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.
Anodic passivation of tin in slightly alkaline solutions
Abstract The anodic oxidation of tin in 0.2 M borate buffer solution has been studied by potentiodynamic, potentiostatic and galvanostatic techniques. It was found that although a large amount of charge is consumed during anodic oxidation, only a fraction of this charge is involved in film growth. The initial stages of metal passivation under dynamic conditions are best described by Mueller's dissolution—precipitation model. Under potentiostatic conditions two different equations describe the kinetics of film formation. For anodic potentials lower than 1.6 V vs sce a logarithmic dependence holds between cathodic charge and time. At higher potentials, the growth rate is controlled by a nucleation process and the rate law is more complicated. Under galvanostatic conditions the logarithms of the growing time is proportional to the inverse of the cathodic charge. These results are discussed in terms of theories of film growth.
Symptomatic Trans-sexualism
A 24-year-old male schizophrenic had a delusion that he was female and had lived his life as a woman for almost two years. Unlike the only other reported case, his ‘symptomatic transsexualism’ responded to the effective treatment of his schizophrenia.