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[en] While the basic mechanisms of anodic and cathodic delamination, i.e. the de-adhesion of polymer coatings from the metal substrate, are already well understood [Industrial Adhesion Problems, Orbital Press, Oxford (1985); Polymeric Materials for Corrosion Control, American Chemical Society, Washington (1986); Corrosion Control by Organic Coatings, NACE, Houston, TX; MRS Bull. 24 (1999) 43; Corros. Sci. 43 (2001) 207; Corros. Sci. 43 (2001) 229; Corros. Sci. 43 (2001) 243; Corros. Sci. 41 (1999) 547; Corros. Sci. 41 (1999) 579; Corros. Sci. 41 (1999) 599], only little is known about the microscopic and submicroscopic aspects of delamination. The main difficulty for a detailed investigation of delamination with a suitably high resolution is that the de-adhesion is a process occurring at a buried interface. On the macroscopic scale Scanning Kelvin Probe Microscopy (resolution of about a few 10 μm) has been the most important method to elucidate the fundamental processes of cathodic and anodic delamination, which in combination with other methods such as photoelectron spectroscopy (XPS) and measurement of the adhesion strength in dependence on distance from the defect helped to develop detailed models [MRS Bull. 24 (1999) 43; Corros. Sci. 43 (2001) 207; Corros. Sci. 43 (2001) 229; Corros. Sci. 43 (2001) 243; Corros. Sci. 41 (1999) 547; Corros. Sci. 41 (1999) 579; Corros. Sci. 41 (1999) 599]. The development of the scanning Kelvin probe force microscopy (SKPFM) opened application of the Kelvin probe technique to the submicroscopic scale. In this paper, first results of these submicroscopic investigations are presented and discussed in view of the earlier results
[en] X-ray photoelectron spectroscopy (XPS) is used to characterize oxides anodically formed on near-surface Ir- and Rh-implanted titanium alloys. The oxidation is performed in a (1 M [Cl-], pH = 1.0) solution in which the chlorine evolution reaction is studied subsequently. Good electrocatalytic properties of the Ir/Ti alloy for this reaction appear to be related to the presence of Ir4+ and Ti4+ at the surface. In the case of the Rh/Ti alloy, poor electrocatalytic properties are observed together with Rh in the O and 1 + valence states and Ti4+ at the surface. (Author)
[en] Highlights: ► The structural and sensing properties of Gd2Ti2O7, Er2TiO5 and Lu2Ti2O7 sensing films grown on Si substrates by reactive co-sputtering. ► The EIS device incorporating a Lu2Ti2O7 sensing film exhibited a higher sensitivity, a larger drift rate, a higher hysteresis voltage, and a larger hysteresis gap than other sensing films. ► The impedance effect of EIS sensors has been investigated using C–V method. -- Abstract: This paper describes the structural and sensing characteristics of Gd2Ti2O7, Er2TiO5, and Lu2Ti2O7 sensing membranes deposited on Si substrates through reactive co-sputtering for electrolyte–insulator–semiconductor (EIS) pH sensors. In this work, the structural properties of Gd2Ti2O7, Er2TiO5, and Lu2Ti2O7 membranes were investigated by X-ray diffraction, atomic force microscopy and X-ray photoelectron spectroscopy. The observed structural properties were then correlated with the resulting pH sensing performances. The EIS device incorporating a Lu2Ti2O7 sensing film exhibited a higher sensitivity (59.32 mV pH−1), a larger drift rate (0.55 mV h−1), a higher hysteresis voltage (5 mV), and a larger hysteresis gap (∼70 mV) compared to those of the other sensing films. This result is attributed to the higher surface roughness and the formation of a thicker interfacial layer at the oxide–Si interface. Furthermore, the impedance effect of EIS sensors has been investigated using capacitance–voltage (C–V) method (frequency-dependent C–V curves). From the impedance spectroscopy analysis, we find that the diameter of a semicircle of an EIS sensor becomes smaller due to a gradual decrease in the bulk resistance of the device with degree of pH value
[en] Tau, a family of microtubule-associated protein (MAP) that exists in six isoforms, is involved in the etiology of Alzheimer’s and upon hypophosphorylation gives rise to neurofibrillary tangles (NFTs) inside neurons. Here, we report the results of an electrochemical investigation into the interaction of Fe(II) and Fe(III) with surface-supported tau (Tau-410, 2N3R). Changes in current density and impedance changes were used to monitor metal-tau interactions and tau-tau interactions. Our detailed electrochemical studies of surface-supported tau protein is supported by X-ray photoelectron spectroscopy (XPS) and by measurement of interactions in solution by circular dichroism (CD) spectroscopy. In addition, we include the effects of tau phosphorylation on the interactions with Fe(II) and Fe(III). Our results clearly demonstrate that a) Fe(II) and Fe(III) bind to the tau protein, b) structural changes occur to tau upon metal binding, c) Fe(II) shows a more pronounced effect, d) phosphorylation affects the metal ion complexation and e) tau-tau interactions are mediated by Fe(II).
