Search results for "coating"
showing 10 items of 2834 documents
Ab Initio Liquid Water Dynamics in Aqueous TMAO Solution
2015
Ab initio molecular dynamics (AIMD) simulations in trimethylamine N-oxide (TMAO)-D2O solution are employed to elucidate the effects of TMAO on the reorientational dynamics of D2O molecules. By decomposing the O-D groups of the D2O molecules into specific subensembles, we reveal that water reorientational dynamics are retarded considerably in the vicinity of the hydrophilic TMAO oxygen (O(TMAO)) atom, due to the O-D···O(TMAO) hydrogen-bond. We find that this reorientational motion is governed by two distinct mechanisms: The O-D group rotates (1) after breaking the O-D···O(TMAO) hydrogen-bond, or (2) together with the TMAO molecule while keeping this hydrogen-bond intact. While the orientatio…
Fabrication of metal nano-structures using anodic alumina membranes grown in phosphoric acid solution: Tailoring template morphology
2007
Abstract The influence of experimental parameters on the morphology of the porous structure and on the formation kinetics has been investigated for anodic alumina membranes (AAM) grown in aqueous H 3 PO 4 at 160 V. It was found that pore aspect ratio and membrane porosity on the solution-side surface are influenced by tensiostatic charge, bath temperature and the presence of Al 3+ ions in solution. Morphological and kinetic data, recorded in different conditions, give useful information on the growth mechanism of pore channels in phosphoric acid solution. Nickel nano-structures have been fabricated using AAM as template. Electroless deposition, performed by adding the reducing agent to a su…
Chemical heterogeneities in nanometric titanomagnetites prepared by soft chemistry and studied ex situ : evidence for fe-segregation and oxidation ki…
2001
Nanocrystalline Fe-based spinels with composition Fe3-xTixO4 are synthesized using soft chemistry. Two steps are involved: precipitation in an aqueous solution followed by thermal annealing under a reducing mixture of N2/H2/H2O gases. Fe-segregation is found inside stoichiometric particles when the powders are studied ex situ; they exhibit a strong surface iron enrichment. This heterogeneity is related to kinetic effects linked to the difference of mobility between Fe2+ and Ti4+ cations during the partial oxidation of cations occurring ex situ. Stresses in the grains induced by oxidation govern the oxidation kinetics and lead to an abrupt compositional variation inside each particle. These…
Study of the Chemical Conversion of Aluminum Alloys by Coupling CFDE and EQCM
2004
The ability of the channel flow double electrode (CFDE) technique and electrochemical quartz crystal microbalance (EQCM) for studying in situ chromate phosphate conversion coating on 5182 aluminum alloys was explored. It was first demonstrated that aqueous Cr(VI) can be analyzed quantitatively with the CFDE technique by reduction into Cr(III) on a graphite electrode. Samples used for EQCM were quartz plated by physical vapor deposition using a 5182 alloy target, allowing thin layers of aluminum alloys with a similar chemical composition to be obtained. EQCM was adapted in order to account for the hydrodynamic conditions in an industrial process, by placing the quartz in a flow cell. In orde…
Structural Characterization of Zirconia Nanoparticles Prepared by Microwave-Hydrothermal Synthesis
2009
Nanocrystalline zirconia powders have been prepared by microwave-hydrothermal synthesis starting from aqueous solution of ZrOCl2·8H2O. Results of investigations on the aqueous suspension stability of the washed zirconia nanopowders by dynamic light scattering showed that the suspension, constituted by superaggregates of nanoparticles (131 ± 10 nm), was stable up to 15 days. Nanopowders were investigated by means of transmission electron microscopy and small angle x-ray scattering measurements which proved that the zirconia nanopowder is constituted by small primary nanoparticles of ca. 8 nm that agglomerate forming bigger aggregates of 50 ± 1 nm.
A new method for fluoride determination by using fluorophores and dyes anchored onto MCM-41Electronic supplementary information (ESI) available: IR s…
2002
A new colourimetric and fluorimetric method for fluoride determination in aqueous samples based on the specific reaction between fluoride and silica has been developed and applied on real samples.
Oxidative transformation of aryls using molybdenum pentachloride.
2012
Molybdenum pentachloride combines a strong Lewis acid character with an unusually high oxidation potential creating a powerful reagent for oxidative transformations. Since the oxidative coupling reaction of aryls is induced at an extraordinarily high reaction rate, a variety of labile groups, e.g. iodo, tert-alkyl, etc., are tolerated on the aromatic core. Furthermore, the co-formed molybdenum salts can either be exploited for template effects to obtain uncommon geometries in a preferred manner, or redox-play starts after aqueous workup. Therefore MoCl(5) represents a unique and easily available reagent.
In-situ characterisation of organosilane films formation on aluminium alloys by electrochemical quartz crystal microbalance and in-situ ellipsometry
2005
Abstract Organosilane pre-treatments have been studied intensively during the last years in order to replace hexavalent chromium conversion treatments. The aim of this study is to follow in-situ the formation of this organosilane layer in solution. Two in-situ techniques, spectroscopic ellipsometry and electrochemical quartz crystal microbalance, were used to investigate the mechanism and the kinetics of this protective film formation. In-situ measurements highlight that the organosilane film observed after the drying process is not formed into the solution, but during the emersion and drying step. Hence, it has been possible to characterise the presence of a very thin organosilane layer in…
Effect of Anions and Oxygen on the Kinetics of the Anodic Dissolution of Nickel
2006
An electrochemical impedance spectroscopy study on electrochemical dissolution and active/passive transition of polycrystalline nickel in acid media has been performed in sulfate and nitrate aqueous solutions. Oxygen favors the nickel electrodissolution in a nitrate aqueous acid medium, but the dissolution decreases in the sulfate medium due to nickel passivation. The anion and oxygen effect is analyzed from a model where Ni(I) species are stabilized on the Ni metal surface and all anions present in the solution compete in the neutralization of Ni(I) and Ni(II) and in the solubilization of Ni(II).
29Si NMR and Small-Angle X-ray Scattering Studies of the Effect of Alkaline Ions (Li+, Na+, and K+) in Silico-Alkaline Sols
1999
Alkali−silica reactions (ASR) which occur in concrete can be simulated in laboratory by destabilization of silico-alkaline aqueous solutions by addition of calcium ions. The relevant features of the reaction depend on the nature of alkaline ions (Li+, Na+, or K+) and on the silica/alkaline ratios which fix the distribution of the molecular species in the precursor solution. 29Si NMR spectroscopy and small-angle X-ray scattering (SAXS) techniques were used to study the structure and size distribution of molecular and colloidal species in sols with different silica/alkaline molar ratio and several types of alkaline ions. Experimental SAXS curves were simulated using a simple structural model …