Actinide surfaces

In contrast to the case of bulk properties, very few ab initio calculations have been done for lanthanide or actinide surfaces. Although there has been much interest in the valence state at the surface of lanthanides, this has been treated by other means than first-principles electronic-structure calculations (Johansson and Martensson 1987). However, Hong et al. (1992) considered the Sm surface and applied the FLAPW method to a five-layer fee (100) slab in order to investigate theoretically the possibility of a valence change relative to the bulk. Although the results were not conclusive, this demonstrates the type of problems which can now be addressed by means of the present computational techniques. 

Geckeis H, Klenze R, Kim J1 (1999) Solid-water interface reactions of actinides and homologues sorption onto mineral surfaces. Radiochim Acta 87 13-21... 

The overall distribution of lanthanides in bone may be influenced by the reactions between trivalent cations and bone surfaces. Bone surfaces accumulate many poorly utilized or excreted cations present in the circulation. The mechanisms of accumulation in bone may include reactions with bone mineral such as adsorption, ion exchange, and ionic bond formation (Neuman and Neuman, 1958) as well as the formation of complexes with proteins or other organic bone constituents (Taylor, 1972). The uptake of lanthanides and actinides by bone mineral appears to be independent of the ionic radius. Taylor et al. (1971) have shown that the in vitro uptakes on powdered bone ash of 241Am(III) (ionic radius 0.98 A) and of 239Pu(IV) (ionic radius 0.90 A) were 0.97 0.016 and 0.98 0.007, respectively. In vitro experiments by Foreman (1962) suggested that Pu(IV) accumulated on powdered bone or bone ash by adsorption, a relatively nonspecific reaction. On the other hand, reactions with organic bone constituents appear to depend on ionic radius. The complexes of the smaller Pu(IV) ion and any of the organic bone constituents tested thus far were more stable (as determined by gel filtration) than the complexes with Am(III) or Cm(III) (Taylor, 1972). 

The actinides. The actinides metals are electropositive and very reactive they are pyrophoric in finely divided form. They tarnish rapidly in air forming an oxide protective coating in the case of Th, but more slowly for the other actinides. The metals react with most non-metals. With steam or boiling water, oxide is formed on the surface of the metal and H2 evolves in this way hydrides are produced that react rapidly with water and facilitate further attack on the metals. The oxidation states observed in the chemistry of lanthanides and actinides are shown in Fig. 5.9. Notice the predominant oxidation state III for the lanthanides... 

Rutherford backscattering spectrometry spect A method of determining the concentrations of various elements as a function of depth beneath the surface of a sample, by measuring the energy spectrum of ions which are backscattered out of a beam directed at the surface. roth-or-ford bak,skad-3-rir spek tram-o-tre rutherfordium chem A chemical element, symbolized Rf, atomic number 104, a synthetic element the first element beyond the actinide series, and the twelfth transuranium element., r3lh 3t fdr-de-3m ... 

I 72 Surface Organo-lanthanide and -Actinide Chemistry PMS.j + [NRjls... 

I 12 Surface Organo-fanthanide and -Actinide Chemistry Table 12.8 Continued... 

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