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 process study of Zn-30Sn high-temperature lead-free solder
The corrosion process of Zn-30Sn high-temperature solder alloy was investigated in neutral 0.5 M NaCl solution at room temperature (25 ± 0.5 °C) by Scanning Electron Microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The surface observation by SEM indicates that the surface morphology of Zn-30Sn evolves from the dense particle structure to porous structure, and finally converts to platelet-like structure. Energy Dispersive X-ray Analysis (EDXA) shows that Zn phase is corroded preferentially due to no Sn compound was observed. The outer surface of corrosion product was confirmed as Zn(OH)<inf>2</inf> by XPS. Dominant corrosion products were characterized as a mixture of ZnO, Zn(OH)<inf>2</inf> and Zn<inf>5</inf>(OH)<inf>8</inf>Cl<inf>2</inf>·H<inf>2</inf>O. The corrosion process was further discussed in detail.
An Ultrasensitive Analytical Method Based on Chemiluminescence Sensing Electrochemical Parallel Catalytic Reaction Event
An ultrasensitive electrochemiluminescence (ECL) method on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed for improving ECL analytical characteristics using vanadate(V) as a representative. Vanadate(V) could be electrochemically reduced to generate vanadate(II) which could be chemically oxidized by potassium periodate to regenerate vanadate(V) and give parallel catalytic wave effect. Then, the reduced product of potassium periodate could react with butyl-rhodamine B to emit a sensitive chemiluminescence signal. The chemiluminescence intensity was correlative with vanadate(V) concentration. The investigation on the electrochemical reaction rate constant (k0) confirmed that the speed of electrochemical reaction was faster than that of the subsequent chemiluminescence reaction. The possibility of the combination of electrochemical parallel catalytic reaction with chemiluminescence signal sensing was proved. The similar ECL behaviors could be observed at zirconia nanowires-Nafion modified electrode. Because of the separation and enrichment effect of the modified electrode on vanadate(V), the selectivity and sensitivity was further improved greatly. Based on these findings, a new concept on the combination of electrochemical parallel catalytic reaction and chemiluminesence signal sensing was proposed and an ultrasensitive ECL method for the determination of vanadate(V) was developed at zirconia nanowires-Nafion modified electrode. Under the optimum experimental conditions, the ECL intensity was linear with the concentration of vanadate(V) in the range of 2.0×10−12 mol/L–2.0×10−10 mol/L. The detection limit was 8.0×10−13 mol/L, which was more than 6 orders of magnitude lower than that observed by electrochemical current transduction for electrochemical parallel catalytic reaction at zirconia nanowires-Nafion modified electrode.