Search results for "SILICA"
showing 10 items of 1092 documents
Durcissement de matériaux pour l’optique et la photonique destinés à l’utilisation dans un environnement énergétique
2008
Influence du rayonnement X sur des fibres et préformes canoniques dopées au phosphore
2009
The relevance of point defects in studying silica-based materials from bulk to nanosystems
2019
The macroscopic properties of silica can be modified by the presence of local microscopic modifications at the scale of the basic molecular units (point defects). Such defects can be generated during the production of glass, devices, or by the environments where the latter have to operate, impacting on the devices’ performance. For these reasons, the identification of defects, their generation processes, and the knowledge of their electrical and optical features are relevant for microelectronics and optoelectronics. The aim of this manuscript is to report some examples of how defects can be generated, how they can impact device performance, and how a defect species or a physical phenomenon …
Near‐IR Radiation‐Induced Attenuation of Aluminosilicate Optical Fibers
2021
The X-ray radiation-induced attenuation (RIA) growth kinetics are studied online in different single-mode aluminosilicate optical fibers in the near-IR (NIR) domain to evaluate their potential in terms of dosimetry. The optical fibers differ by Al contents, core sizes, drawing parameters, and also by a preform deposition process. The data show no dependence of the RIA on all these parameters, a positive result for the design of point or distributed radiation detectors exploiting RIA to monitor the dose. The RIA growth rate is unchanged for dose rates changing from 0.073 to 6.25 Gy(SiO2) s−1, and the RIA linearly increases with the dose up to 2 kGy(SiO2). Small but noticeable RIA changes are…
Study of the Effect of Two Phases in Li4SiO4–Li2SiO3 Ceramics on the Strength and Thermophysical Parameters
2022
This research was funded by the Science Committee of the Ministry of Education and Science of the Republic of Kazakhstan (No. BR11765580). The research of the team from Latvia (A.M., V.P. and A.I.P.) has been carried out within the framework of the EUROfusion Consortium, funded by the European Union via the Euratom Research and Training Programme (Grant Agreement No. 101052200—EUROfusion). Views and opinions expressed are however those of the author(s) only and do not necessarily reflect those of the European Union or the European Commission. Neither the European Union nor the European Commission can be held responsible for them. The research was partly (A.M., V.P. and A.I.P.) performed in …
High accessibility and chemical homogeneity in mesoporous materials: silicas, gold-containing composites and phosphates
2015
El trabajo recopilado en esta tesis está basado en la formación de materiales mesoporosos y sus posibles usos como catalizadores. Este trabajo se ha estructurado en cuatro partes diferenciadas. En primer lugar se presenta una breve introducción a los materiales mesoporosos revisando su evolución en la historia, los diferentes métodos de síntesis, su versatilidad en cuanto a funcionalización y aplicaciones y acabando con un repaso al trabajo realizado en el grupo de investigación. El segundo capítulo está centrado en el mejor conocimiento de la sílice UVM-7, un material mesoporoso de carácter bimodal desarrollado por el grupo. En primer lugar se estudia en detalle la estructura del material …
Removal of silicon from CFB-derived fly ash leachate in the context of phosphorus recovery
2018
High concentrations of dissolved silica in the acid leachate impose two major challenges on precipitation based recovery of phosphorus (P). Firstly, co-precipitation of colloidal silica in the acidic regimes decreases the purity and value of precipitated P-products. In addition, silica scaling on internal surfaces of equipment is also a problematic issue in industrial operations. Therefore, removal of dissolved silica prior to P-recovery process minimizes the risks of Si-contamination in P-products and Si-scaling. In the present study, silica removal was achieved by accelerated silica polymerization with higher acidity and ionic strength of mineral acid, which also assisted the leaching of …
Selective encapsulation and enhancement of the emission properties of a luminescent Cu(I) complex in mesoporous silica
2018
We describe a synthetic approach to prepare new luminescent silica‐based materials through the encapsulation of a neutral copper(I) complex inside the pores of mesoporous silica nanoparticles (MSN). The copper(I) complex is present, in the solid state, as two polymorphs, blue and yellow emissive, and in solution it shows a pale yellow color that is also mirrored by an emission in the yellow‐orange region of the electromagnetic spectrum. The X‐ray structures of single crystals have been obtained for both polymorphs. The complex encapsulation in MSN is achieved by its entrapment inside micelles followed by condensation of the silica source. Interestingly, the entrapment leads to the isolation…
Metallocenes and post-metallocenes immobilized on ionic liquid-modified silica as catalysts for polymerization of ethylene
2014
Abstract The supported ionic liquid (SIL) strategy was used for the first time to metallocene and post-metallocene heterogeneous catalysts for olefin polymerization. The metal complexes: Cp2TiCl2, Cp2ZrCl2, FI–Ti, and Sal–Ti were immobilized in the 1-(3-triethoxysilyl)propyl-3-methylimidazolium alkylchloroaluminate ionic liquid, anchored on the surface of the mesoporous amorphous silica. The SIL systems were characterized by FTIR, 29Si NMR, N2 adsorption, EA, AAS, TG, and SEM techniques. The developed supported catalytic systems were found to be active in the ethylene polymerization and produce the polyethylene of various properties.
Ethylene polymerization using vanadium catalyst supported on silica modified by pyridinium ionic liquid
2016
Vanadium catalyst systems (SIL1–3A(B)/V) for ethylene polymerization were obtained by immobilization of the Cp2VCl2precursor (V) in the ionic liquid -[3-(triethoxysilyl)propyl]pyridinium chloride (IL), modified by AlCl3 and AlEtCl2(A) or AlEt2Cl (B), and supported on three types of silica carrier S1–3. The properties of the ionic liquid supports were determined using Fourier transform infrared spectroscopy, Brunauer–Emmett–Teller measurements, scanning electron microscopy and elemental analysis. The best results (above 2 tons PE (mol V)−1(0.5 h)−1) were obtained using the catalyst system SIL3B/V. Addition of ethyl trichloroacetate is possible in the ionic liquid medium and it further increas…