Control of the hydrophobicity of rare earth oxide coatings deposited by solution precursor plasma spray by hydrocarbon adsorption

The basis of the hydrophobicity of lanthanide rare earth oxides(REOs)has been the subject of considerable debate.To explore this question,the wetting behaviors and surface compositions of hierarchicallystructured Yb_(2)o_(3)(one of the REOs)coatings and non-REO Al_(2)o_(3)coatings deposited via solution precursor plasma spray process were investigated in this work.The Yb_(2)o_(3)coatings were subjected to a number of post-deposition treatments including vacuum(1-15 Pa)treatment,Ar-plasma treatment,heat treatment(400℃),long-time air exposure and ultra-high vacuum(1×10^(-7)Pa)treatment.Subsequent characterization showed that different post-deposition treatments resulted in different wetting behavior for the Yb_(2)o_(3)coatings which correlated with the content of hydrocarbon on the surface.Yb_(2)o_(3)coatings exhibited reversible transitions between superhydrophobicity after vacuum treatment and superhydrophilicity after Ar-plasma or heat treatment,linked to hydrocarbon adsorption onto and desorption from the surface.Yb_(2)o_(3)coatings after long-time air exposure and ultra-high vacuum treatment both remained hydrophilic and showed a smaller hydrocarbon content than coatings after vacuum treatment.Al_(2)o_(3)coatings with hierarchical surface structures similar to the Yb_(2)o_(3)coatings showed an increase in WCA to only-170 after the same vacuum treatment,indicating the REO has a much higher affinity for hydrocarbon adsorption than Al_(2)o_(3),and that the content of hydrocarbon adsorbed on the surface of the REO determined the wetting behavior.