Zirconium Oxide Coating on Anodized Aluminum by the Sol‐Gel Process Combined with Ultraviolet Irradiation at Ambient Temperature

Instead of the conventional sol‐gel process in which heat treatment is used to form a dense composite film after dipping/withdrawing a substrate into/from the sol, a new sol‐gel process incorporating ultraviolet (UV) irradiation at ambient temperature has been attempted to improve the alkaline corrosion resistance of aluminum. A sol‐gel film prepared by UV irradiation at ambient temperature indicated that alkaline corrosion resistance is superior in the range of 2.4 times to 2.6 times that of the conventional composite film heated at 573 K. The densification of the coating layer due to the elimination of residual organics induced by photoexcitation was responsible for the improvement in alkaline corrosion resistance. The high alkaline corrosion resistance of the irradiated film may be attributed to the formation of a dense coating layer and the self‐repairing action caused by repetition for preparation and dissolution of the reactant in the penetrating path of NaOH solution into the composite film.