Showing papers in "Journal of The Electrochemical Society in 1966"

Environmental Factors Affecting the Critical Potential for Pitting in 18–8 Stainless Steel

Abstract: The concept of a critical potential below which pitting of 18–8 and other passive alloys does not occur in aqueous Cl− media is affirmed. Increasing Cl− concentration shifts the critical potential to more active values. The potential is shifted to more noble values by presence of other anions, e.g., , , , , sufficient concentrations of which act as pitting inhibitors. Lowering of temperature similarly enobles the critical potential. The shift at 0°C exceeds the oxidation‐reduction potential for accounting for resistance of 18–8 to pitting in solutions at ice temperature but not at room temperature. The critical potential is not affected appreciably in the acid pH range; it moves markedly in the noble direction in the alkaline range corresponding to observed resistance to pitting in alkaline Cl− media. These results are interpreted in terms of competitive adsorption of Cl− and other anions for sites on the alloy surface. Only at a sufficiently high surface concentration of Cl− is oxygen, making up the passive film, displaced locally, and passivity thereby destroyed resulting in a pit. The special behavior of inhibition and factors affecting reproducibility of measurements are discussed.

The Effect of Oxide Volatilization on the Oxidation Kinetics of Cr and Fe‐Cr Alloys

Abstract: The oxidation of Cr and Fe‐Cr alloys which form scales involves at least two processes: (i) the solid‐state, diffusive transport of ionic species, with parabolic kinetics, and (ii) the oxidation of to a volatile species, probably , with linear kinetics. The effects of this second reaction cannot be neglected, either in interpretation of short‐term oxidation results, or in predicting long‐term oxidation behavior. In this paper equations are derived which describe the oxidation behavior of a system in which both diffusive and gas/oxide interface processes occur simultaneously. According to the model, the oxide scale grows to a limiting thickness which is determined by the parabolic rate constant and the surface‐reaction rate constant; as the limiting thickness is approached, a transition from parabolic to linear kinetics takes place. The model is applied to the oxidation of Cr and Fe‐Cr alloys, and good agreement with experimental data is found.

The preparation and properties of vapor- deposited epitaxial InAs sub 1-x P sub x using arsine and phosphine.

Abstract: Vapor phase epitaxial production of indium arsenic phosphide crystalline layers, discussing electron mobilities, electrical resistivities and doping

Electrochemical Behavior of Semiconductors under Illumination

Abstract: In contrast to metals, the average free energy of electrons can be changed in semiconductors to a great extent by illumination Especially the concentration of minority electronic carriers can differ by orders of magnitude from the equilibrium value This has two major effects on electrode processes: (a) change of charge distribution and potential drops in the space charge layer; and (b) variation of the rate of electrode reaction in which minority carriers are involved Some examples are given for those effects at various semiconductors

A Method for Determination of the Permeation Rate of Hydrogen Through Metal Membranes

Abstract: A sensitive electrochemical method for the precise measurement of diffusion coefficients and permeation rates of hydrogen through metal membranes is described A mathematical analysis of the pertinent diffusion equations is given Suggestions are made regarding uses of the method

Periodic Variation of Exchange Current Density of Hydrogen Electrode Reaction with Atomic Number and Reaction Mechanism

Abstract: The works on hydrogen electrode reaction have been increasingly accumulated during the last decade. These works are much more reliable than earlier ones, in­ asmuch as the special precaution has been taken against contaminations of solution and electrode surface. Survey of the results shows that the activity of metals for the reaction in terms of the exchange current density, io (Acm -2), varies in a wide range, namely from log io = -1.2 on Pd to -12.9 on Pb and even on the same metal, from -3.15 to -7.04 on Au (ef Table 1). Such variations in the activity may be caused by several factors such as bulk property of electrode material, surface state of the electrode and solution. The present note is concerned with the relation of the exchange current density of various metals to their position in the Periodic Table and with the decision of the determining factor of the activity.

Semiconductor Joining by the Solid‐Liquid‐Interdiffusion (SLID) Process I . The Systems Ag‐In, Au‐In, and Cu‐In

Abstract: The acronym SLID is used to describe a process whereby high‐temperature phases are formed by diffusion in the presence of liquid. A technique is discussed which utilizes these phenomena in producing high‐temperature‐stable bonds which have been fabricated at low temperatures. The binary systems Ag‐In, Au‐In, Cu‐In among others exhibit these characteristics. Photomicrographs and electron probe microanalysis data are presented to identify and describe the phases formed in these bonds. Some applications for the use of this joining technique are suggested in addition to the feasibility of extending this method to the use of ternary and higher order alloy SLID systems.

