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Growth and field crystallization of anodic films on Ta–Nb alloys

  • Autori: Komiyama, S.; Tsuji, E.; Aoki, Y.; Habazaki, H.; Santamaria, M.; DI QUARTO, F.; Skeldon, P.; Thompson, G.
  • Anno di pubblicazione: 2012
  • Tipologia: Articolo in rivista (Articolo in rivista)
  • OA Link:


The growth behavior of amorphous anodic films on Ta–Nb solid solution alloys has been investigated over a wide composition range at a constant current density of 50 Am−2 in 0.1 mol dm−3 ammonium pentaborate electrolyte. The anodic films consist of two layers, comprising a thin outer Nb2O5 layer and an inner layer consisting of units of Ta2O5 and Nb2O5. The outer Nb2O5 layer is formed as a consequence of the faster outward migration of Nb5+ ions, compared with Ta5+ ions, during film growth under the high electric field. Their relative migration rates are independent of the alloy composition. The formation ratio, density, and capacitance of the films show a linear relation to the alloy composition. The susceptibility of the anodic films to field crystallization during anodizing at constant voltage increases with increasing niobium content of the alloy.