ZrO2 films were coated on aluminum etching foil by the sol-gel method to apply ZrO2 as a dielectric material in an aluminum(Al) electrolytic capacitor. ZrO2 films annealed above 450˚C appeared to have a tetragonal structure. The withdrawal speed during dip-coating, and the annealing temperature, influenced crack-growth in the films. The ZrO2 films annealed at 500˚C exhibited a dielectric constant of 33 at 1 kHz. Also, uniform ZrO2 tunnels formed in Al etch-pits 1μm in diameter. However, ZrO2 film of 100-200 nm thickness showed the withstanding voltage of 15 V, which was unsuitable for a high-voltage capacitor. In order to improve the withstanding voltage, ZrO2-coated Al etching foils were anodized at 300 V. After being anodized, the Al2O3 film grew in the directions of both the Al-metal matrix and the ZrO2 film, and the ZrO2-coated Al foil showed a withstanding voltage of 300 V. However, the capacitance of the ZrO2-coated Al foil exhibited only a small increase because the thickness of the Al2O3 film was 4-5 times thicker than that of ZrO2 film.

A ZrO2 coating solution containing ZrO2 photo-catalysis, which is transparent in visible light, was prepared by the hydrolysis of alkoxide, and thin films on the SiO2 glass substrate were formed in a dipcoating method. These thin films were heat-treated at temperatures ranging from 250˚C-800˚C and their characteristics were subjected to thermal analysis, XRD, spectrometry, SEM, EDS, contact angle measurement, and AFM. Tetragonal ZrO2 phase was found in the thin film heat treated at 450˚C, and anatase TiO2 phase was detected in the thin film heat-treated at 600˚C and above. The thickness of the films was approximately 300 nm, and the roughness was 0.66 nm. Thus, the film properties are excellent. The films are super hydrophilic with a contact angle of 4.0˚; moreover, they have self-cleaning effect due to the photo catalytic property of anatase TiO2.