Search results for "DIOXIDE"
showing 10 items of 1250 documents
Evaluation of 2,3-epoxypropyl groups and functionalization yield in glycidyl methacrylate monoliths using gas chromatography
2014
Abstract Poly(glycidyl methacrylate- co -ethylene dimethacrylate) (poly(GMA- co -EDMA)) is most frequently used as parent monolith to obtain stationary phases with a variety of surface chemistries for liquid chromatography and capillary electrochromatography. Functionalization is performed by opening the accessible 2,3-epoxypropyl groups of the monolith with a suitable reagent. The number of 2,3-epoxypropyl groups which are accessible before and after the functionalization reaction, and the grafting yield, are important parameters, required both to optimize functionalization and to interpret the chromatographic performance of functionalized monoliths. In this work, a method capable of provi…
Synchrotron diffraction study of the isothermal oxidation of uranium dioxide at 250°C
2003
ABSTRACTThe structural evolution of UO2 during its oxidation to U3O8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases that are likely to appear during the long-term storage of spent nuclear fuel. Our results are in disagreement with the literature in which the existence of an intermediate cubic phase is not reported. Instead, an α-U3O7 tetragonal phase (c/a < 1) was mentioned but not definitively observed. These previous interpretations may have been the result of poor instrumental resolution.
Defects at the TiO2(100) surface probed by resonant photoelectron diffraction.
2006
We report photoelectron diffraction (PED) experiments of weakly sub-stoichiometric TiO 2 (100) rutile surfaces. Apart from standard core-level PED from the Ti-2p3/2 line, we have studied valence band PED from the defect induced Ti-3d states in the insulating band gap. For maximum yield, the latter were resonantly excited at the Ti-2p absorption edge. The PED patterns have been analyzed within the forward scattering approximation as well as by comparison with simulated PED patterns obtained in multiple scattering calculations. The analysis shows that the defect induced Ti-3d charge is mainly located on the second layer Ti atoms. © 2007 Elsevier B.V. All rights reserved.
Analysis of Dissolved-Gas Atomization: Supercritical CO2 Dissolved in Water
2010
Supercritical dissolved-gas atomization is an atomization process in which carbon dioxide at temperature and pressure above its critical point is used as the atomizing gas. The spray characteristics in terms of droplets size and distribution have been experimentally studied using a laser diffraction method based on a Malvern apparatus. The main parameter that influences the droplets size is the gas-to-liquid mass ratio (GLR); the injection pressure in the range of 7.4-13 MPa has a minor effect. Upon variation of the GLR from 0.5 to 3, the droplet mean diameter changes from about 8.0 to 2.0 μm; very narrow droplet size distributions are also produced. From the point of view of the atomizatio…
The Significance of Ionic Bonding in Sulfur Dioxide: Bond Orders from X-ray Diffraction Data
2012
A novel refinement technique for X‐ray diffraction data has been employed to derive S-O bond orders in sulfur dioxide experimentally. The results show that ionic S-O bonding dominates over hypervalency.
Contribution of the synchrotron diffraction study of the oxidation of uranium dioxide at 250○C
2004
The structural evolution of UO 2 during its oxidation into U 3 O 8 at 250°C in air was studied by in-situ synchrotron X-ray diffraction on the D2AM-CRG beamline at ESRF. The aim of this study is to determine the phases which are likely to appear during a long term storage of used nuclear fuel. Our results are in disagreement with the literature where the existence of the secondary cubic phase is not reported, and an α-U 3 O 7 tetragonal phase (c/a < 1) is also mentioned but definitely not observed. These previous interpretations are possibly due to a poor instrumental resolution, inducing a sensible broadening of the diffraction peaks. Particularly, the fact that the instrumental resolution…
Peracetylated β‐cyclodextrin as solubilizer of arylphosphines in supercritical carbon dioxide
2006
Abstract Effect of peracetylated β-cyclodextrin on the solubility of diphenyl(4-phenylphenyl)phosphine in supercritical carbon dioxide medium has been investigated. As shown by gravimetric measurements, the presence of cyclodextrin (CD) (1 equivalent) allows to increase the solubility of phosphine (P) in supercritical carbon dioxide (scCO 2 ) (40 °C, 35.2 MPa, nominal system density 0.89 g/mL). This solubility enhancement was attributed to host–guest interactions in scCO 2 as the P was recovered in the form of an inclusion complex. Furthermore, a diffuse reflectance spectroscopy study on the samples recovered after the experiments and on various CD/P solid mixtures obtained by co-grinding i…
Copolymerization of VDF and HFP in Supercritical Carbon Dioxide: A Robust Approach for Modeling Precipitation and Dispersion Kinetics
2012
A kinetic model is developed for the heterogeneous free-radical copolymerization of vinylidene fluoride and hexafluoropropylene in supercritical CO 2. The model accounts for polymerization in both the dispersed (polymer-rich) phase and in the continuous (polymer-free) supercritical phase, for radical interphase transport, diffusion limitations, and chain-length-dependent termination in the polymer-rich phase. A parameter evaluation strategy is developed and detailed to estimate most of the kinetic parameters a priori while minimizing their evaluation by direct fitting. The resulting model predictions compare favorably with the experimental results of conversion and MWD at varying monomer fe…
Synthesis of hydrophilic polymers in supercritical carbon dioxide in the presence of a siloxane-based macromonomer surfactant: Heterogeneous polymeri…
2003
Batch free radical polymerization of 1-vinyl-2-pyrrolidone (VP) in super- critical carbon dioxide (scCO2) was studied in the presence of a reactive polysiloxane surfactant (PDMS-mMA). Phase behavior investigation showed that when the initial concentration of the surface active macromonomer was higher than 2.5% w/w with respect to the monomer, the reaction mixture, in the absence of efficient stirring, was initially opaque to the visible light, and it slowly turned to an orange tint. Polymeriza- tion experiments carried out with surfactant concentration higher than the aforemen- tioned value proceeded with a fast kinetics, and led to the formation of spherical nanoparticles with almost quant…
Dispersion polymerization of methyl methacrylate in supercritical carbon dioxide stabilized with poly(ethylene glycol)-b-perfluoroalkyl compounds
2004
Abstract In this work selected components of an easily synthesible class of poly(ethylene glycol)-perfluoroalkyl block compounds were tested as stabilizers for the dispersion polymerization of methyl methacrylate in scCO 2 . As already observed in the case of different block surfactants the anchor soluble balance (ASB) of the stabilizer is the crucial parameter affecting the efficacy of the stabilization and the kinetics of the polymerization process. When stabilizers with appropriate ASB were used, high molecular weight poly(methyl methacrylate) was synthesized under the form of microspherical polymer particles with yields ranging up to 80%. In these experiments the occurrence of a gel-eff…