Investigation on the effectiveness of the repair method 8.3 “Corrosion protection by increasing the electrical resistivity” in chloride-containing concrete Part 2: Chloride redistribution in concrete after application of a system sealing surface protective coating

This DFG-funded research project aimed to gain a better understanding of the mechanisms of the W-Cl repair principle within the framework of fundamental investigations, to contribute to the creation of the necessary basis for a broader application of the repair principle in practice. The focus was on the development of a model to describe the chloride redistribution after the application of a system sealing surface protective coating. On the basis of Fick's second law of diffusion, a mathematical model with a self-contained analytical solution was developed, with the help of which the chloride redistribution after application of a system sealing surface protective coating can be calculated under the idealized assumption of complete water saturation of the concrete. Furthermore, the influence of the dehydration of the concrete, expected as a result of the application of the repair principle W-Cl, on the chloride redistribution was investigated. On the basis of laboratory tests and numerical simulations, material-specific reduction functions were developed to quantify the relationship between the chloride diffusion coefficient and the ambient humidity.     

Influence of the Temperature on Coccolith-Containing Systems from Emiliania huxleyi Cultivations

Thermogravimetric analysis of a coccolith-containing biogenic broth showed a three-step degradation process. According to this system behavior, the biogenic broth was heated to specific temperatures and characterized in terms of its morphology, surface chemistry, and crystallinity. The elemental and organic composition of the treated samples was also evaluated and compared to the reference material. The presented results were acquired in an effort to exploit pretreatment scenarios for such a biogenic system that would improve and support a separation process.     

Ballistic behavior of plain and reinforced concrete slabs under high velocity impact

This work presents a numerical simulation of ballistic penetration and high velocity impact behavior of plain and reinforced concrete slabs. In this paper, we focus on the comparison of the performance of the plain and reinforced concrete slabs of unconfined compressive strength 41 MPa under ballistic impact. The concrete slab has dimensions of 675 mm × 675 mm × 200 mm, and is meshed with 8-node hexahedron solid elements in the impact and outer zones. The ogive-nosed projectile is considered as rigid element that has a mass of 0.386 kg and a length of 152 mm. The applied velocities vary between 540 and 731 m/s. 6 mm of steel reinforcement bars were used in the reinforced concrete slabs. The constitutive material modeling of the concrete and steel reinforcement bars was performed using the Johnson-Holmquist-2 damage and the Johnson-Cook plasticity material models, respectively. The analysis was conducted using the commercial finite element package Abaqus/Explicit. Damage diameters and residual velocities obtained by the numerical model were compared with the experimental results and effect of steel reinforcement and projectile diameter were studies. The validation showed good agreement between the numerical and experimental results. The added steel reinforcements to the concrete samples were found efficient in terms of ballistic resistance comparing to the plain concrete sample.     

Growth behavior of aluminum borate whiskers on zirconia toughened alumina (ZTA) particle surface

In this work, B₄C-covered zirconia-toughened alumina (ZTA) particles are prepared and oxidised at 1050 °C for different times (0, 2, 4, and 8 h) in air. The X-ray diffraction and electron probe micro-analysis results show that the covering layer is mainly composed of oxide B₂O₃ intermetallics, residual B₄C particles, and Al₁₈B₄O₃₃ whiskers. The scanning electron microscopy results show that the growth of Al₁₈B₄O₃₃ whiskers on the ZTA particles enhances with increasing heat preservation time; the optimum holding time is determined to be 8 h Al₂O₃ in the ZTA particles diffuse into the covering layer and combine with B₂O₃ to form Al₁₈B₄O₃₃ whiskers; the Al₁₈B₄O₃₃ whiskers grow via the liquid-solid mechanism.     

