Effect of some addition agents on the electrodeposition of cadmium from acidic chloride baths

Abstract

In this paper a further development of a chloride-based cadmium plating bath containing 0.3 M CdCl 2·( 5 2 )H 2O, 0.1 M HCl, 0.4 M H 3BO 3 and 2.0 M NH 4Cl (bath I) is described. The influences of the individual addition agents thiourea, coumarin, Ni 2+ ions and I - ions on the characteristics of cadmium electrodeposition from acidic chloride electrolytes containing 0.3 M CdCl 2·( 5 2 )H 2O, 0.1 M HCl, 0.4 M H 3BO 3, 2.0 M NH 4Cl, 0.5 M sodium potassium tartrate and 5 g gelatin 1 -1 (bath II) were studied. Bath II including a combination of the four above-mentioned additives was denoted bath III. The additive-containing bath III produced a brighter but less hard cadmium deposit than the additive-free bath II. The individual effects of melamine, 3-methyl-4- p-methoxyphenylazopyrazol-5-one, dimethylformamide (DMF) and DMF with biacetyl-bis-(benzoylhydrazone) on the cathodic polarization and current efficiency of cadmium electrodeposition from baths II and III, as well as on the morphology and microhardness of the as-plated cadmium deposits, were investigated and discussed. However, each of the additives employed exerted, to a different extent, a polarization-increasing effect and a change in the growth morphology of the cadmium deposits from either bath II or bath III. The additives melamine, DMF and DMF with biacetyl-bis(benyzoylhydrazone) failed to achieve any improvement in the brightness of the cadmium deposits from either bath II or bath III but increased the hardness of those from bath III. 3-methyl-4- p-methoxyphenylazopyrazol-5-one led to the production of the brightest cadmium electrodeposits (from bath III) and the hardest cadmium electrodeposits (from bath II).