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by two stages: the initial stage corresponded to a single-layer sulphide film which in the second stage was partially superseded by a two-layer film.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.