Gadolinium

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64 europiumgadoliniumterbium
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Gd

curium
Gd-TableImage.png
General
Name, Symbol, Number gadolinium, Gd, 64
Chemical series lanthanides
Group, Period, Block n/a, 6, f
Appearance silvery white
Gd,64.jpg
Atomic mass 157.25(3) g/mol
Electron configuration [Xe] 4f7 5d1 6s2
Electrons per shell 2, 8, 18, 25, 9, 2
Physical properties
Phase solid
Density (near r.t.) 7.90 g/cm³
Liquid density at m.p. 7.4 g/cm³
Melting point 1585 K
(1312 °C, 2394 °F)
Boiling point 3546 K
(3273 °C, 5923 °F)
Heat of fusion 10.05 kJ/mol
Heat of vaporization 301.3 kJ/mol
Heat capacity (25 °C) 37.03 J/(mol·K)
Vapor pressure (calculated)
P/Pa 1 10 100 1 k 10 k 100 k
at T/K 1836 2028 2267 2573 2976 3535
Atomic properties
Crystal structure hexagonal
Oxidation states 3
(mildly basic oxide)
Electronegativity 1.20 (Pauling scale)
Ionization energies
(more)
1st: 593.4 kJ/mol
2nd: 1170 kJ/mol
3rd: 1990 kJ/mol
Atomic radius 180 pm
Atomic radius (calc.) 233 pm
Miscellaneous
Magnetic ordering ferromagnetic
Electrical resistivity (r.t.) (α, poly)
1.310 µΩ·m
Thermal conductivity (300 K) 10.6 W/(m·K)
Thermal expansion (100 °C) (α, poly)
9.4 µm/(m·K)
Speed of sound (thin rod) (20 °C) 2680 m/s
Speed of sound (thin rod) (r.t.) (α form) 54.8 m/s
Shear modulus (α form) 21.8 GPa
Bulk modulus (α form) 37.9 GPa
Poisson ratio (α form) 0.259
Vickers hardness 570 MPa
CAS registry number 7440-54-2
Notable isotopes
Main article: Isotopes of gadolinium
iso NA half-life DM DE (MeV) DP
152Gd 0.20% 1.08×1014 year α 2.205 148samarium
154Gd 2.18% Gd is stable with 90 neutrons
155Gd 14.80% Gd is stable with 91 neutrons
156Gd 20.47% Gd is stable with 92 neutrons
157Gd 15.65% Gd is stable with 93 neutrons
158Gd 24.84% Gd is stable with 94 neutrons
160Gd 21.86% >1.3×1021y β-β- 1.7 160Dy

Gadolinium (chemical symbol Gd, atomic number 64) is a silvery white metallic element and a member of the lanthanide series of chemical elements. It is considered one of the "rare earth metals."[1] Compounds containing gadolinium may be found in such technologies as microwave ovens, televisions, nuclear propulsion systems, magnetic resonance imaging (MRI), and positron emission tomography (PET.)

Contents

Occurrence and isolation

Gadolinium at a purity in excess of 99.9 percent

In nature, gadolinium is found not as the free element but in various minerals such as monazite and bastnäsite. It occurs in only trace amounts in the mineral gadolinite. Both gadolinium and gadolinite were named after the Finnish chemist and geologist Johan Gadolin.

Today, gadolinium is isolated by techniques such as ion exchange and solvent extraction, or by the reduction of its anhydrous fluoride with metallic calcium.

History

In 1880, Swiss chemist Jean Charles Galissard de Marignac examined samples of didymium and gadolinite by spectroscopy and observed the unique spectral lines produced by gadolinium. French chemist Paul Émile Lecoq de Boisbaudran separated gadolinia, the oxide of gadolinium, from Mosander's yttria in 1886. The element itself was isolated only recently.[2]

Notable characteristics

Gadolinium is an inner transition metal (or lanthanide) that lies in period 6 of the periodic table, between europium and terbium. It is malleable and ductile. Unlike other rare earth elements, gadolinium is relatively stable in dry air; however, it tarnishes quickly in moist air and forms a loosely adhering oxide that spalls off and exposes more surface to oxidation. Gadolinium reacts slowly with water and is soluble in dilute acid.

At room temperature, gadolinium crystallizes to produce its "alpha" form, which has a hexagonal, close-packed structure. When heated to 1508 Kelvin, it transforms into its "beta" form, which has a body-centered cubic structure.

Gadolinium has the highest thermal neutron capture cross-section of any (known) element (about 49,000 barns), but it also has a fast burn-out rate, limiting its usefulness as a material for nuclear control rods.

Gadolinium becomes superconductive below a critical temperature of 1.083 K. It is strongly magnetic at room temperature and exhibits ferromagnetic properties below room temperature.

Gadolinium demonstrates a magenetocaloric effect whereby its temperature increases when it enters a magnetic field and decreases when it leaves the magnetic field. The effect is considerably stronger for the gadolinium alloy Gd5(Si2Ge2).[3]

Isotopes

Naturally occurring gadolinium is composed of 5 stable isotopes, 154Gd, 155Gd, 156Gd, 157Gd and 158Gd, and 2 radioisotopes, 152Gd and 160Gd, with 158Gd being the most abundant (24.84 percent natural abundance). Thirty radioisotopes have been characterized with the most stable being 160Gd with a half-life of more than 1.3×1021 years (the decay is not observed, only the lower limit on the half-life is known), alpha-decaying 152Gd with a half-life of 1.08×1014 years, and 150Gd with a half-life of 1.79×106 years. All of the remaining radioactive isotopes have half-lives that are less than 74.7 years, and the majority of these have half lives that are less than 24.6 seconds. This element also has 4 meta states with the most stable being 143mGd (t½ 110 seconds), 145mGd (t½ 85 seconds) and 141mGd (t½ 24.5 seconds).

