Development of an electrophoretic sol-gel coating process for porous metals

An electrophoretic sol-gel coating process was developed for applying to surface modification of metallic materials with complicated shapes such as porous metals. In this process, sol-gel transformation is directly induced on the substrates. In the present work, the formation of TiO2 coating layer on SUS 304 substrates is discussed as a practical example of the coating process. The colloidal particles derived from hydrolysis of titanium tetraisopropoxide in ethanol can be deflocculated using a small amount of CaCl2 to form a transparent solution. When a dc voltage of 1-5 V was applied between the substrate (cathod) and counter electrode in this solution, the gel film was formed on the substrate. After subsequent water-soaking and annealing processes, the coating layers with no cracking were obtained successfully on the substrate. As the results of X-ray photoelectron spectroscopy, the coating layers were found to consist of TiO2 doped with Ca2+ ions.