Search results for "Silicate"
showing 10 items of 413 documents
Formation and accumulation of radiation-induced defects and radiolysis products in modified lithium orthosilicate pebbles with additions of titanium …
2016
Abstract Lithium orthosilicate (Li4SiO4) pebbles with 2.5 wt.% excess of silicon dioxide (SiO2) are the European Union's designated reference tritium breeding ceramics for the Helium Cooled Pebble Bed (HCPB) Test Blanket Module (TBM). However, the latest irradiation experiments showed that the reference Li4SiO4 pebbles may crack and form fragments under operation conditions as expected in the HCPB TBM. Therefore, it has been suggested to change the chemical composition of the reference Li4SiO4 pebbles and to add titanium dioxide (TiO2), to obtain lithium metatitanate (Li2TiO3) as a second phase. The aim of this research was to investigate the formation and accumulation of radiation-induced …
Solidification of ion exchange resins saturated with Na+ ions: Comparison of matrices based on Portland and blast furnace slag cement
2017
International audience; Ion exchange resins (IERs) are widely used by the nuclear industry to decontaminate radioactive effluents. After use, they are usually stabilized and solidified by encapsulation in cementitious materials. However, for certain combinations of cement and resins, the solidified waste forms can exhibit strong expansion, possibly leading to cracking of the matrix. In this work, the behaviour of cationic resins in the Na$^+$ form is investigated in Portland cement (CEM I) or blast furnace slag cement (CEM III/C) pastes at early age in order to have a better understanding of the swelling process. The results show that during the hydration of the CEM I paste, the resins exhi…
The structural properties of soda–silicate sols and of the lime–soda–silicate gel formation
1999
Abstract Alkaline silicate solutions were prepared with varying SiO 2 –Na 2 O ratios, Rm=[SiO 2 ]/[Na 2 O]=2 or 3, with a constant silica concentration equal to 1.5 M. The structure and the number fraction of different silicate molecular species present in the solutions were classically determined for molar ratio Rm=2 using 29 Si nuclear magnetic resonance ( 29 Si NMR). In the case of the sample with Rm=3, for which no NMR data was available, we used small-angle X-ray scattering (SAXS) experiments to get this information. The SAXS model was previously tested with Rm=2 silicate solution. When Ca ++ is added to alkaline silicate solutions, a gel is obtained under well-defined conditions. The …
Bimodal copper oxide nanoparticles doped phase for the extraction of highly polar compounds by in-tube solid-phase microextraction coupled on-line to…
2020
Abstract Polymers obtained from tetraethyl orthosilicate (TEOS) and triethoxymethylsilane (MTEOS) have been functionalized with different metal and metal oxide nanoparticles (NPs), and used as coatings of extractive capillaries for the extraction of polar compounds by in-tube solid-phase microextraction (IT-SPME) coupled on-line to nano-liquid chromatography (nano-LC). The extraction capabilities of the new phases have been studied using several triazinic herbicides with log of octanol/water partition coefficients (Kow) ranging from -0.7 to 3.21 under reversed phase chromatographic conditions. Best extraction efficiencies for the most polar compounds (log Kow ≤ 2.3) were typically obtained …
Evidence for fractional condensation and reprocessing at high temperatures in CH chondrites
2003
We performed a detailed study of silica-rich components (SRC) in the paired CH chondrites Acfer 182 and 207. These SRCs appear either as chondrules or fragments, and they contribute <0.1 vol% to the bulk meteorite. They usually contain a silica and a silicate portion. Both portions are, in most cases, cryptocrystalline and have bulk SiO2-concentrations between 65 and 85 wt%. The silicate generally has a pyroxene normative composition. The silica often appears as blebs within the silicate matrix or vice versa. If there are no blebs, silica and silicate still form rounded interfaces. The SRCs are depleted in refractory elements like Ca, Al, and Ti relative to CI. A few SRC- like objects are e…
Melting phlogopite-rich MARID: Lamproites and the role of alkalis in olivine-liquid Ni-partitioning
2018
Abstract In this study, we show how veined lithospheric mantle is involved in the genesis of ultrapotassic magmatism in cratonic settings. We conducted high pressure experiments to simulate vein + wall rock melting within the Earth's lithospheric mantle by reacting assemblages of harzburgite and phlogopite-rich hydrous mantle xenoliths. These comprised a mica-, amphibole-, rutile-, ilmenite-, diopside (MARID) assemblage at 3–5 GPa and 1325–1450 °C. Melting of the MARID assemblages results in infiltration of melt through the harzburgite, leading to its chemical alteration. At 3 and 4 GPa, melts are high in K2O (> 9 wt%) with K2O/Na2O > > 2 comparable to anorogenic lamproites. Higher pressure…
Effect of heating of organo-montmorillonites under different atmospheres
2009
Abstract We studied the influence of heating on the behaviour of two organo-montmorillonites paying particular attention to the possible degradation effects of the organic modifier under different atmospheres. Hoffmann elimination and anucleophilic substitution on the nitrogen led to rapid degradation of the modifier. As confirmed by deconvoluted FTIR spectra, the presence of oxygen accelerated the degradation rate. The degradation products of the modifier (α-olefins transforming into various carboxyl compounds if oxygen is present) initially increased the basal spacing, followed by a collapse of the particle layers when the decomposition products migrated toward the surface and eventually …
Stability and nature of the volume collapse of ε-Fe2O3 under extreme conditions
2018
Iron oxides are among the major constituents of the deep Earth’s interior. Among them, the epsilon phase of Fe2O3 is one of the less studied polymorphs and there is a lack of information about its structural, electronic and magnetic transformations at extreme conditions. Here we report the precise determination of its equation of state and a deep analysis of the evolution of the polyhedral units under compression, thanks to the agreement between our experiments and ab-initio simulations. Our results indicate that this material, with remarkable magnetic properties, is stable at pressures up to 27 GPa. Above 27 GPa, a volume collapse has been observed and ascribed to a change of the local env…
From Maya Blue to “Maya Yellow”: A Connection between Ancient Nanostructured Materials from the Voltammetry of Microparticles
2011
The yellow hue of a series of samples from wall paintings in several Mayan archaeological sites can be attributed to the presence of indigoid compounds, including isatin and dehydroindigo, attached to palygorskite, a local phyllosilicate clay. SEM/EDX, TEM, UV/Vis spectroscopy, and voltammetry of microparticles show that the ancient Mayas could prepare indigo, Maya Blue, and "Maya Yellow" during successive stages. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Effect of Morphology and Size of Halloysite Nanotubes on Functional Pectin Bionanocomposites for Food Packaging Applications
2017
Pectin bionanocomposite films filled with various concentrations of two different types of halloysite nanotubes were prepared and characterized in this study as potential films for food packaging applications. The two types of halloysite nanotubes were long and thin (patch) (200-30 000 nm length) and short and stubby (Matauri Bay) (50-3000 nm length) with different morphological, physical, and dispersibility properties. Both matrix (pectin) and reinforcer (halloysite nanotubes) used in this study are considered as biocompatible, natural, and low-cost materials. Various characterization tests including Fourier transform infrared spectroscopy, field emission scanning electron microscopy, rele…