The accumulation of ice on the surface of aircraft inevitably leads to a change in their shape, which can entail such negative phenomena as an increase in aerodynamic drag and a decrease in lift. And in the event of icing of the measuring and control equipment, the controllability of the apparatus is also violated. To combat icing, special reagents are usually used - anti-icing agents. But large surface areas of aircraft require large amounts of chemicals, which are expensive and harmful to the environment.

Specialists from the Institute of Physical Chemistry and Electrochemistry. A. N. Frumkin of the Russian Academy of Sciences (IPCE RAS) proposed a fundamentally different approach to solving the problem. They have developed coatings on aircraft aluminum alloys that can prevent surface icing of structural elements and aircraft equipment. The secret of coatings is their hydrophobicity - they are practically not wetted with water. On superhydrophobic coatings, a drop of water takes an almost spherical shape and rolls down even with a slight inclination of the surface - less than 10 ° (optimal - 3-4 °). As a result, ice does not form on the surface.

The first such superhydrophobic coatings were described by researchers from the Institute of Physics and Chemistry of the Russian Academy of Sciences in their article published in 2017 in the journal ACS Nano. The method of obtaining superhydrophobic coatings on an aluminum magnesium alloy is based on laser treatment of the alloy surface with subsequent chemical adsorption of a hydrophobic agent - fluorooxysilane. The metal surface is irradiated with ultrashort (nanosecond) laser pulses. Moreover, the laser beam "passes" over the metal surface many times. Such ultra-short pulses of IR laser radiation have a high energy, upon absorption of which the material evaporates, and as a result of several such laser passes, the metal surface acquires a texture - a hierarchical roughness. It is also called multimodal texture.

Irradiation of the surface of a metal alloy occurs in air, in the presence of atmospheric gases, and the interaction of powerful radiation with a metal surface is accompanied by a chemical reaction with these gases. The surface compounds formed in this process change the physicochemical properties of the surface layers, including their adsorption capacity.

The hydrophobicity of the surface is an important but insufficient property for materials used in structural elements of aviation technology, experiencing mechanical and thermal loads. The hydrophobic coating must be durable, corrosion-resistant and resistant to UV radiation, which inevitably affects aviation materials during flights.

Researchers at the Institute of Physics and Chemistry of the Russian Academy of Sciences focused their new research on a thorough study of the mechanisms that contribute to the chemical and mechanical strength of superhydrophobic coatings and on the selection of optimal laser treatment modes for their production. They changed two adjustable parameters: the speed of the laser beam and the line density as it travels over the surface. By changing these parameters of multi-pass processing, it is possible to create a surface layer with precisely specified properties, including one that is resistant to various influences. Considering that multi-pass slows down the production process, it was important to choose such a mode for creating a stable superhydrophobic coating that would not compromise the economic efficiency of the processing process.

Kirill Emelianenko, Senior Researcher of the Institute of Physical Chemistry and Mathematics, Ph.D. in Physics and Mathematics, and his colleagues conducted many experiments, changing the modes of laser texturing of the surface, and selected the most suitable ones, that is, those in which a layered multicomponent structure is formed that meets all the requirements.

The top nanostructured coating layer is mainly composed of aluminum oxide, which reflects UV rays, which provides UV resistance. However, this layer is not very resistant to abrasive loads that arise during collisions of a surface moving at a high speed with dust particles. The underlying layer contains nanoinclusions of aluminum oxynitrides, which provide high abrasive, chemical and corrosion resistance of the coating (acid and alkaline precipitates falling on the metal surface can act as corrosive agents in the atmosphere in addition to water). And, finally, the third, deep layer with large pores dampens (dampens) the arising mechanical stresses and prevents the appearance of cracks.

“We have proposed significantly faster modes of laser processing without reducing the required functional properties: a new family of coatings is processed one and a half to four times faster,” says Kirill Emelianenko. - This is important for aviation, since, as a rule, the elements of aviation equipment subject to icing are of a fairly large size. In addition, the new coatings are resistant to UV radiation from the sun - very few superhydrophobic coatings have been described in the literature. 

such a property. Again, this is very important, because at high altitudes, the effect of ultraviolet radiation is very significant. "