Interaction of titanium with smectite within the scope of a spent fuel repository: a spectroscopic approach

AbstractThe Swedish and Finnish nuclear waste repository design, KBS-3H, foresees horizontal emplacement of copper canisters-bentonite modules surrounded by a titanium shell. The interaction of titanium with bentonite was studied here using a combination of wet chemistry and a spectroscopic approach to evaluate the potential impact of Ti corrosion on the clay. For natural analogue clays with high Ti contents, spectroscopic investigations showed that titanium occurs as crystalline TiO2. In contrast, the Ti in the MX-80 bentonite occurs in the clay structure, presumably in the octahedral sheet. Hydrothermal tests conducted at 200°C using synthetic montmorillonite showed little if any change in the montmorillonite structure at near-neutral and acidic conditions. Under alkaline conditions, limited alteration was observed, including the formation of trioctahedral clay minerals and zeolite. These changes, however, occurred independently of the addition of Ti. In the batch tests conducted at 80°C, Ti did not occur as separate TiO2particles. The comparison of experimental data with spectroscopic simulations provides sound evidence that Ti was incorporated in a neoformed phyllosilicate structure.</jats:p

Pure and Zr-doped YMnO3+δ as a YSZ-compatible SOFC cathode: a combined computational and experimental approach

A thorough study of the Y1−xZrxMnO3+δ series is presented with the objective to use these materials as SOFC cathodes. These pure and Zr-doped yttrium manganites exhibit a layered hexagonal structure similar to a peculiar 5-fold bipyramidal coordination of manganese that makes them intrinsically different from the traditional cube-like perovskite with [MnO6] octahedra, creating the conditions conducive for oxygen uptake at a low temperature in the case of the layered manganite. Zr for Y doping enables the maintenance of oxygen excess such as interstitial oxygen atoms (Oi) located in the equatorial plane of the bi-pyramids. These over-stoichiometric interstitial oxygen sites are clearly evidenced by the maximum entropy method (MEM) applied to neutron diffraction data, and density functional theory (DFT) calculations are used to model the structural accommodation of Zr and excess oxygen. Mn reduction to Mn2+ is found to be energetically unfavourable, as proved both experimentally and by DFT calculations. Hence, zirconium is found to both stabilize the excess oxygen compared to pure YMnO3 and possibly provide an oxygen ion migration path with a lower energy barrier. The main consequence is a possible MIEC behaviour in Zr-doped YMnO3, as suggested by both the conductivity measurements and theoretical calculations. The initial EIS measurements are very promising and raise the series and its original structure to the rank of materials of interest for application as SOFC electrodes

The deep-water Peyssonnelia beds from the Balearic islands (Western Mediterranean)

Peyssonnelia bed distribution on continental shelf bottoms of the Balearic Islands (Western Mediterranean) ranges from 40 to 90 m depth. Different species of Peyssonnelia dominate these bottoms and, according to multivariate techniques, two main assemblages have been distinguished: the Peyssonnelia rosa-marina beds and the Peyssonnelia sp. beds, together with some transition samples between Peyssonnelia and maërl beds. Erect red algae are always abundant. Although average yearly irradiance reaching these beds is only 6.4-0.3% of subsurface irradiance, the species richness averages 45 species per sample (1600 cm2) and mean biomass is 2835 g dw. m-2. The high carbonate content of the living algae of these bottoms suggests that they are important contributors to the production of sediments in the Balearic continental shelf.Peer reviewe