Is hydrophobicity an intrinsic characteristic of rare-earth-oxide (REO) coatings?

Some recent publication reported observing intrinsic hydrophobicity in rare-earth oxides (REOs), that seem to be promising for developing durable, ceramic superhydrophobic surfaces as alternative to less durable polymeric alternatives. Recently, thermal spraying, has been employed to deposit REOs, aiming to produce microtextured superhydrophobic coatings. However, there seems to be a disagreement in the literature as whether the apparent hydrophobicity of REOs is due to hydrocarbon contamination and REOs like other metal oxides are intrinsically hydrophilic.

In this work, suspension plasma sprayed (SPS) coatings as well as simply pressed and sintered samples are prepared and tested in various conditions and compositions, in an effort to test the validity of the hypothesis: “REOs can demonstrate intrinsic hydrophobicity in certain conditions”. The wetting behavior of samples is studied, as sprayed, after treatment in ultra-high vacuum, conventional vacuum, cleaned in boiling water and cleaned using ion beam. XPS and EDX are used to study the surface composition of the samples and SEM and confocal laser microscopy are used to study the morphology of the surfaces. Finally, some practices are suggested to test any new rare-earth oxide coatings to examine whether their apparent hydrophobicity is an intrinsic behavior or a result of contamination.