Growth and Degradation of an Anodic Oxide Film on Titanium in Sulphuric Acid Observed by Ellipso-microscopy

The surface of polycrystalline titanium polarised anodically in 0.05 mol dm−3 sulphuric acid was monitored using an ellipso-microscope. During dynamic polarisation, a patch-like bright image was seen on an ellipso-microscopic view, and the brightness and image changed with increase in potential. The change in the brightness and image mainly corresponded to growth of an anodic oxide film on the surface. An in situ monitoring using the ellipso-microscope revealed that the film formation rate was dependent on the crystallographic orientation of the substrate. Breakdown of the film induced in a solution containing bromide ions was also monitored using the microscope. Prior to the pitting propagation, the surface was partially changed with flow of a large anodic current. AES measurement revealed that the formation of bromo-oxide resulted in localised film degradation followed by pitting corrosion.