Oxide films voids

Figure 15. Schematic presentation of the Li/Pc interphase r5, 6] A, native oxide film B, freshly formed SEI C, void D, PE (solid)...

Figure 12. Schematic diagram of the evolution of an anodic Ti02 nanotube array (a) Formation of a compact oxide layer, (b) Formation of pits due to the dissolution and breakdown of the barrier oxide film, (c) The barrier layer at the bottom of the pits is relatively thin and this leads to the enhanced electric field assisted dissolution of Ti02, which results in further pore growth, (d) Voids formed in the inter-pores region, (e) Fully developed nanotube array with a corresponding top view [51].

During the period of the current decay, there are two competitive processes, densification to form the barrier layer and dissolution of barrier layer to form the porous layer. Under the high electrical field strength (constant voltage mode), the densification of the aluminium oxide films is favoured for process durations shorter than 3700 s. When the constant voltage was kept for a long anodisation time (beyond 10900 s), the dissolution of the aluminium oxide film becomes more dominant. Thus, the film could be contaminated by inward migration of the electrolyte into the film or by formation of micro-voids. 

The studies revealed that WS exhibited more pitting than on MS and deterioration of coated panels was highest at PI. Chloride ions accelerated corrosion at PI and corrosion rate on WS is almost equal with MS. WS showed compact protective oxide film at P3 and its corrosion rate was found lower than MS for aU the environments. Stable corrosion rate was found at P2 and P3 on WS and presence of SO2 helped to prevent deterioration of weathering steels at these two sites. Performance of scribed coated panels with MS substrate was inferior with respect to WS substrate. Rust morphologies on MS showed lot of voids and micro cracks at all sites but compact, acicular oxides were formed on WS at P2 and P3 sites. 

Macdonald DD (1993) On the formation of voids in anodic oxide films rai aluminum. J Electrochem Soc 140 27-30... 

It should be noted that in a vapour phase the liquid layer on the surface of a sensitive element of the sensor (zinc oxide) must be sufficiently thin, so that it would not produce any influence on the diffusion flux of oxygen through this layer. Possible lack of the film continuity (the presence of voids) does not prevent determination of concentration of oxygen in the bulk of the cell by the vapour - gas method. In this case, one deals with a semi-dry method. On the contrary, the presence of a thick liquid layer causes considerable errors in measuring t, because of different distribution of oxygen in a system gas - liquid layer -semiconductor film (this distribution is close to that in the system semiconductor film - liquid), in addition to substantial slowing down of oxygen diffusion in such systems. 

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