Showing papers on "Electrode potential published in 1975"

X-ray photoelectron spectroscopic studies of oxide films on platinum and gold electrodes

Abstract: The oxide films produced by anodic oxidation of gold and platinum have been studied by X-ray photoelectron spectroscopy. The change in the amount of each species present, with electrode potential, has been investigated. It is demonstrated that X-ray reduction occurs for these systems but that it can be minimised by a suitable choice of experimental conditions.A study of the intensities of the photoelectron peaks demonstrates how the thickness of an oxide layer and the true surface area of the electrode may be determined.

The Quantum Yield of Photolysis of Water on TiO2 Electrodes

Abstract: The quantum yield of the photo-currents in the electrochemical cell, n-TiO2/electrolyte/Pt, was measured under monochromatic illumination of TiO2 at various electrode potentials. It has been found that the quantum yield is very small (10−3) in case where no voltage was applied from outside, getting smaller with illumination intensity. The results of measurements of the quantum yield, together with those of the electrode potential of TiO2, at various conditions are explained from the energy level scheme of the semi-conductor and redox potentials in the solution. The very small efficiency of this photo-galvanic cell as a light energy converter has been attributed to the small difference between the flat-band potential of the TiO2 electrode and the reduction potential of H+.

On the Nature of Electrochemical Reactions at a Crack Tip during Hydrogen Charging of a Metal

Abstract: The electrochemical conditions within cracks in metals undergoing cathodic hydrogen charging in acid solutions are analyzed. The gradients of the electrical potential and concentrations of the various ionic species and the current distribution are calculated for a model crack. The actual potential profiles were measured in slots in Fe, Ni, and Cu samples during hydrogen charging using an electrical potential probe. The measured potential drop in the electrolyte in the slots of all three metals is often very large, e.g., 0.5V. This is about an order of magnitude larger than that calculated, and is in general at odds with the usually implicit assumption that the electrode potential is not an important variable within a growing crack. The reason for this discrepancy is shown to be the large potential variation caused by the presence of trapped hydrogen gas bubbles in the slot.The measured electrode potentials in the slot during cathodic hydrogen charging are in the region of metal dissolution in the case of the two base metals, Fe and Ni. On the other hand, the outer surface of these metals is under perfect cathodic protection for the typical impressed cathodic currents of 5 or 10 mA cm−2. Subsequent tests of electrolyte samples taken from within slots while the current was flowing, indeed, showed the presence of relatively large amounts of iron and nickel ions indicating that anodic dissolution of iron and nickel occurs within the slots, though not at the outer surface during cathodic hydrogen charging. Analysis of the solution at the outer surface of the slot under conditions of impressed current showed the absence of significant concentrations of metal ions.

Electrically biased two electrode, electrochemical gas sensor with a H.sub.2

Abstract: The instant invention relates to an electrochemical sensor for detecting gases or vapors such as carbon monoxide, alcohol NOX etc. The gas sensor includes either a solid polymer ion-exchange-membrane electrolyte or a liquid electrolyte adsorbed in a suitable matrix, a catalytic sensor electrode and a combination counter/reference electrode. A biasing voltage is applied between the electrodes. The biasing voltage is made equal to or larger than the oxidation/reduction potential of a platinum/air electrode and is also greater than the reversible oxidation/reduction potential of the gas or vapor to be detected. As a result, the gas or vapor to be detected is rapidly oxidized at the sensor electrode to produce a current proportional to the mass of the gas present in the incoming stream, while at the same time, making the device insensitive to air. The counter/reference electrode is of a novel construction to provide optimum reversible hydrogen evolution and a hydrogen buffering or storage arrangement to maintain the reference electrode potential substantially constant at 0.0 volts. The electrode is fabricated of a noble metal alloy. Associated with the electrode is a perforated foil such as palladium which has a high solubility for hydrogen. The molecular hydrogen produced at the counter/reference electrode is absorbed in the palladium. An invariant hydrogen atmosphere is thus maintained at the counter/reference electrode so that the reference electrode voltage is kept substantially at zero volts.

