ZnCo-Electrodeposition Baths Based on Alkaline Chloride-Gluconate Electrolytes Containing Quaternary Ammonium Compounds

This paper reports a study of the electrodeposition of Zn-Co alloys from alkaline chloride-gluconate electrolytes containing quaternary amines as additives. The effects on the electrochemical behavior of ZnCo deposition of two quaternary ammonium compounds, N-benzyl-3-carboxylpyridinium chloride (3NCP) and a polyamine (PA) were investigated, and the influence of the cobalt content in the plating bath was studied. The mechanism of electrodeposition of the ZnCo alloys in these alkaline media was anomalous. The two additives caused different inhibition degrees of the cathodic process, the effect of PA being stronger. Also, the results first showed that the cobalt complexes shift the cathodic peak of ZnCo electrodeposition due to de-adsorption of cobalt-gluconate complexes. According to the results, the adsorption of PA partially inhibited the zinc-alloy deposition, and the deposition of ZnCo occurred in two voltammetric steps. The incorporation of the organic additives in the bath modified the composition, morphology, and crystallographic structure of the ZnCo deposits, with PA forming compact grains oriented preferentially to high index pyramidal and prismatic textures and 3NCP producing more highly oriented, compact, and fine-grained deposits. The combination of the two additives induced a synergistic effect, producing deposits whose morphology was refined, with crystals formed on the nanometric scale with a prismatic orientation. (C) 2009 The Electrochemical Society. [DOI:10.1149/1.3208010] All rights reserved.