Copper used underground is exposed to natural water in which bicarbonate, phosphate, chloride and sulfate ions are the principal anions usually present [Gilbert (1988); Larochelle et al. (1988)]. Each ion plays a different role in accelerating or hindering the dissolution of the metal depending on the ion concentration, potential, pH range temperature and other ambient conditions. The ions also influence the physical and chemical properties of the film even if they are not detectable on the surface. In practice tin is used as an electrodeposited coating on steel and copper to protect them against corrosion and is therefore exposed to attack by solutions mentionned above.

Recently, we investigated the electrochemical behavior of tin [Drogowska et al. (1991)] and copper [Drogowska et al. (1992, 1993); Milosev et al. (1992)] in the presence of bicarbonate and phosphate ions in aqueous solutions together with the effect of different concentrations of chloride and sulfate ions.  In alkaline or neutral bicarbonate [Drogowska et al. (1991, 1992, 1993); Milosev et al. (1992)] and phosphate [Drogowska et al. (1991, 1992, 1993)] solutions, a highly passivating film forms on the surface of copper and tin.  Extensive research has shown that passive films generally grow as bilayers, consisting of a defective, crystalline solid barrier layer and a precipitated upper layer formed by hydrolysis of the cations rejected from the base.  In bicarbonate and phosphate solutions, a higher concentration of bicarbonate or phosphate causes an increase in the anodic current, indicating that homogeneous dissolution of copper and tin surfaces occurs in both solutions, although the presence of chloride or sulfate ions is necessary to promote localized corrosion.

The present review deals mainly with the passivation and localized attack of copper and tin in near-neutral aqueous solutions of pH 8, as investigated in Refs. [Drogowska et al. (1991, 1992, 1993); Milosev et al. (1992)].