Ice Phobic Coating Associated to Low Power Electromechanical Deicers

Executive Summary:

Ice adhesion and accretion on surfaces such as aircraft presents long recognised problems with respect to safety, efficiency and operational costs. Current active ice removal methods, such as electromechanical de-icers, are often based on melting or breaking already formed ice layers. In addition to their undesired weight and design complexity, these active anti-icing approaches require substantial energy for their operation. Passive solutions such as icephobic coatings have also been evaluated with varying success. Recently, coatings preventing ice accretion have been the subject of more attention stimulated by the remarkable water repellent properties of superhydrophobic surfaces. If superhydrophobic coatings are also not able to fully prevent ice accretion, the development of highly efficient hybrid low power systems combining active electromechanical de-icers and passive icephobic coatings remains highly promising to reduce the ice adhesion. This development and the design optimisation of a hybrid solution require a deeper understanding of the links between superhydrophobicity and anti-icing properties.

To this end, the ICEAGE project aimed at evaluating superhydrophobic coatings regarding ice adhesion reduction and erosion resistance in combination with electromechanical de-icers. Two types of nanostructures (pillars and holes) with two lateral sizes (100 and 500 nm) have been created with selected resins, regarding their elasticity and structurability (deliverable D3.1). These nanostructures have been generated by combining nanosphere lithography, etching, and replication techniques. Holey samples are expected a) to be more erosion resistant than pillared ones, and b) to prevent the formation of strongly adhering ‘Wenzel ice’ (ice penetrating inside the structures).

Produced samples have been tested regarding the ice adhesion, and the resistance to cracking and erosion. Based on agreed specifications (D1.1), dedicated set-ups have been designed and fabricated (D2.2). The samples exhibited all a good cracking resistance (no delamination) along with an exceptionally low ice adhesion (shear strength < 50 kPa), 10 times lower than the ice adhesion of reference surfaces, i.e. aluminium and commercial coatings (D1.2). Moreover, this ice adhesion of the ICEAGE samples remains low over a large temperature range down to -45°C. Finally, the erosion test demonstrated that the holey samples with a large size (500 nm) exhibit the best erosion resistance of the structured samples. Nevertheless, erosion resistance may be improved by selecting a better resin. In addition to indoor tests, outdoor exposure and bombardment with a snow gun have been performed (D2.3). Surprisingly, the small pillared sample (100 nm) showed a good resistance to the exposure test. In addition, all the nanostructured samples resisted very well to the snow gun test compared to the reference samples, confirming the ranking of the ice adhesion test.

The low ice adhesion nanostructured layer is foreseen to be coated on the metallic surface of an electromechanical de-icer. Based on experimental conditions proposed by the Topic member, vibration modes of a coated aluminium plate have been determined to shed the ice layer (D2.1).

In order to prepare a more realistic ice wind tunnel test, large samples (A4 sized) have been prepared with two highly promising nanostructures: large holes and small pillars (D3.2). A step-and-repeat process has been designed to form these large area samples from an elementary 7x7 cm sized nanostructured block. After the hydrophobisation step, the produced samples exhibit a similarly high water contact angle as the equivalent small samples. These large area samples are expected to be evaluated in icing wind tunnel to confirm the excellent anti-icing performances measured in the lab (D4.1).