228 research outputs found
Lâacido-basicitĂ©
La longue histoire des acides et des bases (selon lâacception actuelle) suit pas Ă pas lâĂ©volution des connaissances expĂ©rimentales et des modĂšles thĂ©oriques de la chimie. Initialement, elle est indissociable de celle des sels qui lâa prĂ©cĂ©dĂ©e puis accompagnĂ©e. Ces derniers sont connus depuis lâAntiquitĂ©Â ; ce sont des substances qui ont une forme solide (ou concrĂšte), qui sont hydrosolubles et manifestent une indiffĂ©rence vis-Ă -vis des colorants vĂ©gĂ©taux. ĂlevĂ©s au rang de principes par Parac..
Structure analysis of vitusite glassâceramic waste forms using extended X-ray absorption fine structures
Vitusite glassâceramic waste forms were developed and the local environments of the Nd3+ ions in the waste forms were analyzed using extended X-ray absorption fine structure (EXAFS) spectroscopy. A second shell was observed in the Fourier transform (FT) of the EXAFS Nd LIII-edge spectra with the formation of vitusite crystals in the glass matrix. This second shell was attributed to the presence of the NdâP and NdâNa ion pairs constituting the vitusite crystal. The preferred incorporation of Nd3+, P5+, and Na+ inside the crystalline phases surrounded by the glass matrix increased the chemical durability of the glassâceramics
Corrosion protection of Al(111) by 8-hydroxyquinoline: a comprehensive DFT study
8-Hydroxyquinoline (8HQ) is a new green corrosion inhibitor. DFT-D calculations are performed to investigate the adsorption of 8HQ and derivatives on the Al(111) surface from low to high coverage. From Ξ = 0.20 to 0.66, the adsorption energies are â1.12, â2.41, â1.66 and â3.44 eV per molecule for 8HQ, and its tautomer, its hydrogenated and its dehydrogenated species, independently of the coverage. In contrast, the geometry of the adsorbates changes between coverage up to 0.66 and the full monolayer (Ξ = 1). The creation of a dipole at the molecule/metal interface reduces the work function of aluminum. To further evaluate the modification of the reactivity of the surface, adsorption of O2 on the Al(111) surface covered by the organic layer is investigated. O2 dissociation takes place for Ξ = 0.66. When the Al surface is fully covered (Ξ = 1), the reduction of O2 and the oxidation of Al atoms do not occur
Modelling the sulfate capacity of simulated radioactive waste borosilicate glasses
The capacity of simulated high-level radioactive waste borosilicate glasses to incorporate sulfate has been studied as a function of glass composition. Combined Raman, 57Fe Mössbauer and literature evidence supports the attribution of coordination numbers and oxidation states of constituent cations for the purposes of modelling, and results confirm the validity of correlating sulfate incorporation in multicomponent borosilicate radioactive waste glasses with different models. A strong compositional dependency is observed and this can be described by an inverse linear relationship between incorporated sulfate (mol% SO42â) and total cation field strength index of the glass, ÎŁ(z/a2), with a high goodness-of-fit (R2 â 0.950). Similar relationships are also obtained if theoretical optical basicity, Îth (R2 â 0.930) or non-bridging oxygen per tetrahedron ratio, NBO/T (R2 â 0.919), are used. Results support the application of these models, and in particular ÎŁ(z/a2), as predictive tools to aid the development of new glass compositions with enhanced sulfate capacities
Speciation, Luminescence, and Alkaline Fluorescence Quenching of 4-(2-methylbutyl)aminodipicolinic acid (H2MEBADPA)
4-(2-Methylbutyl)aminodipicolinic acid (H2MEBADPA) has been synthesized and fully characterized in terms of aqueous phase protonation constants (pKa\u27s) and photophysical measurements. The pKa\u27s were determined by spectrophotometric titrations, utilizing a fully sealed titration system. Photophysical measurements consisted of room temperature fluorescence and frozen solution phosphorescence as well as quantum yield determinations at various pH, which showed that only fully deprotonated MEBADPA2â is appreciably emissive. The fluorescence of MEBADPA2â has been determined to be quenched by hydroxide and methoxide anions, most likely through base-catalyzed excited-state tautomerism or proton transfer. This quenching phenomenon has been quantitatively explored through steady-state and time-resolved fluorescence measurements. Utilizing the determined pKas and quenching constants, the fluorescent intensity of MEBADPA2â has been successfully modeled as a function of pH
Restes humains et collections universitaires: une histoire dans la peau: Le cas d'Atifu
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The Brussels Faculty of Medicine: in between creation, diffusion and education of knowledge (1794 - 1914). A general overview
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Donner une nouvelle vie au patrimoine scientifique. PrĂ©servation et valorisation des collections scientifiques de lâUniversitĂ© Libre de Bruxelles
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