Transport rare earth complexes

New approaches for development of specific carriers for use in liquid membrane are described (i) computer-aided design of cation-specific carriers and (ii) functionalization of rare earth complexes as anion carriers. A new series of Li(I) and Ag(I) ion-specific carriers are successfully designed using MM2, MNDO and density functional calculations. Computer chemistry provides a rational basis for design and characterization of cation-specific carriers of armed crown ether-and podand-types. Lipophilic lanthanide tris(p-diketonates) are shown to be a new class of membrane carriers. They form 1 1 complexes with anionic guests and mediate transport of amino acid derivatives. Since these complexes exhibit different anion transport properties from those of crown ethers, further applications of rare earth complexes offer promising possibilities in the development of specific anion carriers for liquid membrane systems. 

However, a large number of complexing agents of all kinds with chemistries designed for specific metal ions have been reported in the literature. The tertiary amine Alamine 336 is widely used to transport anions such as U02(S04)4- and CfiOj [44-46], The macrocyclic crown ether family has also been used to transport alkali and rare earth metals [47,48] ... 

Langmuir-Blodgett (LB) technique has been also used for the preparation of Pc-based OFET, as it allows the fine control of both the structure and the thickness of the film at the molecular level [226,227], OFET devices based on amphiphilic tris(phthalocyaninato) rare earth, triple-decker complexes have been prepared by LB technique, showing good OFET performances [228], More recently, ambipolar transport has also been realized in OFET devices through a combination of holeconducting CuPc and n-conducting Cgo fullerene, in which the asymmetry of the... 

Recently one of the solutions to overcome this problem has been proposed.This does concern surface modification of the pyrochlore-based oxide.s. It is known that cerium and zirconium chlorides provide vapor phase complexes with aluminum chloride at elevated temperatures.The new surface modification technique utilizes the formation of these vapor complexes to remove and modify the top surface of the pyrochlore ceria-zirconia solid solution. This method is named "chemical filing". Application of the above complexes formation has already been demonstrated for the vapor phase extraction and mutual separation of rare earths based on the so-called chemical vapor transport (CVT). ... 

For both PAA and HA, the lability of rare earth element interactions is greater for the smaller molecular weight fractions of each poly electrolyte. Similar observations have been reported for Cu(II) dissociation from size fractionated HA (22). Interestingly, the smaller size fractions of HA have been shown to the most effective in transporting Am(III) and Cm(III) through sandy aquifers (25). Consequently, the influence and affect of polyelectrolyte size must be considered when predicting the mobility of these complexes in natural systems. 

Materials which have extremely low volatility and the potential to serve therefore as non-reactive substrates and supports include zirconia, titania, and alumina. The rare earth oxides, represented by lanthana and ceria, also show very low volatility and can be expected to resist vapor-transport-assisted sintering and corrosion. Of the alkaline earth oxides, MgO is superior to all others, although the alkaline earth aluminate complex oxides can be much more stable (e. g., by a factor of 1000 for BaO) than the alkaline earth oxides. 

Another way to intercalate nonvolatile halides is through complexation in the vapor phase. By forming a volatile adduct, a nominally nonvolatile halide can be transported to graphite a molecule at a time, thereby allowing intercalation. The first example of this technique was with the C0CI2-AICI3 system , and it has also been used for the trichlorides of rare earth elements . 

As a pyrometallurgical approach, Ozaki et al. (1999) studied the appUcatimi of the chemical vapor transport method described in Section 2.3.1. Used polishing powder was chlorinated by chlorine gas at 1000 °C, and transported along the temperature gradient via gaseous complex with aluminum chloride. The rare-earth chlorides were mainly crmdensed over the temperature range of 457-947 C. The purity of the rare-earth chlorides in this temperature range was about 95%. 

The discovery of proton conduction in SrCeOa doped with rare earths such as trivalent Yb, when treated in hydrogen and/or water vapor (Iwahara et al. 1981a), opened up a new class of ionic conductors in which protons, present only as a minor constituent, can migrate by a simple hopping mechanism, in contrast with the low-temperature protonic conductors in which hydrogen is a major constituent and its transport involves complex mechanisms. 

The electron wave vectors at the Fermi level in metals are more likely, rather than the wave vectors of phonons, to make a significant contribution to the heat transport. These phonons can interact with electrons, and thus, an effect of phonon-electron scattering is to be expected in metals at all temperatures. One fails, however, to observe phonon-electron scattering in pure metals at high temperatures because of the complexity of the Kl separation. One can separate and and observe phonon-electron scattering in rare earth metals and metal-like compounds which contain rare earth elements, due to the low mobility of electrons which increases p considerably and hence decreases k ) (Oskotski and Smirnov 1971, Khusnutdinova et al. 1971, Luguev et al. 1975a). 

Zvarova and Zvara [73, 74] have demonstrated that at moderate temperatures (under 250 °C) lanthanide chlorides, actinide chlorides, and other chlorides can be separated by gas chromatography if use is made of an inert gas and aluminum chloride vapor as components of the carrier gas. The method relies on aluminum chloride vapor forming gaseous complexes with rare-earth chlorides, which are then transported by the carrier gas. The excess of aluminum chloride inhibits dissociation of the... 

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