Progress in Tin-Nickel Electroplating

An investigation of the effect of fluoride concentration on alloy deposition from tin-nickel electrolytes is described. Evidence for the existence and stability of the complexes SnF4—and SnF6—is adduced; deposition of the alloy NiSn is shown to be associated with the formation of the complex SnF4—. Deposition of bright tin-nickel alloy plate is not possible from solutions in which uncomplexed Sn²⁺ ions are present. The relation between [Na+] and [Sn^IV] in the chloride-fluoride electrolyte is discussed.

In the light of the information thus gained some modifications in the constitution of the electrolyte and in maintenance procedure for the practical deposition of the tin-nickel alloy are suggested. Such modifications have for their aim (a) maintenance of the fluoride concentration at the optimum value, (b) reduction of the loss of hydrofluoric acid, when the bath is working, to a minimum.