Rare earths performance testing

Previous active countercurrent tests performed in compact contactors (10 mm in diameter, 4-5 mL holdup per stage) on highly saline waste (-380 g/L of Na, Al, Fe, Cr, and Ni) had demonstrated that 99.9% of the actinides could be recovered with the rare earth elements (REEs) in six stages (93). 

Despite the fact that results of hardness tests are impossible to interpret in terms of any single fundamental mechanical property of materials, they are probably the simplest mechanical property tests to perform. Also, it is frequently the only mechanical test that can be employed when material is not available in substantial quantities as has been the situation in rare earth research. Nevertheless, carefully conducted hardness tests often are a sensitive means for detecting differences in impurity concentrations and for classifying metals. 

Simultaneously, the synthesis of ammonia from the elements was also tested over RE-TM intermetallic compounds by the same group (42). Here, 36 intermetallic compounds of rare earth elements and the transition metals Fe, Co, and Ru were evaluated. In the case of the ammonia synthesis, the rare earth component is transformed to the corresponding nitride and the transition metal is finely divided thereon. Some of the compounds showed an even higher specific activity than commercial catalysts used at that time. Later, the catalysts based on the intermetallic compound CeNis-j Cox (x = 0-5) were oxidized in a controlled way prior to the catalytic characterization in the Fischer-Tropsch reaction (43). The reasons to oxidize the compound before use were twofold. On the one hand, the material can be handled in air afterwards, whereas the intermetallic compound itself is not stable in air. Second, the oxidation can be better controlled and reproduced if it is not performed in situ. A review on the early work on these catalysts is available by Wallace (44). 

In an effort to reduce fuel cell manufacturing cost, low-priced rare earth minerals are being considered. Rare earth minerals such as lanthanum are used in making cathodes for the solid oxide fuel cell. Lower purity minerals, such as lanthanide manganite, are being tested to determine whether these materials will perform without serious degradation of fuel cell performance. 

EEI has used both commercially sintered silver powder with 1-mm-thick electrodes and sintered silver powder with in-house electrodes made from an ABj-type metal-hydride alloy (also known as lanthanum-nickel alloy) using rare earth material for initial laboratory cell test evaluations. Introduction of rare earth material improves the oxidation resistance during the alloy manufacturing process. The ABj-type metal-hydride alloy should be widely used in sealed Ni-MH batteries. The use of rare earth metal lanthanum will provide improved electrical performance, enhanced reliability, and ultra-high longevity for the sealed Ni-MH and Ag-MH battery systems. 

This section looks at some of the experimental results related to immersion performance testing for the various rare earths and finishes with some surface studies that provide some insight into the corrosion inhibition delivered by exposure to rare earths. 

The comparative performance in electrochemical testing of the RECC processes and the boehmite type coatings developed in rare earth salt solutions against chromate suggest that, even in the nnsealed condition, these coatings provide significant protection. ... 

Anwander and cowotkers (Gerstberger et al., 1999) immobilized rare-earth complexes on the mesopororrs silicate MCM-41 by first grafting [R N(SiHMe2)2 3(thf) c] onto MCM-41, followed by surface-confined ligand exchange with Hfod. This procedure yielded [MCM-41]R(fod) c(thf)3, (R = Sc, Y, La). The performance of this catalyst was tested in the hetero Diels-Alder reaction between trans-l-methoxy-3-trimethylsilyloxy-l,3-butadiene and ben-zaldehyde. A comparable activity was found for the yttiium(III) and scandium(III) com-... 

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