Anodic Profile Research Articles

Computational study of water transport in proton exchange membrane fuel cells

A computational fuel cell dynamics framework is used to develop a unified water transport equation for a proton exchange membrane fuel cell (PEMFC). Various modes of water transport, i.e., diffusion, convection and electro-osmotic drag, are incorporated in the unified water transport equation. The water transport model is then applied to elucidate water management in three-dimensional fuel cells with dry-to-low humidified inlet gases after its validation against available experimental data for dry oxidant and fuel streams. An internal circulation of water with the aid of counter-flow design is found to be of vital importance for low-humidity operation, for example, in the portable application of a PEMFC without an external humidifier. The general features of water transport in PEMFCs are discussed to show various water transport regimes of practical interest, such as anode water loss, cathode flooding, and the equilibrium condition of water at the channel outlets, particularly for limiting situations where anode and cathode water profiles acquire an equilibrium state. From the practical point of view, the effects of the flow arrangement, membrane thickness, and inlet gas humidity as important determinants of fuel cell performance are also analyzed to elucidate fuel cell water transport characteristics.

Freezing of soybeans influences the hydrophobicity of soy protein

By using quartz-crystal microbalance (QCM) and cyclic voltammetric (CV) techniques, the effect of freezing on the hydrophobicity of soy protein was investigated. The results were compared to those of a sodium dodecyl sulfate (SDS) binding method. In the QCM studies the highest protein load onto the hydrophobic ethanethiol-monolayer was found with heated soy protein from frozen soybeans (HSFS), followed by heated soy protein from unfrozen soybeans (HSUS), unheated soy protein from frozen soybeans (USFS), and unheated soy protein from unfrozen soybeans (USUS). In the CV studies, it was found that values of an anodic profile decreased with adsorption time: it was the greatest with HSFS, followed by HSUS and USFS, and least wth USUS. Results of SDS binding capacity were found to be in line with those results of a QCM and CV measurements, indicating freeze treatment increased the hydrophobicity of soy protein regardless of heating. In addition, QCM and CV measurements were found to be very convenient to determine the hydrophobicity of soy protein successfully.

Novel corrosion experiments using the wire beam electrode. (IV) Studying localised anodic dissolution of aluminium

An electrochemically integrated multi-electrode array namely the wire beam electrode (WBE) has been applied in novel experiments to study the anodic dissolution behaviour of aluminium (AA1100), which was exposed to corrosive media with and without the presence of corrosion inhibitor potassium dichromate. The objective of this work is to demonstrate the applicability of the WBE for investigating corrosion processes under anodic polarisation. Anodic current measurements and mapping have been made, for the first time, with the WBE surface being anodically polarised. Pitting potential as well as anodic dissolution profile has been successfully determined by mapping anodic dissolution currents over the anodically polarised WBE surface. The pitting potential determined using the WBE method was found to correlate well with that determined using the conventional pitting scan method; and the anodic dissolution profile determined using the WBE method was found to correlate with maps obtained using the scanning reference electrode technique (SRET). Potassium dichromate was found to significantly affect the pitting potential, anodic dissolution profile and pitting initiation characteristics of aluminium. Two mechanisms of localised corrosion initiation have been identified. For WBE surface under free corrosion or low anodic polarisation conditions, the initiation of localised corrosion was found to be due to the disappearance of minor anodes, which lead to accelerated dissolution of a few major anodes. For WBE surface under large anodic polarisation, the initiation of localised corrosion was found to be due to the formation of active new anodic sites. This work suggests that the WBE method is useful for understanding the electrochemical behaviour of localised anodic processes, and their dependence on externally controllable variables.

Electrochemical behaviour of lead electrode in Na 2SO 4 solutions

The electrochemical behaviour of Pb electrode in aqueous Na 2SO 4 solutions (pH=6.8) has been studied by means of cyclic voltammetric and potentiostatic current–time transient techniques. The anodic polarisation profiles exhibit three well defined peaks A 1, A 2 and A 3 corresponding to the formation of PbSO 4, PbO and PbO 2, respectively prior to oxygen evolution potential. The reverse cathodic curves show three cathodic peaks C 1–C 3 and a plateau C 4 prior to hydrogen evolution potential. The peak C 1 is related to the reduction of upper PbO 2 to PbSO 4. The peak C 2 is due to the reduction of the inner PbO 2 to PbO. The composite peak C 3 is due to the reduction of both PbO and PbSO 4 to Pb. The plateau C 4 is ascribed to the formation of PbH 2. The heights of the anodic and cathodic peaks increase with increasing scan rate, temperature and repetitive cycling. The formation of PbSO 4 layer proceeds under diffusion controlled of SO 4 2−. The formation of the inner PbO is via a nucleation and growth mechanism under charge transfer and OH − diffusion control.

