Electrochemical behavior of Sn-xZn lead-free solders in aerated NaCl solution
Electrochemical corrosion behavior of Sn-xZn solder alloys (i.e. hypoeutectic Sn-6.5Zn, eutectic Sn-9Zn and hypereutectic Sn-12Zn, in wt.%) in aerated 0.5 M NaCl solution was investigated by electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques, aiming to assess the effect of Zn content on the corrosion behavior of Sn-Zn alloys. Scanning electron microscopy (SEM) equipped with EDX, X-ray diffraction (XRD) were performed to characterize the surface morphology and to identify the chemical composition of the corrosion products, respectively. It is found that increasing Zn contents lead to an increase in corrosion current density and the corrosion potential shifted towards more negative values, revealing that the corrosion rates increase in the order of: Sn-6.5Zn <; Sn-9Zn <; Sn-12Zn. The acquired electrochemical impedances were successfully fitted with an equivalent circuit model. Fitted results reveal that total impedance decreased with increasing Zn content, indicating that Sn-6.5Zn alloy exhibits the highest corrosion resistance. The results are further confirmed by surface morphology characterization of the corrosion products, which shows a more homogeneous product film for lower Zn content. Analysis of the corrosion products indicates that oxide hydroxychlorides are the dominant corrosion products. Based on the obtained results, it is suggested that Sn-Zn alloy with lower Zn content appears to be more attractive in terms of superior corrosion resistance.
Corrosion characterization of tin–lead and lead free solders in 3.5 wt.% NaCl solution
Abstract The corrosion resistance of Sn–Pb and several candidate lead free solders were investigated in 3.5 wt.% NaCl solution through potentiodynamic polarisation. Results showed that in NaCl solution lead free solders had better corrosion resistance than Sn–Pb solder and the corrosion resistance of lead free solders was similar, but the corrosion resistance of Sn–Ag solder was better than that of Sn–Ag–Cu and Sn–Cu solders. The corrosion products for Sn–Pb solder had a two-layered structure with Sn-rich phases at the outer layer and looser Pb-rich phases at the inner layer. The loose Pb-rich layer was detrimental to the corrosion property. The corrosion product on the surface of all these solders was tin oxide chloride hydroxide.
Inhibition of copper corrosion by isatin in aerated 0.5 M H2SO4
The corrosion inhibition of commercial copper by means of isatin was studied in aerated 0.5 M H2SO4 in the temperature range 25–55 °C using weight-loss, potentiodynamic and spectrophotometric tests, and determination of double layer capacitance. Inhibition efficiencies up to 94% in the concentration range of 1×10−4–7.5×10−3 M of isatin were obtained. The corrosion rates estimated with weight-loss measurements were higher than those correspondingly determined with the potentiodynamic test, especially at higher concentrations of inhibitor. This is in accord with other researches that have pointed out the limitation of the Tafel line extrapolation method in the determination of corrosion rates. The kinetics of cuprous and cupric ion formation and UV–visible spectra support the formation hypothesis of a complex between copper and isatin. The adsorptive behaviour of isatin on copper 0.5 M H2SO4 was also investigated.