The development of flaws containing γ′-crystalline alumina regions in barrier anodic films on aluminium
✍ Scribed by K. Shimizu; S. Tajima; G.E. Thompson; G.C. Wood
- Publisher
- Elsevier Science
- Year
- 1980
- Tongue
- English
- Weight
- 709 KB
- Volume
- 25
- Category
- Article
- ISSN
- 0013-4686
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✦ Synopsis
Transmission electron microscopy has been employed to study the formation and development of regions containing y'-crystalline alumina surrounding flaws in anodic barrier films formed on aluminiumin aqueous ammonium borate solutions . The formation of crystalline alumina islands at these localized sites becomes more readily evident when the forming voltage approaches about 100 V and they grow radially with further increase in the forming voltage.
The radial growth of the islands and their population density is influenced by increase of hulk temperature of the electrolyte, but is almost unaffected by the concentration of the electrolyte and applied anodizing current density . The population density of the flaws and, hence, y'crystalline alumina islands is strongly dependent on the surface condition of the metul and varies from about 2 4 x 10 8 em -2 on the as-received specimen to less than W o ... 2 on the eleclropulished specimen .
The islands of crystalline alumina are thought to form in the vicinity of flaws in the original substrate, by conversion of the barrier film formed by the usual ionic processes, due to local Joule heating effects .