Gadolinium

Notable characteristics

Gadolinium is a silvery white, malleable and ductile rare earth metal with a metallic luster. It crystalizes 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 eart elements, Gadolinium is relatively stable in dry air; however, it tarnishes quickly in moist air and forms a losely adhering oxide that spalls off and exposes more surface to oxidation. Gadolinium reacts slowly with water and is soluble in dilute acid.

Gadolinium also 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 is in fact the only metal to exhibit ferromagnetic properties except for fourth period transition metals.

Applications

Gadolinium is used for making gadolinium yttrium garnets[?], which have microwave applications; gadolinium compounds also are used for making phosphors for colour TV tubes, and solutions of compounds are used as intravenous contrasts to enhance images in patients undergoing magnetic resonance imaging. Gadolinium is also used for manufacturing compact discs and computer memory.

Gadolinium also possesses unusual superconductive properties, with as little as 1% of Gadolinium improving the workability and resistance of Iron, Chromium and related alloys to high temperatures and oxidation.

In the future, Gadolinium ethyl sulfate, which has extremely low noise characteristics, may be used in masers; furthermore, Gadolinium's high magnetic movement and its Curie temperature which lies just at room temperature suggest applications as a magnetic component for sensing hot and cold.

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 for the first time.

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

Biological role

Gadolinium has no known biological role, but is said to stimulate the metabolism.

Occurrence

Gadolinium is never found in nature as the free element, but is contained in many minerals such as gadolinite, monazite and bastnasite. 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[?]
  • GdCl₃⋅6H₂O[?]
• Bromides[?]
  • GBr₃[?]
• Iodides[?]
  • GdI₂[?]
  • GdI₃[?]
• Oxides
  • Gd₂O₃[?]
• Sulfides[?]
  • Gd₂S₃[?]
• Selenides[?]
  • GdSe[?]
• Tellurides
  • Gd₂Te₃[?]
• Nitrides[?]
  • GdN[?]

Isotopes

Naturally occurring Gadolinium is composed of 5 stable isotopes, 154-Md, 155-Md, 156-Md, 157-Md and 158-Md, and 2 radioisotopes, 152-Md and 160-Md, with 158-Md being the most abundant (24.84% natural abundance). 30 radioisotopes have been characterized with the most stable being 160-Md with a half-life of 1.3E+21 years, 152-Md with a half-life of 1.08E+14 years, and 150-Md with a half-life of 1.79E+6 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 143m-Gd (t_½ 110 seconds), 145m-Gd (t_½ 85 seconds) and 141m-Gd (t_½ 24.5).

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

Precautions

All gadolinium compounds should be regarded as highly toxic. Gadolinium compounds are skin and eye irritants and perhaps carcinogenic. The metal dust presents a fire and explosion hazard.

External links

• WebElements.com - Gadolinium (http://www.webelements.com/webelements/elements/text/Gd/index)
• EnvironmentalChemistry.com - Gadolinium (http://environmentalchemistry.com/yogi/periodic/Gd)
• It's Elemental - Gadolinium (http://education.jlab.org/itselemental/ele064)