Showing papers in "Journal of The Electrochemical Society in 1985"

A General Energy Balance for Battery Systems

Abstract: A general energy balance for battery systems has been developed. This equation is useful for estimating cell thermal characteristics. Reliable predictions of cell temperature and heat‐generation rate are required for the design and thermal management of battery systems. The temperature of a cell changes as a result of electrochemical reactions, phase changes, mixing effects, and joule heating. The equation developed incorporates these effects in a complete and general manner. Simplifications and special cases are discussed. The results of applying the energy balance to a mathematical model of the cell discharged through two different reaction mechanisms are given as examples. The examples illustrate how the energy equation may be applied to a specific system to examine the relative contributions corresponding to the terms in the equation. The examples show that the processes involved in cell heat generation may be complex and that the application of a sufficiently general energy equation is advantageous.

Modification of the Electrochemical and Corrosion Behavior of Stainless Steels with an Electroactive Coating

Abstract: Electroactive polyaniline coatings have been deposited on ferritic stainless steels. The coatings appear to be deposited over the passive metal oxide film but can undergo electron transfer with the metal. Polyaniline immobilized on the alloys imparts a form of anodic protection which stabilizes the materials in mineral acids. Electrochemical and SEM characterization results are presented, and effects of coating application techniques are discussed. Oscillations in the open‐circuit voltage occur in solutions containing a high enough concentration of chloride ion to initiate pitting at potentials dictated by the coating. Inhibition of localized corrosion may also be obtainable for favorable systems.

AC Impedance Analysis of Polycrystalline Insertion Electrodes: Application to Li1 − xCoO2

Abstract: It is argued that a porous insertion electrode can be modeled, for purposes of ac impedance analysis, by a modified Randles equivalent circuit containing a generalized constant-phase-angle impedance in series with the double-layer capacitance. The impedance spectrum of the disintercalation system Li/sub 1//sup -/..integral..CoO/sub 2/ showed two time-dependent semicircles, indicating the need for a further modification of the equivalent circuit by a physical process tha could be represented by a resistor/capacitor combination. An adsorption process and a Li/sup +/-ion-electrolyte surface layer are each shown to refine to identically low R factors and to be represented by equivalent circuits that transform on into the other, each having circuit values with reasonable values for the physical processes represented. Time-dependent experiments could eliminate the adsorption models, and electron microscopy gave direct evidence for the surface-laye model; further indirect evidence came from constant-voltage experiments and the preparation of electrodes with greater electrode/electrolyte interface area. Although propylene carbonate appears to be kinetically stabl in contact with Li/sub 1//sup -/..integral..CoO/sub 2/ at potentials of up to 4.5V vs. lithium, mixtures of propylene carbonate with oxide particles having /chi/ = 0.34 produce thick polymer films.

Thermal oxidation of silicon in dry oxygen growth-rate enhancement in the thin regime. I: Experimental results

Abstract: Mesure de la croissance de 800 a 1000°C. L'importance de l'epaisseur est independante de l'orientation du substrat, de la densite du dopage et de la pression partielle d'oxygene

Molecular Layer Epitaxy

Abstract: Application avec succes (et pour la premiere fois) de la methode d'epitaxie par couche moleculaire a la croissance de couches GaAs en utilisant AsH 3 comme gaz contenant As et le trimethylgallium comme gaz contenant Ga. Caracterisation des couches

Surface Composition of Stainless Steels during Anodic Dissolution and Passivation Studied by ESCA

Abstract: A molybdenum containing austenitic steel was exposed in hydrochloric acid at various potentials in the active and passive ranges of the alloys. The surface compositions were analyzed by the ESCA technique. The influence of pretreatment by ion bombardment and mechanical polishing on the passivation behavior was investigated. The passive film formed on the surface consists mainly of a mixed Fe‐Cr‐Mo oxide. The average content of Cr3+ in the oxide is about 70%. The inner layers of the oxide product consist mainly of Cr oxide. The Ni content in the oxide is low. The concentration and the chemical state of Mo is potential dependent. At low potentials in the passive range, the four‐valency state is predominant, while at high potentials Mo exists mainly in its six‐valency state. On the surface of the oxide, a layer of hydroxide is present. Chloride ions are incorporated into the passive film. The thickness of the passive film increases with the potential in the passive range from 10 to 15A. The composition of the metal phase changes during active dissolution. Thus, the alloying elements are enriched on the surface and thereby control the dissolution rate, control overpotentials, and provoke passivation of the alloy.

