Development of nanostructured coatings for protecting the surface of aluminum alloys against corrosion and ice accretion

Ice and wet snow accretion on outdoor structures is a severe challenge for cold climate countries. A variety of de-icing and anti-icing techniques have been developed so far to counter this problem. Passive approaches such as anti-icing or icephobic coatings that inhibit or retard ice accumulation on the surfaces are gaining in popularity.;Metal corrosion should also be taken into account as metallic substrates are subject to corrosion problems when placed in humid or aggressive environments. Development of any ice-releasing coatings on aluminum structures, as they must be durable enough, is therefore closely related to anti-corrosive protection of that metal.;Accordingly, series of experiments have been carried out to combine reduced ice adhesion and improved corrosion resistance on flat AA2024 substrates via thin films of single and double layer alkyl-terminated SAMs coatings. More precisely, alkyl-terminated aluminum substrates were prepared by depositing layer(s) of 18C-SAMs on BTSE-grafted AA2024 or mirror-polished AA2024 surfaces. This alloy is among the most widely used aluminum alloys in transportation systems (including aircraft), the military, etc. The stability of the coatings in an aggressive environment, their overall ice-repellent performance as well as their corrosion resistance was systematically studied.;The stability of one-layer and two-layer coatings in different media was tested by means of CA measurements, demonstrating gradual loss of the hydrophobic property after ~1100-h-long immersion in water, associated by decrease in water CA. Surface corrosion was observed in all cases, except that the double-layer coating system provided improved anti-corrosive protection.;All single layer coatings showed initial shear stress of ice detachment values of ~1.68 to 2 times lower than as-received aluminum surfaces and about ~1.22 to 1.5 times lower than those observed on mirror-polished surfaces. These values gradually increased after as many as 5 to 9 successive icing/de-icing cycles, implying a certain amount of decay of the coatings. The double-layer coating system initially showed shear stress of ice detachment values about ~2 times lower than as-received aluminum surfaces and ~1.5 times lower than those observed on mirror-polished aluminum surfaces as references. These values gradually increased after as many as 9 successive icing/de-icing cycles.;In addition, the hydrophobic property of coated surfaces was investigated after the icing/de-icing cycle to study their stability after ice releasing, showing therein a decrease in CA values. As a result, the ice-releasing performance of coated samples was found to be time-dependent. The electrochemical studies demonstrated that the corrosion potential of samples covered by single layer hydrophobic coatings increased slightly while their corrosion current density decreased as compared to bare substrate. However, the corrosion potential of samples covered by double-layer hydrophobic coatings increased significantly, and their corrosion current density decreased by 4 orders of magnitude as compared to those on the uncoated samples. These results showed that the used under layer on AA2024 provides particularly enhanced corrosion resistance which would be an excellent approach to improve the anti-corrosive performance of metallic surfaces for outdoor application instead of current-in-use toxic chromate-based coatings. In addition, the electrochemical impedance spectroscopy survey showed a higher phase angle and thus a lower ionic permeation for the double layer coating system, leading to a better insulating property of that coating. These evidences confirm that the BTSE/18C-SAMs behaves close to an ideal capacitor compared to 18C-SAMs alone, as a leaky capacitor. On the other hand, based on results obtained from total impedance vs. frequency, the impedance values are higher for double layer coating compared to single coating, indicating thereby a more packed film with fewer defects.;Finally, this research work revealed the feasibility of preparing coatings combining reduced adhesion of ice to aluminum surfaces and protection against corrosion.