Effects of electrolyte species and their combination on film structures and dielectric properties of crystalline anodic alumina films formed by two-step anodization+1

Abstract

The effects of electrolyte species and their combination during the two-step anodization of anodic oxide films formed in various ammonium salts solutions on aluminum in terms of the crystallinity and dielectric properties for use as an electrolytic capacitor were investigated. The aluminum substrates were pretreated by dipping in boiling water to form a hydrated layer. Anodic films were annealed at 500°C after the first anodization. The CV (capacitance C multiplied by withstand voltage V) of the films formed with a second anodization in ammonium borate was higher than that of the films formed using the same electrolyte for the first and second anodizations. The increase in CV due to the improved crystallinity when using borate for the second anodization and the following electrolytes for the first anodization increased in the order salicylate < succinate < tartrate < phosphate < citrate < adipate < borate. When phosphate or organic electrolytes were used in the second anodization, considerable spike noise was observed. However, the spike noise was significantly suppressed when borate was used in the second anodization. ©2013 The Japan Society for Technology of Plasticity.