"Robust Self-Cleaning Surfaces from Suspension HVOF Sprayed Rare Earth Oxide Ceramics Coatings"

Self-cleaning surface is usually achieved by coating with polymeric modifiers, which however are not durable against harsh environment. A known family of rare-earth (RE) oxide ceramics have recently been found to exhibit intrinsic hydrophobicity, even after exposure to high temperatures and abrasive wear. In this work, CeO₂ coatings were developed for hydrophobic application using suspension high velocity oxy-fuel (SHVOF) spraying on to a selection of alloy substrates including nickel superalloy, stainless steel, and aluminium alloy. A commercial aqueous suspension with a solid concentration of 30 wt.% sub-micron CeO₂ particles was sprayed under different flame heat powers by changing the flow rate of fuel gas (hydrogen) and oxygen. This resulted in significant differences in coating properties and their hydrophobic behaviour. SHVOF sprayed CeO₂ coatings provided unique topographical features which resulted in super-hydrophobic self-cleaning surfaces with contact angles over 150 degrees. Field emission gun scanning electron microscopy (FEG-SEM), X-ray Diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were used to analyse the coatings’ surface morphology, cross-sectional microstructure, phase and surface chemistry. The present approach to the production of water-repellent surfaces from RE oxide coatings using SHVOF has provided the advantages of mechanical robustness with practical applications onto alloy components.