Bioinspired directional structures for inhibiting wetting on super-melt-philic surfaces above 1200 °C

How do surface structures inhibit high-temperature wetting?

Inspired by rice leaves with anisotropic wettability, researchers from Southwest Jiaotong University have created bioinspired directional structures (BDSs) by femtosecond laser ablation, inhibiting the wetting of high-temperature melt (>1200 °C).

This work, published in the International Journal of Extreme Manufacturing, provides a new idea for inhibiting the wetting of molten droplets on the super-melt-philic surfaces under high-temperature conditions.

The most commonly used thermal barrier coatings (TBCs) composed of Y₂O₃-stabilized ZrO₂ are essential for the dependable operation of gas-turbine engines used for aviation, power generation, and marine under high-temperature conditions. When air containing CaO-MgO-Al₂O₃-SiO₂ (CMAS) silicate is ingested into the engines, the TBCs are easily corroded by molten CMAS (commonly melting temperature > 1200 ^oC), leading to the failure and peeling of the TBCs.

As an alternative, inhibiting the wetting and spreading of the CMAS melt on the super-CMAS-melt-philic TBCs is promising to alleviate corrosion from the source. However, there are two major challenges in applying the superhydrophobic principle to decrease the wettability of the molten CMAS to the TBCs. A significant difference in physicochemical properties exists between molten CMAS and water, and commonly employed organic chemical modifiers for superhydrophobicity inevitably suffer oxidation and decomposition at high temperatures, resulting in limited options for modifiers. Creating conventional micro/nanostructures on super-CMAS-melt-philic TBCs generally increases the wettability of CMAS according to the Wenzel model.

Nature always brings us diverse inspirations to develop advanced artificial systems. Unlike lotus leaves, rice leaves show anisotropic wettability because the energy barrier provided by the directional macrogroove arrays hinders the movement of water in the direction perpendicular to the grooves. Can the bioinspired directional structures inhibit the high-temperature wetting of CMAS by providing anisotropic energy barriers?

Using femtosecond laser ablation, the authors fabricate bioinspired directional structures on zirconia surfaces. When molten droplets come into contact with the structured surfaces, if the three-phase contact line (TCL) moves parallel to the groove direction, there is no need to overcome the energy barrier. On the contrary, the motion of TCL perpendicular to the groove direction needs to overcome a certain energy barrier. Due to the presence of anisotropic energy barrier, the wetting of molten CMAS along the radial direction of the structures is inhibited.

The design strategy might provide a new solution for inhibiting the wetting of high-temperature melt on super-melt-philic surfaces.

The researchers are continuing the work, hoping to inhibit the dynamic wetting of high-temperature molten droplets. They also want to make sure that the structures offer good performance for inhibiting the wetting of other high-temperature melt.

About IJEM:

International Journal of Extreme Manufacturing (IF: 16.1, consecutive 1st in the Engineering, Manufacturing category) is a new multidisciplinary and open-access after double-anonymous peer reivew journal uniquely covering the full spectrum of extreme manufacturing.

The journal is devoted to publishing original articles and reviews of the highest quality and impact in the areas related to the science and technology of manufacturing functional devices and systems with extreme dimensions (extremely large or small) and/or extreme functionalities, ranging from fundamental science to cutting-edge technologies that support the manufacturing of high-performance products involving emerging techniques and breaking the limits of currently known theories, methods, scales, environments, and performance.

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