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The influence of some sulphur-containing anions on the anodic behaviour of zinc in an alkaline medium

Journal of Electroanalytical Chemistry
Publication Date
DOI: 10.1016/0022-0728(95)04344-6
  • Zinc
  • Anodic Dissolution
  • Passivation
  • Pitting
  • Potentiodynamics


Abstract The anodic behaviour of Zn in 0.1 M NaOH containing various concentrations of Na 2SO 4, Na 2SO 3, Na 2S, Na 2S 2O 3 or NH 4SCN was studied by means of the potentiodynamic technique, complemented by X-ray diffraction analysis and scanning electron microscopy. In the absence of sulphur-containing anions in solution, the cyclic voltammogram displays two anodic peaks in the forward scan prior to reaching the oxygen evolution potential. The first anodic peak A 1 is related to the electroformation of Zn(OH) 2, while the more positive peak A 2 is assigned to the formation of ZnO 2. The reverse scan exhibits a reactivated anodic peak A 3 and one cathodic peak C 1 prior to reaching the hydrogen evolution potential. The presence of either SO 2− 4 or SO 2− 3 stimulates the active dissolution of Zn while the presence of S 2− (and/or SH −), S 2O 2− 3 or SCN − inhibits it, presumably as a result of electroformation of sulphur-containing solid phases preceding the formation of Zn(OH) 2. Also, the presence of one of the cited anions studied in the alkali solution produces pitting of Zn at a certain specific pitting potential. The existence of pitting is confirmed by scanning electron microscopy. The aggressiveness of the sulphur species decreases in the order SCN − > SO 2− 4 > SO 2− 3 > S 2O 2− 3 > S 2−. The pitting potential decreases with increasing concentration of the sulphur species.

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