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On the corrosion resistance of porous electroplated zinc coatings in different corrosive media |
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| Authors: | Y Hamlaoui F Pedraza |
| Affiliation: | a Institut des Sciences et Sciences de l’Ingénieur, Centre Universitaire de Souk-Ahras, BP 1553, 41000 Souk-Ahras, Algeria b Laboratoire de Génie de l’Environnement, Université Badji Mokhtar, BP 1223, 23020 El Hadjar-Annaba, Algeria c Laboratoire d’Etudes des Matériaux en Milieux Agressifs (LEMMA), Pôle Sciences et Technologie, Université de La Rochelle, Avenue Michel Crépeau, 17042 La Rochelle Cedex 1, France |
| Abstract: | The corrosion resistance of an electroplated (EP) Zn coating whose surface was chemically etched to produce surface defects (pores) is investigated in this work. Impedance and DC polarisation measurements were employed to study the behaviour of such coating in various corrosive media (NaCl, NaOH and rain water). Four different faradaic relaxation processes were clearly revealed in different NaCl concentrations (from 0.1 to 1 M). In the most concentrated solutions at least three relaxation processes at low frequencies (LF) appeared and were related to zinc deposition and dissolution. At lower concentrations and depending on the pH, only one process was observed. The charge transfer resistance (Rct) and the corrosion current (Icorr) were practically stable in the pH range 5-10. In deaerated NaCl 0.1 M, the EIS diagrams showed two time constants at very close frequencies. From the EIS diagrams the porous nature of the coating was highlighted and showed that the dissolution mechanisms occurred at the base of the pores. |
| Keywords: | A Electroplated zinc coating A Pores B Electrochemical impedance spectroscopy C Corrosion |
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