Chemical Vapor Deposition of Ruthenium and Ruthenium Dioxide Films

Abstract: The preparation of Ru and RuO/sub 2/ thin films by organometallic chemical vapor deposition and an investigation of the films' properties are reported. Ru is of interest for metallization in integrated circuit fabrication because its thermodynamically stable oxide, RuO/sub 2/, also exhibits metallic conductivity. As a result, oxidation during processing of Ru is a less critical concern than in current metallization technology. Taking advantage of the benefits of chemical vapor deposition, such as conformal coverage and low temperature, damage-free deposition, we have deposited Ru, RuO/sub 2/, and Ru/RuO/sub 2/ by pyrolysis of three organoruthenium complexes. Films of a given phase composition were deposited under a wide variety of conditions and exhibited large variations in electrical resistivity and carbon content. The best Ru film, produced from Ru/sub 3/(CO)/sub 12/ at 300/sup 0/C in vacuum, had a resistivity of 16.9 ..mu cap omega..-cm and exhibited excellent adhesion to Si and SiO/sub 2/ substrates. The best RuO/sub 2/ film, produced from Ru(C/sub 5/H/sub 5/)/sub 2/ at 575/sup 0/C in O/sub 2/, had a resistivity of 89.9 ..mu cap omega..-cm and similarly exhibited excellent adhesion. Rutherford backscattering studies show tha Ru and RuO/sub 2/ films are effective diffusion barriers between Al and Si upmore » to annealing temperatures of about 550/sup 0/ and 600/sup 0/C (1/2 h exposure), respectively. Thus, they are significantly better than the currently used W films, which are only effective to about 500/sup 0/C.« less

Some Performance Characteristics of a Prussian Blue Battery

Abstract: Neff (1978), Ellis et al. (1981), and Itaya et al,. (1982) have studied the thermodynamic and kinetic characteristics of the electrochemical oxidation and reduction of thin films of Prussian blue (PB) on various substrates. The present note has the objective to point out the feasibility of a Prussian blue battery, taking into account also the determination of some preliminary performance characteristics of a Prussian blue battery. It is shown that two half-cells could be combined to make a PB battery which, in the uncharged state, would consist of PB as both anode and cathode. One of the major problems encountered is the adherence of the PB deposit on the carbon substrate. 9 references.

Stochastic Models of Pitting Corrosion of Stainless Steels I . Modeling of the Initiation and Growth of Pits at Constant Potential

Abstract: A stochastic model for pit initiation is developed, involving as parameters an initiation frequency for pit nuclei, a death probability for unstable pits, and a critical age which defines the transition between a stable and an unstable pit. Emphasis is placed on validating methods for data analysis to recover the parameters of the model from observed current‐time series. Such methods are developed and tested using data generated by computer simulation of the process. The expected induction time for stable pit initiation is derived. Results for the statistics of ensembles of current‐time transients are given. Methods of analysis of the spectral power density of the current, taking into account the nonstationary process of stable pit propagation, are considered.

Anodic Oxidation of Reductants in Electroless Plating

Abstract: The anodic oxidation of reductants (hypophosphite, formaldehyde, borohydride, dimethylamine borane, and hydrazine) was studied on different metal electrodes (Au, Pt, Pd, Ag, Cu, Ni, and Co) at various temperatures, with special interest in the catalytic aspect of electroless plating. The rate of the anodic oxidation strongly depended on the pH value, the concentration of reductants, and the nature of the metal electrode. The catalytic activities of the metals for the anodic oxidation of different reductants were evaluated by the potentials at a reference current density. The order of the catalytic activity with metal varied depending on the nature of the reductants. The catalytic activity series thus obtained can be utilized for choosing the reductant suitable for the metal to be deposited. Arrhenius plots of the anodic currents on different metals at a reference potential yielded their respective straight lines. Some correlations were observed between the catalytic activity and the activation energy. The catalytic activity series was discussed in connection with that for hydrogen electrode reaction.

Epitaxial Growth and Characterization of β ‐ SiC Thin Films

Abstract: Crack‐free monocrystalline films having very smooth final surfaces may be reproducibly grown at 1600 K and 760 torr on (100) Si substrates using and and if the Si is initially reacted with the alone. This initial step produces a buffer layer which reduces the mismatches in expansion coefficients and lattice parameters and thus allows the subsequent growth of the film to a thickness exceeding 5 μm. It is necessary to heat the Si wafers from room temperature to the reaction temperature in a and environment rather than preheating the substrates to the reaction temperature. An off‐axis orientation of the Si in excess of approximately 3° results in a very rough final growth surface on the film.

