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Gadolinium

Gadolinium

Gist

Gadolinium (Gd) is a soft, silvery-white rare-earth metal known for its paramagnetic properties, which make it useful as a contrast agent in MRI scans to improve image clarity of tissues and organs. It's also used in nuclear reactors as control rods, in high-temperature devices due to its good resistivity, and in certain microwave applications and televisions. While highly beneficial, its toxicity in its free form means it's always chelated (bound to an organic molecule) when used in medicine, though concerns about long-term deposition in the brain and body persist for some agents.

Gadolinium is primarily used as a contrast agent in magnetic resonance imaging (MRI). It enhances the visibility of certain tissues and structures, improving diagnostic accuracy in various medical conditions. Beyond MRI, gadolinium has other applications in nuclear reactors, high-end magnets, and even in some older color televisions.

Summary

Gadolinium is a chemical element; it has symbol Gd and atomic number 64. It is a silvery-white metal when oxidation is removed. Gadolinium is a malleable and ductile rare-earth element. It reacts with atmospheric oxygen or moisture slowly to form a black coating. Gadolinium below its Curie point of 20 °C (68 °F) is ferromagnetic, with an attraction to a magnetic field higher than that of nickel. Above this temperature it is the most paramagnetic element. It is found in nature only in an oxidized form. When separated, it usually has impurities of the other rare earths because of their similar chemical properties.

Gadolinium was discovered in 1880 by Jean Charles de Marignac, who detected its oxide by using spectroscopy. It is named after the mineral gadolinite, one of the minerals in which gadolinium is found, itself named for the Finnish chemist Johan Gadolin. Pure gadolinium was first isolated by the chemist Félix Trombe in 1935.

Gadolinium possesses unusual metallurgical properties, to the extent that as little as 1% of gadolinium can significantly improve the workability and resistance to oxidation at high temperatures of iron, chromium, and related metals. Gadolinium as a metal or a salt absorbs neutrons and is, therefore, used sometimes for shielding in neutron radiography and in nuclear reactors.

Like most of the rare earths, gadolinium forms trivalent ions with fluorescent properties, and salts of gadolinium(III) are used as phosphors in various applications.

Gadolinium(III) ions in water-soluble salts are highly toxic to mammals. However, chelated gadolinium(III) compounds prevent the gadolinium(III) from being exposed to the organism, and the majority is excreted by healthy[9] kidneys before it can deposit in tissues. Because of its paramagnetic properties, solutions of chelated organic gadolinium complexes are used as intravenously administered gadolinium-based MRI contrast agents in medical magnetic resonance imaging.

The main uses of gadolinium, in addition to use as a contrast agent for MRI scans, are in nuclear reactors, in alloys, as a phosphor in medical imaging, as a gamma ray emitter, in electronic devices, in optical devices, and in superconductors.

Details

Gadolinium (Gd) is a chemical element, a rare-earth metal of the lanthanide series of the periodic table.

Gadolinium is a moderately ductile, moderately hard, silvery white metal that is fairly stable in air, although with time it tarnishes in air, forming a thin film of Gd2O3 on the surface. Gadolinium reacts slowly with water and rapidly with diluted acids—except hydrofluoric acid (HF), in which a stable protective layer of GdF3 forms and prevents the metal from further reaction. Gadolinium is the only lanthanide that is ferromagnetic near room temperature; its Curie point (ferromagnetic ordering) is 293 K (20 °C, or 68 °F). Above this temperature the metal is a very strong paramagnet.

Gadolinium was discovered by Jean-Charles Galissard de Marignac and Paul-Émile Lecoq de Boisbaudran. Marignac separated (1880) a new rare earth (metallic oxide) from the mineral samarskite, and Lecoq de Boisbaudran obtained (1886) a fairly pure sample of the same earth, which with Marignac’s assent he named gadolinia, after a mineral in which it occurs that in turn had been named for the Finnish chemist Johan Gadolin. Gadolinium occurs in many minerals along with the other rare earths but is obtained primarily from bastnasite. It is also found in products of nuclear fission. In Earth’s crust gadolinium is as abundant as nickel.

