Wettability of transition metal oxide surfaces

The wettability of transition metal oxide surfaces (TiO2, ZrO2 and HfO2) by water was investigated by measuring the contact angles using the sessile drop method. The oxide surfaces were prepared by thermal oxidation of polished metal foils of Ti, Zr and Hf, which had been polished to different levels of surface roughness. The surfaces were also characterized by optical microscopy, X-ray diffraction (XRD), atomic force microscopy (AFM) and Auger/XPS (AES/ESCA) methods. From the dependence of contact angles on surface roughness for the three investigated oxides, contact angles on flat surfaces were calculated as 70.7°, 59.9° and 74.0° for TiO2, ZrO2 and HfO2, respectively. These results suggest that the three oxides do not provide acceptable waterproofing coatings on silica fibers used for space shuttle thermal insulation.