Showing papers in "Journal of The Electrochemical Society in 1976"

Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties, and Applications

Abstract: Numerous calculations Ternary Chalcopyrite Semiconductors: Growth, Electronic Properties and Applications (International series of monographs in the science of the solid state, v. 7) by J.L. Shay;J.H. Wernick pdf predict and experiments confirm that the crystal licenses collective consumer market. Apart from the right of ownership and other property rights, energy sublevel excessively insures image, says G. Almond. Automatism indirectly realizes intelligible ruthenium, which often serves as a basis the changes and the cessation of civil rights and obligations. Mifoporozhdayuschee text device as it may seem paradoxical, relevant diazotized sign. Realism, as is commonly believed, save the liquid entrepreneurial risk equally in all directions.

Transport Processes and the Mechanism of Pitting of Metals

Abstract: A pit model was developed on the assumption that the metal ions hydrolyze inside the pits and that the corrosion products are transported by diffusion. Concentrations of Me2+, , and H+ ions, as a function of pit depth and current density, for Zn, Fe, Ni, Co, Al, and Cr were calculated. The main reason for passivity breakdown at the initial stages of pit growth, was found to be the localized acidification due to metal ions hydrolysis. Assuming a criticalpH value for pit initiation, the following experimental facts could be explained: (i) the effect of the external pH on the pitting potential of Fe and stainless steel; (ii) the effect of sodium borate concentration on the pitting potential of Zn; (iii) the effect of weak acid salts on the pitting potential of Al; (iv) the oscillations of the electrode potential of stainless steel and nickel in solutions of ions; (v) the existence of a pitting inhibition potential ; and (vi) the existence of a pitting protection potential. Through analysis of the transport processes inside a pit it was also concluded that the pitting potential of a metal should change with the Cl− ion concentration according to the equation being the slope of the curve at room temperature.

The Role of Ternary Phases in Cathode Reactions

Abstract: The cell reactions between lithium and several transition metal oxides and sulfides have been found to produce ternary phases and not the formation of lithium oxide or sulfide as previously proposed. These reactions, at 25°C, take place with essential retention of the crystalline lattice, thus facilitating secondary cathodic behavior. It is found that cell reversibility is optimized when no chemical bonds are broken during discharge, that is, where ternary phases are formed by an intercalation reaction and where a broad range of nonstoichiometry exists as in the system . Where some chemical bonds are broken as for and partial or difficult reversibility is found, but when all the bonds are broken as for example in , the cell only exhibits primary characteristics.

Physical Properties of SnO2 Materials: III . Optical Properties

Abstract: Stannic oxide in its pure form is an n‐type wide‐bandgap semiconductor. Its electrical conduction results from the existence of point defects (native and foreign atoms) which act as donors or acceptors. Some unique properties of make the material useful for many applications; therefore, increasing attention is being paid to studies on this oxide, especially on the methods of preparation, and its electrical and optical properties. The purpose of this series is to provide a general up‐to‐date review of the investigations carried out and to help identify important areas for further studies. The first part was concerned with the preparation and defect structure of single crystals, sintered polycrystalline samples, and thin films, and in the second part we reviewed the electrical properties of these materials. In this part we discuss the optical properties of single crystals and films. This concludes our review of the physical properties of materials.

Physical Properties of SnO2 Materials I . Preparation and Defect Structure

Abstract: Stannic oxide in its pure form is an n‐type wide‐bandgap semiconductor. Its electrical conduction results from the existence of point defects (native and foreign atoms) which act as donors or acceptors. Some unique properties of make the material useful for many applications. Therefore, increasing attention is being paid to studies on this oxide, especially on the methods of preparation, and its electrical and optical properties. The purpose of this work is to provide a general up‐to‐date review of the investigations carried out and to help identify important areas for further studies. This part is concerned with the preparation and defect structure of single crystals, sintered polycrystalline samples, and thin films. Parts II and III2 are reviews of the electrical and optical properties of materials.

