Controlling limiting length of tunnels on Al foil electroetched in
HCl-H2SO4 solution
HCl-H2SO4 solution
(Beijing Key Laboratory for Corrosion, Erosion and Surface Technology,
University of Science and Technology Beijing, Beijing 100083, China)
University of Science and Technology Beijing, Beijing 100083, China)
Abstract: The limiting length of tunnels, llim, of Al foil electro-etched in HCl-H2SO4 solution and the corresponding anodic polarization curves in the same solution were measured. It is found that there is a dependence of llim on the potential difference, ∆φ, between the pitting potential, φpit, and the corrosion potential, φcorr, of Al foil, when the temperature and H2SO4 concentration of HCl-H2SO4 electrolyte are changed. The dynamic equation on the tunnel growing and the linear equation between llim and ∆φ were deduced by analyzing the relationship among the over-potential on Al foil surface, the transport over-potential in tunnel solution and the over-potential at tunnel tip during the electro-etching. The results show that the growing velocity of tunnels decreases with their extending in length and the changing trend of llim can be judged by measuring ∆φ, which supplies a , convenient access to explore new kinds of etchants.
Key words: electrolytic capacitor; aluminum foil; electro-etching; anodic polarization; pitting