Detection of Initial Stage of Aluminum Corrosion in NaCl Solution Utilizing Surface Plasmon Resonance

Surface plasmon resonance (SPR) spectra on Al films in the Kretschmann configuration is investigated aiming at the rapid detection of the Al corrosion in NaCl solution. The angle of the dip, occurred in the SPR spectra, was observed to decrease in the first 20 min and then increase with the increase of the immersion time. Calculations based on a simple multilayer model suggest that the observed initial decrease and the subsequent increase in the dip angle correspond to the thinning of the oxide layer and that of Al, respectively. The model also explains the observed deepening of the dip. The decrease in the effective Al thickness is estimated to be about 10 nm after the immersion in 3 wt% NaCl solution for 20 hours, though the quantitative discussion becomes difficult for longer immersion time. The corrosion is surely detectable for the change smaller than 5 nm in the effective Al thickness corresponding to the immersion time of 2 hours. The results indicate that the SPR-based method is promising for detecting the initial stage of Al corrosion in nanoscale.