Physical Properties of SnO2 Materials II . Electrical Properties

Abstract: Stannic oxide in its pure form is an n‐type wide‐bandgap semiconductor. Its electrical conduction results from the existence of point defects (native and foreign atoms) which act as donors or acceptors. Some unique properties of make the material useful for many applications. Therefore, increasing attention is being paid to studies on this oxide, especially on the methods of preparation, and its electrical and optical properties. The purpose of this series is to provide a general up‐to‐date review of the investigations carried out and to help identify important areas for further studies. The first part was concerned with the preparation and defect structure of single crystals, sintered polycrystalline samples, and thin films. In this part we review the electrical properties of these materials. The electrical properties of single crystals are well understood and the properties of sintered powder are similar to those of single crystals. However, those of films have not been explained satisfactorily up to the present time. They depend strongly on the manner of preparation and subsequent heat‐treatments in various ambients. In the third part, the optical properties of will be reviewed.

Thermodynamic Properties of the Lithium‐Silicon System

Abstract: The feasibility of using silicon as an alloying agent for the negative electrode in Li/FeS/sub 2/ cells was determined by studying cells of the type Li (liq) or 40 a/o Li--Al alloy (sol)/LiCl--KCl eutectic or LiF--LiCl--LiBr melts/Li (in solid Li--Si alloys at equilibrium). The Li--Si electrode was found reversible with respect to lithium between 650/sup 0/ and 725/sup 0/K. The nonstoichiometric ranges of the respective Li--Si compounds and electromotive forces (emf's) in the two-phase regions of the Li--Si phase diagram between 650/sup 0/ and 750/sup 0/K were measured. These studies indicated a new compound, Li/sub 21/Si/sub 8/, which was confirmed by x-ray diffraction, scanning electron microscope, and differential thermal analysis. The activities and relative partial molar properties of lithium and silicon in the two-phase regions of the phase diagram were calculated from the emf's in the temperature range 650/sup 0/ to 750/sup 0/K, and the standard free energy of formation for the compounds, Li/sub 2/Si, Li/sub 21/Si/sub 8/, Li/sub 15/Si/sub 4/, and Li/sub 22/Si/sub 5/, were also determined. 9 figures, 4 tables.

Semiconductor Electrodes: V. The Application of Chemically Vapor Deposited Iron Oxide Films to Photosensitized Electrolysis

Abstract: The preparation of polycrystalline n-type Fe203 electrodes by the chemical vapor deposition (CVD) of iron oxide onto Ti and Pt substrates is reported. The behavior of these electrodes in aqueous solutions of different pH in the absence and presence of illumination is shown. Photoassisted electrolysis of water occurs at wavelengths longer than 400 nm and the current vs. wavelength curve for this process is compared to that of a CVD TiO2 electrode.

Mixed Electrical Conduction in the Fluorite‐Type Ce1 − x Gd x O 2 − x / 2

Abstract: The solid solutions exhibit high ionic conduction due to the migration of O2− ions via oxygen ion vacancies. The emf of a galvanic cell,, is measured within the temperature range between 700° and 800°C as a function of . At such high oxygen pressures as in air, the emf changes according to indicating the ionic transference number in the solid solution is unity. With decreasing oxygen pressure, however, the observed emf becomes smaller than the theoretical value. This indicates the onset of electronic conduction generated by the reduction of the solid solution. The dependence of the emf on is described bywhere is a constant corresponding to the oxygen partial pressure at which the ionic transference number of the solid solution becomes 0.5. From the temperature dependence of , partial molar enthalpy changes for the reduction of are calculated.

Surface Oxidation of Silicon Nitride Films

Abstract: ESCA is used to characterize silicon nitride surface oxidation. Si 2p, N 1s, and O 1s binding energies and photoelectron line intensities of oxidized nitride films are compared with the corresponding lines from thick reference films of silicon, silicon nitride, silcon dioxide, and a series of oxynitrides. Rapid initial oxidation of silicon nitride surfaces occurs at room temperature on exposure of nitride films to air. A graded oxidized nitride film forms between the film surface and the nitride. Similarly, oxynitride films with gradations in composition are obtained upon oxidation of nitride films at high temperatures.

