ATOMIC FORCE MICROSCOPY STUDY OF PIT FORMATION DURING ANODIC ETCHING OF ALUMINUM

摘要

Atomic Force Microscopy (AFM) was used to investigate the topographic characteristics of pitting sites during anodic galvanostatic etching of high-purity aluminum foils in hot baths containing HC1 and H_2SO_4. For as-received foils, surface pits nucleate only during the first 150 ms of etching at potentials as much as 3-4 V higher than the pitting potential. Pit sites near ridges are strongly preferred to an extent which depends on the purification process used in foil manufacture. Pit sites are more numerous and evenly distributed after pretreatment in NaOH, and can be activated at low potentials. In situ AFM observations of NaOH treated foils at room temperature in 1 M HC1 and 1 M H_2SO_4 show that a large number of dissolution sites are produced during NaOH immersion.