X-RAY PHOTOELECTRON SPECTROSCOPY (XPS) AND CURRENT CAPACITY STUDY OF Al-Zn AND Al-Zn-Sn ALLOYS DISSOLUTION BEHAVIOUR IN TROPICAL SEAWATER

Abstract

The passivation of the Al-Zn-xSn alloys can be explained by the spontaneous formation of a protective oxide film that further impedes the reaction of aluminium with aggressive environments. The properties of corrosion product and oxide layer on Al-Zn-xSn alloys in tropical seawater were studied at room temperature using current capacity measurements and X-ray photoelectron spectroscopy (XPS) techniques. The results showed that alloying addition was observed to influence the electrochemical behaviour of this alloy. The current capacity measurement showed that 0.5 Sn (wt.%)
improved the anode performance by increasing its current efficiency. However, further increase of the wt.% of Sn produced a negative impact on the alloys by reducing the value of its current efficiency. The presence of 1.5 Sn (wt.%) in the alloy increased the formation of local cathodic sites and thus, reduced anode efficiency to only 70%. The study also showed that the alloys with low Sn content and impurities (Fe) produce anode efficiency of up to 85%. Based on the XPS analysis, the oxide film formed on the Al-Zn-xSn alloy consists of a mixture of SnO and SnO2, which play a key role in
creating oxide layer defect, reducing the electrical resistance at metal-electrolyte interface and activating the electrochemical dissolution on the alloy surface.

Keywords: Al-Zn-Sn alloy; oxide layer; x-ray photoelectron spectroscopy (XPS); electrochemical;
current capacity.

Description