Effect of sulphate and molybdate ions on pitting corrosion of aluminium by using electrochemical noise analysis

The effects of sulphate and molybdate ion additives on the pitting corrosion of pure aluminium were investigated as a function of anion concentration by using potentiodynamic polarisation experiment and electrochemical noise measurement. The cumulative probability determined from shot-noise theory was quantitatively analysed by using the Weibull distribution function based upon a stochastic theory. From the statistical variation in the frequency of events, it was found that the width of the distribution of the frequency of events was broader in the presence of sulphate ions. On the other hand, the distribution of the frequency of events shifted to a lower frequency region in the presence of molybdate ions. From the results, it was concluded that both sulphate and molybdate ions retards the pit initiation. Moreover, from the two linear regions in one Weibull probability plot, it was concluded that pitting corrosion was clearly distinguished from uniform corrosion in the stochastic analysis.