Enthalpy Measurements of Direct Current Plasma Jets Used for ZrO<SUB>2</SUB> · Y<SUB>2</SUB>O<SUB>3</SUB> Thermal Barrier Coatings

This study combines enthalpy probe measurements in a direct current (DC) plasma jet under atmospheric conditions and the characterization of sprayed coatings. Two different nozzle diameters were used as anode profiles. A detailed description of the experimental setup is given together with preliminary results. These results emphasize the usability of enthalpy probe measurements in thermal plasma jets for obtaining temperature distributions. For zirconia, the deposition efficiency, density, and structure of the coatings formed with the different anode profiles were compared.

Voltammetric Identification of Lead(II) and (IV) in Mediaeval Glazes in Abrasion-Modified Carbon Paste and Polymer Film Electrodes. Application to the Study of Alterations in Archaeological Ceramic

Direct identification of lead(II) and (IV) in glazed ceramics by cyclic voltammetry and differential pulse voltammetry is described. Characteristic cathodic and anodic profiles are obtained for microsample coatings in Paraloid B72-film electrodes immersed in NaCl and HAc/NaAc media. The electrochemical response of PbO, PbO2 and Pb3O4, and a series of test specimens of glaze is compared with that of microsamples extracted from the glaze of blue and white decorated ceramic produced in Manises (Spain) in the 15th century which have been buried in a damp place. Under abrasive conditions, striping peaks at –0.12 and –0.25 V (vs. SCE) appear for Pb(IV) centers and, at –0.55 and –0.75 V, for Pb(II) centers. The weathering process is accompanied by a significant decrease of the total lead content and an enhancement of the Pb(IV)/Pb(II) ratio suggesting that a significant fraction of Pb(II) ions is released. Electrochemical data are compared with those obtained from SEM/EDX.

Identification of inorganic pigments from paintings and polychromed sculptures immobilized into polymer film electrodes by stripping differential pulse voltammetry

Inorganic pigments in paintings and polychromed sculptures are studied by cyclic voltammetry and differential pulse stripping voltammetry using micro-sample coatings in Paraloid B72-film modified electrodes. Characteristic cathodic and anodic differential pulse profiles were obtained in the +0.4 to −1.0 V vs. SCE potential range for different cadmium, copper, lead, mercury and zinc pigments used in traditional colour palettes. Under optimized conditions, excellent reproducibility was obtained. Microsamples extracted from polychromed sculptures, wall paintings, canvas paintings, panel paintings and altarpieces from Spain, Ethiopia and Italy from the 12th to the 20th centuries have been analyzed and cadmium, copper, lead, mercury and zinc pigments such as cadmium red, cadmium yellow, azurite, copper resinate, malachite, verdigris, lead–tin yellow, lead white, minium, Naples yellow, vermilion, chrome orange, chrome yellow and white zinc have been identified by this technique in agreement with PLM, SEM/EDX, XRD and FT-IR analysis.

Express-control system of superconducting microcircuits fabrication technology by anodization spectroscopy method

The work is concerned to the fabrication technology of superconductive Josephson junctions Nb/AlO x -Al/Nb and to the development of the anodization spectroscopy method for the express-control system of the technology. We describe the technique of the anodization spectroscopy procedures for estimations of thin films and multilayered structures parameters, such as the thickness of films and interfaces, the oxygen contamination, the degree of nonstoichiometry. It is shown, that anodization spectroscopy is useful to investigate such technological parameters as the uniformity and intensity of deposition, ion etching, oxidation. We have experimentally investigated the correlation between technological conditions, anodization profiles and volt-ampere characteristics of Josephson junctions. It is shown that the optimal technology includes the magnetron deposition (V Nb = 5.0 nm/s, V Al = 3.0 nm/s) and oxidation at magnetron plasma. This conclusion is obtained by means of the anodization spectroscopy and confirmed by volt-ampere characteristics. The totality of developed procedures allowed to create the unified express-control system we use for the superconductive technology Nb/AlO x -Al/Nb. The system may be applied to other thin-film technologies.