Electrode Kinetics of Oxygen Evolution and Dissolution on Rh, Ir, and Pt‐Rh Alloy Electrodes

Abstract: Cathodic and anodic Tafel parameters, stoichiometric numbers, and decay kinetics have been determined on rhodium, iridium, and platinum‐rhodium alloy electrodes. Two regions of constant for a given substrate were observed. The catalytic activity of the substrates in acid solution above about 1.4v (vs. N.H.E.) was On the anodic side, the alloy substrate tends to behave as Rh, on the cathodic side as Pt. Time decay behavior was conventional except for the alloy surface, where the decay from the anodic side behavior resembled that on Pt. The stoichiometric number on Rh, Ir, and Pt‐Rh was about 2. Rate‐determining steps have been determined unambiguously by the criteria mentioned because of the existence and helpful diagnostic nature of two distinct values for on the anodic side, and because of the availability of stoichiometric numbers. After anodic polarization, Pt‐Rh electrodes behave as if the substrate were an individual area of Pt and Rh oxides. A model which rationalizes this deduction is suggested.

High‐Temperature Oxidation III . Zirconium and Hafnium Diborides

Abstract: The oxidation of zone melted specimens of and was studied at temperatures of 1200°–2000°K and at oxygen partial pressures of 1–700 Torr in helium. Parabolic rate behavior was observed. For above 1400°K an activation energy of was determined. Below 1400°K the activation energy is much lower, and the mechanism of oxidation is different, probably because of the presence of boron oxide in the condensed phase. Below 1300°K, the parabolic rate constant appears to be directly proportional to oxygen partial pressure; at 1830°K, the rate constant is independent of oxygen pressure. For in the range 1480°–1870°K an activation energy of was observed. Around 1970°K, the transition temperature for the monoclinic to tetragonal phase change in , there is a sharp increase in the rate of oxidation. The parabolic rate constant for total oxygen consumption increases as the power of the oxygen partial pressure at 1630° and 1760°K.

Photocurrents Produced by Ultraviolet Irradiation of Mercury Electrodes II . Factors Influencing Photocurrents Caused by Electron Emission

Abstract: The influence on the photocurrent of factors such as wavelength, scavenger concentration, ionic strength, diffusion coefficient of the hydrated electron, and the nature of products of the scavenging reaction, is considered. The discussion is illustrated by experimental data obtained by a variety of methods, and some preliminary results for substantially monochromatic light are described which lead to approximate relative rate constants for the scavenging of hydrated electrons by some simple inorganic ions and molecules.

Theory of Potentiostatic and Galvanostatic Charging of the Double Layer in Porous Electrodes

Abstract: A theory of potentiostatic and galvanostatic transients which occur during charging of the double layer in porous electrodes is developed. Solutions are presented for transients due to charging processes in the interior of idealized, one‐dimensional porous and tubular electrodes of finite length. In addition, the effect of IR drop which occurs in solution between the tip of the reference electrode capillary and the front surface of the porous electrode is calculated. The effect of the external surface of the electrode on the charging transients is also assessed. Solutions for charging transients are presented for the case of potentiostatic and galvanostatic single pulse methods, for measurements made with square waves of current or voltage, and for triangular current or voltage sweeps. The effect of the conductivity of the metallic phase on the observable transients is considered. Graphical solutions of the theoretical equations are presented.

The Mechanical Properties of Thin Anodic Films on Aluminum

Abstract: The measured stresses associated with the growth of oxide on the surface of aluminum are much lower than those calculated from the Pilling‐Bedworth ratio. The magnitude of the stresses in alumina formed anodically on pure aluminum is shown to be dependent on the rate of formation. Some experiments are described which show that, even at low temperatures, the presence of a large ionic flux will permit the deformation of alumina providing a mechanism by which the growth stresses can be relieved.

An Ellipsometric Determination of the Mechanism of Passivity of Nickel

Abstract: The capacity of nickel in acid solution have been followed by means of ellipsometry under conditions of potentiostatic control of the material at various points in the passivation current-potential diagrams and also with automated equipment which allows the recording of the ellipsometer reading under transient conditions. It is found possible to evaluate the refractive index, thickness, and light adsorption of the film at all parts of the process. The film begins to form at the first inflection on the current-potential diagram, but after the current reaches its maximum point, it does not change further in thickness. When the current begins to descend, there is a parallel rapid increase in the electronic conductivity of the film. Passivation arises from a critical increase in semiconduction of the film on the surface. The increase in electronic conductivity reduces the field available for the encouragement of anodic dissolution and transport through the film. Hence, dissolution ceases, i.e., passivity, occurs.

The Kinetics and Mechanism of Oxidation of Superpurity Aluminum in Dry Oxygen I . Apparatus Description and the Growth of “Amorphous” Oxide

Abstract: A vacuum microbalance and furnace assembly was constructed and employed to determine the growth kinetics of oxide films on aluminum. Using electropolished foil samples of geometric area 80 cm2, and making corrections for spurious weight changes arising from thermal diffusion effects, film thickness changes as small as 0.3Aa could be reliably detected. In addition to kinetic data, the structure of representative oxide films was examined by electron microscopy. It was found that only "amorphous" oxide grew for about the first 10 hr at 454°C and for shorter periods at 478° and 505°C, the weight gain data being in good accord with an equation similar to that proposed by Mott and Cabrera for the growth of very thin oxide films, an approximate integrated form of which is sometimes referred to as the inverse logarithmic equation. The data could not be represented satisfactorily by either a parabolic oxidation law or a direct logarithmic law.