Chemo-mechanical characterization of hydrated calcium-hydrosilicates with coupled Raman- and nanoindentation measurements

Celitement is a new type of cement that is based on hydraulic calcium-hydrosilicate (hCHS). It is produced by mechanochemical activation of Calcium-Silicate-Hydrates (C-S-H) in a grinding process. Due to the lack of typical clinker minerals, its CaO/SiO_{2} (C/S) ratio can be minimized from above 3 (as in Ordinary Portland Cement) down to 1, which significantly reduces the amount of CO_{2} released during processing. The reaction kinetics of hCHS differs from that of classical clinker phases due to the presence of highly reactive silicate species, which involve silanol groups instead of pure calcium silicates and aluminates and aluminoferrites. In contrast to Portland cement, no calcium hydroxide is formed during hydration, which otherwise regulates the Ca concentration. Without the buffering role of Ca(OH)_{2} the concentration of the dissolved species c(Ca^2+) and c(SiO_{4}^4−) and the corresponding pH must be controlled to ensure a reproducible reaction. Pure hCHS reacts isochemically with water, resulting in a C-S-H phase with the same chemical composition as a single hydration product, with a homogeneous distribution of the main elements Ca and Si throughout the sample. Here we study via nanoindentation tests, the mechanical properties of two different types of hardened pastes made out of Celitement (C/S = 1.28), with varying amounts of hCHS and variable water to cement ratio. We couple nanoindentation grids with Raman mappings to link the nanoscale mechanical properties to individual microstructural components, yielding in-depth insight into the mechanics of the mineralogical phases constituting the hardened cement paste. We show that we can identify in hardened Celitement paste both fresh C-S-H with varying density, and C-S-H from the raw material using their specific Raman spectra, while simultaneously measuring their mechanical properties. Albeit not suitable for phase identification, supplemental EDX measurements provide valuable information about the distribution of alkalis, thus further helping to understand the reaction pattern of hCHS

Silver zeolite-loaded silicone elastomers: a multidisciplinary approach to synthesis and antimicrobial assessment

A multidisciplinary approach has been applied to the preparation of antibacterial Ag zeolite/silicone elastomer composites aimed at products that satisfy a range of requirements, namely good mechanical properties after zeolite incorporation and strongly antibacterial. Zeolite X was synthesised and used as antibacterial agent after ion-exchange with silver. The high level of silver (14 wt%) within the zeolite enabled the preparation of antibacterial composites containing a relatively low level of zeolite (2 wt%). The composites showed strong efficacy against Escherichia coli and Staphylococcus epidermidis. Organic functionalization of the zeolite with organo-silanes prior blending with the matrix usefully improved composite mechanical properties and reduced color development in Ag zeolite containing silicone elastomers. Organo-silane modification did not substantially affect the antibacterial performance of the materials; the number of viable cells of both Gram-positive and Gram-negative bacteria was reduced to beyond detection limits within 24 hours of incubation. Efficacy of the Ag zeolite containing composites against the yeast Candida albicans was found to be substantially less than observed with the two bacteria. This study demonstrates that evaluation of polymer composites needs to be performed via a multidisciplinary approach in order to avoid compromising a particular aspect of the materials' design, characteristics or performance, including the use of reliable testing methods to determine the latter

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

Studies of materials’ properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications

The ANKA-IR2 Nanoscope and Micro- and Nanospectroscopy Applications

We report on a newly developed and integrated microscopy and nanoscopy station at the ANKA-IR2 beamline. We further elucidate how vibrational near-field and microspectroscopy can give new insights in medical applications

Terapascal static pressure generation with ultrahigh yield strength nanodiamond

Studies of materials’ properties at high and ultrahigh pressures lead to discoveries of unique physical and chemical phenomena and a deeper understanding of matter. In high-pressure research, an achievable static pressure limit is imposed by the strength of available strong materials and design of high-pressure devices. Using a high-pressure and high-temperature technique, we synthesized optically transparent microballs of bulk nanocrystalline diamond, which were found to have an exceptional yield strength (~460 GPa at a confining pressure of ~70 GPa) due to the unique microstructure of bulk nanocrystalline diamond. We used the nanodiamond balls in a double-stage diamond anvil cell high-pressure device that allowed us to generate static pressures beyond 1 TPa, as demonstrated by synchrotron x-ray diffraction. Outstanding mechanical properties (strain-dependent elasticity, very high hardness, and unprecedented yield strength) make the nanodiamond balls a unique device for ultrahigh static pressure generation. Structurally isotropic, homogeneous, and made of a low-Z material, they are promising in the field of x-ray optical applications