Anodization barrier

Specific structural features are observed in the formation of composite oxides. Kobayashi, Shimizu, and their co-workers have, in a series of papers, reported studies of the structure of barrier alumina films, anodically formed on aluminum covered by a thin (5 nm) layer of thermal oxide.198,199 Their experiments have shown that the thermally oxidized thin layer generally contains y- alumina crystals of about 0.2 nm size. This layer does not have a pronounced effect on ionic transport in the oxide during anodization. Also, islands of y -alumina are formed around the middle of anodic barrier oxides. They are nucleated and developed from tiny crystals of y -Al203 and grow rapidly in the lateral direction under prolonged anodization.198,199... 

McDevitt, N. T., and Baun, W. L., Some Observations of the Relation Between Chemical Surface Treatments and the Growth of Anodic Barrier Layer Films, Air Force Materials Laboratory Technical Repot 76-74, June 1976. 

The electrochemical behaviour of metals in anhydrous HF has been reviewed by Vijh, with particular attention to anodization, open-circuit corrosion, film formation, anodic dissolution, and evolution of F2. The dependence of the F2 overpotential at Ni in anhydrous HF on the current density has been investigated. At low current densities the overvoltage was mainly due to the potential difference across the anodic barrier film, whereas at high current density the electronic conduction of the film increased appreciably, resulting in a decrease in the potential drop. Other workers have shown that the process of H2 discharge in HF is affected by the addition of NaF, presumably by reducing the overvoltage on nickel. 

Figure 4.4.29. Interfacial defect generation/annihilation reactions that occur in the growth of anodic barrier oxide films according to the Point Defect Model (D. Macdonald [1999]). m = metal atom, = cation vacancy on the metal sublattice of the barrier layer, MP = interstitial cation, Mu = metal cation on the metal sublattice of the barrier layer, Vo = oxygen vacancy on the oxygen sublattice of the barrier layer, Oo = oxygen anion on the oxygen sublattice of the barrier layer, = metal cation in solution.

Zhu HY, Colclasuie AM, Kee RJ, Lin YB, Barnett SA (2006) Anode barrier layers Jot tubular solid-oxide fuel cells with methane fuel streams. J Power Sources 161 413... 

Lin Y, Zhan Z, Barnett SA (2006) Improving the stability of direct-methane solid oxide fuel cells using anode barrier layers. J Power Sources 158 1313... 

N. T. McDevitt and W. L. Baun, Some observations of the relation between chemical surface treatments and the growth of anodic barrier layer films. Air Force Materials Lab. AFML-TR-76-74 (June 1976). 

Shimizu K., Thompson G.E. and Wood, G.C. (1981), Direct observation of the duplex nature of anodic barrier films on aluminium Thin Solid Films, 81,39-44. 

Figure 9.4 y (V) characteristics in FN representation for a 120-nm-thick iayer of MEH-PPV sandwiched between various anode materiais and aiuminum. Numbers indicate anodic barrier heights caicuiated according to Equation 9.17. (From Parker, i. D., J. Appl. Phys., 75, 1656, 1994. With permission.)... 

Figure 15. Steady current density in the passive potential region as a function of solution pH. The cd reached the stationary value in the solution at pH lower than 5 in 1 h oxidation at each potential, however, it does not reach at pH higher than 5 in which the cd was plotted after Ih oxidation. Reprint from N. Sato and T. Noda, Ion Migration in Anodic Barrier Oxide Films on Iron in Acidic Phosphate Solutions , Electrochim. Acta, 22 (1977) 839, Copyright 1977 with permission from Elsevier Science.

Anodize, barrier A non-porous anodic oxide that can be formed on materials such as aluminum, titanium, and niobium. The thickness of the oxide is proportional to the anodizing voltage applied. 

---