Dielectric properties of Al–Si composite oxide films formed on electropolished and DC-etched aluminum by electrophoretic sol-gel coating and anodizing |
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Authors: | M Sunada H Takahashi T Kikuchi M Sakairi S Hirai |
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Institution: | (1) Graduate School of Engineering, Hokkaido University, Sapporo, Japan;(2) Facaulty of Engineering, Muroran Institute of Technology, Muroran, Japan |
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Abstract: | Highly pure aluminum specimens (99.99%) after electropolishing and DC-etching were covered with SiO2 films by electrophoretic sol-gel coating and were anodized in neutral boric acid/borate solutions. Time-variations in cell
voltage during electrophoretic sol-gel coating and in anode potential during anodizing were monitored. Structure and dielectric
properties of the anodic oxide films were examined by scanning electron microscopy (SEM), transmission electron microscopy
(TEM), energy-dispersive X-ray (EDX), and electrochemical impedance spectroscopy (EIS). It was found that electrophoretic
sol-gel coating forms uniform SiO2 films on the surface of both electropolished and DC-etched specimens. Anodizing of specimens after electrophoretic coating
lead to the formation of anodic oxide films consisting of two layers: an inner alumina layer and an outer Al–Si composite
oxide layer. The anodic oxide films formed, thus, had slightly higher capacitances than those formed on aluminum without any
coating. Higher heating temperatures after electrophoretic deposition caused the increase in capacitance of anodic oxide films
more effectively. Anodizing in a boric acid solution after SiO2 coating on DC-etched foil allowed the anode potential to reach a value higher than 1,000 V, resulting in 39% higher capacitances
than those on specimens without SiO2 film.
Dedicated to Professor Su-Il Pyun on the occasion of his 65th birthday. |
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Keywords: | Aluminum Electrolytic capacitor Electrophoretic deposition Sol-gel coating Composite oxide film |
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