Effects of Addition of Sulfuric Acid on the Etching Behavior of Al foil for Electrolytic Capacitors II. Microstructures of Dielectric Layers and AC Impedance Analysis

Aluminium foil for electrolytic capacitors was anodized at the voltage of 100V and 140V for 10 minutes in ammonium adipate solution to form aluminum oxide layer on aluminum substrate as an dielectric film. The thickness, the stoichiometry and the crystal structure of the layer were investigated by using RBS and TEM . In addition EIS technique was employed to study the effects of addition of sulfuric acid on the increment of the foil surface area. It was found that the thickness values of the layers anodized at 100V and 140V were about 130 nm and 190 nm respectively and the stoichiometry of the elements of aluminum and oxygen was 2:3. The anodic oxide layer was shown to be amorphous. but the structure irradiated with electron beam resulted in the transformation into crystalline structure of $-Al_2$ . From a comparison of the impedance results and the capacitance variation to investigate the ef- fects of sulfuric acid addition to the etching bath of hydrochloric acid, the EIS techinque could be useful to analyze the capacitance variation.