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A theoretical study is presented of the effects of bubbles attached to the surface of a gas‐evolving electrode, with emphasis on their influence on the local current distribution and on the potential drop at the electrode. The mathematical model accounts for the combined influence of (i) ohmic obstruction within the electrolyte, (ii) area masking on the electrode surface, which raises surface overpotential by increasing the effective current density, and (iii) decreased local supersaturation, which lowers the concentration overpotential. The electrolytic transport is described by potential theory, and the dissolved gas is assumed to obey steady‐state diffusion within a concentration boundary layer. The coupled field equations are solved numerically using the boundary‐element method. The model is applied to hydrogen evolution in potassium‐hydroxide solution. For gas evolution in the Tafel kinetic regime, the current distribution is nearly uniform over the unmasked electrode area, and the increase in surface overpotential is the dominant voltage effect. However, outside the Tafel regime (e.g. on cathodes of greater catalytic activity) the current density is strongly enhanced near the bubble‐contact zone, and the supersaturation‐lowering effect is quite strong, largely offsetting the ohmic and surface‐overpotential effects. Proceeding from a set of base conditions, we perform a systematic examination of attached‐bubble effects, their relative importance, and their dependence on system variables.

Agitation effects on normalNiFe electrodeposition have been systematically investigated using a rotating ring‐disk electrode. Alloy compositions and bath current efficiencies have been shown to vary widely over the range of plating current densities and rotation speeds used. An analysis of partial currents as a function of electrode potential has shown that the Fe deposition reaction is mass‐transport controlled at sufficient cathodic potentials, and that the diffusivity of the Fe2+ ion is the same for both the reduction to Fe0 and the oxidation to Fe3+. In agreement with the observations of Dahms and Croll, the Ni deposition reaction is inhibited when Fe is codeposited. This inhibition effect, manifest as a cathodic shift in the Ni polarization curve, increases in magnitude with increased agitation. The dependence of Ni inhibition on agitation is seen only under conditions at which Fe deposition is mass‐transfer influenced, which suggests that Ni inhibition is primarily dependent on the flux of Fe2+ to the electrode surface. The rate of hydrogen evolution during normalNiFe deposition shows the same dependence on potential and agitation as it does in a Ni2+‐ and Fe2+‐free bath on a normalNiFe substrate.

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A model has been developed to predict current distribution in electrodeposition onto substrates that contain lithographic patterns. The aim of the work was to understand the strong effects that substrate patterning can exert on the thickness distribution of plated films. Based on the familiar potential-theory model for secondary current distribution in electrochemical cells, the model is applicable at length scales that are large compared to the individual features of a pattern. The pattern is described entirely as a continuous distribution of"active-area density," a property that reflects any relative change in the electroactive area of the substrate due to the pattern. The active-area density enters the expression that relates the surface overpotential to the current density. An implementation of the model, using the boundary-element method, has been applied to several problems that illustrate the effects of substrate patterning on current distribution. For each example, the dimensionless groups that characterize the current distribution have been identified, general solutions have been obtained over wide parameter ranges, and behavioral trends have been interpreted.

The NiFe electrodeposition is studied using an RRDE in a deposition bath containing NaCl, H3BO3, 0.2 M Ni2+ and 0.005 M Fe2+ at pH 3. Agitation is found to have a strong effect on both alloy composition and current efficiency over a wide range of plating current density and rotation speed.

Pit growth was studied in 80Ni-20Fe sputtered thin films by analysis of images of the growing pits. The pit current density was found to increase with pit growth potential until reaching a limiting value. The limiting current density increased with decreasing film thickness. The mass-transfer resistance to the active pit wall exceeds by an order of magnitude that predicted from a simple radial-diffusion model. It is suggested that the undercut, remnant passive film collapses over the pit wall causing a constriction. A voltage component calculation matches the data rather well and indicates that pit growth below the limiting current density is limited by a combination of ohmic, concentration, and surface activation considerations.The study of pitting in thin films is of interest because of differences in behavior compared to pitting in bulk alloys. Thin films often have different properties and certainly have more stringent requirements in terms of allowable material loss. Furthermore, thin films provide a unique opportunity for studying pit growth since the whole pit is visible during the growth process. As a result, no assumptions need be made regarding the active pit area during growth.Pits were previously shown to penetrate thin metallic films quickly and reach the substrate 1 . They grow subsequently in a two-dimensional fashion with walls perpendicular to the substrate. This initial study was performed on approximately 1500 Å thick Al films, and the average pit current density was calculated from images of the growing pits. The pit current densities were found to be large (tens of A/cm 2 ) and independent of time during pit growth. There was, however, an influence of pit growth potential. At the highest growth potentials, the pit current density was rather independent of potential, and the pits were very round in shape. At lower potentials, the pit current density varied approximately linearly with potential, and the pits were more irregular in shape. At the lowest growth potentials, the pit perimeters were extremely convoluted, and the calculated pit current density was again independent of potential, although the latter was determined to be an artifact of the calculation as discussed below. Pit growth was described to be under mass-transport control in the highest potential region and under mixed ohmic/charge-transfer control at lower potentials.The alloy studied in this work is Permalloy, a NiFe alloy. The early investigations of this alloy focused on its oxidation and atmospheric corrosion behavior [2][3][4][5][6] . Recently, studies of the