and glassmakers, because it filters out the yellow light and infrared (heat) radiation.

Biological role

Praseodymium has no known biological role. It has low toxicity.

Natural abundance

Praseodymium occurs along with other lanthanide elements in a variety of minerals. The two principal sources are monazite and bastnaesite. It is extracted from these minerals by ion exchange and solvent extraction.

Praseodymium metal is prepared by reducing anhydrous chloride with calcium.

---

It appears to me that if one wants to make progress in mathematics, one should study the masters and not the pupils. - Niels Henrik Abel.

Nothing is better than reading and gaining more and more knowledge - Stephen William Hawking.