Rare earths, term

Solid-State Lasers. Sohd-state lasers (37) use glassy or crystalline host materials containing some active species. The term soHd-state as used in connection with lasers does not imply semiconductors rather it appHes to soHd materials containing impurity ions. The impurity ions are typically ions of the transition metals, such as chromium, or ions of the rare-earth series, such as neodymium (see Lanthanides). Most often, the soHd material is in the form of a cylindrical rod with the ends poHshed flat and parallel, but a variety of other forms have been used, including slabs and cylindrical rods with the ends cut at Brewster s angle. 

Rare-Earth Silicides. Rare-earth sihcides, in the form of a ferroalloy that contain up to 33% rare earths, are used increasingly by the iron and steel industries. Whereas the term sihcides is no longer used for alloys of this type, it is stih in common usage for these materials. Eor nodular iron, addition... 

The purity of the cerium-containing materials depends on the appHcation as indicated in Table 3, and purity can mean not only percentage of cerium content but also absence of unwanted components. For some uses, eg, gasoline production catalysts, the lanthanides are often used in the natural-ratio without separation and source Hterature for these appHcations often does not explicitly mention cerium. Conversely, particulady in ferrous metallurgy, cerium is often assumed to be synonymous with rare-earth or lanthanide and these terms are used somewhat interchangeably. 

A rare-earth-exchanged zeolite increases hydrogen transfer reactions. In simple terms, rare earth forms bridges between two to three acid sites in the catalyst framework. In doing so, the rare earth protects... 

Thus far, we have focused exclusively upon the block metals. For some, the term transition elements defines just these J-block species for others, it includes the rare earth or lanthanoid elements, sometimes called the inner transition elements . In this chapter, we compare the elements with respect to their valence shells. In doing so, we shall underscore concepts which we have already detailed as well as identifying both differences and similarities between certain aspects of main and inner transition-metal chemistry. We make no attempt to review lanthanoid chemistry at large. Instead our point of departure is the most characteristic feature of lanthanoid chemistry the +3 oxidation state. 

But first the synthesis had to come John was interested in reduced metal halides, particularly for the post-transition metals cadmium, galHum, and bismuth (his Ph.D. dissertation was on anhydrous aluminum halides and mixed halide intermediates, a good start for what was to come ). However, he was not yet actively interested in rare-earth metals and their remarkable solubility in their halides. But these elements lured him one floor below where Adrian Daane headed the metallurgy section of Spedding s empire. He knew how to produce rare-earth metals with high purity and in sufficient quantity and also how to handle tantalum containers. What if one gave it a tr/ and reduced some rare-earth metal halides (John insists that this term is used correctly) from their respective metals at high temperatures under appropriate conditions. 

Ewart A, Hawkesworth CJ (1987) The Pleistoeene-Reeent Tonga-Kermadee are lavas Interpretation of new isotopic and rare earth data in terms of a depleted mantle somce model. J Petrol 28 495-530 Fumkawa F (1993a) Magmatic processes under arcs and formation of the volcanic front. J Geophys Res 98 8309-8319... 

The purest grade of europium metal available from the Lindsay Chemical Division of American Potash is 99.9% Eu in terms of rare earth content, but it may contain up to 1% of other metal impurities (mainly tantalum when prepared in tantalum vessels) and typically contains 2.8 mol % oxygen.6... 

Rare earth elements are the general term for 15 kinds of lanthanide elements (La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Py, Ho, Er, Tm, Yb, Lu) together with Sc and Y elements. They prefer trivalent states in the complex formation, though three elements (Eu, Sm, Yb) can assume tri- and divalent stateos and Ce a tri- or tetravalent state. Their ionic radii are fairly large (1.0-1.17 A) and their electronegativities are low (1.1-1.2). In fact, the former are much larger than those of... 

Rare-earth metah—a loose term for less well-known metallic elements. They include the so-called rare-earths. The rare-earths are not actually rare (scarce) historically, some of them were just difficult to find, isolate, and identify. 

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