Neodymium components

Comparative Studies with Different Neodymium Components... 

Gr. neos, new, and didymos, twin) In 1841, Mosander, extracted from cerite a new rose-colored oxide, which he believed contained a new element. He named the element didymium, as it was an inseparable twin brother of lanthanum. In 1885 von Welsbach separated didymium into two new elemental components, neodymia and praseodymia, by repeated fractionation of ammonium didymium nitrate. While the free metal is in misch metal, long known and used as a pyrophoric alloy for light flints, the element was not isolated in relatively pure form until 1925. Neodymium is present in misch metal to the extent of about 18%. It is present in the minerals monazite and bastnasite, which are principal sources of rare-earth metals. 

Figure 16 shows the charge-discharge cycle characteristics of alloys in which part of the nickel component was replaced with cobalt. Misch metal (Mm), which is a mixture of rare earth elements such as lanthanum, cerium, praseodymium, and neodymium, was used in place of lanthanum. It was found that the partial replacement of nickel with cobalt and the substi-... 

By measuring the temperature dependence of second-harmonic generation (SHG) of the neodymium laser wavelength at 1.06 pm in sodium nitride for five different radiation geometries which correspond to the five nonvanishing components of the nonlinear susceptibility tensor, Vogt etal. 3 2) could determine these tensor components and the coherence length 1 = 4 2 re the... 

Supported Ziegler-type neodymium surface species (54, see below) have been prepared by mixing molecular components composed of [Nd(naph)3] (derived from naphthenonic acids) and alkyl aluminium reagents such as Al2Et3Cl3, Al( Bu)3 and/or Al( Bu)2H at 50-60°C with silica (source QiLu Petrochemicals Co., China) [158-160]. Although the immobihzed neodymium species are iU-defined, the materials display interesting properties in butadiene polymerization (Section 12.4.1.2). 

Mischmetall is a cheap alloy of the light lanthanides cerium, lanthanum, and neodymium are the main components. Benzaldehyde was added over a period of 14 h. 

Hoskins and Soffer (117) measured the fluorescent lifetime of the neodymium 4Fy2 state in yttrium oxide. They found a value of approximately 260 /zsec both at room temperature and at liquid-nitrogen temperature. They also observed a weaker long-lived component in the decay. They were unable to say whether this was evidence for a low-transition-probability ion site, or an effect of trapping of the resonance radiation near 0.9 /x. They report laser action, with a threshold of 260joules. This is a fairly high value for most crystalline materials. 

Use of a flexible aminosubstituted cyclopentadienyl ligand afforded a mononuclear species with the bulky silox ligand as alkoxide component. Only one donor arm is required to achieve a sterically saturated 8-coordinated neodymium center (Fig. 30, Table 14) [207]. 

Scheme 5 Catalyst component neodymium bis(2-ethylhexyl)phosphate (NdP = Nd(P204)3)...

Another feature of Nd-catalyzed BD polymerization which is reported by various authors is the reduction of cis- 1,4-content by the addition of donor compounds. The respective increase of trans- 1,4-moieties and decrease of cis- 1,4-moieties is also observed when the amount of the alkyl aluminum cocatalyst is increased. This feature does not depend on the nature of the Nd component and has for example been comparatively studied for three different catalyst systems (1) NdV/DIBAH/EASC, (2) neodymium neopen-... 

Numerous binary and ternary diene polymerization initiator systems with neodymium as the rare-earth metal component have been designed empirically and investigated since the early discoveries in the 1960s. Commercially used neodymium-based catalysts mostly comprise Nd(III) carboxylates, aluminum alkyl halides, and aluminum alkyls or aluminum alkyl hydrides [43, 48,50-52]. Typically, the carboxylic acids, which are provided as mixtures of isomers from petrochemical plants carry solubilizing aliphatic substituents R. They are treated with the alkylaluminum reagents to generate the active catalysts in situ (Scheme 11). 

Crucially, discrete Ln/Al organometallics were unambiguously identified as intermediates of the commercially applied neodymium-based diene polymerization and subsequently employed in binary initiator mixtures. Particularly for the industrially relevant O-only bonded carboxylate- and alk(aryl)oxide rare-earth metal components, the use of pre-alkylated Ln derivatives developed into valuable structure-reactivity relationships partially uncovering the blackbox, which is provided by ternary Ziegler Misch-katalysatoren. Accordingly, rare-earth metal centers provide a unique stereo-... 

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