Praseodymium

2008/9 Schools Wikipedia Selection. Related subjects: Chemical elements

59 cerium ← praseodymium → neodymium - ↑ Pr ↓ Pa Periodic Table - Extended Periodic Table
General
Name, Symbol, Number	praseodymium, Pr, 59
Element category	lanthanides
Group, Period, Block	n/a, 6, f
Appearance	grayish white
Standard atomic weight	140.90765 (2)  g·mol−1
Electron configuration	[Xe] 4f3 6s2
Electrons per shell	2, 8, 18, 21, 8, 2
Physical properties
Phase	solid
Density (near r.t.)	6.77  g·cm−3
Liquid density at m.p.	6.50  g·cm−3
Melting point	1208  K (935 ° C, 1715 ° F)
Boiling point	3793  K (3520 ° C, 6368 ° F)
Heat of fusion	6.89   kJ·mol−1
Heat of vaporization	331   kJ·mol−1
Specific heat capacity	(25 °C) 27.20  J·mol−1·K−1
Vapor pressure P(Pa) 1 10 100 1 k 10 k 100 k at T(K) 1771 1973 (2227) (2571) (3054) (3779)
Atomic properties
Crystal structure	hexagonal
Oxidation states	3 (mildly basic oxide)
Electronegativity	1.13 (Pauling scale)
Ionization energies ( more)	1st:  527   kJ·mol−1
	2nd:  1020  kJ·mol−1
	3rd:  2086  kJ·mol−1
Atomic radius	185   pm
Atomic radius (calc.)	247  pm
Miscellaneous
Magnetic ordering	no data
Electrical resistivity	( r.t.) (α, poly) 0.700 µΩ·m
Thermal conductivity	(300 K) 12.5  W·m−1·K−1
Thermal expansion	( r.t.) (α, poly) 6.7 µm/(m·K)
Speed of sound (thin rod)	(20 °C) 2280 m/s
Young's modulus	(α form) 37.3  GPa
Shear modulus	(α form) 14.8  GPa
Bulk modulus	(α form) 28.8  GPa
Poisson ratio	(α form) 0.281
Vickers hardness	400  MPa
Brinell hardness	481  MPa
CAS registry number	7440-10-0
Selected isotopes
Main article: Isotopes of praseodymium iso NA half-life DM DE ( MeV) DP 141Pr 100% 141Pr is stable with 82 neutrons 142Pr syn 19.12 h β- 2.162 142Nd ε 0.745 142Ce 143Pr syn 13.57 d β- 0.934 143Nd
References

Praseodymium (pronounced /ˌpreɪzioʊˈdɪmiəm/ or /ˌpreɪsioʊˈdɪmiəm/) is a chemical element that has the symbol Pr and atomic number 59.

Characteristics

Praseodymium is a soft silvery metal in the lanthanide group. It is somewhat more resistant to corrosion in air than europium, lanthanum, cerium, or neodymium, but it does develop a green oxide coating that spalls off when exposed to air, exposing more metal to oxidation. For this reason, praseodymium should be stored under a light mineral oil or sealed in glass.

Applications

Uses of praseodymium:

• As an alloying agent with magnesium to create high-strength metals that are used in aircraft engines.
• Praseodymium forms the core of carbon arc lights which are used in the motion picture industry for studio lighting and projector lights.
• Praseodymium compounds give glasses and enamels a yellow colour.
• Praseodymium is used to colour cubic zirconia yellow-green, to simulate peridot.
• Praseodymium is a component of didymium glass, which is used to make certain types of welder's and glass blower's goggles.
• Praseodymium mixed with silicate crystal has been used to slow a light pulse down to a few hundred meters per second.
• Praseodymium alloyed with nickel (PrNi₅) has such a strong magnetocaloric effect that it has allowed scientists to approach within one thousandth of a degree of absolute zero.
• Doping praseodymium in fluoride glass allows it to be used as a single mode fibre amplifier.
• Praseodymium oxide in solid solution with ceria, or with ceria-zirconia, have been used as oxidation catalysts.

