Phosphor, 140 rare earth metals

Rare-earth metals Rare-earth phosphors Rare earths... 

A detailed study of two rare-earth metals under one set of reaction conditions, for example, yielded the two composition phase diagrams, shown in Fig. 14.2, for the Fu and La thiophosphate systems [3]. To prepare these phase diagrams, we varied the alkah metal, the rare-earth metal, and the phosphorous concentration to kept the sulfur concentration constant We prepared similar studies in... 

The source of luielium to date has been the processing of the other heavy rare-earth metals. Because of very limited availability, little research Was conducted on lutetium until the mid-1960s Most of these studies now are concentrating on prospective uses in phosphors, semiconductor, and other electronic circuitry components. A lulclium dilhalocvaninc complex has received much consideration recently for application in large, thin screens for television projection. 

The use of organophosphorus acids, such as di(2-ethylhexyl)phosphoric acid (D2EHPA di(2-ethylhexyl) monohydrogen phosphate 2 R = C4H9CH(Et)CH2), is now well established in the recovery of base metals. This reagent has found commercial application in the separation of cobalt from nickel,67 68 the separation of zinc from impurities such as copper and cadmium,69 the recovery of uranium,68 beryllium70 and vanadium,71 and in separations involving yttrium and the rare-earth metals.72 73... 

The solvent extraction of rare-earth nitrates into solutions of TBP has been used commercially for the production of high-purity oxides of yttrium, lanthanum, praseodymium and neodymium from various mineral concentrates,39 as well as for the recovery of mixed rare-earth oxides as a byproduct in the manufacture of phosphoric acid from apatite ores.272 273 In both instances, extraction is carried out from concentrated nitrate solutions, and the loaded organic phases are stripped with water. The rare-earth metals are precipitated from the strip liquors in the form of hydroxides or oxalates, both of which can be calcined to the oxides. Since the distribution coefficients (D) for adjacent rare earths are closely similar, mixer—settler assemblies with 50 or more stages operated under conditions of total reflux are necessary to yield products of adequate purity.39... 

Figure 4. The atomic density, or molarity, of the principal allotropes of the elements as a function of atomic number Z at room temperature and atmospheric pressure. The values for the noble gases have been extrapolated to STP. For sulfur, the values are shown with increasing molarity in the order S,, c-S8, c-S7, and and c-S6. The values for phosphorous correspond to white and black phosphorus, respectively, in the order of increasing molarity. Lines corresponding to covalence 2 and 3 have been drawn for the rare-earth metals and for the actinide elements. From [50].

The photoluminescence spectra of these catalysts were observed at 77 K, with a Amax 470 nm when the catalysts were excited at approximately 290 nm after the evacuation at various temperatures. The intensity (i.c., yield) of the phototuminescence depended on the evacuation temperature. The yield increased with increasing evacuation temperature, passing through a maxmium at 573 K. The yield was almost the same for the different catalysts, but the shape of the spectrum was influenced by factors such as the presence of other rare earth metal impurities which act as phosphors in the La203 framework and of surface OH groups. These observations suggest that the phototuminescence should be attributed to the... 

Catalytic activity of rare earth elements (i.e., lanthanides, symbol Ln) in homogeneous catalysis was mentioned as early as 1922 when CeCls was tested as a true catalyst for the preparation of diethylacetal from ethanol and acetaldehyde [1]. Solutions of inorganic Ln salts were subsequently reported to catalyze the hydrolysis of carbon and phosphorous acid esters [2], the decarboxylation of acids [3], and the formation of 4-substituted 2,6-dimethylpyrimidines from acetonitrile and secondary amines [4]. In the meantime, the efficiency of rare earth metals in heterogeneous catalysis, e. g., as promoters in lanthanide (element mixtures)-... 

The protonation of organo-rare-earth metal species through a-bond metathesis plays a key role in many catalytic applications described below. The high reactivity of rare-earth metals for insertion of unsaturated carbon-carbon multiple bonds [18], in conjunction with smooth o-bond metathesis, allows to perform catalytic small molecule synthesis. This route is atom efficient, economic, and opens access to nitrogen-, phosphorous-, silicon-, boron-, and other heteroatom-containing molecules. The most important catalytic applications of organo-rare-earth metals involving the o-bond metathesis process will be discussed in this review. 

A rather outstanding example of acidic extractants is that of alkyl phosphoric acid, in particular die-2-ethyl hexylphosphoric acid (DEHPA) which has been used in the extraction of uranium, nickel, zinc, cobalt, chromium and many other metals (46). Dodecyl phosphoric acidics also used in uranium extraction (46). A large number of carboxylic acids may be used to extract a variety of metals these include naphtenic acids for base metals and rare earth metals, a-bromolauric acid, pivalic acid etc. Versatic acids (which is a trade mark of Shell Co.) have a general formulae of ... 

Cationic alkylamine extractants were introduced in 1948 (Smith and Page 1948) for uranium production on an industrial scale. A few years later similar reagents based on phosphorous or arsenic, e.g., tetraphenylphosphonium and tetraphenylarsonium cations were introduced (Tribalat 1949). Today tertiary amines like trioctylamine extractants play a very important role in uranium production. Amines and quaternary ammonium salts are also used for production of many other metals, e.g., rare earth metals. 

Europium is the most reactive of the rare earth metals. It is quickly oxidized in air and ignites at about 150°C. Yttrium oxysulfide, doped with europium, is used in phosphors to give red colors in television screens. 

In what follows, the role of activator is played by one of the ions of the rare earth metals (R ions). Research on these phosphors in particular has considerably advanced the understanding of characteristic luminescence, since the properties of these phosphors can be studied on simple model compounds. This is possible because of the similarity between these ions. The host lattice may be, for instance, a compound of the ions La , or Lu . The latter ions do not absorb ultraviolet radiation. Rare earth ions, for example Eu or Tb , are now substituted for a small proportion of the host lattice ions. These R ions occupy in the host lattice the crystallographic sites of La, Y or Lu in a virtually random distribution. It is possible in this way to make phosphors whose chemical constitution is well defined. 

The ELM process has been used extensively to extract organics from aqueous feed, e.g., phenol from water (13-15), in hydrometallurgical separations, like zinc from waste water (16-18) and uranium from wet process phosphoric acid (19,20), and in the recovery of rare earth metals (23,24),... 

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