Photostimulated Luminescence (PSL) and Color Centers in BaFX : Eu2 + ( X = Cl , Br , I ) Phosphors

Abstract: Single crystals of BaFX:Eu/sup 2 +/ phosphors have been prepared. Optical absorption spectra and stimulation spectra measured with polarized light are in good agreement with each other. The experimental ESR spectra of the F-rich and X--rich undoped BaFX powder phosphors which have been x-rayed coincide with the calculated spectra of F(X-) and F(F-) centers, respectively. In addition, the decrease of the ESR signal intensity with light exposure is substantially in agreement with the stimulation spectra for each case. It is concluded that the PSL of BaFX:Eu/sup 2 +/ phosphors is caused by the liberation of electrons trapped at F centers created by the x-ray exposure.

Gas Permeation Properties of Solid Polymer Electrolyte (SPE) Membranes

Abstract: Gas permeation properties for Nafion membranes and their composites were investigated under various conditions. The permeability coefficients of Nafion depended greatly on the water content, the cation form, and the ion‐exchange capacity. The gas permeation rate through a same sample varied with temperature, pressure, and membrane thickness. The permeabilty of hydrogen was about twice as great as that of oxygen. The electrocatalyst plated on the membrane did not serve as a barrier for gas permeation, but the structure of the catalyst layer played an important role in gas permeation during water electrolysis.

Polymer Films on Electrodes XVI . In Situ Ellipsometric Measurements of Polybipyrazine, Polyaniline, and Polyvinylferrocene Films

Abstract: Ellipsometry was used to study the electrodeposition of polymer films formed by oxidation of bipyrazine, polyvinylferrocene, and aniline. For polymeric films of limited thickness displaying good optical characteristics (i.e., high reflectivity, uniform coverage, and homogeneity), the film refractive index and thickness were determined. Nonideal ellipsometric behavior was observed when film morphology varied with film growth. Polyvinylferrocene films in were shown to be 15% thicker in the oxidized form than in the reduced form.

Mass Spectrometric Study of Ga ( CH 3 ) 3 and Ga ( C 2 H 5 ) 3 Decomposition Reaction in H 2 and N 2

Abstract: Decomposition of trimethylgallium (TMG) and triethylgallium (TEG) in hydrogen and nitrogen atmospheres was studied by a quadrupole mass analyzer. The decomposition reactions of TMG in and in and of TEG in and in take place in the temperature ranges 370°–460°, 450°–570°, 220°–330°, and 270°–380°C, respectively. The reaction mechanisms are hydrogenolysis for TMG in , homolytic fission for TMG in , and β elimination for TEG in both and . The hydrogenolysis of TMG follows homogeneous first‐order kinetics on TMG concentration.

An Analysis of Particle Adhesion on Semiconductor Surfaces

Abstract: This paper constitutes an analysis of the forces of adhesion of small particles to surfaces, most specifically as applied to semiconductor surfaces. The primary forces of adhesion of small, less than 50 μm diam particles on a dry surface are van der Waals forces. These van der Waals forces of adhesion can increase as a function of time due to particle and/or surface deformation which increases the contact area; micron‐size particles can be held to surfaces by forces exceeding 100 dyn, which corresponds to pressures of 109 dyn/cm2 or more. Total forces of adhesion for micron‐size particles exceed the gravitational force on that particle by factors greater than 106. Electrostatic forces only become important and predominate for particles larger than 50 μm diam. Immersion of the adhered particle system can, in some cases, greatly reduce the total adhesion force, first by shielding of the electrostatic and van der Waals attractions, and also by adding double layer repulsion because of dipolar alignment of liquid molecules or dissolved ions at the surfaces. Double layer interactions may, however, also add to the attractive forces if dipoles align properly for attraction. An important consideration is the possibility that if the particles are not removed by the liquid immersion, then a liquid bridge can be formed by capillary action between the particle and surface upon removal from the liquid. This would add a very large capillary force to the total force of adhesion. This capillary force has been shown to remain, in some cases, even when the system is baked at above the liquid boiling point for more than 24h. Removal of these small particles from surfaces is in theory possible but is in practice extremely difficult. It is clear that emphasis should be placed on prevention of particle deposition rather than on counting on achieving subsequent removal.

