dysprosium

dysprosium (Dy), chemical element, a rare-earth metal of the lanthanide series of the periodic table.

Dysprosium is a relatively hard metal and is silvery white in its pure form. It is quite stable in air, remaining shiny at room temperature. Dysprosium turnings ignite easily and burn white-hot. The metal slowly reacts with water and quickly dissolves in diluted acids—except hydrofluoric acid (HF), in which it forms a protective layer of insoluble DyF₃. The metal is a very strong paramagnet above approximately 180 K (−93 °C, or −136 °F); it is antiferromagnetic between about 90 (−183 °C, or −298 °F) and 180 K and ferromagnetic below 90 K.

French chemist Paul-Émile Lecoq de Boisbaudran first found this element (1886) associated with holmium and other heavy lanthanides; French chemist Georges Urbain later (1906) was able to prepare a reasonably pure fraction. Some important mineral sources of dysprosium are laterite ionic clays, xenotime, fergusonite, gadolinite, euxenite, polycrase, and blomstrandine. It also occurs in the products of nuclear fission.

The naturally occurring isotopes are all stable and have mass numbers 164 (natural abundance 28.3 percent), 162 (25.5 percent), 163 (24.9 percent), 161 (18.9 percent), 160 (2.33 percent), 158 (0.10 percent), and 156 (0.06 percent). Excluding nuclear isomers, a total of 29 radioactive isotopes of dysprosium are known. They range in mass from 138 to 173. The least stable is dysprosium-139 (half-life 0.6 second), and the most stable is dysprosium-154 (half-life 3.0 × 10⁶ years).

Commercial separation is performed by liquid-liquid extraction or ion-exchange methods. The metal has been prepared by metallothermic reduction of the anhydrous halides with alkali or alkaline-earth metals. The metal is further purified by vacuum distillation. Dysprosium exists in three allotropic (structural) forms. The α-phase is close-packed hexagonal with a = 3.5915 Å and c = 5.6501 Å at room temperature. When cooled below ~90 K, the ferromagnetic ordering is accompanied by an orthorhombic distortion, β-Dy, of the hexagonal close-packed lattice. The β-phase has a = 3.595 Å, b = 6.184 Å, and c = 5.678 Å at 86 K (−187 °C, or −305 °F). The γ-phase is body-centred cubic with a = 4.03 Å at 1,381 °C (2,518 °F).

The major use of dysprosium is as an alloying addition to Nd₂Fe₁₄B permanent magnet materials (in which some of the neodymium is substituted with dysprosium) to increase both the Curie point and especially the coercivity and, therefore, improve the high-temperature performance of the alloy. The metal is also a component of magnetostrictive Terfenol D (Tb_0.3Dy_0.7Fe₂). Dysprosium is used in control rods for nuclear reactors because of its relatively high neutron-absorption cross section; its compounds have been used for making laser materials and phosphor activators, and in metal halide lamps.

Chemically, dysprosium behaves as a typical trivalent rare earth and forms a series of pale yellow compounds in which its oxidation state is +3.