GADOLINIUM

(Gd), chemical element, rareearth metal of transition Group IIIb of the periodic table. Silvery white and moderately ductile, the metal reacts slowly with oxygen and water. Below 17 C it is ferromagnetic and at very low temperatures, superconducting. Credit for the discovery of gadolinium is shared by J.-C.-G. de Marignac and P.-. Lecoq de Boisbaudran. Marignac separated (1880) a new rare earth (metallic oxide) from the mineral samarskite; 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 monazite. It is found also in the products of nuclear fission. Commercial separation depends upon ion-exchange techniques. The metal has been produced by thermoreduction of the anhydrous chloride or fluoride by calcium. Gadolinium is used for certain electronic components and high-temperature refractories and as an alloying agent. H. Kamerlingh Onnes first produced (1923) temperatures below 1 K by magnetic cooling using gadolinium sulfate. Gadolinium has the highest absorption cross section for thermal neutrons of any natural isotope of any element (49,000 barns), which suggests its use in nuclear reactor control rods. The seven natural stable isotopes have mass numbers between 152 and 160; the species of highest mass numbers are more abundant. Gadolinium is trivalent in all of its compounds; it behaves as a typical rare earth. Its salts are white, and its solutions are colourless. atomic number 64 atomic weight 157.250 melting point 1,311 C boiling point 3,233 C specific gravity 7.898 (25 C) valence 3 electronic config. 2-8-18-25-9-2 or (Xe)4f 75d16s2