Application of Kramers‐Kronig Transforms in the Analysis of Electrochemical Systems I . Polarization Resistance

Abstract: A Kramers‐Kronig transform that is useful for validating electrochemical and corrosion impedance data is employed to calculate the polarization resistance from the frequency‐dependent imaginary component. Applications of the transform in the analysis of experimental impedance data for carbon steel in solution at ambient temperature and for aluminum and Al‐0.1P‐0.1In‐0.2‐Ga‐0.01Tl alloy in solution at 25°C are discussed.

Li / Li1 + x V 3 O 8 Secondary Batteries Synthesis and Characterization of an Amorphous Form of the Cathode

Abstract: This paper reports a new synthesis route applied to obtain Li{sub 1+x}V{sub 3}O{sub 8}. Instead of the conventional high-temperature technique leading to the crystalline form, a solution technique producing the amorphous form has been used. This material, after dehydration, shows an electrochemical performance exceeding that of the crystalline one. The rationale for this behavior mainly lies in the microscopic factors, i.e., in the possibility for the unit cell of amorphous Li{sub 1+x}V{sub 3}O{sub 8} to insert up to 9 Li{sup +}, instead of six for crystalline Li{sub 1+x}V{sub 3}O{sub 8}. Furthermore, the absence of a long-range crystallographic order reduces the length of the pathways through which Li{sup +} ions diffuse. This and the favorable morphology endow amorphous Li{sub 1+x}V{sub 3}O{sub 8} with a high rate capability. The higher energy content afforded by this new form (theoretical value, 935 Wh/kg, based on the electrodes weight) can be exploited in long-cycling cells at high rates.

Photoactive Synthetic Polycrystalline Pyrite ( FeS2 )

Abstract: Polycrystalline layers of As‐doped pyrite have been produced in bromine atmosphere with the aim of developing this sulfide material for solar energy applications. Its photoelectrochemical behavior in contact with an aqueous electrolyte was investigated. It operated as a photoelectrochemical solar cell and showed reasonably stable behavior under illumination. Optical measurements performed on show that visible light is absorbed in an extremely thin layer of 160A in spite of the apparently indirect gap of this semiconductor . This would make this photosensitive material an interesting candidate for thin‐layer solar cells. Scanning electron micrographs of the samples reveal well‐developed crystallites of about 5–10 μm with distinct boundaries. Scanning laser spot analysis over macroscopic areas (5 mm) showed homogeneous as well as inhomogeneous regions. The photoelectric properties of these first polycrystalline pyrite samples studied are poor, but there is presently no reason to assume that they cannot be developed.

V 2 O 5 ‐ P 2 O 5 Glasses as Cathode for Lithium Secondary Battery

Abstract: During past two decades, the importance of rechargeable lithium cells has been emphasized and a large variety of materials has been discovered and evaluated for use as reversible cathodes and electrolytes. Materials that undergo intercalation or topochemical reactions with lithium have been investigated as candidates for cathodes in nonaqueous secondary lithium cells (1). Recent interest in researching cathode active materials has mainly focussed on crystalline transition metal chalcogenides. On the other hand, electrochemical behaviors of several amorphous materials have been reported, for example MoS/sub 2/,MoS/sub 3/,V/sub 2/S/sub 5/ (2) and LiV/sub 3/O/sub 8/ (3). However, no successful cycling behavior has been obtained except for MoS/sub 2/ in the amorphous state. This paper reports electrochemical data on rechargeable vanadate glasses in the system V/sub 2/O/sub 5/-P/sub 2/O/sub 5/.

Stochastic Models of Pitting Corrosion of Stainless Steels II . Measurement and Interpretation of Data at Constant Potential

Abstract: The experimental evaluation of the parameters of a general stochastic model for the initiation of pitting corrosion on stainless steels is described. The variation of these parameters with experimental conditions is used in the development of a microscopic model. A microscopic model which accords with the observed behavior attributes the initiation of pitting corrosion to the production and persistence of gradients of acidity and electrode potential on the scale of the surface roughness of the metal. The observed fluctuations are related to fluctuations in the hydrodynamic boundary layer thickness. A pit becomes stable when it exceeds a critical depth related to the surface roughness.

