Electrodeposition of Tin as a Bright Coating

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Abstract
Bright ductile deposits of tin have been obtained from acid stannous sulphate to which wood tar dispersed in aqueous solution by a suitable agent has been added. The dispersing agent used was octyl sulphuric acid but some alternatives are possible. Whole distillates from either hardwood or softwood have been found to contain the active agent but fractions of tar prepared and marketed for special uses may not contain it. The agent is a neutral component of the tar, distilling in the range of 150–200° and may be destroyed by prolonged heating. Operation of a 90 l. plating bath containing 8 g/1. tar has consistently given bright deposits at current densities of 8–30 A/sq ft with cathode agitation and has given good promise of solution stability. Barrel-plating at 12–18 A/sq ft has given good results. Brittle deposits may be produced by the use of unsuitable dispersing agents for the tar, excessive tar additions or too high a current density, but the limits imposed are not impractical. Promising results have also been obtained with the addition of the tar preparation to chloride/fluoride tin plating baths.

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