Dissolution behavior of anodic oxide films formed in sulfanic acid on aluminum

摘要

Chemical dissolution of the barrier layer of porous oxide films formed on an aluminum foil (99.5% purity) in 1.5 M sulfanic acid after immersion in a 2 mol dm~(-3) sulphuric acid at 50 deg C was studied.The barrier layer thickness before and after dissolution was determined using a re-anodizing technique.Re-anodizing was conducted in 0.5 mol dm~(-3) H_3BO_3/0.05 mol dm~(-3) Na_2B_4O_7 solution.We found that the change in the porous oxide growth mechanism was observed at the anodizing voltage of 30 V.Taking into account this result chemical dissolution behaviour of the barrier layer of porous films formed at 20 V and 36 V and also the influence of annealing of oxide films at 200 deg C were studied.We showed the interplay between the dissolution rates and charge distribution across the barrier layer.We conclude that the outer and middle layers have negative space charges and the inner layer has positive space charges.