抄録
Anodic oxidation of aluminum in the non-aqueous solution of NMF (N-methyl formamide)-boric acid system was studied and the mechanism of oxide film formation was discussed.
NMF, having dielectric constant of as high as 182, is a high ionizing solvent, which is a promising electrolyte for anodizing aluminum.
Al of 99.99% in purity was anodized in 1mol H3BO3 solution at room temperature at constant current density or at constant bath voltage for various periods. During anodizing, samples were slowly moved in the electrolyte by an anode rocker. Light brown colored or often opaque oxide film was formed, which was very hard and very insulating up to 700v.
The presence of organic radicals was proved to be very probable by IR and ESR spectra and DTA analysis, and they were related with the film color.
It was also proved that a trace of water was essential for the normal growth of oxide film. Therefore, the following mechanism was proposed;
6OH-+2Al=Al2O3+3H2O+6e
and 6HCONCH3-+2Al=Al2O3+3HCONHCH3+3CH3CN+6e