Effect of addition of palladium on properties of Ag 2Hg 3 (γ 1) phase

The effect of palladium addition on the microstructure, compressive strength, creep rate and mercury release rate of Ag 2Hg 3 (γ 1) phase was evaluated. Experimental results indicated that fairly pure γ 1 phase could be fabricated using the present trituration method. The heat treatment of γ 1 at 90 °C increased porosity level, increased dimensional shrinkage, increased mercury vapour release and enhanced the formation of β 1 phase. Addition of palladium in γ 1 slowed down the amalgamation reaction, largely suppressed the phase transition to β 1 and caused a slight shift in open circuit potential toward the anodic direction. Although the overall anodic polarization profiles did not show a significant effect of palladium, scanning electron microscopy revealed morphological differences between pure and palladium-containing γ 1. Addition of palladium in γ 1 also increased compressive strength, increased creep resistance, and largely reduced both mercury vapour and ion release rates. Considering overall performance, the optimal palladium content in γ 1 seems to be in the range between 0.50 and 0.75 wt%.

The cathode design problem in electrochemical machining

Prior procedures for cathode (tool) design in electrochemical machining have been plagued by limited applicability, inaccuracy, and nonconvergence. We develop and test a new approach to this problem which overcomes these difficulties by employing a finite element method within an optimization formulation. A least-squares minimization of the deviation of the simulated anode (workpiece) shape from that desired is performed, yielding a set of parameters in a predefined representation which uniquely define an optimal cathode shape. Cathode shapes are designed to produce a variety of anode shapes, even anode profiles with nearly discontinuous slope have been obtained.

Noise-free anodization profiles of multi-layer structures using an evaporated silicon monoxide mask

In recent years, the anodization process has been developed into an analytical tool for the assessment of multilayer structures. This is usually achieved by using a constant current supply and monitoring the growth of the oxide layer, through the multilayer, by measuring the increase in the voltage developed across the anodization cell. In this paper, it is described how a silicon monoxide film has been used as the masking material in order to overcome the problem of electrical breakdown of the mask. This enables noise free anodization profiles to be obtained from multilayer structures.

Comparison of anodization spectroscopy with SIMS and RBS measurements for the characterization of Nb/AlAlO x/NB Josephson junction structures

The thin tunneling barrier in a Nb/AlAlO x /Nb was characterized by anodization spectroscopy, SIMS and RBS. From the anodization spectroscopy we can get the film thickness from the voltage span and, most importantly, also the sharpness of the Nb/AlO x and Al/Nb interfaces around the tunneling barrier. Comparison of the anodization profiles with SIMS depth profiles and RBS spectra shows that the anodization spectroscopy can be used to characterize the junction quality.

Fabrication of high quality Nb/AlO/sub x/-Al/Nb Josephson junctions. II. Deposition of thin Al layers on Nb films

The surface of thin Al layers deposited on Nb films with different sputtering parameters was studied. The anodization profile and X-ray photoelectron spectroscopy (XPS) confirmed that the underlying Nb layer is wet by a thin 2.9-nm Al layer, and the oxide formation on the Nb layer is completely suppressed. The excellent surface coverage is due to the affinity of Al for Nb and is quite different from the degraded coverage of Al on Si. It was observed that the surface coverage of Al on Nb depends on the film characteristics of the underlying Nb layers. Nb/AlO/sub x/-Al/Nb junctions with lower Nb layers deposited with different sputtering parameters were fabricated. The authors verified that the quality of the junction is closely related to the surface coverage as analyzed by the anodization profiles and XPS. >

Fabrication of high quality Nb/AlO/sub /x-Al/Nb Josephson junctions. III. Annealing stability of AlO/sub /x tunneling barriers

For pt.II see ibid., vol.2, p.84 (1992). Changes in current-voltage characteristics of Nb/AlO/sub /x-Al/Nb Josephson junctions due to annealing are studied. The surface of the Nb counterelectrode was plasma-nitrided to clarify the effects of oxygen diffusing from it. From anodization profiles, it was confirmed that surface nitridation protects the tunneling barrier from oxygen diffusion. Surface nitridation improved the junction stability for long annealing. The decrease in critical current at initial annealing was found to be independent of nitridation. The annealing stability of AlN/sub /x barrier junctions, compared to that of AlO/sub /x barrier junctions, was measured, and it was concluded that the decrease at initial annealing is due to changes in the AlO/sub /x barrier itself.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Nb-Al oxide-Nb junctions for 3 mm SIS receivers

The authors describe their fabrication process of Nb-Al oxide/Nb tunnel junctions with integrated filter structure. The process includes the lift-off stencil technique and liquid anodization. The quality of the junctions with areas down to about 1 mu m2 is discussed and the trilayers are analysed by anodization spectroscopy. The occurrence of proximity effect structures for trilayers with thick (160 AA) Al films and for trilayers with poor anodization profiles is demonstrated. Finally the mixer performance of a two-junction array is outlined in the range around 100 GHz.

