Dysprosium

Dysprosium is a chemical element with the symbol Dy and atomic number 66.

Notable characteristics
Dysprosium is a rare earth element that has a metallic, bright silver luster, relatively stable in air at room temperature, but dissolving readily in dilute or concentrated mineral acids with the emission of hydrogen. It is soft enough to be cut with bolt-cutters (but not with a knife), and can be machined without sparking if overheating is avoided. Dysprosium's characteristics can be greatly affected even by small amounts of impurities.

Applications
Dysprosium is used, in conjunction with vanadium and other elements, in making laser materials. Its high thermal neutron absorption cross-section and melting point also suggests that it is useful for nuclear control rods. Dysprosium oxide (also known as dysprosia), with nickel cement compounds, which absorb neutrons readily without swelling or contracting under prolonged neutron bombardment, is used for cooling rods in nuclear reactors. Dysprosium-cadmium chalcogenides are sources of infrared radiation for studying chemical reactions. Furthermore, dysprosium is used for manufacturing compact discs. Because it is highly paramagnetic, dysprosium has been used as a contrast agent in magnetic resonance imaging.

As a component of Terfenol-D (an alloy that expands or contracts to a high degree in the presence of a magnetic field), dysprosium is of use in actuators, sensors and other magenetomechanical devices.

Below 85K dysprosium is ferromagnetic, with a high susceptibility. It is often used for the fabrication of nanomagnets, particularly in research. Its usefulness, however, is limited by its high readiness to oxidise.

History
Dysprosium was first identified in Paris in 1886 by French chemist Paul Émile Lecoq de Boisbaudran. However, the element itself was not isolated in relatively pure form until after the development of ion exchange and metallographic reduction techniques in the 1950s. The name dysprosium is derived from the Greek δυσπροσιτος [dysprositos] = "hard to obtain". Part of the difficulty lay in dysprosium being especially close in its behavior to the far more abundant yttrium, during many of the separation technologies that were used in the 19th century. This overshadowed the fact that dysprosium was the most abundant of the heavy lanthanides.

Occurrence
Dysprosium is never encountered as a free element, but is found in many minerals, including xenotime, fergusonite, gadolinite, euxenite, polycrase, blomstrandine, monazite and bastnasite; often with erbium and holmium or other rare earth elements. Currently, most dysprosium is being obtained from the ion-adsorption clay ores of southern China. In the high-yttrium version of these, dysprosium happens to be the most abundant of the heavy lanthanides, comprising up to 7-8% of the concentrate (as compared to about 65% for yttrium).

Compounds
Nearly all dysprosium compounds are in the +3 oxidation state, and are highly paramagnetic. Holmium(III) oxide (Ho2O3) and Dysprosium(III) oxide (Dy2O3) are the most powerfully paramagnetic substances known.

Dysprosium compounds include:


 * Fluorides: DyF3
 * Chlorides: DyCl2, DyCl3
 * Bromides: DyBr2, DyBr3
 * Iodides: DyI2, DyI3
 * Oxides: Dy2O3
 * Sulfides: Dy2S3
 * Nitrides: DyN

See also dysprosium compounds.

Isotopes
Naturally occurring dysprosium is composed of 7 stable isotopes, 156Dy, 158Dy, 160Dy, 161Dy, 162Dy, 163Dy and 164Dy, with 164-Dy being the most abundant (28.18% natural abundance). 28 radioisotopes have been characterized, with the most stable being 154Dy with a half-life of 3.0x106 years, 159Dy with a half-life of 144.4 days, and 166Dy with a half-life of 81.6 hours. All of the remaining radioactive isotopes have half-lifes that are less than 10 hours, and the majority of these have half lifes that are less than 30 seconds. This element also has 5 meta states, with the most stable being 165mDy (t½ 1.257 minutes), 147mDy (t½ 55.7 seconds) and 145mDy (t½ 13.6 seconds).

The primary decay mode before the most abundant stable isotope, 164Dy, is electron capture, and the primary mode after is beta minus decay. The primary decay products before 164Dy are terbium isotopes, and the primary products after are holmium isotopes.

Precautions
As with the other lanthanides, dysprosium compounds are of low to moderate toxicity, although their toxicity has not been investigated in detail. Dysprosium does not have any known biological properties.