Electrochemically driven three-phase interlines into insulator compounds: electroreduction of solid SiO2 in molten CaCl2.

The electrochemical reduction of solid SiO2 (quartz) to Si is studied in molten CaCl2 at 1173 K. Experimental observations are compared and agree well with a novel penetration model in relation with electrochemistry at the dynamic conductor|insulator|electrolyte three-phase interlines. The findings show that the reduction of a cylindrical quartz pellet at certain potentials is mainly determined by the diffusion of the O(2-) ions and also the ohmic polarisation in the reduction-generated porous silicon layer. The reduction rate increases with the overpotential to a maximum after which the process is retarded, most likely due to precipitation of CaO in the reaction region (cathodic passivation). Data are reported on the reduction rate, current efficiency and energy consumption during the electroreduction of quartz under potentiostatic conditions. These theoretical and experimental findings form the basis for an in-depth discussion on the optimisation of the electroreduction method for the production of silicon.     

Water density in the electric double layer at the insulator/electrolyte solution interface

I studied the spatial structure of the thick transition region between n-hexane and a colloidal solution of 7-nm silica particles by X-ray reflectivity and grazing incidence small-angle scattering. The interfacial structure is discussed in terms of a semiquantitative interface model wherein the potential gradient at the n-hexane/sol interface reflects the difference in the potentials of "image forces" between the cationic Na(+) and anions (nanoparticles) and the specific adsorption of surface charge at the interface between the adsorbed layer and the solution, as well as at the interface between the adsorbed layer and n-hexane. The X-ray scattering data revealed that the average density of water in the field approximately 10(9)-10(10) V/m of the electrical double layer at the hexane/silica sol interface is the same as, or only few percent higher (1-7%) than, its density under normal conditions.     

Three-phase interlines electrochemically driven into insulator compounds: a penetration model and its verification by electroreduction of solid AgCl

A dynamic three-phase interline model has been developed for the reduction of a solid insulating metal compound to the metal in a suitable electrolyte, focusing on the electrochemically driven penetration of the process (or the three-phase interlines) into the insulator. Consideration is given to the effects of electrochemical, concentration and ohmic polarizations in the reduction-generated porous metal layer on top of the solid compound. Under potentiostatic conditions, reduction in the depth direction (penetration) becomes progressively slower as a result of the rising ohmic and concentration polarizations, whilst the electrochemical polarization exerts a declining effect. The quantitative equations established here also provide simple methods for the determination of some kinetic parameters of the reduction process, including rho (total resistivity) and D(R) (diffusion coefficient). The model has been experimentally verified by electrochemical reduction of solid AgCl with two novel metal|AgCl cylinder electrodes in aqueous solutions.     

Modelling the electric double layer at electrode/electrolyte interfaces

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Dilute gravity flows: A phenomenological model in thin layer theory

We present a simple model for the equations of the motion of turbidity flows. The flow is treated as a deformable geometrical object, parametrized by four characteristic quantities linked to the flow: U, the mean motion velocity of the flow object; l, its length; h, its height; φ, the particles' volumetric concentration. To characterise their temporal evolution, we assume that the gravity flow of a finite volume of particulate mixture reflects the balance between the driving gravity force, the turbulent friction, the spreading due to pressure forces, the incorporation of the ambient fluid, and the deposition and/or the erosion of particles. Special emphasis is placed on the search for analytical solutions over long periods. The study shows the evolution of solutions for three physical cases and includes comparison with numerical and analogical experiments.     

Planar electric double layer for a restricted primitive model electrolyte at low temperatures

Monte Carlo simulation and the modified Poisson-Boltzmann theory are used to investigate the planar electric double layer for a restricted primitive model electrolyte at low temperatures. Capacitance as a function of temperature at low surface charge is determined for 1:1, 2:2, 2:1, and 3:1 electrolytes. Negative adsorption can occur for 1:1 electrolytes at low surface charge with low electrolyte concentration. The 1:1 electrolyte diffuse layer potential as a function of surface charge displays a maximum at low densities. At high densities, the diffuse layer potential is negative with a negative slope. The Gouy-Chapman-Stern theory fails in this low-temperature regime, whereas the modified Poisson-Boltzmann theory is fairly successful in this regard.     

