Cathodic reduction of passivation films with two components was used to obtain their chemical composition and to deduce the number of oxide layers. The results obtained agreed with those given by Auger analysis. The effects of pH variation, of molybdenum additions, and of chromium substitution by aluminium or silicon in the alloy are qualitatively deduced from cathodic reduction curves. It also appears that the classification of alloys with respect to corrosion resistance is related to the reduction time of the passivated films, particularly to the length of the Cr2O3 or mixed (Cr1−xXx)2O3 (X = Al or Si) reduction stages.
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