Characterization of ramiform precipitates formed on SiO2–TiO2 gel coatings by electric field hot water treatment

The shape of the precipitates on sol–gel derived SiO2–TiO2 coatings at the negative electrode changed from granular to ramiform by applying an electric field to the substrates during a hot water treatment, whereas such changes in the shape of titania nanocrystals with the electric field were not observed at the positive electrode. The granular and ramiform precipitates were identified as anatase (TiO2) and hydrated titania (n(TiO2) · mH2O), respectively. The ramiform shape of the titania precipitates became significant with increasing the applied voltage, while the coatings gradually became dark-colored due to the reduction of Ti4+ to Ti3+. The coatings with ramiform precipitates showed an excellent wettability for water.