Nano-scale spatial confinement can alter chemistry at mineral–water interfaces. These nano-scale confinement effects can lead to anomalous fate and transport behavior of aqueous metal species. When a fluid resides in a nanoporous environments (pore size under 100 nm), the observed density, surface tension, and dielectric constant diverge from those measured in the bulk. To evaluate the impact of nano-scale confinement on the adsorption of copper (Cu2+), we performed batch adsorption studies using mesoporous silica. Mesoporous silica with the narrow distribution of pore diameters (SBA-15; 8, 6, and 4 nm pore diameters) was chosen since the silanol functional groups are typical to surface environments. Batch adsorption isotherms were fit with adsorption models (Langmuir, Freundlich, and Dubinin–Radushkevich) and adsorption kinetic data were fit to a pseudo-first-order reaction model. We found that with decreasing pore size, the maximum surface area-normalized uptake of Cu2+ increased. The pseudo-first-order kinetic model demonstrates that the adsorption is faster as the pore size decreases from 8 to 4 nm. We attribute these effects to the deviations in fundamental water properties as pore diameter decreases. In particular, these effects are most notable in SBA-15 with a 4-nm pore where the changes in water properties may be responsible for the enhanced Cu mobility, and therefore, faster Cu adsorption kinetics.Electronic supplementary materialThe online version of this article (10.1186/s12932-018-0057-4) contains supplementary material, which is available to authorized users.
Calcite (CaCO3) is one of the most abundant minerals in the Earth’s crust, and it is susceptible to subcritical chemically-driven fracturing. Understanding chemical processes at individual fracture tips, and how they control the development of fractures and fracture networks in the subsurface, is critical for carbon and nuclear waste storage, resource extraction, and predicting earthquakes. Chemical processes controlling subcritical fracture in calcite are poorly understood. We demonstrate a novel approach to quantify the coupled chemical-mechanical effects on subcritical fracture. The calcite surface was indented using a Vickers-geometry indenter tip, which resulted in repeatable micron-scale fractures propagating from the indent. Individual indented samples were submerged in an array of aqueous fluids and an optical microscope was used to track the fracture growth in situ. The fracture propagation rate varied from 1.6 × 10−8 m s−1 to 2.4 × 10−10 m s−1. The rate depended on the type of aqueous ligand present, and did not correlate with the measured dissolution rate of calcite or trends in zeta-potential. We postulate that chemical complexation at the fracture tip in calcite controls the growth of subcritical fracture. Previous studies indirectly pointed to the zeta-potential being the most critical factor, while our work indicates that variation in the zeta-potential has a secondary effect.
Investigations of superconductive joints were performed using an infiltration technique. Gaps between two domains of were prepared mechanically and subsequently filled with powder. Barium cuprate liquid prepared by the peritectic decomposition of was infiltrated into the gap between the two domains. Microstructural analysis indicates a local epitaxy of the solder.
Texturing of superconductors is essential to achieve high critical current densities. For coatings or coated conductors the symmetry-anisotropy of the substrate has a major impact on the formation of a biaxial texture. The substrate symmetry is broken for example by a rolling texture in the RABiTS process or by anisotropic damage in the IBAD process. However, anisotropy can also be introduced by using multiphase substrates, providing an anisotropic but regular arrangement of the individual phases. Such an arrangement leads to anisotropic growth conditions owing to the different properties of the phases involved. Moreover, nucleation is probably influenced by the aligned boundaries between the substrate phases. As a preliminary result obtained from infiltration of regularly arranged fibres, preferred growth along the fibre directions is observed.
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