Repassivation kinetics of pure aluminium in aqueous alkaline solutions using the abrading electrode technique

The repassivation kinetics of pure aluminium has been studied as functions of applied anodic potential and pH in alkaline solutions by using the abrading electrode technique. The repassivation rate of the abraded bare surface of pure aluminium increased with increasing applied anodic potential, whil... Full description

The repassivation kinetics of pure aluminium has been studied as functions of applied anodic potential and pH in alkaline solutions by using the abrading electrode technique. The repassivation rate of the abraded bare surface of pure aluminium increased with increasing applied anodic potential, while it decreased with increasing pH of the solution. These results reveal that the growth rate of passivating oxide film is enhanced by applied electric field, but it is lowered due to the chemical attack by hydroxyl ions. Based upon the experimental results, the repassivation kinetics of pure aluminium in aqueous solution can be classified into three groups with pH of the solution. A single- staged behaviour in anodic current transient appears in weakly alkaline solution below 0.001 M NaOH in 0.5 M Na sub 2 SO sub 4 in which the oxide dissolution rate is very low. In contrast, when the oxide dissolution rate is intermediate (0.001 M and 0.1 M NaOH+0.5 M Na sub 2 SO sub 4 ), the anodic current transient shows a two-staged behaviour which results from the attack by OH exp - ions. Otherwise, in the case the oxide dissolution rate is very high above 1 M NaOH in 0.5 M Na sub 2 SO sub 4 , a three-staged behaviour in anodic current transient was observed: high repassivation rate in the initial stage due to a high formation rate of the oxide film on the abraded bare surface; zero value of the repassivation rate in the second stage due to the dissolution of the oxide film by the attack of OH exp - ; high repassivation rate in the third stage due to a lowered dissolution rate of the oxide film.