Search results for "Surfaces"

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).

Composite Thin Film by Hydrogen-Bonding Assembly of Polymer Brush and Poly(vinylpyrrolidone)

2005

Based on hydrogen-bonding layer-by-layer (LBL) assembly in aqueous solution, poly(vinylpyrrolidone) (PVPON) and a spherical polymer brush with a poly(methylsilsesquioxane) (PSQ) core and poly(acrylic acid) (PAA) hair chains were used to fabricate composite multilayer thin films. Hydrogen bonding as the driving force was confirmed by FT-IR spectrometry. A simple method (Filmetric F20) was introduced to determine the thickness and refractive index of the films. The film thickness was found to be a linear function of the number of bilayers. The average increase in thickness per bilayer is 28.3 nm. The film morphology was characterized with scanning electron microscopy and atomic force microsco…

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 …

Zeta-Potential Study of Calcium Silicate Hydrates Interacting with Alkaline Cations

2001

An investigation into the interaction between alkaline cations and calcium silicate hydrates (CSH) was conducted by electrokinetic measurements, which provided information on the nature of the interface between the solid and its equilibrium solution. Calcium constitutes for the CSH surface a potential-determining cation. A model of the CSH surface could be proposed, accounting for the experimental evolution of the CSH zeta potential. The necessity of studying the zeta-potential evolution of the system as a function of the calcium activity, instead of its concentration, was underlined. The results obtained suggest a specific interaction between cesium and the CSH surface, whereas sodium and …

Ellipsometric and fluorescence microscopic investigations of a cyclam derivative at the air/water interface

1993

Thermal and Chemical Stability of Thiol Bonding on Gold Nanostars

2015

The stability of thiol bonding on the surface of star-shaped gold nanoparticles was studied as a function of temperature in water and in a set of biologically relevant conditions. The stability was evaluated by monitoring the release of a model fluorescent dye, Bodipy-thiol (BDP-SH), from gold nanostars (GNSs) cocoated with poly(ethylene glycol) thiol (PEG-SH). The increase in the BDP-SH fluorescence emission, quenched when bound to the GNSs, was exploited to this purpose. A maximum 15% dye release in aqueous solution was found when the bulk temperature of gold nanostars solutions was increased to T = 42 °C, the maximum physiological temperature. This fraction reduces 3-5% for temperatures …