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   Gd

GADOLINIUM

(gadolinite a mineral named for Gadolin, a Finnish chemist)

Gd at. wt. 157.25
   at. no. 64
   m.p. 1312°C
   b.p. 3233°C 
   sp. gr. 7.898 (25°C) 
   valence 3. 

Gadolinium's oxide (Gadolinia), was separated by Marignac in 1880 and Lecoq de Boisbaudran independently isolated the element from Mosander's "yttria" in 1886. The element was named for the mineral gadolinite from' which this rare-earth was originally obtained. Gadolinium is found in several other minerals, including monazite and bastnasite, which are of commercial importance. The element has been isolated only in recent years. With the development of ion-exchange and solvent extraction techniques, the availability and price of gadolinium and the other related rare earth metals has greatly improved. Seventeen isotopes of gadolinium are now recognized. Seven occur naturally. The metal Qan be prepared by the reduction of the anhydrous fluoride with metallic calcium. As with other related rare earth metals, it is silvery white, has a metallic luster, and is malleable and ductile. At room temperature, gadolinium crystallizes in the hexagonal, close-packed a form. Upon heating to 12620C a gadolinium transforms into the fi form, which has a body centered cubic structure. The metal is relatively stable in dry air, but in moist air, it tarnishes with the formation of a loosely adhering oxide film which spalls off and exposes more surface to oxidation. The metal 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). Natural gadolinium is a mixture of seven isotopes. Two of these, Gd155 and Gd157 have excellent capture characteristics, but they are present naturally in low concentrations. As a result, gadolinium has a very fast burnout rate and has limited use as a nuclear control rod material. It has been used in making gadolinium yttrium garnets, which have microwave applications. Compounds of gadolinium are used in making phosphors for color TV tubes. The metal has unusual superconductive properties. As little as 1 % gadolinium has been found to improve the workability and resistance of iron, chromium, and related alloys to high temperatures and oxidation. Gadolinium ethyl sulfate has extremely low noise characteristics and may fitid use in duplicating the performance of h.f. amplifiers, such as the maser. The metal is ferromagnetic. Gadolinium is unique for its high magnetic moment and for its special Curie temperature (above which ferromagnetism vanishes) lying just at room temperature. This suggests uses as a magnetic component that senses hot and cold. The price of the metal is $1.25/gm. or $250/lb.

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