Person-Indexing Registers, Stardom, Auteurism

The objective of this study was to elucidate the role of anions in reactions on an oxide-free aluminum alloy surface. The scrape potential technique was employed to measure three parameters, at open circuit, that are pertinent to the corrosion reaction. These are: (1) Vsc, the potential of the metal scraped free of the passive film; (2) Vss, the steady state potential following passivation, and (3) dV/dt, the decay in potential during the formation of the passive reaction product. Experiments were conducted in sodium halide solutions of 0.1 to 04.0N concentration and of various pH's. All parameters were found to be anion, pH, and concentration dependent up to approximately 1.5M concentration. In this concentration range and at neutral pH, the anodic reaction rate on the fresh metal surface was observed to be anion dependent. This rate following the order F- >Br- >Cl-. High negative values of Vss were observed in F- and OH- solutions. After scraping was stopped, and while the reaction product film was being formed, the potential decayed in the positive direction, linearly, in the millisecond range. This time is of the same order as the relaxation times of similar metal-anion complexation reactions. The linear decay rate (dV/dt1) was associated with the formation of metal-anion complexes following metal oxidation and preceeding the formation of the reaction product film. It is concluded that the role of the anion in metal dissolution lies in the formation of metal anion species at the fresh metal surface. The nature of these species directs the rate of formation and characteristics of the reaction product film.

In the framework of new ecological challenges, many plant extracts appear as promising green corrosion inhibitors. Their efficiency is generally attributed to the antioxidant properties of secondary metabolites, as flavonoid molecules, which are produced by plants in order to fight against environment attacks. However, due to the large number of molecules contained in plant extracts, the corrosion inhibition mechanisms remain largely unknown. This paper focuses on the inhibiting effect on steel corrosion of different model flavonoid molecules with various structures. In acidic medium, polarization measurements and electrochemical impedance spectroscopy (EIS) measurements, performed in HCl 0.1 M in a water/ethanol medium, show slight inhibition efficiency (both anodic and cathodic) of pure flavonoid molecules, through an adsorption mechanism, directly linked to their structure. Actually, the best performances are obtained with molecules characterized by two adjacent OH groups on the B-ring (catechol group), which explains the chelation of Fe2+. Regarding the anticorrosion efficiency of a diluted natural extract (from orange peel as example in this work), it is enhanced compared to isolated flavonoid molecules (naringin, neohesperidin) thanks to the formation of a thick surface film with organic macromolecules, limiting the diffusion of oxidant species, as revealed by both SEM observations and EIS data. In more alkaline medium, at pH 4, the corrosion behavior is governed by the formation of a tri-dimensional conversion film made of iron and flavonoid, as revealed by SEM observations. For a deeper understanding, the corresponding organo-metallic compounds were synthesized from precipitation at pH 4 of iron salt in presence of flavonoid molecules (rutin) and investigated by Raman spectroscopy and X-ray Absorption Spectroscopy measurements (XAS). Results show that the formation of conversion products requires the octahedral coordination of Fe3+ by the O atoms of the catechol group attached to the B-ring. From an electrochemical point of view, a cathodic inhibition attributed to the oxygen scavenger role of the antioxidant molecules was observed. Nevertheless, the anodic protection depends on the covering properties of the conversion film (when it is formed), related to the molecule structure. Figure 1

Electrochemical oxidation of o-aminophenol in aqueous acidic medium: formation of film and soluble products

The gas-phase ion-molecule reactions of the Me3SiN(H)SiMe2+ ion, obtained by electron ionization from Me3SiN(H)SiMe3, have been studied in a Fourier transform ion cyclotron resonance spectrometer in order to understand the mechanistic details of an important chemical system presently used in film formation. This silyl cation has been observed to undergo addition reactions at electron rich centers to form stable adducts that may undergo further methane elimination in the case of alcohols and amines. The most important feature of these reactions is the fact that a metathesis type reaction can be observed in the presence of H2O, and other hydrogen labile substrates like alcohols, leading to the formation of the corresponding oxygen-containing ion, i.e. Me3SiOSiMe2+. For alcohols (ROH), facile formation of a tertiary product ion, presumably corresponding to an Me3Si-O-Si(Me)=O+-R structure with elimination of an amine reveals the strong tendency of these nitrogen-containing ions to undergo metathesis type reactions with oxygen containing substrates.

