Formation of Al 2O 3–Bi 4Ti 3O 12 nanocomposite oxide films on low-voltage etched aluminum foil by sol–gel processing

Abstract

A water-based bismuth titanate Bi 4Ti 3O 12 (BTO) sol was synthesized by mixing bismuth nitrate, tetra- n-butyl titanate, lactic acid, acetic acid and distilled water. The sol was applied to low-voltage etched aluminum foil by dip-coating. The crystallization process of Bi 4Ti 3O 12 on low-voltage etched aluminum foil was measured by thermal gravimetry–differential scanning calorimetry (TG–DSC) and high-temperature X-ray diffraction (HT-XRD). It was found that Bi 4Ti 3O 12 sol first converted into intermediate phase Bi 1.74Ti 2O 6.624, then transformed into perovskite phase Bi 4Ti 3O 12. After annealed at 600 °C for 30 min in air, the low-voltage etched aluminum foil covered with Bi 4Ti 3O 12 sol was anodized galvanostatically in 15 wt.% ammonium adipate solution. The voltage–time variation during anodizing was monitored and recorded. The structure and composition of samples were investigated by field emission scanning electron microscopy (FE-SEM) and energy dispersive X-ray analysis (EDAX). Results showed that the anodic composite oxide film was composed of an inner Al 2O 3 layer and an outer Bi 4Ti 3O 12 layer. The specific capacitance and the product of specific capacitance and withstanding voltage of samples with a BTO coating were about 56.64% and 43.77% larger than that without a BTO coating.