In nature the element occurs as a mixture of six stable isotopes—gadolinium-158 (24.84 percent), gadolinium-160 (21.86 percent), gadolinium-156 (20.47 percent), gadolinium-157 (15.65 percent), gadolinium-155 (14.8 percent), and gadolinium-154 (2.18 percent)—and one radioactive isotope, gadolinium-152 (0.20 percent). Odd-numbered isotopes have extremely high nuclear absorption cross sections, with that of gadolinium-157 reaching 259,000 barns. As a result, the naturally occurring mixture of gadolinium isotopes also has a very high nuclear absorption cross section on the order of 49,000 barns. Excluding nuclear isomers, a total of 32 radioactive isotopes of gadolinium ranging in mass from 133 to 169 and having half-lives from 1.1 seconds (gadolinium-135) to 1.08 × 1014 years (gadolinium-152) have been characterized.

Commercial separation of the metal is done using solvent-solvent extraction or ion-exchange techniques. The metal has been produced by metallothermic reduction of the anhydrous chloride or fluoride by calcium. Gadolinium exists in two allotropic forms. The α-phase is close-packed hexagonal with a = 3.6336 Å and c = 5.7810 Å at room temperature. The β-phase is body-centred cubic with a = 4.06 Å at 1,265 °C (2,309 °F).

The major uses of gadolinium compounds include hosts for phosphors for fluorescent lamps, X-ray intensifying screens, and scintillators for X-ray tomography, and as a magnetic resonance imaging (MRI) contrast agent (in the form of water-soluble chelates). Other uses are in shields and control rods of nuclear reactors (due to its very high nuclear absorption cross section) and as a component of yttrium gadolinium garnet, which is employed in communications.

Gadolinium sulfate, Gd2(SO4)3―7H2O, was used by American chemist William F. Giauque and his graduate student D.P. MacDougal in 1933 to reach temperatures below 1 K (−272 °C, or −458 °F) by adiabatic demagnetization. Gadolinium metal was employed by Gerald V. Brown as an active element of a near-room-temperature magnetic refrigerator prototype, which in 1976–78 reached a temperature span of nearly 80 °C (176 °F) using a magnetic field of 7 teslas and a water-based heat-exchange fluid. Since then the metal became the magnetic refrigerant material of choice for numerous continuously operating laboratory magnetic refrigeration devices. In 1997 American materials scientists Vitalij Pecharsky and Karl Gschneidner, Jr., discovered the giant magnetocaloric effect in Gd5(Si1 − xGex)4 compounds; this discovery gave a strong impetus toward the development and commercialization of magnetic refrigeration technology.

Gadolinium displays the oxidation state +3 in all its compounds; it behaves as a typical rare earth. Its salts are white, and its solutions are colourless.

Element Properties

atomic number  :  64
atomic weight  :  157.25
melting point  :  1,313 °C (2,395 °F)
boiling point  :  3,273 °C (5,923 °F)
specific gravity  :  7.901 (24 °C, or 75 °F)
oxidation state  :  +3.

Additional Information:

Appearance

A soft, silvery metal that reacts with oxygen and water.

Uses

Gadolinium has useful properties in alloys. As little as 1% gadolinium can improve the workability of iron and chromium alloys, and their resistance to high temperatures and oxidation. It is also used in alloys for making magnets, electronic components and data storage disks.

Its compounds are useful in magnetic resonance imaging (MRI), particularly in diagnosing cancerous tumours.

Gadolinium is excellent at absorbing neutrons, and so is used in the core of nuclear reactors.

Biological role

Gadolinium has no known biological role, and has low toxicity.

Natural abundance

In common with other lanthanides, gadolinium is mainly found in the minerals monazite and bastnaesite. It can be commercially prepared from these minerals by ion exchange and solvent extraction. It is also prepared by reducing anhydrous gadolinium fluoride with calcium metal.

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