Sodium silicate | EPFL Graph Search

Sodium silicate is a generic name for chemical compounds with the formula Na2xSiyO2y+x or (Na2O)x·(SiO2)y, such as sodium metasilicate Na2SiO3, sodium orthosilicate Na4SiO4, and sodium pyrosilicate Na6Si2O7. The anions are often polymeric. These compounds are generally colorless transparent solids or white powders, and soluble in water in various amounts. Sodium silicate is also the technical and common name for a mixture of such compounds, chiefly the metasilicate, also called waterglass, water glass, or liquid glass. The product has a wide variety of uses, including the formulation of cements, passive fire protection, textile and lumber processing, manufacture of refractory ceramics, as adhesives, and in the production of silica gel. The commercial product, available in water solution or in solid form, is often greenish or blue owing to the presence of iron-containing impurities. In industry, the various grades of sodium silicate are characterized by their SiO2:Na2O weight ra

Dimensional and structural control of silica aerogel membranes for miniaturized motionless gas pumps

Eunho Jeong, Bo Jiang, Nayoung Kim, Matthias M. Koebel, Thomas Maeder, Paul Muralt, Shuangyi Zhao

With growing public interest in portable electronics such as micro fuel cells, micro gas total analysis systems, and portable medical devices, the need for miniaturized air pumps with minimal electrical power consumption is on the rise. Thus, the development and downsizing of next-generation thermal transpiration gas pumps has been investigated intensively during the last decades. Such a system relies on a mesoporous membrane that generates a thermomolecular pressure gradient under the action of an applied temperature bias. However, the development of highly miniaturized active membrane materials with tailored porosity and optimized pumping performance remains a major challenge. Here we report a systematic study on the manufacturing of aerogel membranes using an optimized, minimal-shrinkage sol–gel process, leading to low thermal conductivity and high air conductance. This combination of properties results in superior performance for miniaturized thermomolecular air pump applications. The engineering of such aerogel membranes, which implies pore structure control and chemical surface modification, requires both chemical processing know-how and a detailed understanding of the influence of the material properties on the spatial flow rate density. Optimal pumping performance was found for devices with integrated membranes with a density of 0.062 g cm–3 and an average pore size of 142.0 nm. Benchmarking of such low-density hydrophobic active aerogel membranes gave an air flow rate density of 3.85 sccm·cm–2 at an operating temperature of 400 °C. Such a silica aerogel membrane based system has shown more than 50% higher pumping performance when compared to conventional transpiration pump membrane materials as well as the ability to withstand higher operating temperatures (up to 440 °C). This study highlights new perspectives for the development of miniaturized thermal transpiration air pumps while offering insights into the fundamentals of molecular pumping in three-dimensional open-mesoporous materials. Keywords: aerogel membrane; miniaturized gas pump; sodium silicate; low-temperature cofired ceramics; Knudsen flow

Amer Chemical Soc2015

Nightclub

David Viladomiu Ceballos

Nightclub peut être considéré comme un espace nostalgique reflétant un medium actuel. Il représente la forme la plus physique de l'instantanéité, la simultanéité et l'intensité d'internet. Le message de ce dernier a été la dissolution de toute condition d'échelle et de forme d'action ou d'association humaine. Nightclub semble contenir et condenser ces conditions au sein d'une délimitation spécifique. Contradictoirement, c'est par la définition d'un périmètre précis, sans signification évidente, que Nightclub, rejetant toute règle et tout jugement, permet la liberté. Si son état physique semble rétrograde, Nightclub est protagoniste d'une intensité urbaine actuelle et d'un paysage prospectif. La délimitation permet la création de conditions urbaines et de structures sociales nouvelles, générées par la production de natures artificielles. Un “apparatus” capable de performer et de fournir des “third places” pour les masses métropolitaines. Le pragmatisme de Nightclub donne lieu à la coexistence d'Apollo et de Dionysus. Il maintient ensemble création de soi et socialisation et au travers d'un environnement hédoniste extrême, pousse à leur apparition la plus physique, sexe. Nightclub: dispositif performatif clos pour contre-villes de désirs individuels.

2017

Vertical changes of the Co and Mn speciation along a lateritic regolith developed on peridotites (New Caledonia)

Gabrielle Dublet, Vincent Noel

Because they can host significant amounts of Co, the Mn-oxides are commonly considered as the major Co-bearing mineral species in lateritic environments. However, little is known about the process leading to the formation and/or the weathering of these Co-rich Mn-oxides. This lack of knowledge is mainly due to the fact that Co concentrations are too low in primary silicates for classical speciation analysis. In this study, we investigated both Co and Mn speciation in a 64 m thick lateritic regolith developed upon peridotites in New Caledonia, by combining High Energy Resolution Fluorescence Detection X-ray absorption Near Edge Structure (HERFD-XANES) spectroscopy at the Co K-edge with classical XANES spectroscopy at the Mn K-edge, bulk chemistry (ICP) and mineralogy (XRD). The results obtained provide new insights into the evolution of Co and Mn speciation as a function of the weathering stages. Co and Mn primarily occur as Co(II) and Mn(II, III) in olivine and serpentine in the bedrock. During the first weathering stage, these forms of Co and Mn are progressively oxidized toward Co(III) and Mn(III, IV), which occur mainly as Co(III)-bearing Mn(III/IV)-oxides in the transition between the saprolite and the laterite. In the uppermost lateritic horizons, long-time weathering resulted in a strong leaching of Co and Mn, and the remaining of these elements occurs as Co(II) and Mn(III) substituting for Fe(III) in goethite. This latter scavenging process emphasizes the importance of Fe-oxides for the long-term stabilization of Co and Mn in such deeply weathered laterites. (C) 2017 Elsevier Ltd. All rights reserved.

Pergamon-Elsevier Science Ltd2017

Dimensional and structural control of silica aerogel membranes for miniaturized motionless gas pumps

Eunho Jeong, Bo Jiang, Nayoung Kim, Matthias M. Koebel, Thomas Maeder, Paul Muralt, Shuangyi Zhao

Amer Chemical Soc2015