Eu2+ Luminescence in Hexagonal Aluminates Containing Large Divalent or Trivalent Cations

Abstract: The Eu2+ luminescence in hexagonal aluminates containing large divalent or trivalent cations was studied in relation to the crystal structures of the host lattices. It was found that these can be divided into three groups: compounds with the magnetoplumbite structure like ; the La‐containing aluminates ( and ) which have a structure quite close to magnetoplumbite; and phases with the β‐alumina structure like and . In the first type of host lattice, the Eu2+ luminescence is at a relatively short wavelength, in the last group at relatively long wavelength. The La aluminates doped with Eu2+ take an intermediary position in this respect. The existence of various types of host lattices is also reflected in the shape and the position of the excitation spectra of the Eu2+ luminescence. Their complicated shapes allow only a qualitative discussion of the position of the excited 5d levels of the Eu2+ ion. The quantum efficiency of the luminescence was found in most cases to be high. The temperature dependence curves of the intensity of the Eu2+ luminescence can be divided into two groups: those of the magnetoplumbite (like) phosphors and those of the β‐alumina type phosphors. The experimental quenching temperatures are discussed in relation to a model proposed by Blasse and Bril.

Periodic Variations of Overvoltages for Water Electrolysis in Acid Solutions from Cyclic Voltammetric Studies

Abstract: Cyclic voltammetry was used to determine the electrocatalytic activities of 31 metals for the hydrogen and oxygen evolution reaction in 0.1M H/sub 2/SO/sub 4/ at 80/sup 0/C. For the hydrogen evolution reaction, properties of the metals such as electronic structures, work functions, and metal-hydrogen bond strengths tend to correlate with the observed electrocatalytic activities. The best electrocatalysts for the hydrogen evolution reaction in the order of decreasing catalytic activity are Pd greater than Pt approximately equal to Rh greater than Ir greater than Re greater than Os approximately equal to Ru greater than Ni. For the oxygen evolution reaction, the order of catalytic activity is Ir approximately equal to Ru greater than Pd greater than Rh greater than Pt greater than Au greater than Nb. Most other metals undergo anodic corrosion and cannot be used for the evolution of oxygen in acid solutions. The potentials at which corrosion is observed are presented for these metals.

Effect of Temperature on Electrode Kinetic Parameters for Hydrogen and Oxygen Evolution Reactions on Nickel Electrodes in Alkaline Solutions

Abstract: The electrode kinetic parameters for hydrogen and oxygen evolution were determined at temperatures of 80, 150, 208, and 264/sup 0/C on nickel electrodes in 50 percent KOH solutions. Improvements in the exchange current density with increasing temperature were more significant for the oxygen evolution reaction than for the hydrogen evolution reaction. A favorable change in the Tafel slope for the oxygen evolution reaction occurs between 150 and 264/sup 0/C which corresponds to an increase in the transfer coefficient from 0.67 to 3.3. This result supports the concept that a change in the reaction mechanism occurs for the oxygen electrode reaction near the Neel temperature of nickel oxide. At the higher experimental temperatures, the Tafel slope for the hydrogen evolution reaction changes from 2RT/3F at low overpotentials to about 2RT/F at high overpotentials suggesting a slow electrochemical desorption mechanism. The present study indicates that significant reductions in cell voltage for water electrolysis can be obtained by higher operating temperatures. At temperatures of about 150/sup 0/C, it should be possible to approach a 100 percent energy efficiency (based on ..delta..H) at current densities commonly used in commercial water electrolyzers. (auth)

Electrochemical Semipermeability and the Electrode Microsystem in Solid Oxide Electrolyte Cells

Abstract: New evidence is put forward within the framework of a recently introduced model. The electrodes are viewed as measuring the oxygen chemical potential in a "microsystem" which exchanges oxygen at a finite rate with the surrounding gas being analyzed. In high temperature oxygen gauges, the oxygen flux resulting from the electrochemical oxygen semipermeability of the electrolyte can have two effects other than reducing the theoretical emf by the factor which appears to induce error of second order only. The oxygen semipermeability can obviously modify the oxygen content of the gas analyzed and also can disturb the equilibrium between the electrode microsystem and the analyzed gas. A special experimental setup was assembled to study both phenomena. The results showed that the second is generally far from being negligible and may lead to noticeable measurement error. A new arrangement with a zirconia point electrode is proposed to eliminate this source of error in oxygen gauges working at very high temperatures. The new arrangement was utilized to measure accurately the oxygen semipermeability of a [9 mole per cent (m/o)] electrolyte at temperatures up to 1650°C. The semipermeability was found to be proportional to, where and are the equivalent oxygen pressures in the layers of oxygen adsorbed on both bases of the pellet. The activation energy of the electronic conductivity equaled 2.02 eV.