The primary decay mode before the most abundant stable isotope, 158Gd, is electron capture and the primary mode after is beta minus decay. The primary decay products before 158Gd are element Eu (europium) isotopes and the primary products after are element Tb (terbium) isotopes.

Compounds

Compounds of gadolinium include:

  • Fluoride
    • gadolinium(III) fluoride (GdF3)
  • Chloride
    • gadolinium(III) chloride (GdCl3)
  • Bromide
    • gadolinium(III) bromide (GdBr3)
  • Iodide
    • gadolinium(III) iodide (GdI3)
  • Oxide
    • gadolinium(III) oxide (Gd2O3)
  • Sulfide
    • gadolinium(III) sulfide (Gd2S3)
  • Nitride
    • gadolinium(III) nitride (GdN)

Applications

Gadolinium is used for making gadolinium yttrium garnets, which have microwave applications, and gadolinium compounds are used for making phosphors for color TV tubes. Gadolinium is also used for manufacturing compact discs and computer memory.

Gadolinium is used in nuclear marine propulsion systems as a burnable poison. The gadolinium slows the initial reaction rate, but as it decays other neutron poisons accumulate, allowing for long-running cores. Gadolinium is also used as a secondary, emergency shut-down measure in some nuclear reactors, particularly of the CANDU type.

Gadolinium also possesses unusual metallurgic properties, with as little as one percent of gadolinium improving the workability and resistance of iron, chromium and related alloys to high temperatures and oxidation.

Because of their paramagnetic properties, solutions of organic gadolinium complexes and gadolinium compounds are used as intravenous radiocontrast agents to enhance images in medical magnetic resonance imaging (MRI). Magnevist is the most widespread example.

In X-ray technology, gadolinium is contained in the phosphor layer suspended in a polymer matrix at the detector. Terbium-doped gadolinium oxysulfide (Gd2O2S: Tb) at the phosphor layer converts X-rays released from the source into light.

A single crystal of gadolinium oxyorthosilicate (GSO) is used as a scintillator in medical imaging equipment such as positron emission tomography (PET). Another new scintillator for detecting neutrons is gadolinium orthosilicate (GSO - Gd2SiO5: Ce).

Gadolinium gallium garnet (Gd3Ga5O12) is a material with good optical properties. It is used in the fabrication of various optical components and as a substrate for magneto–optical films.

In the future, gadolinium ethyl sulfate, which has extremely low noise characteristics, may be used in masers. Furthermore, gadolinium's high magnetic moment and low Curie temperature (which lies at room temperature) suggest applications as a magnetic component for sensing heat and cold.

Due the extremely high neutron cross-section of gadolinium, this element is very effective for use with neutron radiography.

Biological role and precautions

Gadolinium has no known biological role. As in the case of the other lanthanides, gadolinium compounds have low-to-moderate toxicity, but their toxicity has not been investigated in detail. In the case of patients on dialysis, some data suggest that it may cause nephrogenic systemic fibrosis, formerly known as nephrogenic dermopathy.[4]

See also

Notes

  1. The term "rare earth metals" (or "rare earth elements") is a trivial name applied to 16 chemical elements: scandium, yttrium, and 14 of the 15 lanthanides (excluding promethium), which occur naturally on Earth. Some definitions also include the actinides. The word "earth" is an obsolete term for oxide. The term "rare earth" is discouraged by the International Union of Pure and Applied Chemistry (IUPAC), as these elements are relatively abundant in the Earth's crust.
  2. In older literature, the natural form of the element is often called an "earth," meaning that it came from the Earth. Accordingly, gadolinium is the element that comes from the earth called gadolinia. Earths are compounds of the element, with one or more other elements. Two common combining elements are oxygen and sulfur. For example, gadolinia contains gadolinium oxide (Gd2O3).
  3. Karl Gschneidner, Jr. and Kerry Gibson, "Magnetic Refrigerator Successfully Tested," Ames Laboratory News Release (December 7, 2001). Retrieved June 21, 2007.
  4. T. Grobner, “Related Articles, Gadolinium—a specific trigger for the development of nephrogenic fibrosing dermopathy and nephrogenic systemic fibrosis?” Nephrol Dial Transplant 21(4) (April 2006): 1104-1108.

References

  • “Gadolinium.” Los Alamos National Laboratory, Chemistry Division. Retrieved June 21, 2007.
  • Chang, Raymond. 2006. Chemistry 9th edition. New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031
  • Cotton, F. Albert and Geoffrey Wilkinson. 1980. Advanced Inorganic Chemistry 4th edition. New York: Wiley. ISBN 0471027758
  • Greenwood, N. N. and A. Earnshaw. 1998. Chemistry of the Elements 2nd edition. Oxford, U.K.; Burlington, MA: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654 Online version
  • Jones, Adrian P., Frances Wall, and C. Terry Williams (eds.). 1996. Rare Earth Minerals: Chemistry, Origin and Ore Deposits. The Mineralogical Society Series. London: Chapman and Hall. ISBN 0412610302
  • Stwertka, Albert. 1998. Guide to the Elements Rev. edition. Oxford: Oxford University Press. ISBN 0195080831

External links

All links retrieved November 23, 2013.

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