The Year-Long Development of Microorganisms in Uncompacted Bavarian Bentonite Slurries at 30 and 60 °C.

In the multibarrier concept for the deep geological disposal of high-level radioactive waste (HLW), bentonite is proposed as a potential barrier and buffer material for sealing the space between the steel canister containing the HLW and the surrounding host rock. In order to broaden the spectra of appropriate bentonites, we investigated the metabolic activity and diversity of naturally occurring microorganisms as well as their time-dependent evolution within the industrial B25 Bavarian bentonite under repository-relevant conditions. We conducted anaerobic microcosm experiments containing the B25 bentonite and a synthetic Opalinus Clay pore water solution, which were incubated for one year at 30 and 60 °C. Metabolic activity was only stimulated by the addition of lactate, acetate, or H2. The majority of lactate- and H2-containing microcosms at 30 °C were dominated by strictly anaerobic, sulfate-reducing, and spore-forming microorganisms. The subsequent generation of hydrogen sulfide led to the formation of iron-sulfur precipitations. Independent from the availability of substrates, thermophilic bacteria dominated microcosms that were incubated at 60 °C. However, in the respective microcosms, no significant metabolic activity occurred, and there was no change in the analyzed biogeochemical parameters. Our findings show that indigenous microorganisms of B25 bentonite evolve in a temperature- and substrate-dependent manner.

Immediate Release 3D-Printed Tablets Produced Via Fused Deposition Modeling of a Thermo-Sensitive Drug.

PURPOSE: Dissolution speeds of tablets printed via Fused Deposition Modeling (FDM) so far are significantly lower compared to powder or granule pressed immediate release tablets. The aim of this work was to print an actual immediate release tablet by choosing suitable polymers and printing designs, also taking into account lower processing temperatures (below 100°C) owing to the used model drug pantoprazole sodium. METHODS: Five different pharmaceutical grade polymers polyvinylpyrrolidone (PVP K12), polyethylene glycol 6000 (PEG 6000), Kollidon® VA64, polyethylene glycol 20,000 (PEG 20,000) and poloxamer 407 were successfully hot-melt-extruded to drug loaded filaments and printed to tablets at the required low temperatures. RESULTS: Tablets with the polymers PEG 6000 and PVP K12 and with a proportion of 10% pantoprazole sodium (w/w) demonstrated a fast drug release that was completed within 29 min or 10 min, respectively. By reducing the infill rate of PVP tablets to 50% and thereby increase the tablet porosity it was even possible to reduce the mean time for total drug release to only 3 min. CONCLUSIONS: The knowledge acquired through this work might be very beneficial for future FDM applications in the field of immediate release tablets especially with respect to thermo-sensitive drugs.

Porosity and distribution of water in perlite from the island of Milos, Greece.

A perlite sample representative of an operating mine in Milos was investigated with respect to the type and spatial distribution of water. A set of different methods was used which finally provided a consistent view on the water at least in this perlite. Infrared spectroscopy showed the presence of different water species (molecular water and hydroxyl groups / strongly bound water). The presence of more than 0.5 mass% smectite, however, could be excluded considering the cation exchange capacity results. The dehydration measured by thermal analysis occurred over a wide range of temperatures hence confirming the infrared spectroscopical results. Both methods point to the existence of a continuous spectrum of water binding energies. The spatial distribution of water and/or pores was investigated using different methods (CT: computer tomography, FIB: scanning electron microscopy including focused ion beam technology, IRM: infrared microscopy). Computer tomography (CT) showed large macropores (20 - 100 µm) and additionally revealed a mottled microstructure of the silicate matrix with low density areas up to a few µm in diameter. Scanning electron microscopy (FIB) confirmed the presence of µm sized pores and IRM showed the filling of these pores with water. In summary, two types of pores were found. Airfilled 20 - 100 µm pores and µm-sized pores disseminated in the glass matrix containing at least some water. Porosity measurements indicate a total porosity of 26 Vol%, 11 Vol% corresponding to the µm-sized pores. It remains unsolved wether the water in the µm-sized pores entered after or throughout perlite formation. However, the pores are sealed and no indications of cracks were found which indicated a primary source of the water, i.e. water was probably entrapped by quenching of the lava. The water in these pores may be the main reason for the thermal expandability which results in the extraordinarily porous expanded perlite building materials.

Effects of hydrogen on the formation of aligned carbon nanotubes by chemical vapor deposition.

Well-aligned carbon nanotubes with controllable properties were grown on porous silicon substrates by thermal chemical vapor deposition. The morphologies of the carbon nanotubes were varied with the introduction of H2 during the catalyst activation and/or carbon nanotube growth processes. It was found that H2 promotes the growth of carbon nanotubes while preventing the formation of spherical amorphous carbon particles. Without the introduction of H2 during the C2H2 thermal decomposition, aligned carbon nanotubes mixed with spherical carbon particles were formed on the substrate. However, with the introduction of H2, pure carbon nanotubes were synthesized. These nanotubes also had uniform diameters of 10-20 nm, which is much smaller than nanotubes synthesized without H2. The average growth rate of nanotubes was also affected by the introduction of hydrogen into the reaction chamber during nanotube growth. With the addition of hydrogen, the average growth rate changed from 78 nm/s to 145 nm/s. A possible growth mechanism, including the effect of a high ratio of H2 to C2H2, is suggested for the growth of these well-aligned carbon nanotubes with uniform diameters.