Abstract
To evaluate effect of hydroxide and chloride ions on dissolution of iron and titanium, anodic polarization behaviour has been investigated in both xNaCl+yHCI and xHCIO4+yHCI solutions (x+y=4.50kmol·m-3). The anodic dissolution of iron in low [H+] -concentrated chloride and highly acidic-low [Cl-] solutions can be interpreted by the hydroxide mechanism. On the other hand, it is explained by the chloride mechanism for highly acidic-high [Cl-] and high [H+] -concentrated chloride solutions. The amount of adsorbed intermediate, ΔQ measured using a channel flow double electrode method increases with decreasing the concentration of [H+] in low [H+] -concentrated chloride solutions and increasing that of [Cl-] in highly acidic-high [Cl-] solutions. X-ray photoelectron spectroscopy shows that the hydroxide mechanism brings. γ-FeOOH and Fe2O3 as the final reaction products, while the products by the chloride mechanism are FeCl2 and FeCl3. The anodic dissolution of titanium is characterized that the hydroxide mechanism does not occur and hydroxide ions act as an inhibitor to the chloride mechanism.