Plasma deposition of hydrogenated GeC films in a three-electrode reactor — plasma diagnostics using indirect methods

A MoS2 layered thin film was grown by atmospheric-pressure solution-based mist CVD on a 30 mm2 large-area substrate at 400 °C, which is a significantly lower growth temperature than that of conventional CVD. The film formation was reliably confirmed by Raman spectroscopy, grazing incidence X-ray diffraction (GIXD), and transmission electron microscope (TEM). Possibly, film formation energy was decreased by dissolving (NH3)6Mo7O24 ∙ 4H2O in methanol owing to formation of an intermediate product, whose decomposition temperature was lower than 760 °C — the decomposition temperature observed in thermogravimetric-differential thermal analysis (TG-DTA). Optical constants were derived by spectroscopic ellipsometry measurements, whose results indicate the reasonably good quality of MoS2 and the suitability of mist CVD in response to the large-area low-temperature growth request from industry.

Combined chemical and EIS study of the reaction of zinc coatings under alkaline conditions

An XPS study of the passive and transpassive behavior of molybdenum in deaerated 0.1 M HCl

The contact wear behavior of a dental ceramic composite containing 92 wt % silica glass and alumina filler particles in a polymeric resin matrix was examined. Because this composite is used for dental restorations, the tests were conducted under contact conditions that were relevant to those that exist in the mouth. Wear tests were conducted on a pin-on-disk tribometer with water as a lubricant. Results on wear volume as a function of load indicated two distinct regimes of wear. The wear volume increased slightly as the load was increased from 1 to 5 N. As the load was further increased to 10 N, the wear volume increased by one order of magnitude. At loads above 10 N (up to a maximum of 20 N), the wear volume was found to be independent of load. Examination of the wear tracks by SEM revealed that a surface film had formed on the wear tracks at all loads. Examination of these films by TEM showed that the films contained a mixture of small gamma-Al2O3 crystallites and glass particles. FTIR analysis of the adhered films indicated the presence of hydrated forms of silica and alumina, suggesting reaction of filler particles with water. Chemical analysis by ICP-MS of water samples collected after the wear tests confirmed the presence of Al and other elemental constituents of the filler particles. It is proposed that three simultaneous processes occur at the sliding contact: tribochemical reactions and film formation, dissolution of the reacted products, and mechanical removal of the film by microfracture. At low loads, wear occurs primarily by a tribochemical mechanism, i.e., formation and dissolution of the reaction products. At higher loads, wear occurs by a combination of tribochemical processes and mechanical detachment of the surface film.

This work focuses on the corrosion of aluminium in alkaline solution particularly at pH 11.0. The pH value plays a key role in corrosion processes. In a certain pH range, either the metal dissolves or protective films may be formed. For performing electrochemical measurements at a precisely adjusted pH value a setup, the so called ‘impedance titrator’ is used, that allows adjusting and controlling of pH value very precisely, while characterising the film properties. Electrochemical impedance spectroscopy is performed to investigate the formation of corrosion products. By keeping the pH at a constant value and simultaneously offering the system a constant hydroxide concentration, film formation takes place under defined conditions and a full kinetic characterisation becomes possible. This special system is required as the behaviour of aluminium in alkaline solution is quite complex and a various number of competing reactions like oxide film formation and dissolution occur.