Electrochemistry at High Pressures: A Review

High pressure electrochemical studies are potentially dangerous and less immediately implemented than conventional investigations. Technical obstacles related to properties of the working electrode material, preparation of its surface, availability of suitable reference electrodes, and the need for specially designed high pressure equipment and cells may account for the relative lack of experimental data on electrochemistry at high pressures. However, despite the stringent requirements for system and equipment stability, significant developments have been made in recent years and the combination of electrochemical methods with high hydrostatic pressure has provided useful insights into the thermodynamics, kinetics, and other physico‐chemical characteristics of a wide range of redox reactions. In addition to fundamental information, high pressure electrochemistry has also lead to a better understanding of a variety of processes under non‐classical conditions with potential applications in today's industrial environment from extraction and electrosynthesis in supercritical fluids to measurement of the pH at the bottom of the ocean. The purpose of this article is to detail the experimental pressurizing apparatus for electroanalytical measurements at high pressures and to review the relevant literature on the effect of pressure on electrode processes and on the properties of aqueous electrolyte solutions.     

The polarization model for hydration/double layer interactions: the role of the electrolyte ions

The interactions between hydrophilic surfaces in water cannot be always explained on the basis of the traditional Derjaguin-Landau-Verwey-Overbeek (DLVO) theory, and an additional repulsion, the "hydration force" is required to accommodate the experimental data. While this force is in general associated with the organization of water in the vicinity of the surface, different models for the hydration were typically required to explain different experiments. In this article, it is shown that the polarization-model for the double layer/hydration proposed by the authors can explain both (i) the repulsion between neutral lipid bilayers, with a short decay length ( approximately 2 A), which is almost independent of the electrolyte concentration, and, at the same time, (ii) the repulsion between weakly charged mica surfaces, with a longer decay length ( approximately 10 A), exhibiting not only a dependence on the ionic strength, but also strong ion-specific effects. The model, which was previously employed to explain the restabilization of protein-covered latex particles at high ionic strengths and the existence of a long-range repulsion between the apoferritin molecules at moderate ionic strengths, is extended to account for the additional interactions between ions and surfaces, not included in the mean field electrical potential. The effect of the disorder in the water structure on the dipole correlation length is examined and the conditions under which the results of the polarization model are qualitatively similar to those obtained by the traditional theory via parameter fitting are emphasized. However, there are conditions under which the polarization model predicts results that cannot be recovered by the traditional theory via parameter fitting.     

Optimisation of an electronic amplifier applied to electrolyte/insulator/semiconductor structure

This paper reports on the final development of a MOSFET-based amplifier for the electrical characterisation of chemical field-effect capacitors (ChemFEC) based on electrolyte/insulator/semiconductor (EIS) capacitive structure. Experimental demonstration is performed through the study of SiO₂/Si₃N₄ ion sensitive field-effect capacitor (ISFEC) sensors for pH measurement. This study deals with the amplification's properties according to the ISFEC and MOSFET electrical characteristics. Thus, the ISFEC transition from the accumulation to the inversion regime is shown to be responsible for a non-linear phenomenon. Nevertheless, thanks to a compromise between the ISFEC flat-band voltage and the MOSFET threshold voltage, linear responses are evidenced on the [2-12] pH range. Thus, the non-linear phenomenon observed in previous works is clarified. The detection structure evidences linear responses, which is an essential parameter for sensors. Finally, high detection sensitivities are obtained on a small pH range due to this non-linearity.     

Polarisation phenomena occurring at Cu/semiconducting Te layer/electrolyte interfaces studied by rapid pulse techniques

Tellurium films of different thickness are cathodically deposited on copper substrate using sodium tellurite solutions ofpOH 3.95. The kinetics of the primary processes and modes of conduction occurring at the Cu/Te layer/electrolyte interfaces are studied using rapid galvanostatic rectangular pulses. Approximate values for the specific conductance of the surface layer are calculated from the experimental resistance overpotential. Activation over-potentials are explained in view of charge transfer reactions associated with reactions occurring at the electrode/solution interface.

