From the CRC handbook of Chemistry and Physics, CRC Press, Cleveland, 55th ed., 1974-75 "The Elements" by C.R. Hammond. page B-6
GADOLINIUM (gadolinite - a mineral named for Gadolin, a Finnish chemist), Gd; at. wt. 157.25; at. no. 64; m.p. 1313 +/- 1 C; b.p. 3266 C; sp.gr. 7.9004 (25 C); valence 3. Gadolinia, the oxide of gadolinium, 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 commerical importance. The element has been isolated only in recent years. With the development of ion-exchange and solvent extraction techniques, the availability and the price of gadolinium and the other rare-earth metals have greatly improved. Seventeen isotopes of gadolinium are now recognized. Seven occur naturally. The metal can 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 alpha form. Upon heating to 1262 C alpha gadolinium transfromrs into the beta form, which has a body-centered cubic structure. The metal is relatively stable in dry air, but in moiste 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, Gd(155) and Gd(157) 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. Compunds 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 termperatures and oxidation. 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.