Ellipsometric Study of Film Formation on Iron in Sodium Sulphate Solutions in the pH range 6–12

Abstract: The optical properties of surface films and the kinetics of their growth on iron in de-aerated Na2SO4 solutions of pH 6–12 were studied by means of ellipsometry, at open circuit potential and in the range of anodic polarisation potentials. In solutions of pH 6-10, the properties of surface films formed at constant potentials are dependent upon the electrode potential. At potentials below 500 m VNHE, the films exhibit low complex indices of refraction (n = 1·36–1·50, k = O·002–0·1) and grow linearly with time. The films formed at pH 6–10 above SOD mVNHE, and those grown at pH 12 in the whole range of anodic potentials, grow according to a logarithmic law and are protective. These films exhibit a complex refractive index, n = 2·4 (1—0·08i), and are composed of iron oxide.

Metal plating on aluminum

Abstract: An improved process for metal plating on aluminum wherein a zinc immersion coating is applied to the aluminum to dissolve undesirable oxides on the aluminum surface. The improvement comprises a controlled dissolution of the zinc layer followed by immediate plating of the surface with another metal such as nickel. The dissolution of the zinc surface is monitored by immersing the zinc-coated aluminum, together with a nickel electrode, in an electrolytic bath and monitoring the electrode potential difference between the electrodes. The subsequent metal plating step is commenced when the electrode potential difference between the electrodes falls about 100-200 millivolts below the initial electrode potential difference at the particular temperature and bath composition.

The Dependence of the Photocurrent at the Metal-Electrolyte Interface on Electrode Potential

Abstract: The Gurney theory of charge transfer at the metal-electrolyte interface is extended to the case of photoemission. It is found that the simple Gurney model is not sufficient to explain the results observed by a number of independent workers. In order to explain the observed linear dependence of the 0.4 power of the photocurrent on electrode potential it is found necessary to allow explicitly for the existence of a layer of solvent molecules at the metal surface. This layer of molecules con- stitutes a potential energy barrier to electron transfer with a width of about 0.28 nm and a height (with respect to the Fermi level of the metal) of about 560 kJ mol-1 for water. The model is geometrically quite similar to that used in the very successful Brodsky model but differs in physical interpretation of the surface potential energy barrier.

Electrode for percutaneous polarographic measurements

Abstract: An electrode for percutaneous polarographic measurements and, in particular, an oxygen electrode for the percutaneous measurement of the partial pressure or tension of oxygen in human or animal bodies, including a carrier or support portion for the actual measuring electrode as well as, if the case requires, for the reference electrode; a gas-permeable membrane forming an electrode covering on the application side of the latter; an electrolyte introduced between the membrane and the electrode application surface, as well as connectors for the connection of the measuring electrode, respectively, the reference electrode, to a power supply and measuring unit Only the measuring electrode is covered with a membrane merely on the application side thereof for the enclosure of an electrolyte, and the thus membrane-covered measuring electrode is inserted into a recess which is formed in the carrier portion so as to be readily separated from the carrier portion

Voltammetric investigation of the kinetics of alkali metal cation reduction in N,N-dimethylformamide

Abstract: The standard electron-transfer heterogeneous rate constant of lithium, potassium, sodium and caesium amalgams in N,N-dimethylformamide was ascertained employing cyclic voltammetry in an effort to relate the presence of a non-equilibrium electrode reaction at the dropping lithium amalgam electrode to the variation of the lithium amalgam electrode potential with amalgam electrode con- figuration, i.e. whether streaming, dropping or stationary. Such variations are not observed at other alkali metal amalgam electrodes. In the dipolar aprotic solvents the standard electron-transfer heterogeneous rate constant for the Li(Hg) electrode increases as the solvating power for Li+ decreases, i.e. dimethyl sulphoxide < di- methylformamide < propylene carbonate. Water is a much stronger solvator of Li+ than is propylene carbonate, but the electron transfer is faster in water than in propylene carbonate; the important role of entropic contributions in ion solvation is discussed as an explanation.

