Silver nanocluster/silica composite coatings obtained by sputtering for antibacterial applications

Silver nanocluster silica composite coatings were deposited by radio frequency co-sputtering technique on several substrates. This versatile method allows tailoring of silver content and antibacterial behaviour of coatings deposited on glasses, ceramics, metals and polymers for several applications. Coating morphology and composition as well as nanocluster size were analyzed by means of UV-Visible absorption, X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FESEM), electron dispersive spectroscopy (EDS), X-ray Photoelectron Spectroscopy (XPS) and Atomic Force Microscopy (AFM). The antibacterial effect was verified through the inhibition halo test against standard bacterial strain, Staphylococcus aureus, before and after sterilization process. Tape test demonstrated a good adhesion of the coatings to the substrate

Geochemical considerations for Hot, Dry Rock Systems

Circulating systems intended to model the P-T conditions found in the natural HDR (Hot Dry Rock) geothermal system at Los Alamos have been built. Experiments with these systems have determined the following parameters for the ''down hole'' reservoir: sample weight loss, circulating solution composition, textural changes in the rock, mineral loss from the rock and effects of chemical additives on rock erosion. The analyses of solutions generated from rock-water interactions in the experimental systems show the extremely dilute nature of the working fluid. These solutions are not brines. Silica scaling in the surface heat exchanger was found to account for the difference between loss of sample rate and analyzed silica in the solution. The weight loss data indicate that there was continuous transport of silica from the ''down hole'' rock to the heat exchanger. Experiments contrasting felsic and mafic rocks in the HDR concept indicate that a reservoir consisting of glass bearing basaltic rock would tend to produce greater scaling problems than systems emplaced in granite. Experimental results suggest that Na{sub 2}CO{sub 3} solutions may provide a means of increasing permeability and thereby increasing the effective heat transfer area of the reservoir. A brief description is given of a small test loop for simulating the flow of a geothermal solution through a heat exchanger. This loop, which is being built, will be used to study the coagulation and precipitation of silica under conditions similar to those expected in the field

Early stage reactivity and in-vitro behavior of silica-based bioactive glasses and glass-ceramics

The surface reactivity of different sets of glasses and glass-ceramics belonging to the SiO2\u2013P2O5\u2013 CaO\u2013MgO\u2013K2O\u2013Na2O system have been investigated. The attention was focused on the role of their composition on the bioactivity kinetics, in terms of pH modifications, silica-gel formation and its evolution toward hydroxycarbonatoapatite, after different times of soaking in simulated body fluid. Glasses and glass ceramics have been characterized by thermal analysis, SEM-EDS observations and phase analysis (XRD). XPS measurements have been carried out on the most representative set of sample in order to evaluate the evolution of the surface species during the growth of silica-gel and hydroxycarbonatoapatite. The response of murine fibroblast 3T3 to the material before and after a conditioning pre-treatment (immersion in SBF) has been investigated on the same set of samples in order to point out the role of the bioactivity mechanism on cell viability. The main differences among the various glasses have been related to the modifier oxides ratio and to the MgO content, which seems to have an influence on the glass stability, both in terms of thermal properties and surface reactivity. The surface characterization and in vitro tests revealed few variations in the reactivity of the different glasses and glass-ceramics in their pristine form. On the contrary, the different surface properties before and after the pre-treatment in SBF seem to play a role on the biocompatibility of both glass and glass-ceramics, due to the different ion release and hydrophilicity of the surfaces, affecting both cell viability and protein adsorption