Real surface area of the aluminium electrode in sodium chloride solution

Abstract

By combining the techniques of electrochemical slow potentiodynamic, AC impedance and atomic force microscopy (AFM), it 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 ((Latin small letter o with stroke) 0.25 μm) 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 μC cm-2 and thickness dox ≈ 2.0 nm for the barrier layer of the surface film was estamited. The outer part of the film is porous, partly as amorphous A1(OH)3, or crystalline bayerite (Al2O3-3H2O).

Pokazano je, kombinovanim korišćenjem tehnika spore potenciodinamike, AC impedance i atomske mikroskopije (AFM), da su razlike u brzinama anodnog rastvarača Al u 0,5 M NaCl u oblasti između korozionog i piting potencijala, a koje se zapažaju u eksperimentima, prvenstveno posledica razlike u površinskoj hrapavosti različito pripremljenih elektroda. Pokazano je da se mehaničkim brušenjem (finoća 400) i poliranjem Al2O3 pastom (0,25 mm) dobija razlika faktora hrapavosti za oko 6 puta. Uz pomoć AFM tehnike za određivanje faktora hrapavosti procenjena je prava kapacitivnost elektroda od 4,63 mF cm–2 i debljina barijernog sloja oksida od dox ≈ 2,0 nm. Spoljašnji porozni sloj je delimično amorfan Al(OH)3 ili kristalinični bajerit (Al2O3.3H2O).