Search results for "SILICA"
showing 10 items of 1092 documents
A new hydrous Al-bearing pyroxene as a water carrier in subduction zones
2011
Abstract A new Hydrous Al-bearing PYroxene (HAPY) phase has been synthesized at 5.4 GPa, 720 °C in the MgO–Al2O3–SiO2–H2O model system. It has the composition Mg2.1Al0.9(OH)2Al0.9Si1.1O6, a C-centered monoclinic cell with a = 9.8827(2), b = 11.6254(2) c = 5.0828(1) A and β = 111.07(1)°. The calculated density is 3.175 g/cm3 and the water content is 6.9% H2O by weight. Its structure has been solved in space group C2/c by the recently developed automated electron diffraction tomography method and refined by synchrotron X-ray powder diffraction. HAPY is a single chain inosilicate very similar to pyroxenes but with three instead of two cations in the octahedral layer, bonded to four oxygens and…
A New Monte Carlo Method for the Titration of Molecules and Minerals
2007
The charge state of molecules and solid/liquid interfaces is of paramount importance in the understanding of the reactivity and the physico-chemical properties of many systems. In this work, we porpose a new Monte Carlo method in the grand canonical ensemble using the primitive model, which allows us to simulate the titration behavior of macromolecules or solids at constant pH. The method is applied to the charging process of colloidal silica particles dispersed in a sodium salt solution for various concentrations and calcium silicate hydrate nano-particles in a calcium hydroxide solution. An excellent agreement is found between the experimental and simulated results.
Uptake of silica covered Quantum Dots into living cells: Long term vitality and morphology study on hyaluronic acid biomaterials
2015
Quantum Dots (QDs) are promising very bright and stable fluorescent probes for optical studies in the biological field but water solubility and possible metal bio-contamination need to be addressed. In this work, a simple silica-QD hybrid system is prepared and the uptake in bovine chondrocytes living cells without any functionalization of the external protective silica shield is demonstrated. Moreover, long term treated cells vitality (up to 14 days) and the transfer of silica-QDs to the next cell generations are here reported. Confocal fluorescence microscopy was also used to determine the morphology of the so labelled cells and the relative silica-QDs distribution. Finally, we employ sil…
Understanding the Acidic Properties of the Amorphous Hydroxylated Silica Surface
2019
Amorphous silica is an intrinsic challenging system to study. In the last decades, some particular chemical properties have been discovered and described, but their description and understanding at the molecular level are experimentally difficult. Therefore, theoretical quantum chemical methods and descriptors, combined with experimental input, are a very appropriate set up to tackle this topic. In this study, the acidity of silanol groups of amorphous silica in hydrated conditions is investigated. Special attention has been drawn to the chemical shift, but also Bader charges, and vibrational frequencies with their intensities. The known bimodal acidity behavior was recovered and rationaliz…
Synthesis of refractory metal nuggets and constraints on the thermal histories of nugget-bearing Ca, Al-rich inclusions
2015
Tiny refractory metal nuggets are mainly observed inside Ca, Al-rich inclusions (CAIs) from chondritic meteorites and are commonly assumed to be condensates from a solar composition gas. However, recent detailed studies of metal nugget compositions and their comparison with predictions from condensation show that the observed abundance patterns are extremely difficult to achieve in this way. As a test for the proposed alternative, precipitation from a silicate liquid, we conducted melting experiments, in which nine different refractory metals (nugget components) were equilibrated with each other along with a CAI-like liquid at reducing conditions. When quenched, minerals similar to those in…
Titania–Silica Materials for Enhanced Photocatalysis
2015
Mesoporous titania–organosilica nanoparticles comprised of anatase nanocrystals crosslinked with organosilica moieties have been prepared by direct co-condensation of a titania precursor, tetrabuthylortotitanate (TBOT), with two organosilica precursors, 1,4-bis(triethoxysilyl) benzene (BTEB) and 1,2-bis(triethoxysilyl) ethane (BTEE), in mild conditions and in the absence of surfactant. These hybrid materials show both high surface areas (200–360 m2 g−1) and pore volumes (0.3 cm3 g−1) even after calcination, and excellent photoactivity in the degradation of rhodamine 6G and in the partial oxidation of propene under UV irradiation, especially after the calcination of the samples. During calci…
Irradiation effects on the absorption edge of silica glass
2007
Abstract Vacuum ultraviolet absorption experiments were carried out on a variety of specimens of amorphous silica β-irradiated at different doses from ∼103 to 5 × 106 kGy. Changes in the width of the absorption (Urbach) edge were investigated. These changes strongly depend on the kind of silica considered: in particular the Urbach energy of silica of industrial manufacture increases in the irradiated samples, whereas in sol–gel silica it is poorly influenced by the irradiation. The fictive temperature of the different materials before and after irradiation was also monitored. The changes of the Urbach energy and of the fictive temperature are tentatively discussed considering the disorder d…
Neutron-induced defects in optical fibers
2014
We present a study on 0.8 MeV neutron-induced defects up to fluences of 1017 n/cm2 in fluorine doped optical fibers by using electron paramagnetic resonance, optical absorption and confocal micro-luminescence techniques. Our results allow to address the microscopic mechanisms leading to the generation of Silica-related point-defects such as E', H(I), POR and NBOH Centers.
centers induced by γ irradiation in sol–gel synthesized oxygen deficient amorphous silicon dioxide
2007
The effects of room temperature γ-ray irradiation up to a dose of ∼1300 kGy are investigated by Electron paramagnetic resonance (EPR) measurements in amorphous silicon dioxide (a-SiO2) produced by a sol-gel synthesis method that introduces O{triple bond, long}Si{single bond}Si{triple bond, long}O oxygen deficiency. We have found that exposure to radiation generates the Eγ′ center with the same spectral features found in high purity commercial a-SiO2. The maximum concentration of defects induced in this sol-gel material indicates that its resistance to radiation is comparable to that of synthetic fused a-SiO2. The concentration of Eγ′ center increases with irradiation, featuring a sublinear …
Nanoparticles and their influence on radionuclide mobility in deep geological formations
2012
International audience; This article gives an overview of the current status of knowledge concerning the role of nanoparticles (inorganic and organic) in deep geological host rocks and the potential influence of these nanoparticles on radionuclide migration in far-field systems. The manuscript is not intended to be a full review paper or overview paper concerning nanoparticles, here the intention is to refer to recent publications but to highlight the progress made in the 6th framework project IP FUNMIG (Fundamental processes of radionuclide migration) and the open literature over the past 5 a concerning the process understanding of nanoparticle related issues in the three host rock formati…