Investigation of the tunnel barrier in Nb-based junctions prepared by sputtering and electron beam evaporation

Nb-based tunnel junctions prepared by DC magnetron sputtering and electron beam evaporation are compared. Tunnel barriers consisting of Nb oxide, Al oxide and Si oxide are analyzed by anodization, Auger electron, and inelastic electron tunneling spectroscopy. Results obtained from Nb/sub 2/-Si oxide/Si-Nb/sub 1/ and Pb/Bi-Si oxide/Si-Nb/sub 1/ structures are presented. Nb and Si were deposited by electron beam evaporation and Pb/Bi from tantalum boats. Silicium oxide has a relatively low dielectric constant ( in SiO/sub 2/ approximately=4, in SiO approximately=6) and is thus of interest for tunnel barriers. The anodization profile of Nb/sub 2/-Si oxide Si-Nb/sub 1/ layers for Si thickness up to 10 nm are discussed. Pb/Bi-Si oxide/Si-Nb/sub 1/ junctions showed reasonably good quality Si thickness between 0.5 and 1 nm. The presence of Si in the barrier is confirmed by the inelastic electron tunnel spectrum (d/sup 2/I/dV/sup 2/ as a function of junction bias voltage V) which shows the longitudinal and transversal acoustic phonons of Si.

Evaluation of AlOx barrier thickness in Nb Josephson junctions using anodization profiles

Using anodization profiles, we have analyzed the thin AlOxAl tunneling barrier in a Nb/AlOxAl/Nb Josephson junction. We measured the voltage width at the AlOxAl barrier in the profiles and found that it is closely related to the AlOxAl thickness. We proposed a way to evaluate this thickness from the voltage width. The anodization profile is useful in diagnosing the 4.2 K critical current density of Josephson junctions even at room temperature.

Characterization of Nb/AlOx-Al/Nb Josephson junctions by anodization profiles

The thin tunneling barrier in a Nb/AlOx-Al/Nb Josephson junction was characterized by anodization profiles. Our studies focused on Nb/AlOx and Al/Nb interfaces in Nb/AlOx-Al/Nb junctions made by varying certain process parameters. The interface quality was checked by the anodization profiles and was greatly affected by film thickness, layer sequence, annealing treatment, and the existence of a thin oxide. By comparing the profiles with the junction characteristics measured at 4.2 K, we confirmed that the interface sharpness in the profiles is related to the junction quality. The anodization profile is a useful tool to diagnose the tunneling barrier interfaces in Nb/AlOx-Al/Nb Josephson junctions, especially at room temperature during fabrication.

Effect of grain size on ECM performance

The conditions at the gap in Electrochemical machining (ECM) process are complex and random in nature due to the transient effects of a large number of parameters and their interactions. Therefore, the problems related to work and tool shape prediction and the characterization of surfaces generated by ECM are not completely resolved. This paper examines two aspects of ECM performance. The reduction in the experimentally measured values of the final gap with the increase in work specimen grain size is used to develop a correction factor. The prediction of the anode profile based on the correction factor and the improved cosθ method compares well with the anode cavity profile measured with a specially designed and built instrument. The characterization of the ECM generated surface profiles by Data Dependent Systems (DDS) has led to the characteristic shape or Green's function and a component by component wavelength decomposition. The characteristic shape is correlated with the distribution of potential gradient or current in the gap. The percent contribution by the shorter wavelength to the total power or variance has been found to decrease with the increase in feed rate as well as in grain size.

The effect of electrode shape on the voltage of hall/heroult cells—I. carbon anodes/wetted cathodes

Two-dimensional profiles assumed by carbon anodes suspended over shaped, wetted cathodes in the Hall process for aluminum production and the cell voltage of each configuration were calculated. Cathodes shaped as square waves, sine waves and triangular waves were used. Designation of a region of lower conductivity adjacent to the anode simulated the presence of carbon dioxide bubbles. The profile of the anode did not penetrate the shape of the cathode. A dimensionless group characterizing the response of the anode profile to a wave sculpted into the cathode is ▪ where s| is the stoichiometric coefficient, p is the reaction order, n is the number of electrons transferred, b o is the amplitude of the cathode wave, h o is the minimum separation of anode from the cathode, and γ o is the wavelength of the cathode wave. Cell voltages in all cases were greater than the voltage of a cell having the same amount of gas spread uniformly over a flat plane. Voltage reduction can be achieved if the shape cut into the anode aids removal of gas from the interelectrode region.