Ice protection is an important issue in the aeronautic field, which has been traditionally faced by the use of active systems (systems that need energy support). In last decades, the use of several passive solutions, based on surface engineering strategies, has been explored to replace the active systems, or to decrease their energy consumption. However, so far the idea of completely avoiding ice accretion with a passive system seems utopic. In addition, ice accretion affects different sections of aircrafts, but to present, a single method efficient in all possible icing locations, has not been found. Thus different solutions must be designed for each specific application, and testing should be undertaken attending to the different location issues.

For instance, electrothermal active systems are widely used to protect sensible areas on aircrafts, i. e. leading edges. Those systems increase the surface temperature to avoid ice accretion or release or melt the ice once it has been accreted. As a result, icing in the downstream area of the wing’s chord is caused by exposure to this ice-melted water droplets as well as to direct supercooled water. This is considered as secondary or runback icing resulting in an important challenge in aviation, and the use of anti-icing solutions can perhaps contribute to avoid or reduce this issue.

In this work, 12 materials and references, attending to 5 different anti-icing strategies have been tested using a common methodology. These include Slippery Liquid Infused Porous Surfaces (SLIPS), elastomer coatings, superhydrophobic surfaces and low surface energy materials. The test methodology includes the evaluation of ice adhesion after impact icing in an icing wind tunnel (IWT) as well as ice accretion through direct impinging of supercooled droplets and after melting or heating in an active system in the IWT.

Among the studied materials, several coatings showed ice accretion reduction and some of them also significantly reduced ice adhesion. In general, 2 strategies showed more promising results in terms of anti-icing features: SLIPS and elastomeric coatings. In addition, low roughness, low surface energy and high water droplet mobility (low contact angle hysteresis) were correlated with anti-icing behaviour. These are easy to measure properties which do not require complex equipment that can be considered as indicators of potentially good anti icing and de-icing performance. Results also showed that superhydrophobic solutions reduced runback icing as a result of a reduced interaction of the melted ice droplets with the surface.

Ice accretion can adversely impact many engineering structures in commercial and residential sectors. Although there are many reports of low-ice-adhesion-strength materials, a scalable and durable deicing solution remains elusive, as ice detachment is dominated by interfacial toughness for large interfaces. In this work, two durable quasicrystalline coatings (QC1 and QC2) were applied on aluminum substrates using HVOF thermal spray. XRD confirmed the quasicrystalline phases. Except for the roughest QC2 sample (root-mean-squared roughness ≈ 7 μm), a toughness-mediated regime of fracture was observed when detaching longer lengths of ice from the quasicrystalline coatings. The interfacial toughness was calculated to be 0.9 J/ m² for the smoothest QC1 sample (root-mean-squared roughness ≈ 1.5 μm) and 1.1 J/m² for the smoothest QC2 sample (root-mean-squared roughness ≈ 0.3 μm), demonstrating that low-interfacial toughness coatings are possible to fabricate from metallic materials. Apparent shear strengths as low as 30 and 80 kPa at an ice length of 20 cm were observed for QC1 and QC2, respectively. A small imposed deflection could also dislodge 20 cm-long pieces of accreted ice adhesively. Interfacial toughness increased with surface roughness in line with the concept of a shielding factor that hinders crack propagation. Finally, the mechanical durability of the smoothest QC1 and QC2 samples was confirmed using abrasion, UV irradiation, pencil scratching, elevated temperature, and chemical contamination. Overall, thin quasicrystalline coatings exhibit the unique combination of low interfacial toughness and high durability, leading to long-lasting ice protection applicable to many different surfaces.