Abstract
Simultaneous ellipsometric-potentiostatic measurements were used to study film development on mild steel in borate-boric acid buffer solutions at pH 7.4, with and without 0.005M and 0.0025M KCl. Effects of pre-adsorbed films of barium dinonylnaphthalene sulfonate were also determined. Coulometric and ellipsometric film thicknesses of the anodic films agreed reasonably well. Discrepancies increased when pitting occurred because of surface roughening. Chloride ion reduced the passive range and caused increased corrosion at a lower potential. Pre-adsorbed sulfonate films desorbed rapidly under anodic polarization, but were stable for 0.1 to 0.2 volt cathodic. The initial corrosion rate for the bare steel, determined by the Tafel extrapolation and linear polarization methods, was 4 mpy. The pre-adsorbed sulfonate film reduced the corrosion rate to 1 mpy.