Ellipsometric study of anodic oxide films on titanium in hydrochloric acid, sulfuric acid, and phosphate solution

Abstract: The anodic oxide film on titanium has been studied by ellipsometry and SEM observation. Ex situ multiple‐angle‐of‐incidence and in situ ellipsometric measurements allow the complex refractive index to be estimated at for the titanium substrate and at for the anodic oxide film at wavelength 546.1 nm. The anodic oxide film thickness increases linearly with potential in a range from −0.55 to 7.5V (RHE) at the rate of 2.8 nm V−1 in phosphate solutions of pH 1.6–12.1, 2.5 nm V−1 in solution, and 2.4 nm V−1 in solution. At potentials more positive than 7.5V, the film breaks down, leading to the formation of a thick oxide film probably due to an increased ionic current through the breakdown sites. The film composition is estimated to be or , which suggests the presence of hydroxyl bridge in its bonding structure.

Thermal Oxidation of Silicon in Dry Oxygen: Growth‐Rate Enhancement in the Thin Regime II . Physical Mechanisms

Abstract: In many studies of oxidation kinetics, it has been observed that silicon‐dioxide growth in dry oxygen in the thin film regime (<500A) is faster than predicted by the linear‐parabolic description of the growth of thicker layers. Oxidation‐rate enhancement in the thin film regime was studied in the 800°–1000°C range for a variety of substrate orientations, doping densities, and oxygen partial pressures using in situ ellipsometry. The results were reported in part I of this paper. In this part, the physical mechanisms previously proposed to explain the rate enhancement are discussed. No single model was found to apply under all experimental conditions. A new understanding of the growth‐rate enhancement in the early stages of silicon oxidation in dry oxygen is introduced.

Film Formation and Current Oscillations in the Electrodissolution of Cu in Acidic Chloride Media I . Experimental Studies

Abstract: Etude par la methode du disque tournant. On propose un modele pour la diffusion des ions chlorure a travers la couche poreuse de CuCl afin de rendre compte du comportement oscillatoire

Corrosion Inhibition in Neutral, Aerated Media

Abstract: The concepts of interface and interphase inhibition as two different types of corrosion inhibition mechanisms are discussed briefly. Most of the studies reported in the literature have dealt with interface inhibition in acid media. Experimental results of interphase inhibition have been obtained for a 4340 steel rotating cylinder electrode (RCE) by impedance measurements during exposure over 48h in aerated, neutral , , tapwater and deionized water containing , and mixtures of phosphonic acid/fatty amine or polyacrylic acid/fatty amine. An optimized approach for collecting impedance data for high values and a low frequency limit between 0.4 mHz and 5 mHz has been applied in this study. A very good fit of the experimental data to a theoretical model is observed. For the phosphonic acid/fatty mixture, a second time constant occurs at high frequencies in and , from which the porosity of the inhibitor layer can be calculated.

Effect of Reinforcement on the Pitting Behavior of Aluminum‐Base Metal Matrix Composites

Abstract: This paper examines the effect of graphite and silicon carbide reinforcements on the pitting behavior of graphite/aluminum (Gr/Al) and silicon carbide/aluminum (SiC/Al) metal matrix composites. Electrochemical corrosion tests were performed on both Gr/Al and SiC/Al composite specimens. Identical tests were completed on powder metallurgy processed aluminum and wrought aluminum of the same composition. The electrochemical behavio of the SiC/Al composites was essentially identical to that of the powder processed and wrought aluminum alloys; however, the pitting attack on the SiC/Al composites was distributed more uniformly across the surface, and the pits penetrated to significantly less depths. The presence of graphite in the Gr/Al composites did not cause an electropositive shift in corrosion potential as anticipated, but caused a substantial decrease in resistance to passive film breakdown. This effect is the predominant reason for the poor performance of Gr/Al composites in marine environments.

Assessment of polymer-electrolyte batteries for EV and ambient temperature applications

Abstract: The feasibility of polyether-based all-solid-state cells has been assessed in a joint research and development program. At 80/sup 0/-100/sup 0/C, cells using TiS/sub 2/ or V/sub 6/O/sub 13/ positive-electrode material and exces lithium show high material utilization at 0.5-1.0 mA/cm/sup 2/ and can be cycled more than 250 times. Furthermore, a new family of polyether electrolytes has been found that allows room temperature (26/sup 0/C) operation at 3-20 ..mu..A/cm/sup 2/.