Electrochemical studies on pitting corrosion of tin in sodium borate solutions containing nitrate ions

The purpose of this paper is to study the electrochemical behavior of Sn electrode in Na₂B₂O₇ solutions in the absence and presence of NaNO₃ as a pitting corrosion agent.

The electrochemical behavior of Sn electrode was studied by using cyclic voltammetry and potentiodynamic polarization measurements and complemented with scanning electron microscopy examinations.

This paper shows that in the absence of NO₃ − ions, the anodic polarization of Sn electrode exhibits active/passive transition. Addition of various concentrations of NO₃ − anions to the borate solution enhances active anodic dissolution and tends to break down the passive oxide film at a certain pitting potential. The pitting potential, and hence the pitting corrosion resistance, decreases with increasing NO₃-ion concentration and temperature but increases with scan rate and repetitive cycling. Addition of CrO₄²⁻, WO₄²⁻ or MoO₄²⁻ oxyanions to the borate nitrate solution inhibits the pitting corrosion of Sn.

This is the first study that shows the effect of NO₃ − ion as a pitting corrosion agent.