It is suspected that the as-compacted state of heavily compacted clays used as possible engineered barriers for nuclear waste disposal is time dependent, and that further change may occur in the material, even at constant water content and density. This paper presents an investigation of the time-dependent microstructure changes of an MX80 clay bentonite compacted at various dry densities and water contents. Microstructure investigation is based on mercury intrusion pore size distribution measurements and scanning electron microscopy (SEM). Results obtained by other researchers by using X-ray diffraction at low angles are also used. Statically compacted samples of MX80 were kept at constant volume and water content for various periods of time (1, 30 and 90 days) prior to mercury intrusion and SEM micro-structure investigation. A significant change in micro-structure with time was observed, characterised by a decrease in the inter-aggregate porosity and an increase in the very thin porosity not intruded by mercury (r < 3·7 nm). The former observation is related to the filling of inter-aggregate larger pores by exfoliation, and the latter observation is related to changes that occur in the aggregates within the smectite particles when suction is reduced. These changes are interpreted in the light of an investigation carried out on similar samples using low-angle X-ray diffraction. Changes inside the aggregates are governed by the progressive placement of interlayer water molecules inside the particles together with the subdivision of particles, which gives rise to an interparticle porosity that develops inside the aggregates.

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We perform a quantitative characterization of a microbubble injector in conditions relevant to microgravity. The injector pregenerates a slug flow by using a capillary T-junction, whose operation is robust to changes in gravity level. We address questions regarding the performance under different injection conditions. In particular we focus on the variation of both gas and liquid flow rates. The injection performance is characterized by measuring bubble injection frequency and bubble sizes. We obtain two distinct working regimes of the injector and identify the optimal performance as the crossover region between them.

The growth of rare-earth (RE ) Nd, Tb, Ho, Er, Tm, and Yb) doped KTiOPO 4 (KTP) single crystals from high-temperature solutions [K 2 O-P 2 O 5 -TiO 2 -RE 2 O 3 (or Tb 4 O 7 )] was investigated. The concentration regions of crystallization of RE-doped KTP, the maximum (critical) RE concentrations in the solution without losing the KTP phase and the corresponding upper limit of RE ions incorporated into the KTP lattice were obtained experimentally. The crystallization regions of RE-doped KTP are significantly narrower than the region of undoped KTP. Above a certain critical RE concentration in the solution, RE phosphate phases crystallize. The highest concentration of RE in the crystal is in the range 50-600 ppm and strongly depends on the RE ionic radius. Some double substitutions with Nd and a codopant element can significantly change this concentration. In addition, RE-doped KTP single crystals were grown by the top seeded solution growth (TSSG) technique, and their experimental conditions were compared with those of undoped KTP single-crystal growth. Optical absorption spectra for Ho-, Er-, and Tm-doped KTP were obtained and discussed.