No abstract

Alumina aerogels were prepared through the addition of propylene oxide to aqueous or ethanolic solutions of hydrated aluminum salts, AlCl 3 •6H 2 O or Al(NO 3) 3 •9H 2 O, followed by drying with supercritical CO 2. This technique affords low-density (60-130 kg/m 3), high surface area (600-700 m 2 /g) alumina aerogel monoliths without the use of alkoxide precursors. The dried alumina aerogels were characterized using elemental analysis, highresolution transmission electron microscopy, powder X-ray diffraction, solid state NMR, acoustic measurements and nitrogen adsorption/desorption analysis. Powder X-ray diffraction and TEM analysis indicated that the aerogel prepared from hydrated AlCl 3 in water or ethanol possessed microstructures containing highly reticulated networks of pseudoboehmite fibers, 2-5 nm in diameter and of varying lengths, while the aerogels prepared from hydrated Al(NO 3) 3 in ethanol were amorphous with microstructures comprised of interconnected spherical particles with diameters in the 5-15 nm range. The difference in microstructure resulted in each type of aerogel displaying distinct physical and mechanical properties. In particular, the alumina aerogels with the weblike microstructure were far more mechanically robust than those with the colloidal network, based on acoustic measurements. Both types of alumina aerogels can be transformed to γ-Al 2 O 3 through calcination at 800 o C without a significant loss in surface area or monolithicity.

We report a method for fabricating optical quality silica and silica-titania glasses by additive manufacturing, or 3D printing. Key to this success was the combination of sol-gel derived silica and silica-titania colloidal feedstocks, 3D direct ink writing (DIW) technology, and conventional glass thermal processing methods. Printable silica and silica-titania sol inks were prepared directly from molecular precursors by a simple one-pot method, which was optimized to yield viscous, shear-thinning colloidal suspensions with tuned rheology ideal for DIW. After printing, the parts were dried and sintered under optimized thermal conditions to ensure complete organic removal and uniform densification without crystallization.Characterizations of the 3D-printed pure silica and silica-titania glasses show that they are This article is protected by copyright. All rights reserved. 2 equivalent to commercial optical fused silica (Corning ® 7980) and silica-titania glasses (Corning ULE ® 7972). More specifically, they exhibit comparable chemical composition, SiO 2 network structure, refractive index, dispersion, optical transmission, and coefficient of thermal expansion. 3D printed silica and silica-titania glasses also exhibited comparable polished surface roughness and meet refractive index homogeneity standards within range of commercial optical grade glasses. This method establishes 3D printing as a viable tool to create optical glasses with compositional and geometric configurations that are inaccessible by conventional optical fabrication methods. † denotes value determined by LA-ICP-MS; a-SiO 2 used to represent amorphous SiO 2

Layered clays are shown to have a wide range of blood-clotting properties that appear to be influenced by surface charge. The most active clay clotting agent is as effective as a commercial zeolite hemostatic material, but does not release heat, making it a promising alternative to the zeolite.

Blanke Oberflächen: Trialkyloxoniumsalze sind universelle Reagentien für die Ligandenabspaltung von carboxylat‐, phosphonat‐ und aminpassivierten Nanokristallen zur Bildung von blanken oder BF4−/DMF‐passivierten Oberflächen. Meerwein‐aktivierte dünne PbSe‐Nanokristallfilme (siehe Bild) weisen Lochbeweglichkeiten von 2–4 cm2 V−1 s−1 auf, was Anwendungen dieses Prozesses zur Herstellung von Hochleistungskomponenten in Reichweite bringt.

No abstract

The sorption behavior of Eu(III), Sm(III), Np(V), Pu(V), and Pu(IV) in the presence of calcite and as a function of pH and carbonate alkalinity was measured by batch sorption experiments. Eu(III) and Sm(III) sorption is similar, consistent with their observed aqueous speciation and precipitation behavior. For both rare earth elements, sorption decreases at the highest and lowest measured pHs. This is likely the result of speciation changes both of the calcite surface and the sorber. An increase in the equilibrium CO 2 (g) fugacity results in a shift in the sorption behavior to lower pH, consistent with a predicted aqueous speciation shift. Np(V) and Pu(V) sorption exhibited a strong pH dependence. For Np(V), K d s range from 0 to 217 mL/g suggesting that carbonate aqueous speciation as well as changes in the calcite surface speciation greatly affect Np(V) sorption to the calcite surface. Similar behavior was found for Pu(V). Pu(IV) sorption is also strongly pH dependent. Sorption decreases significantly at high pH as a result of Pu-carbonate complexation in solution. A surface complexation model of Sm(III), Eu(III), Np(V), Pu(V), and Pu(IV) sorption to the calcite surface was developed based on the calcite surface speciation model of Pokrovsky and Schott [1]. Sorption data were fit using one or two surface species for each sorber and could account for the effect of pH and CO 2 (g) fugacity on sorption. A relatively poor model fit to Pu(IV) sorption data at high pH may result from our poor understanding of Pu(IV)-carbonate aqueous speciation. While our surface complexation model may not represent a unique solution to the sorption data, it illustrates that a surface complexation modeling approach may adequately describe the sorption behavior of a number of radionuclides at the calcite surface over a range of solution conditions.

Metal borides have attracted the attention of researchers due to their useful physical properties and unique ability to form high hydrogen-capacity metal borohydrides. We demonstrate improved hydrogen storage properties of a nanoscale Mg–B material made by surfactant ball milling MgB2 in a mixture of heptane, oleic acid, and oleylamine. Transmission electron microscopy data show that Mg–B nanoplatelets are produced with sizes ranging from 5 to 50 nm, which agglomerate upon ethanol washing to produce an agglomerated nanoscale Mg–B material of micron-sized particles with some surfactant still remaining. X-ray diffraction measurements reveal a two-component material where 32% of the solid is a strained crystalline solid maintaining the hexagonal structure with the remainder being amorphous. Fourier transform infrared shows that the oleate binds in a “bridge-bonding” fashion preferentially to magnesium rather than boron, which is confirmed by density functional theory calculations. The Mg–B nanoscale material is deficient in boron relative to bulk MgB2 with a Mg–B ratio of ∼1:0.75. The nanoscale MgB0.75 material has a disrupted B–B ring network as indicated by X-ray absorption measurements. Hydrogenation experiments at 700 bar and 280 °C show that it partially hydrogenates at temperatures 100 °C below the threshold for bulk MgB2 hydrogenation. In addition, upon heating to 200 °C, the H–H bond-breaking ability increases ∼10-fold according to hydrogen–deuterium exchange experiments due to desorption of oleate at the surface. This behavior would make the nanoscale Mg–B material useful as an additive where rapid H–H bond breaking is needed.