Thin anodic oxide overlayers

X-ray Photoelectron Spectroscopy and Scanning Tunneling Microscopy Studies of Thin Anodic Oxide Overlayers on Metal and Alloy Single-Crystal Surfaces... 

Thin anodic oxide overlayers (passive films) can be highly resistant against corrosion. They also play a major role in adhesion, tribology, catalysis and micro-electronics. A better understanding of the relationship of the chemistry and structure to the properties of metal surfaces covered with thin oxide overlayers is needed. 

MARCUS MAURICE Thin Anodic Oxide Overlayers... 

AR-XPS has been extensively used to investigate the chemical composition, the chemical states and the thickness of thin anodic oxide overlayers (passive films) formed on well-defined metal and alloy single crystal surfaces. More recently direct imaging of the surface structure by STM with atomic resolution provided new data on the crystallinity, the epitaxy and the nature of the structural defects existing in the thin oxide layers. Such data are useful... 

Adsorption-induced reconstruction, surface metal atom, 245 Adsorption isotherms, development, 4/,5 Alcohols, role in photooxidation reaction of water on n-Ti02 electrode, 297-308 Alloy single-crystal surface, thin anodic oxide overlayers, 236-244 Alloy surfaces, chemical reconstruction, 246-247... 

As a further example for the meaning of ex situ investigations of emersed electrodes with smface analytical techniques, results obtained for the double layer on polycrystalline silver in alkaline solutions are presented in figme C2.10.3. This system is of seientifie interest, since thin silver oxide overlayers (thickness up to about 5 nm) are formed for sufficiently anodic potentials, whieh implies that the adsorption of anions, cations and water can be studied on the elean metal as well as on an oxide eovered surface [55. 56]. For the latter situation, a changed... 

The aluminium oxide formed in this process has a complex form. It is partially hydrated and has a two-layer structure. At the surface of the metal there is a thin (perhaps 0.025 jum), compact boundary layer and then there is a porous overlayer. The latter has a very open structure and structural techniques (see Fig. 7.13) show it to consist of a collection of parallel tubes perpendicular to the surface. After the anodic oxidation the metal is dipped into a caustic soda solution to precipitate aluminium hydroxide in the pores and hence produce a more robust layer. 

Bond failure can also occur if the surface is anodic relative to another joint component. An example would be clad aluminum adherends where a thin layer of pure aluminum overlays the base alloy. Such a surface layer is designed to be more corrosion resistant than the alloy, but to act as a sacrificial anode should corrosion occur. Although this approach works well for corrosion protection of the substrate material, it can be a disaster for bonded material if the adherend surface/interface corrodes. As a result, American companies tend to use unclad aluminum for bonding and provide other means of corrosion protection, such as painting [1,70]. On the other hand, European companies commonly use clad adherends, but with a thicker oxide (CAA) [6,18,71-73] that provides bondline corrosion protection. 

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