Preparation of titanium dioxide films on etched aluminum foil by vacuum infiltration and anodizing

Highlights: • Al₂O₃–TiO₂ composite films were prepared onto high voltage Al etching foil. • The coated and anodized samples showed multi-layer structures. • The capacitances of TiO₂ coated samples showed an increase of 42%. • The increase in capacitance was mainly due to the Al–Ti composite layer. - Abstract: Al₂O₃–TiO₂ (Al–Ti) composite oxide films are a promising dielectric material for future use in capacitors. In this study, TiO₂ films were prepared on etched Al foils by vacuum infiltration. TiO₂ films prepared using a sol–gel process were annealed at various temperatures (450, 500, and 550 °C) for different time durations (10, 30, and 60 min) for 4 cycles, and then anodized at 100 V. The specimens were characterized using X-ray diffraction, field emission scanning electron microscopy, and field emission transmission electron microscopy. The results show that the tunnels of the specimens feature a multi-layer structure consisting of an Al₂O₃ outer layer, an Al–Ti composite oxide middle layer, and an aluminum hydrate inner layer. The electrical properties of the specimens, such as the withstanding voltage and specific capacitance, were also measured. Compared to specimens without TiO₂ coating, the specific capacitances of the TiO₂-coated specimens are increased. The specific capacitance of the anode Al foil with TiO₂ coating increased by 42% compared to that of a specimen without TiO₂ coating when annealed at 550 °C for 10 min. These composite oxide films could enhance the specific capacitance of anode Al foils used in dielectric materials.