Voltage oscillations during anodizing process of aluminum and their suppression

The barrier anodic alumina (BAA) film formed by aluminum anodization is used as the capacitor dielectric, and the working electrolyte is called the ‘blood’ of the electrolytic capacitor. It is crucial to study the formation process of BAA in working electrolytes for improving the performance of electrolytic capacitor. Here, constant current anodization of pure aluminum was carried out in a neutral working electrolyte composed of ammonium pentaborate and ammonium benzoate without corrosion. It was found that voltage oscillation appears in its voltage-time curve. The FESEM images show that the voltage oscillation in the voltage-time curve leads to the appearance of holes in the BAA. The existence of these holes will inevitably affect the voltage resistance, leakage current and high-temperature resistance of the dielectric film. To eliminate the voltage oscillation phenomenon, the electrolyte was modified by adding ADP (ammonium dihydrogen phosphate) and HYS-01(24-carbon multibranched tetrameric ammonium carboxylate) additives. The interesting findings show that when aluminum was anodized in the working electrolyte with the addition of ADP and HYS-01, the voltage oscillation disappeared, and so did the holes in the BAA. The voltage resistance of dielectric film and leakage current performance were significantly improved after storage at a high-temperature of 130 °C for 500 h.