Effects of storage atmosphere and surface roughness on the hydrophobicity of Gd2O3 thin film and sintered body

Thin films and sintered bodies of Gd2O3 were prepared by alkoxide solution coating or uniaxial pressing of an oxide powder, followed by firing in a synthesized air atmosphere. Both samples were initially hydrophilic after firing. However, their water contact angles increased during storage in ambient air. The surface hydrophobicity was non-existent after ozonation, but it recovered during two weeks of ambient air storage. The hydrophobicization rate of Gd2O3 film was higher than that of SiO2 film. It corresponded to the carbon concentration ratio on the surface. Fourier-transform infrared spectroscopy revealed a difference in stretching vibrations of the OH group at around 3400 and 3600 cm−1 between SiO2 and Gd2O3 films. The hydrophobicization rate of the sintered body depended on storage atmosphere and the temperature when the sample was removed from the furnace. Results suggest that this hydrophobicity originated from the adsorption of organic substances from ambient air onto the surface. Surface roughness of the sintered body also affected hydrophobicity. The Cassie mode contribution was inferred for a surface with a water contact angle without roughness of 65°.