Electrochemical behavior of tin in sodium borate solutions and the effect of halide ions and some inorganic inhibitors

The corrosion of tin electrode in sodium borate (Na2B4O7) solutions was investigated using cyclic voltammetry and potentiostatic current transient techniques. In absence of halide ions, the E/j response exhibits active/passive transition. The active region involves one anodic peak corresponding to the formation of Sn(OH)2 and/or SnO. Addition of Cl−, Br− or I− (C ⩽ 0.01 M) ions inhibits the active dissolution of tin, but higher concentrations enhance the active dissolution and tend to breakdown the passive film and induce pitting attack. The effect of WO42-, MoO42-, NO2- and NO3- as inorganic inhibitors on the pitting corrosion of tin in (0.1 M Na2B4O7 + 0.1 M NaCl) solution has also been studied. The presence of these anions (except NO3-) inhibits pitting corrosion. Chronoamperometry measurements showed that nucleation of pit takes place after an incubation time (ti). The rate of pit nucleation (ti-1) increases with increasing halide ions concentration and applied potentials, but decreases with increasing the concentration of the inorganic inhibitors (except NO3-). The inhibition efficiency of these inhibitors decreases in the order:WO42−>MoO42−>NO2−