Mechanism of methanol decomposition on the Pd/WC(0001) surface unveiled by first-principles calculations

In this study, the decomposition of methanol into the CO and H species on the Pd/tungsten carbide (WC)(0001) surface is systematically investigated using periodic density functional theory (DFT) calculations. The possible reaction pathways and intermediates are determined. The results reveal that saturated molecules, i.e., methanol and formaldehyde, adsorb weakly on the Pd/ WC(0001) surface. Both CO and H prefer three-fold sites, with adsorption energies of −1.51 and −2.67 eV, respectively. On the other hand, CH₃O stably binds at three-fold and bridge sites, with an adsorption energy of −2.58 eV. However, most of the other intermediates tend to adsorb to the surface with the carbon and oxygen atoms in their sp³ and hydroxyl-like configurations, respectively. Hence, the C atom of CH₂OH preferentially attaches to the top sites, CHOH and CH₂O adsorb at the bridge sites, while COH and CHO occupy the three-fold sites. The DFT calculations indicate that the rupture of the initial C–H bond promotes the decomposition of CH₃OH and CH₂OH, whereas in the case of CHOH, O–H bond scission is favored over the C–H bond rupture. Thus, the most probable methanol decomposition pathway on the Pd/WC(0001) surface is CH₃OH → CH₂OH → trans-CHOH → CHO → CO. The present study demonstrates that the synergistic effect of WC (as carrier) and Pd (as catalyst) alters the CH₃OH decomposition pathway and reduces the noble metal utilization.     

Colloidal Synthesis of Hollow Cobalt Sulfide Nanocrystals

Formation of cobalt sulfide hollow nanocrystals through a mechanism similar to the Kirkendall Effect has been investigated in detail. It is found that performing the reaction at > 120 °C leads to fast formation of a single void inside each shell, whereas at room temperature multiple voids are formed within each shell, which can be attributed to strongly temperature‐dependent diffusivities for vacancies. The void formation process is dominated by outward diffusion of cobalt cations; still, the occurrence of significant inward transport of sulfur anions can be inferred as the final voids are smaller in diameter than the original cobalt nanocrystals. Comparison of volume distributions for initial and final nanostructures indicates excess apparent volume in shells, implying significant porosity and/or a defective structure. Indirect evidence for fracture of shells during growth at lower temperatures was observed in shell‐size statistics and transmission electron microscopy images of as‐grown shells. An idealized model of the diffusional process imposes two minimal requirements on material parameters for shell growth to be obtainable within a specific synthetic system.     

Encapsulation and Ostwald Ripening of Au and Au–Cl Complex Nanostructures in Silica Shells

We report a general template strategy for rational fabrication of a new class of nanostructured materials consisting of multicore shell particles. Our approach is demonstrated by encapsulating Au or Pt nanoparticles in silica shells. Other superstructures of these hollow shells, like dimers, trimers, and tetramers can also be formed by nanoparticle‐mediated self‐assembly. We have also used the as‐prepared multicore Au–silica hollow particles to perform the first studies of Ostwald ripening in confined microspace, in which chloride was found to be an efficient mediating ligand. After treatment with aqua regia, Au–Cl complex is formed inside the shell, and is found to be very active under in situ transmission electron microscopy observations while confined in a microcell. This aspect of the work is expected to motivate further in situ studies of confined crystal growth.     

Results from the ORPHEUS dark matter detector

The ORPHEUS dark matter detector consists of 450 g superconducting tin granules with diameters of 28 and 36 μm. The detector has been operating in the shallow site of the underground laboratory in Bern (70 m.w.e). First preliminary results on WIMP detection sensitivity will be presented.     

Method for Preparation of Semiconductor Quantum‐Rod Lasers in a Cylindrical Microcavity

An efficient method for preparation of semiconductor quantum rod films for robust lasing in a cylindrical microcavity is reported. A capillary tube, serving as the laser cavity, is filled with a solution of nanocrystals and irradiated with a series of intense nanosecond laser pulses to produce a nanocrystal film on the capillary surface. The films exhibit intense room‐temperature lasing in whispering‐gallery modes that develop at the film–capillary interface as corroborated from the spacing detected for the lasing modes. Good lasing stability is observed at moderate pump powers. The method was applied successfully to several quantum‐rod samples of various sizes.