Open-Circuit and Potentiodynamic Study on the Electrochemical Behavior of Tin Electrode in Sulphuric Acid and Sodium Hydroxide Solutions

Abstract

The electrochemical behavior of tin electrode in H 2 SO 4 and NaOH solutions is studied in details using open-circuit potential measurements and potentiodynamic polarization techniques. The identification of the elements present in the surface of specimen after immersion in the two test solutions is performed using an energy dispersive X-ray analysis (EDX).Open-circuit potential measurements show that for tin electrode in low concentrations of H 2 SO 4 and NaOH solutions the passivity was increased with dilution. At higher concentrations, dissolution of the pre-immersion oxide film occurs in which the corrosivety of NaOH is higher than that of H 2 SO 4 solutions. Passivation of tin in NaOH solutions appears to take place in two steps. The first involves formation of SnO or Sn(OH) 2 , in the second step oxidation to Sn(OH) 4 takes place.Potentiodynamic polarization techniques illustrate that the dissolution of tin in sulphuric acid occurs through the participation of both OH¯ and SO 4 2-ions through an intermediate of (SnHSO 4 OH) species. The potentiodynamic curves for tin in sodium hydroxide solutions exhibits an active/passive transition. The active dissolution region involves two anodic peaks prior to permanent passivity. The first anodic peak is due to the formation of Sn(OH) 2 while the second peak corresponded to the formation of Sn(OH) 4 in addition to the formation of the soluble stannate ions. Dehydration of unstable Sn(OH) 4 to the stable SnO 2 can occur on the tin electrode during the potential sweep to positive direction. Increasing concentrations of H 2 SO 4 and NaOH solutions led to enhance the corrosion current (i corr. ), and corrosion potentials (E corr ) shift towards more negative values. EDX analysis showed that Sn % present on the surface of tin electrode in 1M of each of NaOH and H 2 SO 4 solutions was 91.82 and 83.52 respectively.