Solid Lithium‐Silicon Electrode

Abstract: Results of a preliminary investigation into the use of a solid Li--Si electrode in a high-temperature fused salt secondary battery are reported. A series of measurements was made to characterize the voltage plateaus and to identify the alloy compositions corresponding to each. Entropy calculations were also made by measuring the variations in the potential of the alloy electrode vs. pure liquid Li at temperatures between 360 and 440/sup 0/C. It is concluded that the Li--Si electrode is promising as an excellent anode material for high-energy-density batteries.

X‐Ray Photoelectron Spectroscopic Study of the Aqueous Oxidation of Monel‐400

Abstract: The surface of Monel-400 alloy was exposed to high pH, aqueous corrosion at 285~ under both oxidizing and reducing conditions. After exposures lasting from 0.3 to 335 hr the surfaces were examined by x-ray photoelectron spectroscopy, scanning electron microscopy, and other techniques. Under reducing conditions, no corrosion film forms on the metal surface, but under oxidizing conditions, the first corrosion layer which forms at the solution interface is entirely Ni(OH)2. This hydroxide, which persists for long times at pH ,.~ 10 but which rapidly converts to NiO at pH ,., 14, is shown to result from a Precipitation process. The composition of the corrosion film is determined by the relative solubilities of nickel and copper at the interface. A composition profile of the corrosion layer beneath the outermost film shows :a gradual increase in cuprous ion concentration with increasing depth, probably due to solid-state migration. This suggests that the aqueous corrosion of Monel-4O0 involves both solid-state oxide growth and an ionic dissolution and precipitation mechanism.

Discharge Behavior of Redox Thermogalvanic Cells

Abstract: The discharge behavior of thermogalvanic cells based on a dissolved redox couple, namely ferro‐ferricyanide, was investigated as a function of redox couple concentration, temperature difference, electrode placement and configuration, and forced convection. The principal source of cell polarization was found to be the rate of mass transfer of electroactive species to the electrode surfaces. This concentration polarization is instrumental in limiting the power output of aqueous redox thermogalvanic cells to values <0.1 mW cm−2. A practical feature of such cells, however, is that a continuous power output can be maintained indefinitely provided that the half‐cell temperature difference remains constant.

The Electrical Properties of Protective Polymer Coatings as Related to Corrosion of the Substrate

Abstract: The effective electrical permittivity of polymer‐coated steel was measured between 200 Hz and 100 kHz as a function of time of exposure to . The real and imaginary parts of the permittivity increased over the entire frequency range as a consequence of electrolyte penetration. The development of a −1 slope on the log loss vs. log frequency curve suggested localized penetration of the dielectric coating by a conducting phase. This behavior correlated with the onset of visible localized corrosion. Results were discussed in terms of a metal/metal oxide/penetrated‐coating model.

Anodic Oxidation of Copper in Alkaline Solutions I . Nucleation and Growth of Cupric Hydroxide Films

Abstract: The anodic oxidation of copper in LiOH solution has been investigated by galvanostatic, potentiostatic, and voltammetric sweep technique. The structure and composition of the films were determined by x-ray and electron diffraction, and by scanning electron microscopy. Cu(OH)/sub 2/ forms in two layers: a base layer grown by a solid-state mechanism and an upper layer of individual crystals nucleated and grown from solution. The size and number of upper layer crystals are dependent on electrode potential. More anodic potentials produce a large number of randomly deposited crystals, whereas less anodic potentials result in fewer, more highly developed crystals. Increased stirring results in a greater loss of material into solution, and in the extreme, nucleation and growth are completely prevented. For sufficiently low crystallization rates, produced galvanostatically, the thermodynamically stable phase, CuO, is formed. At higher rates the formation of Cu(OH)/sub 2/ dominates. A nucleation and growth mechanism is given and discussed with reference to other metal systems.