Electrochemical dissolution of tin in methanesulphonic acid solutions

High-rate electroplating of tin on a moving steel strip is generally carrie d out in cells with dimensionally stable anodes. To obtain a matt tin depos it a concentrated acidic tin methanesulphonate solution containing a small concentration of sulphuric acid is used. The concentrated tin methanesulpho nate solution is prepared by dissolution of tin particles with oxygen in a special column. To describe this dissolution process electrode reactions (n amely, reduction of oxygen, hydrogen peroxide and hydrogen ions on a tin el ectrode and oxidation of tin) were studied using electrochemical techniques . It was concluded that on tin, oxygen is almost entirely reduced to water and that H2O2 cannot corrode tin directly, but its decomposition products, for instance oxygen, can. The exchange current density and the charge trans fer coefficient for the investigated electrode reactions are estimated. The dissolution of tin by oxygen is determined by the kinetic parameters of th e oxygen reduction reaction and by the mass transfer of (i) dissolved oxyge n to and (ii) Sn-2+ ions from the tin electrode surface. Hydrogen evolution can be neglected during the dissolution of tin in the presence of oxygen. Moreover, it was found that the rate of tin corrosion increases with (i) in creasing H+ concentration, (ii) oxygen concentration, (iii) convection inte nsity and (iv) temperature. It is likely that the tin surface is not covere d with oxygen during corrosion in pure methanesulphonic acid solutions, but an oxide layer may be present on the tin surface during oxygen corrosion i n pure sulphuric acid solutions. This oxide layer may hinder the oxygen cor rosion of tin.