Preliminary investigation has demonstrated that surface morphology of epitaxial copper electrodeposits is influenced by the anion of the electrolyte. Effects due to the use of sulfate, sulfamate, dimethylsulfamate, methane-sulfonate, benzene-sulfonate, perchlorate, fluoborate, nitrate, chloride, and acetate anions were studied. Observed changes in surface structural details are consistent with adsorption of the anion on the cathode as an important influencing factor, but other factors can and do produce similar results.It has been observed that iron and chromium can be deposited epitaxially only from singular electrolytes using particular deposition conditions. Iron is so deposited from ferrous Chloride electrolyte (1) and chromium from a fluoride "catalyzed" chromic acid solution (2) at temperatures above 80~ From other electrolytes, deposits of both metals become coarse grained with well-developed preferred orientation. In addition, internal stress decreases as bath temperature is increased. Surface morphology of the plane-facetted epitaxed deposits of iron and chromium is similar in so many respects to that of copper deposits, which have been studied intensively (3-10), that deposition under control of a "bunching mechanism" was concluded to have occurred. It has been shown previously that with similarly specific operating conditions, nickel, cobalt, lead, and zinc (11, 12) are deposited epitaxially with morphologies characteristic of growth by bunching.The cited work has largely been concerned with deposits from sulfate electrolytes. Limited comparisons with copper deposited from perchlorate and nitrate electrolytes (13, 14) indicated that the habit, or characteristic morphology, developed was correlated with overvoltage during deposition. Very similar habit development was observed in deposits from copper sulfamate solutions, but significant detail differences are observable in illustrative photomicrographs (15).In the course of an investigation (16) of mechanisms and kinetics of copper deposition from several electrolytes, results obtained were interpreted as indicative of blocking of deposition sites by specific adsorption of anions as one of several factors which influence growth of electrodeposits. In view of the role of adsorbable additives in practical plating processes (17), it is reasonable to expect that such specific adsorption, the effect of which varies with anion size, can result in modifications of the external form and internal structure of electrodeposits.Since the structure and morphology of iron and chromium are so specifically dependent on the anion used in the electrolyte, the effects of anions of different sizes on the characteristic habit of epitaxiaI copper deposits were examined. Deposits from acidic copper electrolytes were prepared and their surface forms compared to those obtained from the well-studied sulfate electrolytes. ExperimentalSolutions.--With three exceptions, all solutions contained 0.5M cupric salt and 0.5M excess or free acid. In all cases, the solution was prepared by...

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On nickel, copper, iron, and steel substrates, chromium has been deposited epitaxially from a fluoride catalyzed chromic acid electrolyte at temperatures above 80~ Prominent planar facets on the deposit surfaces are parallel to chromium {110} crystallographic planes and have structural details indicative of growth by "bunching." Reflections from these facets differ in intensity, according to orientations of substrate grains, and suggest applications in metallography for study of preferred orientations and contrast improvement of "flat etching" metals.In the course of work reported previously (1), it was observed that appearance and porosity of 0.5 ~m (micrometer) thick chromium deposits depended on the crystallographic orientation of electropolished nickel substrates. It was inferred that the topography and deposit structure of the chromium were significantly affected by interfacial epitaxy. Epitaxy of chromium has previously been observed only in thin (<0.1 ~m) deposits on nickel (2-4) and on copper (5). Anticipating discernible effects on deposit structure, 15-30 ~m deposits from sulfate and sulfate plus silicofluoride catalyzed baths were examined microscopically and by x-ray diffraction. Only the structures and preferred orientations described by Kaiser and Wiegand (6) were found (7). Together with information previously available (8,9), these results indicate that the characteristic structural elements of chromium deposits are submicroscopic crystallites (10-7 to 10 -4 cm), and further investigation of the influence of epitaxy would require that electron microscopy and diffraction be used. No further work was done as it was obvious that epitaxial effects on deposit structure were limited to a very thin zone at the interface.The work was resumed when it was noted that surfaces of chromium deposited from a fluoride catalyzed bath at 85~ consisted of well-formed, apparently crystalline, facets. Strongly epitaxed deposits, it was found, can be plated on a number of different metals. This report describes the procedures employed in an exploration of the characteristics of such epitaxial chromium deposits, using metallographic and x-ray diffraction methods. The results obtained are discussed with reference to the deposition process. ExperimentalThe chromium plating bath, prepared from reagent grade materials and distilled water, contained 250 g/1 (2.5M) chromium trioxide and 5 g/1 (0.25M) fluoride ion (from hydrofluoric acid or sodium fluoride). The bath, in a Teflon beaker, was maintained at temperatures of 75~176 by immersion in a controlled temperature water bath. Anodes were cut from sheet lead and had areas of 120 cm 2. A polyethylene propellertype stirrer was used to provide mild agitation to minimize temperature and concentration gradients. Cathodic current density was varied from 300 to 1500 mA/cm~, but was usually 500-700 mA/cm 2. Power was obtained from a laboratory rectifier (filtered, singlephase full wave) or an electronically regulated constant voltage/current power supply.The cathodes used were nick...

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Conventional bright chromium deposits (0.02-0.05 rail thick) on buffed nickel plates often develop a directionally oriented crack pattern which may adversely affect appearance and corrosion resistance. This cracking was found to occur by interaction of polishing-induced, directional residual stress in a surface layer of the nickel with isotropic internal stress of the chromium deposit. Removal of the stress-containing layer by electropolishing or stress relief by annealing eliminates this cracking. Similar cracking can occur in bright nickel-chromium composites plated on polished steel. Chromium deposits on electropolished nickel are apparently strongly epitaxial. Observed variations in appearance, porosity, and corrosion behavior of deposits on individual grains of wrought nickel correspond to similar variations symmetrically distributed in chromium plated on spherical nickel single crystal. The significance of these observations is discussed.The use, efficacy, and electrochemistry of microcracked chromium in controlling corrosion of copper-nickel-chromium plated coatings for decorative automobile trim have been discussed by a number of authors (1-6). This type of cracking [Type M in Lindsay's (2) classification] is described by Lovell (1) as "... a fine network of cracks extending through the chromium and invisible to the unaided