抄録
When aluminum is anodized in acidic solution such as sulfuric acid, porous film of aluminum oxide (anodized aluminum) is formed on the aluminum surface. In general, detrimental reagents such as sulfuric acid and oxalic acid are used for electrolysis bath, which is cooled at 5-10°C. The conventional technology has several problems that the waste treatment of the electrolysis solution increases year by year and very smoothed aluminum surface is corroded by strongly acidic electrolysis solution easily.
Recently it was found that the carbonic acid aqueous solution, which is made with high-pressure carbon dioxide and water, could be used as the electrolysis solution of anodized aluminum production process. The new electrolysis solution has several advantages as follows. As the electrolysis is carried out without toxic substances, it is safe and harmless to both the environment and human body and the construction and running costs of wastewater treatment can be decreased much. Furthermore the use of new electrolysis solution makes it possible to process aluminum surface with much higher precision comparing with the conventional technologies, because the aluminum surface is hardly corroded by the weak acid of carbonic acid.
Several experiments were carried out using the new electrolysis solution at 40°C, 15MPa, 15-60V and 0.5-10h. Four kinds of aluminum alloys (JIS A1100, A2017, A5052, A6061) with 20mm in length and 10mm in width were used. As a result, aluminum oxide film with the thickness of about 1 m was produced on the aluminum surface. The formation of the oxide film was confirmed by EPMA analysis of the oxygen atom concentration of the aluminum surface.
