Surface Analysis and Electrochemical Behavior of Aluminum Pretreated by Vinyltriethoxysilane Films in Mild NaCl Solution

Electrochemical characteristics, composition and surface morphology of vinyltriethoxysilane (VTES) coatings on aluminum were investigated. The silane coatings were deposited chemically, by immersion in 2 and 5% VTES, and then cured at 100°C during 10 or 30 min. Surface morphology of VTES films was analyzed by scanning electron microscopy, while the composition was investigated by X-ray photoelectron spectroscopy. The corrosion stability of silane coatings was determined by electrochemical impedance spectroscopy in 0.03% NaCl. The results obtained were compared with the standardized analysis in the salt spray chamber. The percentage of the corroded area was determined by optical microscopy coupled with image analysis. The influence of VTES concentration and curing time on the corrosion stability of silane films on aluminum was shown. The highest corrosion stability was obtained for silane films deposited from 5% VTES solution with 30 min curing, while the lowest stability was determined for silane films deposited from 2% VTES solution with 10 min curing. Surface analysis suggests that the coatings with the highest corrosion stability are related to the intensive siloxane bonding (Si–O–Si), which is favored by deposition from more concentrated VTES solution.