Real surface area of the aluminium electrode in sodium chloride solution

By combining the techniques of electrochemical slow potentiodynamic, AC impedance and atomic force microscopy (AFM), ii: was shown that the differences in the anodic dissolution rates of Al in 0.5 NaCl solutions as measured experimentally in the potential region between the corrosion and pitting potential, are mainly due to differences in surface roughness of the electrodes used. It was shown that mechanical grinding and polishing of the electrode surface with emery paper (400 grit) and alumina polishing powder (diameter 0.25 mu m) can produce surfaces differing by a factor of 6 in the roughness factor Ra. By using AFM estimates of the roughness factors a true electrode capacitance of 4.63 mu C cm(-2) and thickness d(ox) approximate to 2.0 nm for the barrier layer of the surface film was estamited. The outer part of the film is porous, partly as amorphous AI(OH)(3), or crystalline bayerite (Al2O3.3H(2)O).