The Interaction of Organic Compounds with the Surface during the Electrodeposition of Nickel

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Abstract
Measurements of the cathode potential were made during electrodeposition of nickel in the presence of 76 organic compounds. The ability of the compound to make the cathode potential more negative at a fixed current density was dependent upon : (a) the acidic or basic character of the compound; (b) the size of the molecule; and (c) the number of available pairs of electrons in the molecule. Available pairs of electrons are defined as those which are capable of being shared with other atoms through association or chemical reaction without breaking completely the original bond between the atoms involved. Cathode polarization was appreciably increased by low concentrations of basic compounds with a large number of available pairs of electrons and/or with a large molecular size. The comparative effectiveness of chemical groups in increasing polarization decreased in the following order: nitrogen in conjugated bicyclic ring, nitrogen in conjugated monocyclic ring, nitrile, aldehyde, amino, nitro, tertiary amine, sulfone, sulfonylamide, sulfonate, carboxyl, ketone, and phenolic or alcoholic hydroxy. Simultaneous measurements of cathode potential and brightness of the surface indicated that the largest compounds required the smallest concentration to brighten the surface, and the smallest compounds required the largest concentration. Brightening first occurred in the majority of instances at a cathode potential 20–50 mv more negative than that of an unadulterated bath. The conclusion was drawn that the lowest concentration required for brightening corresponded to a specific fractional coverage of the surface. Brittleness, peeling, and cracking of the deposit were correlated with high polarizations. The origin of the change of the cathode potential in the presence of organic compounds was attributed to interference at the cathode surface with some stage in the over‐all process, Adsorption experiments with Raney nickel and measurements of the electrode potential in 1N hydrochloric acid indicated that the compounds most effective in increasing the cathode potential were readily adsorbed by nickel. The experiments in hydrochloric acid also indicated that the adsorbed compounds interfered with the electron transfer, and x‐ray measurements reported in another paper indicated that the compounds interfered with crystal growth.
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