Sulphide Tarnishing of Tin in Alkaline Polysulphide Solutions I. Kinetics of film formation and simultaneous dissolution

Abstract

The kinetics of sulphide tarnishing of tin in potassium polysulphide–sodium hydroxide solutions has been investigated at temperatures in the range 22–95°c. The tarnished samples were analysed by coulometric reduction and examined by scanning electron microscopy. The growth rate of the tin sulphide film was usually characterised by two stages: the initial stage corresponded to a single-layer sulphide film which in the second stage was partially superseded by a two-layer film. Simultaneous dissolution of the film was also observed and was most marked in the areas covered by a two-layer film. An analysis of the kinetic data is presented in terms of two separate sulphide growth processes.