CHARACTERIZATION OF SOL-GEL-DERIVED TIO2 COATINGS AND THEIR PHOTOEFFECTS ON COPPER SUBSTRATES

In accordance with the corrosion protection of Cu by n-TiO2 coating under illumination, the relation between the structural characterization and the photoelectrochemical properties of sol-gel-derived TiO2 coating has been investigated utilizing glow discharge spectroscopy, x-ray diffraction, and x-ray photoelectron spectroscopy analysis techniques. As a result of the well-known shrinkage of the gel under heat-treatment, the thickness of the TiO2 coating decreased with increasing heating temperature, about a 50% decrease from 200 to 800 degrees C. Amorphous TiO2 gel was found to be crystallized above 400 degrees C, which gave rise to a great enhancement of the photocurrent of the TiO2 coating. In relating these results to the photoelectrochemical behavior of TiO2-coated Cu, it was revealed that both the significant change in the photocurrent and the existence of Cu oxides in the coating were not the direct reasons which accounted for the critical temperature for TiO2 to impose its photoeffect on the Cu substrate. The dramatic change in the photopotential of TiO2-coated Cu would be explained by the change of Schottky barrier at the TiO2/Cu interface in terms of the Fermi level pinning at the Ti3+ defect level. Nevertheless, the increase in the photocurrent of TiO2 coating was beneficial to move the photopotential of TiO2-coated Cu to a much less noble level. The degradation of the photoeffect of TiO2 coating heated above 800 degrees C was due to the significant diffusion of Cu into the coating.