A comparison is made between potentiostatic (PS) and galvanostatic (GS) polarization processes for studying the degradation mechanism in polymer-coated metals. The PS process integrates effects over the measured system (the coating itself, the coating/metal interface, and the substrate metals), making it difficult to derive information for the coating and substrate separately because the polymer coating still retains a high insulation to prevent the representation of undercoating impedance in the early exposure time. In order to study the coating/metal interface effect, the GS process was applied to furnish a constant DC current- +0.15μA or -0.15μA -on the measured system from the beginning of exposure. The correlation between coating degradation and interfacial adhesion can be evaluated by the visual observation over of coating blister, SEM surface photographs, and X-ray diffraction. The degradation processes occurring between Zn plated steel and the steel with Cu-Ti added. Coating blisters on Zn plated steel are mainly due to the general corrosion behavior of the anodic area. On the other hand, in the case of the steel with Cu-Ti added, interfacial adhesion would deteriorate as a result of cathodic reduction reaction, and be controlled by the diffusion behavior of the reactants.
Recent developments in continuous-strip electroplating processes concern two main features-“high current density operation” and “alloy plating technology”. Current distribution on the cathode strip in a vertical cell is mainly governed by the high ohmic voltage drop in the substrate strip and also plating electrolyte between anode and strip in comparison with electrochemical overpotentials, provided that gas-bubble purging and limited mass-transfer problems are resolved be the use of well designed plating cells. Dependence of alloy content and/or phase on plating current density assures a minimum of variation of current density in a cell. Primary current distributions in vertical plating cells in both the longitudinal and transverse directions were calculated by simplified numerical analysis. Unidirectional current flow is the key assumption in this study, which eliminates the use of Laplace's partial differential equation, based on the particular cell geometry of industrial vertical plating cells. Longitudinal current distribution depends on the ratio of the ohmic resistance of the cathode strip to that induced by the electrolyte in the anode-to-strip gap. Transverse current distribution depends on variations in the anode-to-strip gap across the strip width.
The polarization bahavior of an electroless copper plating solution and the composition, surface appearance and cross section of the deposits have been investigated using EDTA as a complexing agent, and HCHO as a reducing agent The additives used were 2, 2'-dipyridyl (dpy), 4, 4'-dimethyl-2, 2'-dipyridyl (4, 4'-dmdpy) and 6, 6'-dimethyl-2, 2'-dipyridyl (6, 6'-dmdpy) At 70°C, the polarization behavior of baths containing dpy and 4, 4'-dmdpy was in accordance with the mixed potential theory, and copper complex ion was directly reduced to copper As a result, electron diffraction of the deposits revealed Cu alone This is explained by the supposition that dpy and 4, 4'-dmdpy, having a ferroine functional group, are preferentially adsorbed on the working electrode, preventing the alcoholate ion from being adsorbed and causing the characteristic wave of the total polarization curve to disappear Polarization curves obtained from baths containing 6, 6'-dmdpy did not show additivity at 70°C, probably because 6, 6'-dmdpy with a cuproine functional group cannot satisfactorily prevent the adsorption of the alcoholate ion on the working electorode, so that copper complex ion was reduced by two-step reaction and codeposition of Cu2O occured. Grains in the deposits from baths containing dpy and 4, 4'-dmdpy were linked together, while those from baths containing 6, 6'-dmdpy remained comparatively isolated
It is impossible to obtain normal porous oxide films during anodization of Al-coated steels due to peeling at the interface of the Al layer and the steel substrate, as well as due to local dissolution of the steel substrate One of the best methods of preventing these problems is to provide a protective layer such as Ti between the Al layer and the steel substrate. This study investigated the anodizing behavior of Al/Ti double-coated steels in which the initial (Ti) layer was applied by arc-discharge ion plating and the second (Al) layer by vapor deposition, in 15wt% sulfuric acid Results indicated that normal anodic oxide films can be formed on such double coated steels A Ti layer about 1μm thick was found to make possible the anodization of the Al layer Observations by both scanning electron and transmission electron microscopy revealed that the porous oxide film formed on Al/Ti double-coated steel had uniform surface morphology (pore distribution)
The etch pit growth behavior in aluminum foils for electrolytic capacitors during initial DC etching in hydrochloric acid is important in achieving high capacitance, but the relationship between the number of initial pits and pit growth has not been established. In this study, three kinds of foils with different number of initial pits were used. Pit size and pit growth rates were measured for each foil. The pit growth rates were measured by triangle waves, and the pit structures were observed by SEM images of oxide film replicas. The changes in pit size corresponded exactly to a triangle wave of 2Hz at electrolyte temperatures from 70 to 90°C. The pit growth rates for the three kinds of foils were nearly equal at the same electrolyte temperature, and were not influenced by the number of initial pits. The difference in the number of initial pits only affected the pit size.