The presented works prepares the ground for galvanic deposition of metallic overlayers on metal oxide surfaces functionalized by phosphonic acid monolayers. In view of this goal, it is necessary to control the most important factors of the electrodeposition process (e.g. flatness and uniformity of distribution). Because of these requirements, in this work, we study the morphology and the interaction between PO(OH)2-functionalities and an oxide surface. The analysis is carried out using complementary surface analysis techniques, like Atomic Force Microscopy (AFM) and X-ray Photoelectron Spectroscopy (XPS). We have succeeded in creating a blank surface with a RMS roughness of less than 1 nm and a hydroxyl fraction of 17%. The organic deposition was followed in time and it was observed that Volmer Weber multilayer growth was present. Also the influence of carbon contamination was characterized and a methodology is presented to correct the experimental data for this ambient contamination.
To contribute to the current debate about the “ideal” particle size range (sub-2μm vs. supra-2μm), the present study compares the kinetic performance of some commercially available sub-2μm and 3.5μm particles used under quasi-adiabatic conditions via the kinetic plot method. Under the adopted assumption that viscous heating effects can be neglected (which is uncertain in a pressure range above 400bar), the obtained kinetic plots show that, provided each particle size is used in a column with properly optimized length, the gain in separation speed that sub-2μm particle columns might have over maximally performing 2.5μm particle columns is very small. Sub-2μm particle columns can only yield a gain in separation speed in the range of high-speed/low-resolution-separations (total time based on k =10 below 5 or 10min). And even in this range, the actual gain that can be expected is only marginally small (only a few %). The present study hence suggests that the development and the use of particles in the 2–3μm range should deserve more attention than it did in the past few years. However, to be competitive, this 2–3μm material should be packed in relatively long columns, with a packing quality matching that of the current best performing 3.5μm particle columns. The supra-2μm particles should also be able to withstand the same pressures as the sub-2μm particle material one is comparing it to.
SUMMARYTo improve the corrosion resistance and the adhesion properties of aluminium, chemical conversion processes, such as zinc phosphating, are applied. During zinc phosphating of aluminium the co-precipitation of cryolite often occurs. Cryolite needs to be formed in solution to remove Al3 ions, which have a poisoning effect on the phosphating process, away from the surface. Cryolite formation on the surface must be avoided, since it leads to a decrease of the corrosion resistance and of the adhesion properties. In this paper, the influence of mass transport on this co-precipitation competition is reported. The resulting conversion layers are investigated by SEM/EDX. It can be concluded that the amount of mass transfer has a large influence on the formation of both the phosphate and cryolite crystals. Hence, this competition in precipitation is explained in terms of mass transport of the different species involved in the chemical reactions at the surface.
A wall jet electrode reactor possessing a laminar flow regime, suitable for mechanistic studies, is reported. This reactor is different from those describe
A spectro-electrochemical setup of Fourier transform infrared spectroscopy (FTIR) in the Kretschmann geometry and odd random phase multisine electrochemical impedance spectroscopy (ORP EIS) is applied to in situ monitor the effect of an aqueous electrolyte on the polymer/metal oxide interface. The interfacial interactions of an ultrathin polyacrylic acid (PAA) film on an aluminum oxide surface are identified as carboxylate ionic bonds and changes induced by the effect of water diffusion at the interface are monitored in situ. Initially after electrolyte exposure, an increase in ionic bonding is observed. However, eventually the interfacial interactions are replaced by water molecules, leading to macroscopic delamination. By comparing a variation of oxide types, the stability of the interfacial bonds is linked to the amount of free hydroxyl groups on the aluminum oxide surface. An electric equivalent circuit is proposed to model the ORP EIS response of the PAA/aluminum oxide system and the fitted resistance values could be interpreted in a physically meaningful way. Finally, a poly(methyl methacrylate) (PMMA) deposition on aluminum oxide is investigated to explore the effect of a variation in functional groups present at the polymer/metal oxide interface. It is shown that PMMA forms a more stable interface than PAA on native aluminum oxide. This work demonstrates that IR spectroscopy in the Kretschmann geometry and ORP EIS are suited techniques to in situ probe interfacial bonds at polymer/metal oxide systems exposed to aqueous conditions. Moreover, a variation of the surface properties of the metal oxide as well as the functional groups of the polymer alter the stability of their mutual interface when exposed to aqueous conditions.
No abstract is provided for this article.
No abstract is provided for this article.
Supported nanostructures represent the cornerstone for numerous applications in different fields such as electrocatalysis (fuel cells) or electroanalysis (sensors). In contrast to other methods, electrochemical deposition allows the growth of the nanostructures...
