Oxygen adsorbed aluminium oxide

Sheet aluminium can be given a colour by a similar process. The aluminium is first made the anode in a bath of chromic acid (p. 377) when, instead of oxygen being evolved, the aluminium becomes coated with a very adherent film of aluminium oxide which is very adsorbent. If a dye is added to the bath the oxide film is coloured, this colour being incorporated in a film which also makes the remaining aluminium resistant to corrosion. This process is called anodising aluminium. 

Silica gel and aluminium oxide layers are highly active stationary phases with large surface areas which can, for example, — on heating — directly dehydrate, degrade and, in the presence of oxygen, oxidize substances in the layer This effect is brought about by acidic silanol groups [93] or is based on the adsorption forces (proton acceptor or donor effects, dipole interactions etc) The traces of iron in the adsorbent can also catalyze some reactions In the case of testosterone and other d -3-ketosteroids stable and quantifiable fluorescent products are formed on layers of basic aluminium oxide [176,195]... 

The effect was used to detect traces of oxygen [103, 104) produced in the photosynthetic process. TTypaflavine, benzoflavine, Euchrysine 3R, Rheonine 3 A, Rhoduline Yellow, safranine, chlorophyll, and hematoporphyrin adsorbed on silica gel or aluminium oxide were the dyes that were most efficiently quenched. Unfortunately, most dyes are photolabile, and traces of water or ammonia strongly interfere. Hydrogen, nitrogen, methane, ethylene, and carbon dioxide are without influence. The method is suitable for the extremely sensitive determination of oxygen at partial pressures between O.S and 0.006 kPa and is characterized by a fast response tim but requires several seconds for regeneration. 

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