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Polarisationsphänomene an Cu/halbleitende Te-Schicht/Elektrolyt-Phasengrenzen

Zusammenfassung Tellur-Schichten verschiedener Dicke wurden aus Natriumtelluritlösungen vonpOH 3,95 kathodisch auf Kupfer abgeschieden. Es wurden die Kinetik der Primärprozesse und die Art der Leitung an den Cu/Te-Schicht/Elektrolyt-Phasengrenzen mittels schneller galvanostatischer Rechtwinkel-Pulstechnik untersucht. Dabei wurden angenäherte Werte für die spezifische Leitfähigkeit der Oberflächenschicht aus den experimentellen Widerstands-Überpotentialen errechnet. Die Aktivierungsüberpotentiale werden im Hinblick auf Ladungsübertragungsreaktionen in Verbindung mit Reaktionen an der Phasengrenze Elektrode/Lösung erklärt.

     

Electro-catalytic role of insulator/conductor interface in Mg O/PEDOT composite electrodes for dye-sensitized solar cells

Mg O has not been explored as a counter electrode materials for dye-sensitized solar cells(DSSCs)due to its lack of electrical conductivity.However,herein,it is reported that Mg O insulator with conductive poly(3,4-ethylenedioxythiophene):polysty-renesulfonate(PEDOT:PSS)exhibited excellent performance as a counter electrode for DSSCs,leading to a high power conversion efficiency of 7.45%.Furthermore,it was revealed that the interface between Mg O and PEDOT:PSS plays an important electro-catalytic role in the Mg O/PEDOT composite counter electrodes.     

Ionic solvation at the solid/electrolyte interface: A statistical-mechanical approach

We have studied studied the influence of the size of ions on their adsorbability at a solid surface in the presence of a molecular solvent. Ions and molecules are represented respectively by charged hard spheres and dipolar hard spheres and the surface is just a neutral hard wall. We have found that the electrostatic interaction between ions and molecules can induce the exclusion of small ions from the surface. A pure MSA (mean spherical approximation) calculation would not give any effect of the solvation on the ionic density profile. The present calculation is limited to the case of infinite ionic dilution.     

Recombination and charge transfer at the illuminated n-CdTe/electrolyte interface: Simplified kinetic model

The experimental behaviour of the illuminated n-cadmium telluride/aqueous electrolyte interface is presented with a precise analysis of the electrical impedance in acidic medium. Band edge shifts and the photocurrent onset position are observed to depend strongly on the pH value. They are interpreted by considering mainly the kinetics of the different reactions at the interface. An analytical model is then developed allowing the fitting of both current-voltage and impedance curves. The equivalent circuit derived from the model explains the origin and the variation of the recombination resistance observed experimentally.     

Fluorescence microscopy studies of layer/substrate interaction during the Langmuir-Blodgett transfer: Fractional condensation and local layer modification in lipid monolayers at the three-phase line

Transfer fluorescence microscopy reveals the substrate-mediated fractional condensation and phase-selective deposition of dipalmitoylphosphatidylcholine (DPPC) and dimyristoylphosphatidylethanolamine (DMPE) monolayers during the LB-transfer. Preferentially the higher ordered liquid-condensed (LC) state is transferred onto the substrate during the transfer of a monolayer in the LC/LE (liquid/expanded) coexistence state on the water subphase. This is manifested in the directly observable attraction of LC-domains towards the three-phase line and observation of a domain-free gap as consequence of the segregation of the fluorescent probe into the floating monolayer adjacent to the three-phase line. Fingering domain growth nucleating at the three-phase line and the substrate-mediated pressure deposition of probe-free material corroborate the preference of the solid substrate for the higher condensed phase. These observations are caused by changes in the free energy of the monolayer due to the replacement of the aqueous interface by the solid substrate surface.     

