Electrochemical behaviour of bismuth in HCl solutions

Measurements of open circuit potential and electrochemical impedance spectroscopy (EIS) at open circuit condition have been employed to characterize the behaviour of the mechanically polished bismuth surface in hydrochloric acid solution of various concentrations (0.01–1.0 M). The air-formed (pre-immersion) bismuth oxide grows on the surface in all the test solutions, but its thickness decreases as the HCl concentration increases. The impedance results showed that bismuth surface reactivity towards oxide thickening decreases as chloride ions concentration increases as a result of their aggressiveness nature. The equivalent circuit model for fitting the spectra of the EIS data of bismuth in HCl solution indicated that the mechanism of Bi corrosion is controlled by the charge-transfer and diffusion processes. The mechanically polished bismuth surface was examined by scanning electron microscopy before and after immersion in 0.023 M HCl solution. The scanning electron micrographs have shown that the flawed regions formed on the mechanically polished Bi surface were repaired after immersion in the acid solution due to thickening of the oxide film.