Gadollinium

Gadolinium is a chemical element with the symbol Gd and atomic number 64. It is a silvery-white, malleable and ductile rare-earth metal. Gadolinium has exceptionally high absorption of neutrons and therefore is used for shielding in neutron radiography and in nuclear reactors. Because of its paramagnetic properties, solutions of organic gadolinium complexes and gadolinium compounds are the most popular intravenous MRI contrast agents in medical magnetic resonance imaging.

Characteristics

Gadolinium crystallizes in hexagonal, close-packed α- form at room temperature, but, when heated to temperatures above 1235 °C, it transforms into its β- form, which has a body-centered cubic structure.

Gadolinium-157 has the highest thermal neutron capture cross-section among any stable nuclides at 259,000 barns. Only xenon-135 has a higher cross section, 2 million barns, but that isotope is unstable.

It is strongly paramagnetic at room temperature, and exhibits ferromagnetic properties below room temperature. Gadolinium demonstrates a magnetocaloric 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).

Individual gadolinium atoms have been isolated by encapsulating them into fullerene molecules and visualized with transmission electron microscope. Individual Gd atoms and small Gd clusters have also been incorporated into carbon nanotubes.

Unlike other rare earth elements, gadolinium is relatively stable in dry air. However, it tarnishes quickly in moist air, forming a loosely adhering oxide which spalls off, exposing more surface to oxidation.

Gadolinium is a strong reducing agent, which reduces oxides of several metals, into their elements. Gadolinium is quite electropositive and reacts slowly with cold water and quite quickly with hot water to form gadolinium hydroxide:

Gadolinium metal reacts with all the halogens at temperature about 200 °C and dissolves readily in dilute sulphuric acid to form solutions containing the colorless Gd(III) ions, which exist as a [Gd(OH2)9]3+ complexes:

Gadolinium combines with nitrogen, carbon, sulphur, phosphorus, boron, selenium, silicon and arsenic at elevated temperatures, forming binary compounds. In those compounds, Gd mostly exhibit oxidation state +3. Gadolinium(II) halides are obtained by annealing Gd(III) halides in presence of metallic Gd in tantalum containers. Gadolinium also form sesquichloride Gd2Cl3, which can be further reduced to GdCl by annealing at 800 °C. This gadolinium(I) chloride forms platelets with layered graphite-like structure.

Value

The base value of each unit of ranges between 10 and 40Ð per unit, with up to 3 units being found at any one time.

Presence on Mars: Rare