アルミニウム陽極酸化膜への電着における密着機構に関する考察

抄録

To investigate the mechanism of adhesion in plating metals to anodized aluminum, various experiments are carried out. By these experiments, it is found that there are several essential factors controling the adhesive property.
i) Surface roughness: It is obvious that the surface roughness of base metals affects the adhesiveness, and the microscopic roughness is more important than the macroscopic roughness. The surface treated by anodized coating using phosphoric acid has microscopic surface structure and is very homogenious. The microscopic structure becomes the nuclei for the plating and gives very good adhesive.
The surfaces treated by anodized coating using sulphuric acid and oxalic acid do not show such a homogenious microscopic structure.
ii) Cell structure: There are many pores in the surfaces treated by anodized coating. The mean diamater of those pores differs for the different bath. Among the three kinds of bath, the above meutioned phosphoric acid gives the largest and the sulphuric acid the smallest size of pores. Therefore, the number of those pores becomes just reversed in the order above meutioned. This means that the volume of the pores per unit area of the surface treated by phosphoric acid is larger than that treated by other two acids. That is, the oxide film treated by phosphoric acid has the smallest electric-resistance. This cell structure has also much to do with the surface roughness.
iii) Active layer of anodized film: The anodized films treated by phosphoric acid are the most active for reduction. However, if rested in the air or the plating bath for a short time, the high activity gradually decreases. The higher the activity of the anodized film, the better the adhesive can be obtained.
iv) Purity of base metals; The adhesiveness of anodized coating depends also on the purity of the base metals. Impure aluminum shorws better adhesion than pure aluminum. The former has higher electrode-potential than the latter, so that there are more defects in the anodized film resulting in the better adhesiveness.