The effect of sample mass and heating rate on DSC results when studying the fractional composition and oxidative stability of lube base oils

Polarisation studies were performed on 90Cu–10Ni (alloy UNS C70600, hot rolled and annealed) in 3·5% NaCl solutions over a range of initial pH levels. It was found that film formation was dependent on the applied current and the relative concentrations of the ionic species H+, (OH)−, and Cl− in solution which ultimately influenced the formation of the corrosion products. Constant extension rate tests at different applied currents and pH levels suggested that a higher pH level increased the time to failure although no evidence of stress corrosion cracking was found. These observations are rationalised through surface film formation mechanisms.

Creating and preserving the activity of an oxygen cathode in an aprotic organic solvent is a critical barrier that must be overcome to enable energy storage with the lithium – oxygen electrochemical couple. The nucleation and growth of solid products during the oxygen reduction reaction, like lithium peroxide and superoxide, needs to be directed away from the electrocatalyst to prevent passivation and toward sites that facilitate product nucleation and growth. These nucleation sites must also enable electron transport to ensure oxygen evolution during charging. Model cathode surfaces can be used to explore these proximity relationships between electron transfer and product growth sites in situ using electrochemical atomic force microscopy to track solid product formation. We have developed methods for producing a variety decorated electrode substrates on which electron transfer and nucleation sites are separated and these proximity relationships can be studied as a function of the rate and extent of oxygen reduction.The impact of isolating electron transfer sites is demonstrated in the response of highly ordered pyrolytic graphite (HOPG) to ORR in a bis(trifluoromethane) sulfonamide (LiTFSI) - tetraethylene glycol dimethyl ether (TEGDME) electrolyte (Figure 1). The step edges represent line defects with a heterogeneous rate constant many orders of magnitude greater than the adjacent terraces (R. McCreery et al., Anal Chem, 2012). Driving the ORR at relatively slow rates (ca. μA/cm2) results in initial nucleation and growth of particles along these defects with the eventual formation of large particles imbedded in a thin, continuous product film at the point of eventual electrode passivation, In contrast, a uniformly electroactive Au(111) surface exhibits the formation of a continuous thin film without significant particle formation. These results emphasize the fact that a significant amount of the peroxide and superoxide formed during ORR originate from precipitation reactions. The precipitation of lithium peroxide argues that disproportionation of the electrogenerated superoxide takes place in solution and not on the electrode surface. The impact of creating discrete sites for solid product nucleation and growth is explored by decorating graphite with MnO2 particles. The expectation is that an oxide surface should represent a favorable site for the nucleation and growth of the peroxide and superoxide products. β-MnO2 has been shown to exhibit enhanced activity for ORR in LiTFSI:TEGDME (O. Oloniyo et. Al., J Electronic Mater, 2012). Vacuum techniques are used to decorate HOPG with β-MnO2 nanoparticles, where the relative preference for particle growth at step edges and terraces can be controlled with the use of active oxygen. Figure 1 shows an example of directing β-MnO2 growth at the step edges. Conducting ORR on this electrode, at the same current density as for the pristine HOPG surface, shows that product formation occurs as a conformal coating over the β-MnO2nanoparticles. These results indicate that it should be possible to control the location of product nucleation.Voltammetry and chronopotentiometry show that Au(111) is considerably more active for ORR relative to either graphite step edges or β-MnO2 nanoparticles in this LiTFSI:TEGDME electrolyte. We have combined both Au and MnO2 nanoparticles onto graphite with the Au placed at step edges and the MnO2 on the terraces to achieve electron transfer and nucleation site separation. Results from ORR rate and extent studies with these structured electrodes will be presented and discussed. This work is supported as part of the Joint Center for Energy Storage Research, an Energy Innovation Hub funded by the U.S. Department of Energy, Office of Science. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Company, for the U.S. DOE’s NNSA under contract DE-AC04-94AL85000.

Kinetic peculiarities of anodic dissolution of copper and its gold alloys accompanied by the formation of insoluble Cu(I) products

Influence of Bubbles on the Energy Conversion Efficiency of Electrochemical Reactors