Gadolinium

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Gadolinium is a chemical element in the periodic table that has the symbol Gd and atomic number 64.

Contents 1 Notable characteristics 2 Applications 3 History 4 Biological role 5 Occurrence 6 Compounds 7 Isotopes 8 Precautions 9 References 10 External links

Image:Gadolinium.jpg

Notable characteristics

Gadolinium is a silvery white, malleable and ductile rare earth metal with a metallic luster. It crystallizes in hexagonal, close-packed alpha form at room temperature; when heated to 1508 K, it transforms into its beta form, which has a body-centered cubic structure.

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.

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

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.

Applications

Gadolinium is used for making gadolinium yttrium garnets, which have microwave applications, and gadolinium compounds are used for making phosphors for colour 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 1% of gadolinium improving the workability and resistance of iron, chromium and related alloys to high temperatures and oxidation.

Solutions of organic gadolinium complexes are used as intravenous radiocontrast agents to enhance images in medical magnetic resonance imaging.

Because of their paramagnetic properties, gadolinium compounds are used in magnetic resonance imaging.

Gallium Gadolinium Garnet (Gd₃Ga₅O₁₂) is a material with good optical properties, and is used in fabrication of various optical components and as substrate material 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 movement and low Curie temperature (which lies just at room temperature) suggest applications as a magnetic component for sensing hot and cold.

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

History

In 1880, Swiss chemist Jean Charles Galissard de Marignac observed spectroscopic lines due to gadolinium in samples of didymium and gadolinite; 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.

Gadolinium, like the mineral gadolinite, is named after Finnish chemist and geologist Johan Gadolin.

Biological role

Gadolinium has no known biological role.

Occurrence

Gadolinium is never found in nature as the free element, but is contained in many rare minerals such as monazite and bastnasite. It occurs only in trace amounts in the mineral gadolinite which was also named for Johan Gadolin. Today, it is prepared by ion exchange and solvent extraction technique, or by the reduction of its anhydrous fluoride with metallic calcium.

Compounds

Compounds of gadolinium include:

• Fluorides
  • GdF₃
• Chlorides
  • GdCl₃
• Bromides
  • GdBr₃
• Iodides
  • GdI₃
• Oxides
  • Gd₂O₃
• Sulfides
  • Gd₂S₃
• Nitrides
  • GdN

See also gadolinium compounds.

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% natural abundance). 30 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-lifes that are less than 74.7 years, and the majority of these have half lifes that are less than 24.6 seconds. This element also has 4 meta states with the most stable being ^143mGd (t_½ 110 seconds), ^145mGd (t_½ 85 seconds) and ^141mGd (t_½ 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.

Precautions

As with the other lanthanides, gadolinium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail.

References

• Los Alamos National Laboratory – Gadolinium

External links

Template:Commons Template:Wiktionary

• WebElements.com – Gadolinium
• It's Elemental – Gadoliniumca:Gadolini

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