Aluminium oxygen content

The sesquioxide, Cr Oa, containing trivalent chromium, is an amphoteric oxide. It yields chromic salts, such as chromic chloride, CrCla, and sulphate, Cr2(S04)a, which are very stable and show great similarity to the ferric salts and to salts of aluminium as, for example, in the formation of alums. Since, however, chromic oxide functions as a weaker base than chromous oxide, the latter having a lower oxygen content, the chromic salts are more liable to hydrolysis than the chromous salts. This is well marked in the case of the chlorides. Again, in spite of the stability of chromic salts, only a slight tendency to form simple Cr " ions is exhibited, whilst complex ions are formed much more readily, not only complex anions, as in the case of iron and aluminium, but also complex cations, as in the extensive chromammine series. In this respect chromium resembles cobalt and platinum. 

The major factors believed to influence the pitting of aluminium alloys are conductivity, pH, and bicarbonate, chloride, sulphate and oxygen content [2.6]. Because of the interrelationship of the composition and service factors, it is difficult to predict the influence of water on aluminium corrosion from a table of water composition alone. A number of studies have been conducted of synthetic waters containing several metal and salt ions alone and in combination [2.15-2.17]. They found that the corrosion of aluminium was accelerated when salts of copper, chlorides and bicarbonates were present together, compared with cases where only a single impurity was present. In some cases where two of the three constituents were present, there was little corrosion, but with the three species present together, nodular corrosion occurred. 

In all these methods the oxygen content is measured indirectly through determining (usually by photometry) the aluminium content in the undissolved or non-volatilized material, and it is assumed that oxygen occurs in the form of AI2O3. 

In recent times, only occasional studies have been carried out to determine the oxygen content of aluminium alloys by means of chemical processes. 

As has been shown by initial comparison tests with activation analysis techniques under the auspices of Eurisotop and BCR Study Groups, good results are obtained with aluminium-silicon alloys - free from magnesium or only containing less than 3000 pg/g of it - if reducing fusion in a stream of carrier gas is employed in the manner suggested by Kraft and Kahles (47) for the analysis of unalloyed aluminium, with the sole difference that the reaction temperature is increased to 1950°C. Like for unalloyed aluminium, the oxygen contents reported are near the detection limit, and only increase to values of a few pg/g at silicon contents of 7 % or more. 

Table VII-11 Effect of different irradiation modes on the apparent oxygen content of aluminium (194)...

It is thus clear that the apparent oxygen content of aluminium is mainly due to recoil of nuclei into the sample. These recoil nuclei are produced by nuclear reaction with... 

Fig. VII-13 Trend of the "apparent oxygen content" of primary ingot aluminium (275)...

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