A three-phase nonequilibrium model for catalytic distillation

Nonequilibrium model for steady state simulation of catalytic distillation is presented. Mathematical model takes into account both mass and heat transfers across the gas liquid interface and through the liquid-solid (catalyst) interface. Equations describing the mentioned phenomena are based on the effective diffusivity approach. The resulting system of nonlinear algebraic equations was implemented in the FORTRAN programming language and solved by the BUNLSI (Ferraris & Tronconi, 1986) solver. The described model was verified using the experimental data obtained from a continuous distillation column equipped with catalytic packing. As an experimental model system, synthesis of propyl propionate from propan-1-ol and propionic acid was chosen. Comparison of experimental and simulation data is presented, and appropriateness of the developed model for other types of catalytic distillation processes is discussed. Presented at the 35th International Conference of the Slovak Society of Chemical Engineering, Tatranské Matliare, 26–30 May 2008.     

Investigation of the primary processes occurring at the tin/semiconducting layer/electrolyte interfaces by rapid pulse technique: Part II. Studies of the Sn/Te/electrolyte system

Tellurium layers are cathodically deposited on the surface of tin substrate from a sodium tellurite bath of pH 9.67. The electrode is anodically polarized using rapid galvanostatic rectangular pulses. Apparent specific resistance values calculated from resistance overpotentials demonstrate the semiconducting nature of the tellurium layers. The observed resistance, being too high compared to the reported values for Te crystals suggests the presence of amorphous Te in the electrodeposited phase, as well as the persistence of adsorbed hydrogen cathodically formed. Activation overpotentials are interpreted in view of the primary processes probably operating at the electrode/solution interface. These are associated with the corrosion of tellurium, or occasionally tin in its pores.     

Electrodeposition of gold nanoparticles at a solid|ionic liquid|aqueous electrolyte three-phase junction

Gold nanoparticles have been electrodeposited on an electrode through electrogeneration at an ITO|AuCl₄^? solution in an ionic liquid|aqueous electrolyte three-phase junction. The electrodeposition was carried out by inverted double-pulse potential chronoamperometry. The direct reduction of AuCl₄^? ions at the electrode is followed by a counterion transfer through the liquid|liquid interface. Contrary to the electrodeposition from a single ionic liquid phase, scanning electron microscopy reveals that the shape of the resulting nanoparticles is highly angular and well-developed with a diameter of 110 ± 30 nm. Catalytic oxidation of glucose on the modified electrode is demonstrated.     

Label-free detection of rheumatoid factor using YbYxOy electrolyte–insulator–semiconductor devices

In this study, we investigated the effect of yttrium content on the structural properties and sensing characteristics of YbY_xO_y sensing membranes for electrolyte–insulator–semiconductor (EIS) sensors to detect the rheumatoid factor (RF). The YbY_xO_y EIS device prepared at the 60 W plasma condition exhibited a higher sensitivity of 65.77 mV/pH, a lower hysteresis voltage of ∼1 mV, and a smaller drift rate of 0.14 mV/h than did those prepared at the other conditions. We attribute this behavior to the optimal yttrium content in the YbY_xO_y film forming a smooth surface. Furthermore, we used a novel YbTi_xO_y EIS biosensor to measure the RF antigen in human serum because of its rapid and label-free detection. Two different techniques were used for the immobilization of RF antibody onto the surface of an YbTi_xO_y EIS sensor. The RF antibody was directly immobilized on the EIS surface modified with 3-aminopropyltriethoxysilane (APTES) followed by glutaraldehyde (GA). In contrast, a mixture of 1-ethyl-3-(3-dimethylamino-propyl)carbodiimide (EDC) and N-hydroxysuccinimide (NHS) solution was used to functionalize the carboxyl groups at the tail of RF antibodies. RF antibodies functionalized with the active NHS esters were covalently immobilized on the APTES-modified YbTi_xO_y surface. The immobilized RF antibodies on the EIS that are functionalized with the EDC and NHS exhibit higher (41.11 mV/pC_RF) for detection of serum RF antigen in the range 10⁻⁷ to 10⁻³ M, compared to traditional antibody immobilization technique via APTES and GA linkage. The YbTi_xO_y EIS biosensor is a promising analytical tool for RF antigen monitoring due to its good sensitivity, stability and repeatability.