The development of chemical conversion coatings on aluminium

摘要: Abstract The growth of the chemical conversion coatings on aluminium is strongly dependent upon purity metal. For specimens up to 99.99% purity, surface not homogeneous. Flaws are always present in thin oxide layer covering surface; such flaws sited above grain boundaries and cellular associated with impurity segregation substrate. These residual type provide easy paths for electronic conduction an otherwise insulating layer. Consequently, coating (i.e. reduction dichromate species hydrated chromium oxide) occurs preferentially along or However, 99.9996% higher, where structure absent, population density residual-type considerably reduced. proceeds by tunnelling electrons through thin, insulating, passive produce a more uniform appearance than substrates reduced purity.