History

The name praseodymium comes from the Greek prasios, meaning green, and didymos, twin. Praseodymium is frequently misspelled as praseodynium.

In 1841, Mosander extracted the rare earth didymium from lanthana. In 1874, Per Teodor Cleve concluded that didymium was in fact two elements, and in 1879, Lecoq de Boisbaudran isolated a new earth, samarium, from didymium obtained from the mineral samarskite. In 1885, the Austrian chemist baron Carl Auer von Welsbach separated didymium into two elements, praseodymium and neodymium, which gave salts of different colors.

Leo Moser (not to be confused with Leo Moser, a mathematician) investigated the use of praseodymium in glass coloration in the late 1920s. The result was a yellow-green glass given the name "Prasemit". However, a similar color could be achieved with colorants costing only a minute fraction of what praseodymium cost in the late 1920s, such that the colour was not popular, few pieces were made, and examples are now extremely rare. Moser also blended praseodymium with neodymium to produce "Heliolite" glass ("Heliolit" in German), which was more widely accepted. The first enduring commercial use of praseodymium, which continues today, is in the form of a yellow-orange stain for ceramics, "Praseodymium Yellow", which is a solid-solution of praseodymium in the zirconium silicate (zircon) lattice. This stain has no hint of green in it. By contrast, at sufficiently high loadings, praseodymium glass is distinctly green, rather than pure yellow.

Praseodymium has historically been a rare earth whose supply has exceeded demand. Unwanted as such, much praseodymium has been marketed as a mixture with lanthanum and cerium, or "LCP" for the first letters of each of the constituents, for use in replacing the traditional lanthanide mixtures that were inexpensively made from monazite or bastnaesite. LCP is what remains of such mixtures, after the desirable neodymium, and all the heavier, rarer and more valuable lanthanides have been removed, by solvent extraction. However, as technology progresses, praseodymium has been found possible to incorporate into neodymium-iron-boron magnets, thereby extending the supply of the much in demand neodymium. So LC is starting to replace LCP as a result.

Occurrence

Praseodymium is available in small quantities in Earth’s crust (9.5 ppm). It is found in the rare earth minerals monazite and bastnasite, typically comprising about 5% of the lanthanides contained therein, and can be recovered from bastnasite or monazite by an ion exchange process, or by counter-current solvent extraction.

Praseodymium also makes up about 5% of misch metal.

Compounds

Praseodymium compounds include:

• Fluorides: PrF₂, PrF₃, PrF₄
• Chlorides: PrCl₃
• Bromides: PrBr₃, Pr₂Br₅
• Iodides: PrI₂, PrI₃, Pr₂I₅
• Oxides: PrO₂, Pr₂O₃, Pr₆O₁₁
• Sulfides: PrS, Pr₂S₃
• Selenides: PrSe
• Tellurides: PrTe, Pr₂Te₃
• Nitrides: PrN

Isotopes

Naturally occurring praseodymium is composed of one stable isotope, ¹⁴¹Pr. Thirty-eight radioisotopes have been characterized with the most stable being ¹⁴³Pr with a half-life of 13.57 days and ¹⁴²Pr with a half-life of 19.12 hours. All of the remaining radioactive isotopes have half-lives that are less than 5.985 hours and the majority of these have half-lives that are less than 33 seconds. This element also has six meta states with the most stable being ^138mPr (t_½ 2.12 hours), ^142mPr (t_½ 14.6 minutes) and ^134mPr (t_½ 11 minutes).

The isotopes of praseodymium range in atomic weight from 120.955 u (¹²¹Pr) to 158.955 u (¹⁵⁹Pr). The primary decay mode before the stable isotope, ¹⁴¹Pr, is electron capture and the primary mode after is beta minus decay. The primary decay products before ¹⁴¹Pr are element 58 (cerium) isotopes and the primary products after are element 60 (neodymium) isotopes.

Precautions

Like all rare earths, praseodymium is of low to moderate toxicity. Praseodymium has no known biological role.