Lanthanide additives

Kitayama M, Hirao K, Toriyama M, Kanzaki S (1998) Anisotropie Ostwald Ripening in /LSi3N4 with different Lanthanide Additives. In Messing GL, Hirano S, Lange FF (eds) Ceramic Processing Science. Ceram Transactions Ser 83 517 (1999) J Ceram Soc Jpn 107 930 and 107 995... 

The various materials used, along with the lanthanide additive and the applications, are given in the form of tables based on the properties such as mechanical, chemical, electrical and magnetic, emission of radiation and interaction with electromagnetic radiation. The applications based on the mechanical and nuclear properties are given in Table 12.21. 

Conformational analysis of substituted 1,3,2-dioxaphosphorinanes has been achieved using a topological approach (429) rather than the more elaborate random search method. This simplified approach only considers chemically and physically accessible positions for the lanthanide. Using this approach the LIS calculations are found to predict the conformational equilibrium for complexed cis conformers which is in good agreement with that based on the response of the coupling constants J(H-H) and J(P-H) to lanthanide addition. For the trans conformers the two approaches are not in agreement. 

Rhodium supported on y-ALOs is an important component of 3-way automotive catalysts and has been studied by a wide variety of methods [1-5] including ESR. In the last 15 years Rh-species introduced into zeolites of different types (Y, X, L, A, SAPO) have also been examined by several techniques [6-9]. However, most of these methods were applied after the specimens were removed from actual reaction conditions and transferred into the respective characterization instruments and the state or behavior of the catalyst in-situ was arrived at indirectly by inference. Also the deactivation processes or the effect of modifiers is seldom, if ever, determined by direct in-situ observations. We have previously devised a method for high-temperature measurement of ESR-active ions under flow conditions and applied it to characterize specimens containing Cu [10] or Cr " [11]. We have extended this method now to specimens containing Rh. Here, we summarize the results of a study of the interaction of Rh/y-ALOB and Rh/ZSM-5 with different gases and gas mixtures (NO, NO2, CO, propene, O2, H2O) at 120-573 °K. The amount of Rh present in the samples is evaluated quantitatively. The effect of copper and lanthanide addition on the stabilization of by the zeolitic matrix was also investigated. 

McIntosh S, Vohs JM, Gorte RJ (2002) An examination of lanthanide additives on the performance of cu-YSZ cmnet anodes. Electrochim Acta 47 3815-3821... 

Lanthanide luminescence apphcations have already reached industrial levels of consumption. Additionally, the strongly specific nature of the rare-earths energy emissions has also led to extensive work in several areas such as photostimulable phosphors, lasers (qv), dosimetry, and fluorescent immunoassay (qv) (33). 

In 1990 world consumption of lanthanides was approximately 35,000 metric tons (45). The most important markets were the United States /Canada (32.8%), China (18.6%), Europe (15.8%), Japan (14.5%), Eastern Europe (9.5%), the rest of Asia (7.3%), and the rest of the world (1.4%). The principal rare-earth manufacturers in 1993 were Molycorp Inc. and RhcJ)ne-Poulenc in the United States RhcJ)ne-Poulenc and Treibacher Chemische WAG in Europe Shinetsu Chemical, Nippon Yttrium, Mitsubishi Chemical Inc., and Santoku Metal Inc. in Japan Indian Rare Earths in India and several additional companies located in the CIS and in the Baotou, Gansu, Yue Long, and Jiangxi provinces in China. 

Oil field uses are primarily imidazolines for surfactant and corrosion inhibition (see Petroleum). Besides the lubrication market for metal salts, the miscellaneous market is comprised of free acids used ia concrete additives, motor oil lubricants, and asphalt-paving applications (47) (see Asphalt Lubrication AND lubricants). Naphthenic acid has also been studied ia ore flotation for recovery of rare-earth metals (48) (see Flotation Lanthanides). 

HDPE resias are produced ia industry with several classes of catalysts, ie, catalysts based on chromium oxides (Phillips), catalysts utilising organochromium compounds, catalysts based on titanium or vanadium compounds (Ziegler), and metallocene catalysts (33—35). A large number of additional catalysts have been developed by utilising transition metals such as scandium, cobalt, nickel, niobium, molybdenum, tungsten, palladium, rhodium, mthenium, lanthanides, and actinides (33—35) none of these, however, are commercially significant. 