Building temperature control - has solar heat transmission controlled by voltage potential control of heat transmission properties of liquid crystal sheets

Abstract: To regulate the amount of solar energy transmitted to a building the walls are externally covered by sensitive liquid crystal sheet units. The wall is coated with a layer of heat absorbing material, next to which is an electrode. In between this electrode and another electrode is a liquid crystal sheet. A cover sheet protects the complete assembly. The transmission and reflection properties of the liquid crystal sheet can be varied by variation in the electrode potential. For maximum transmission of heat the sheet is made dark thus allowing maximum energy to fall on the dark heat absorbing surface. For minimum transmission the sheet is made clear so as to reflect energy.

An experimental study of a single layer packed bed cathode in an electrochemical flow reactor

Abstract: Experimental measurements are reported for a packed bed electrode consisting of a single planar layer of uniform copper plated spheres located between platinum anodes and restrained by two plane porous PVC diaphragms. Two mass transfer controlled reactions, namely the reductions ofm-nitrobenzene sulphonic acid and copper sulphate, were investigated and the electrochemical mass transfer data in the range 23

Electrostatic sheet holder - for silk screen printing or printed circuits

Abstract: The sheet-holder has an electrode-supporting base, e.g. of rigid PVC, polyethylene or glass-reinforced epoxy and phenolic resins, with the electrodes connected in two sets. Electrical potential is applied to the electrodes to develop an electrostatic field adjacent the surface of the base and electrostatically attract a sheet to the surface. A cover plate over the electrodes is a thin sheet of semiconductor material which is stable under light when conductive and which has a bulk resistivity of no more than 1015 ohm- cms. A charge induced by the electrodes dissipates immediately when the electrode potential is removed in order to release the sheet. The third electrode is pref. PVC.

Development of a minature pCO2 electrode for biomedical applications.

Abstract: A miniaturepCO2 electrode for possible CO2 measurement in a biological system was constructed and evaluated. ThepCO2 electrode employed a miniature pH glass electrode and the Severinghaus configuration. The electrode was evaluated in both gas and liquid phases. A good linear relation existed between the measured electrode potential of thepCO2 electrode and the logarithm of the CO2 concentration at 20°C in both gas and liquid phases. The temperature dependence of the electrode over the temperature range of 20–60°C was evaluated. From 20 to 40°C, a change of CO2 of 0·15%/°C at a CO2 level of 9·6 mole% was observed. The response time,pCO2 and temperature-hysteresis effects, and long-term stability of thepCO2 electrode were also investigated and discussed.

Electron-transfer reactions at semiconducting anodic niobium oxide films

Abstract: Anodic niobium oxide in a n-type semiconductor due to an oxygen deficit. Electron donor densities and the dependence of excitation energies upon donor density were determined from measurements of space-charge capacitances as a function of electrode potential. Rates of Fe(III) reduction and of Fe(II) oxidation were measured at oxide films of different donor densities as functions of electrode potential and pH value. The results indicate electronic states in the space-charge layer below the oxide surface to participate in the electron-transfer reactions. Experimental polarisation curves are compared to curves calculated theoretically. From the shape of the polarisation curve flat-band potentials of the oxide are estimated. The observed polarisation curves are compatible with λ = 1·2 eV for the reorganisation energy of the Fe(CN)3−6/Fe(CN)4−6 redox couple.

Adsorption of Neutral Organic Substances Evaluated from Electrocapillary Curves and Double Layer Capacities

Abstract: Adsorption of neutral organic substances on mercury electrode was evaluated from both electrocapillary curves and differential capacities of the double layer. The results were compared for the adsorption of n-aliphatic alcohols, phenol, and o-cresol in 0.5 M H2SO4. There was some evidence that the electrode potential was more favorable than the charge on the electrode as an electrical variable in the adsorption of the n-aliphatic alcohols. However, the values deduced from the Frumkin model were generally larger than the θ’s obtained from the electrocapillary curves. This discrepancy is probably due to the deviation from the two-condensers-in-parallel model, because, the two condensers were not independent in an actual system. Neither the two-condensers-in-parallel model nor the three-condensers-in-parallel model were applicable to the adsorption of aromatic compounds.