Aluminum was anodized in propylenediamine baths and choline baths containing ammonium fluoride, ammonium tartrate, and ammonium carbonate or ammonium tetraborate, at a bath temperatures of 10°C, 20°C, and 30°C, and at constant bath voltages of 30V, 50V, and 80V. Anodized films thus formed were compared by hardness, alkaline dropping test, dyeing affinity, and pore diameter.
Marten's scratch hardness test showed that the hardest films was obtained in low-temperature baths. Films formed in a high-temperature and high-voltage bath were highly corrosion-resistant. In dyeing affinity, films formed in propylenediamine baths and choline baths containing fluoride and tartrate at 20°C and 30V were superior to films formed in the same baths at 30°C and 80V. SEM of the film surface and cross-sections showed that the film formed in propylenediamine baths containing fluoride, tartrate, and carbonate had larger pores (about 150nm) than these formed in bath containing fluoride and tartrate (about 110nm) at 30°C and 80V. Films formed in choline baths containing fluoride, tartrate, and tetraborate had larger pores (about 90nm) than those formed in baths containing fluoride and tartrate (about 60nm). Large pores were assumed formed by the dissolution of pore walls at higher temperatures and voltages.
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