Kinetics of electrodeposition of Ni-Sn alloy deposits from an acid chloride bath

Abstract

Total and partial polarization curves were determined for the deposition of tin and nickel separately as well as for their codeposition from acidic chloride baths. Using a rotating disc electrode system a detailed study of Ni2+, Sn2+ and H+ reduction processes was made, and the results were compared with similar studies on the deposition of such alloys from the same electrolyte with fluoride addition. It was found that for chloride baths the alloy is deposited with a higher polarization than that for the deposition of each metal separately, which is the reverse of the case of deposition from electrolytes containing fluoride ion additions. Furthermore, for coreduction there is a decrease in the hydrogen discharge overvoltage; the rate of hydrogen reduction considerably exceeds the discharge rate of other alloy components, and the hydrogen reduction reaction is diffusion controlled. The tin reduction reaction (for both separate deposition and codeposition) was found to be diffusion controlled, while for nickel reduction in both cases the reaction kinetics are mixed with the activation kinetics dominant. The dependences of current efficiency and of percentage content of tin in the alloy on current density were also investigated. The investigations showed that, although there exists a considerable difference in the electrocrystallization process of Ni-Sn plate from chloride baths and from baths with F- additions, it is possible to choose electrolysis conditions which will allow plates with good properties to be obtained from the bath which contains chloride only.