Dissolution and passive film formation of Sn and Sn coated steel using atomic emission spectroelectrochemistry

Atomic emission spectroelectrochemistry (AESEC) was used to quantify simultaneously the rates of Sn dissolution and SnO2 film formation for Sn and Sn coated steel in carbonate solution at pH 11.2. The technique is demonstrated by applying different potentiostatic treatments (variable potential and time) and measuring the amount of oxide formed and Sn dissolved during the treatment, and subsequently measuring the open circuit dissolution rate following the treatment. It is observed that the degree of passivation is a strong function of potential and time. Cathodic and low potential anodic potentiostatic treatments lead to a dissolution–precipitation mechanism that does not significantly passivate the surface. The stability of the passive film was investigated as a function of the quantity of oxide generated.

► First simultaneous in situ quantification of Sn dissolution rate and SnO2 film formation.
► Proposition of a methodology to measure the efficiency of passivation conditions for Sn and Sn coated steel.
► Measurement of the quantity of oxide formed during a passivation treatment, correlation with open circuit Sn dissolution rate.
► A weakly passivating oxide is formed (dissolution–precipitation mechanism) in relatively large quantities at −550 mV vs Hg/HgO.
► A strongly passivating Sn(IV) based oxide is formed in nanometric quantities at 300 mV and above.