[en] Highlights: • Plasma pre-treatment of electrodes produces chemical modifications at surface level. • Nitrogen and plasma treatment were studied before inoculation with a mixed microbial consortia. • Plasma treatment accelerates the current development in microbial bio-electrochemical systems. • Plasma enhances the initial attachment of cells. • After treatment, a mature electroactive biofilm is developed in half the time as blank electrodes. -- Abstract: Surface modifications of electrode materials are important for improved performance of microbial bio-electrochemical systems. Here, we studied the effect of pre-treating both glassy carbon and graphite felt electrodes with either an oxygen or a nitrogen plasma before reactor inoculation with a mixed microbial consortia. The plasma produces chemical modifications at the electrode surface level. X-ray photoelectron spectroscopy and water contact angle analysis showed that the plasma removes surface contamination, produces ion implantation and renders the hydrophobic surfaces highly hydrophilic. Plasma pre-treatment considerably accelerated the generation of a bio-electrochemical anodic current after inoculation. Nitrogen plasma pre-treatment yielded the best performance, followed closely by oxygen plasma. Plasma pre-treated electrodes reached a plateau of maximum current density twice as fast as untreated electrodes. Analysis of the current development profiles suggests that the plasma pre-treatment is neither producing a preferential attachment of certain types of bacteria over others nor accelerating the extracellular electron transfer rate. The results indicate that the plasma treatment considerably enhances the initial cell adhesion, which results in subsequently faster biofilm development. Plasma pre-treatment of electrodes is an inexpensive, fast, safe and straightforward technique to achieve more rapid start-up of bio-electrochemical processes
[en] An oxygen plasma treatment was employed to modify the surface of carbon electrodes used in capacitive deionization (CDI). X-ray photoelectron spectroscopy analysis of samples showed that oxygen plasma is mainly attaching oxygenated groups on the PTFE binder used in these electrodes. By functionalizing the binder it can increase the hydrophilicity of the electrode surface and increase the available specific surface area. 2.5 min of plasma treatment resulted in the largest improvement of CDI performance of electrodes. Thermodynamic study of CDI performance showed that the modified electrodes followed Langmuir and Freundlich isotherms resulting from the increased interaction between the enhanced electrodes and water. The kinetic study showed that the CDI process followed a pseudo-first order adsorption kinetics. The calculated adsorption rate constants suggested that plasma modification can accelerate ion adsorption of electrodes
[en] In order to improve the protection abilities of (3-mercaptopropy)trimethoxysilane (MPTS) self-assembled monolayers on copper surfaces, mixed monolayers have been formed successfully by successive immersions in MPTS and in n-dodecanethiol (DT). A newly synthesised molecule, (11-mercaptoundecyl)trimethoxysilane (MUTS), has also been employed to form a thicker organic film on copper surfaces and, thereby, enhance the inhibitory action of the coating. The grafting has been confirmed by X-ray photoelectron spectroscopy (XPS), polarization modulation infrared reflection adsorption spectroscopy (PM-IRRAS) and water contact angle. The protective efficiency of each protective organic film has been evidenced by cyclic voltammetry (CV) and polarization curve measurements (CP). It was shown that the MUTS and unhydrolyzed MPTS/DT films exhibited significant corrosion protection properties
[en] Electrorefining of a silicon-iron material (Si–4.7 at% Fe) in molten NaF-KF at 850 °C was investigated in view of recovering pure Si, using electrochemical techniques, Scanning Electron Microscopy coupled with Energy Dispersive Spectroscopy (SEM-EDS) and Inductively Coupled Plasma with atomic emission spectroscopy (ICP-AES) analyses. The selective electrochemical dissolution of Si was evidenced. Electrorefining runs led to a maximum recovery of 80% of Si initially contained in the material, in the form of a dense deposit at the cathode, with very high current efficiencies. The Si purity was examined and no Fe was detected by ICP-AES analysis: the recovered Si purity was assumed to be higher than 99.99%
[en] The effect of passivation potential on surface crystal structure, apparent thickness and passivity of oxide films formed on pure iron prepared by plasma sputter deposition was investigated. The crystallinity was improved with passivation potential and the width of atomically flat terraces was expanded to 6 nm when passivating at 750 mV for 15 min, as observed by ex situ scanning tunneling microscopy (STM) after aging in air (<30% RH). Apparent thickness and passivity are linearly dependent on passivation potential. The former weakly depends on passivation duration, the latter strongly depends on passivation duration. This is well explained by the correlation between crystal structure and passivity
[en] Using a dual buffer structure, a controlled layer-by-layer deposition process has been developed to fabricate a monolayer Pt coating on carbon fiber with complex network structures. The electrochemical quartz crystal microbalance, current density analyses, and X-ray photoelectron spectroscopy results conclude that the monolayer deposition process accomplishes full coverage on the substrate and that the thickness of the deposition layer can be controlled on a single atom scale. It is found that a dual buffer, comprising a thin Ni coating and an Au nano-film, is necessary to cover carbon fiber substrate to ensure a complete monolayer Pt coverage. Moreover, the Pt monolayer is found to work better than thicker Pt – the best norm in the field, for catalyzing hydrogen evolution reaction.