Abstract
The electrical properties of the anodic oxidation coatings formed in alkaline baths (NH4OH-NH4F bath and NaOH-H2O2 bath) were investigated and compared with those of an anodized film formed in an H2SO4 bath.NaOH-H2O2 film showed a lower value of electric resistance than anodized coatings formed in NH4OH-NH4F or H2SO4 baths, and the value (20μm, 200°C) decreased in the order of NH4OH-NH4F film (1.7×1015Ωcm), H2SO4 film (1.3×1015Ωcm) and NaOH-H2O2 film (6.6×1013Ωcm). The anodized coatings formed in the H2SO4 bath showed higher resistance than the coatings formed in the alkaline baths, and electric resistance of these films increased as the temperature increased.In the same manner, breakdown voltage of the films (5μm, 15°C) decreased in the order of H2SO4 film (75V), NH4OH-NH4F film (45V) and NaOH-H2O2 film (40V). NH4OH-NH4F film (20μm, 100°C: 11.5) showed a higher dielectric constant than H2SO4 (20μm, 100°C: 8.5).From the above results, it is concluded that the pore walls of the NaOH-H2O2 film were non-uniform and branched, and that aluminum hydroxide containing a considerable amount of water was deposited on the pore walls.
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