Process Optimization for Superhydrophobic CeO2 Coatings via Solution Precursor Plasma Spraying Using an Aluminum Arc-Sprayed Bond Coat

Abstract

This research engineers a high-performance superhydrophobic composite system by synergizing an Al arc-sprayed bond coat with a nanostructured CeO₂ topcoat deposited via solution precursor plasma spraying (SPPS). The objective was to utilize the intrinsic micro-roughness of the arc-sprayed layer to stabilize a Cassie–Baxter wetting state without organic modifiers. Optimization of the SPPS process identified the critical parameters for achieving a hierarchical topography: a standoff distance of 7 cm, a liquid feed rate of 42 rpm, a transverse speed of 500 mm/s, and a total of 4 spray passes. This optimized protocol leveraged the “shadowing effect” of the Al bond coat (Ra ~ 13µm), resulting in a 90% reduction in the required spray passes compared to conventional coatings on smooth substrates. Microstructural analysis confirmed the formation of a phase-pure CeO₂ topcoat with a refined crystallite size of 81 nm. The resulting hierarchical architecture yielded a water contact angle of 151° and a contact angle hysteresis of 2°. Mathematical modeling via the Cassie–Baxter equation quantified a liquid–solid contact area fraction of 0.04, indicating that 96% of the droplet base was supported by trapped air pockets. Electrochemical performance evaluated via potentiodynamic polarization and electrochemical impedance spectroscopy after 96 hours of immersion in 3.5 wt.% NaCl demonstrated superior durability. The Al-CeO₂ composite exhibited a 128% increase in corrosion resistance and a 50.5% reduction in the corrosion rate compared to the bare Al bond coat. While the single-layer benchmark system experienced a 95.5% reduction in coating resistance due to electrolyte infiltration, the optimized Al-composite restricted degradation to 40%. Surface chemistry analysis via x-ray photoelectron spectroscopy revealed that the transition to superhydrophobicity is governed by the spontaneous adsorption of airborne volatile organic compounds, ensuring chemical stability up to 450°C. These results establish a robust, industrially scalable manufacturing route for protective coatings in aggressive marine environments.