Hydroxides. Thorium (TV) is generally less resistant to hydrolysis than similarly sized lanthanides, and more resistant to hydrolysis than tetravalent ions of other early actinides, eg, U, Np, and Pu. Many of the thorium(IV) hydrolysis studies indicate stepwise hydrolysis to yield monomeric products of formula Th(OH) , where n is integral between 1 and 4, in addition to a number of polymeric species (40—43). More recent potentiometric titration studies indicate that only two of the monomeric species, Th(OH) " and thorium hydroxide [13825-36-0], Th(OH)4, are important in dilute (<10 M Th) solutions (43). However, in a Th02 [1314-20-1] solubiUty study, the best fit to the experimental data required inclusion of the species. Th(OH) 2 (44). In more concentrated (>10 Af) solutions, polynuclear species have been shown to exist. Eor example, a more recent model includes the dimers Th2(OH) " 2 the tetramers Th4(OH) " g and Th4(OH) 2 two hexamers, Th2(OH) " 4 and Th2(OH) " 2 (43). 

Extensive efforts have been made to develop catalyst systems to control the stereochemistry, addition site, and other properties of the final polymers. Among the most prominant ones are transition metal-based catalysts including Ziegler or Ziegler-Natta type catalysts. The metals most frequentiy studied are Ti (203,204), Mo (205), Co (206-208), Cr (206-208), Ni (209,210), V (205), Nd (211-215), and other lanthanides (216). Of these, Ti, Co, and Ni complexes have been used commercially. It has long been recognized that by varying the catalyst compositions, the trans/cis ratio for 1,4-additions can be controlled quite selectively (204). Catalysts have also been developed to control the ratio of 1,4- to 1,2-additions within the polymers (203). 

An alternative process for opening bastnasite is used ia Chiaa high temperature roastiag with sulfuric acid followed by an aqueous leach produces a solution containing the Ln elements. Ln is then precipitated by addition of sodium chloride as a mixed sulfate. Controlled precipitation of hydroxide can remove impurities and the Ln content is eventually taken up ia HCl. The initial cerium-containing product, oace the heavy metals Sm and beyond have been removed, is a light lanthanide (La, Ce, Pr, and Nd) rare-earth chloride. 

An alternative commercial form of a metallic mixed lanthanide-containing material is rare-earth siUcide [68476-89-1/, produced in a submerged electric-arc furnace by the direct reduction of ore concentrate, bastnasite, iron ore, and quart2. The resulting alloy is approximately 1/3 mischmetal, 1/3 sihcon, and 1/3 iron. In addition there are some ferro-alloys, such as magnesium—ferrosilicons, derived from cerium concentrate, that contain a few percent of cerium. The consumption of metallic cerium is overwhelmingly in the mixed lanthanide form in ferrous metallurgy. 

It is well known, that in aqueous solutions the water molecules, which are in the inner coordination sphere of the complex, quench the lanthanide (Ln) luminescence in result of vibrations of the OH-groups (OH-oscillators). The use of D O instead of H O, the freezing of solution as well as the introduction of a second ligand to obtain a mixed-ligand complex leads to either partial or complete elimination of the H O influence. The same effect may be achieved by water molecules replacement from the inner and outer coordination sphere at the addition of organic solvents or when the molecule of Ln complex is introduced into the micelle of the surfactant. 

The classical methods used to separate the lanthanides from aqueous solutions depended on (i) differences in basicity, the less-basic hydroxides of the heavy lanthanides precipitating before those of the lighter ones on gradual addition of alkali (ii) differences in solubility of salts such as oxalates, double sulfates, and double nitrates and (iii) conversion, if possible, to an oxidation state other than -1-3, e g. Ce(IV), Eu(II). This latter process provided the cleanest method but was only occasionally applicable. Methods (i) and (ii) required much repetition to be effective, and fractional recrystallizations were sometimes repeated thousands of times. (In 1911 the American C. James performed 15 000 recrystallizations in order to obtain pure thulium bromate). 

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