Oxygen in aluminium

The metal thus purified is cast into bars of different sizes. Thereby, the liquid metal has to pass through channels from the holding furnace into the casting implements. The casting channels cover with a thin oxide skin and it is not excluded that parts of this skin enter the liquid rnetal. 

Both oxide types have a negative effect on the further processing of the metal. When bars are rolled into plates, the oxide inclusions cause the formation of dull and porous spots, which make the product useless. In foil production even the presence of oxide plancton has a negative effect as it causes the formation of holes and, in greater accumulation, of cracks. 

In sheet production especially the oxide plancton acts as recombination centers (nuclei) for hydrogen which is always present in atomic form in the molten metal, in which it is 20 times more soluble than in the solid metal. If recombination takes place near the surface of plates, it may cause the formation of holes this phenomenon is especially observed with sheets of about 1 mm thickness. The oxide inclusions resulting from the skins of the casting channels are not only present in the form of aluminium oxides, but can also contain hydroxyl groups, which during the transformation of the aluminium may yield water and hydrogen. The correlation between the presence of oxides and the formation of blow-holes on the sheets is therefore very complex. 

Finally, oxides are important in shaping of aluminium cast products by chips removal when oxides are present, the hardness of the products influences significantly the lifetime of the working tools thus causing additional costs, not only because the tools have to be renewed, but also because the processing yields become worse the more the tools are damaged (2). 

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Colombo, A., Rodari, E. Vacuum-fusion determination of oxygen in aluminium and aluminium-aluminium oxide composites. Anal. Chim. Acta 42, 133 (1968). 

Table VII-1 Chemical methods for determining oxygen in aluminium...

The literature contains a number of processes for determining oxygen in aluminium by reducing fusion, either in vacuo, or by means of a carrier gas these processes have as their object the analysis of either metallic aluminium or of aluminium-oxides. The resulting picture is not uniform, however, and sometimes it is even downright contradictory. 

Aluminium is recommended as the metal to be added, because of its extremely high affinity for oxygen, and the same reaction conditions are maintained as in the determination of oxygen in aluminium (see 1.1.3). The parameters are as follows ... 

Basically, the same limitations as for the determination of oxygen in aluminium or copper alloys apply to this analysis ... 

Numerous papers (228 to 233) deal with the determination of oxygen in aluminium by charged particle activation analysis using protons, helium-3 and helium-4 as activating particles. Vialatte (230) showed that of these methods only He activation allows the determination of low (< 0.2 Mg/g) oxygen concentrations. 

Valladon et al. (237) used triton activation for the determination of oxygen in aluminium. The samples were irradiated for 1-2 h with a 1 mA beam of 3.5 MeV tritons. A 15 jum surface layer was removed by a combination of chemical etching and mechanical grinding (first 2 Mm were removed by etching in a mixture of hydrofluoric and nitric acids, then 10-12 Mm... 

During the seventies important progress has been made in the analysis of oxygen in aluminium as shown in Fig. VII-13 for primary ingot aluminium no longer values of approx. 

Note Indoles, that are substituted with oxygen in position 2 or 3, do not react [11]. The reagent can be employed on silica gel, kieselguhr and Si 50 000 layers. Aluminium oxide layers are not suitable [3]. 

At elevated temperatures in the presence of oxygen the aluminium oxide layer catalyzes the formation of blue fluorescent aluminium oxide surface compounds with 4-hydroxy-3-oxo-A -steroid structures [4]. Aluminium oxide acts as an oxidation catalyst for an activated methylene group. 

The mechanism of cathodic luminescence is distinctly different from other ECL systems. Light is emitted from oxide-covered, so-called valve metal, electrodes, namely aluminium and tantalum, during the reduction of peroxodisulfate, hydrogen peroxide, or oxygen, in aqueous solution, at relatively low potentials (<10 V). The mechanism involving persulfate, for example, is as follows. A conduc-... 

Fig. 1. Stopping force on oxygen ions in aluminium Comparison of Bohr and Bethe formulae with measurements from numerous laboratories compiled in Ref. [6]. From Ref. [7].

As shown in Fig. 1.28, a reaction vessel (cylinder) was made of 18-8 Cr stainless steel. The inner room for sample preparation, into which a platinum crucible was fitted, was sealed by screwing up a stainless steel disc wrapped in aluminium foil. This vessel can be used under the conditions that the reaction temperature is below 600 °C and the oxygen pressure is lower than 1000 atm. The experimental procedure is as follows place the weighed CrOj into the crucible, seal quickly, heat the vessel using an outer heater, and then keep it at a set temperature. 

There are many other ingredients that are added to explosive compositions which in themselves are not explosive but can enhance the power of explosives, reduce the sensitivity, and aid processing. Aluminium powder is frequently added to explosive and propellant compositions to improve their efficiency. Ammonium nitrate (NH4N03) is used extensively in commercial explosives and propellants. It is the most important raw material in the manufacture of commercial explosives and it also provides oxygen in rocket propellant compositions. Some of the properties of ammonium nitrate are presented in Table 2.22. 

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