The determination of oxygen in aluminium

It is also possible that extraneous oxides are present in the metal, such as residues of furnace linings and the like. 

In the methods to be considered under this heading, the intention is either to dissolve the metallic aluminium in such a way that the oxygen compounds present are not attacked, or to volatilize the aluminium in the form of chloride by treatment with an active gas stream, in such a way that the oxygen compounds do not react in the process and are not carried along in the gas stream either. Furthermore, all these reactions must be carried out in such a way that no new oxygen compounds are formed during the processes concerned, by the action of water, steam or oxygen. 

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. 

Critical investigations (2) (25-27) have shown that none of these processes are sufficiently selective. It has been found that certain aluminium-oxygen compounds are converted partially in exactly the same manner as metallic aluminium. Other aluminium compounds, particularly in aluminium-silicon alloys, remain in the isolation residues to a certain extent and are thus incorrectly determined as oxygen. Residues of metallic aluminium must also be expected in the fractions isolated. 

The formation of aluminium-oxygen compounds during the solution or volatilization process cannot be excluded and the analysis of alloys causes additional difficulties. 

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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... 

The results of initial attempts (46) to solve the problem by the use of chemical methods of separation, such as gaseous chlorine or bromine/ methanol, for example, do not stand up to critical evaluation any more than those relating to the determination of oxygen in unalloyed aluminium. The bromine-methanol process in particular is subject to a serious systematic error, since it ultimately responds to aluminium amounts, present in the undissolved silicon component of the alloy, as if they were Al O, and thus reports them as oxygen. 

Systematic errors due to matrix effects in 14 MeV neutron activation analysis have been studied by several authors. These studies were relative to the determination of oxygen in steel (187)(190), in aluminium (196) and in any matrix (197)(198)(199)(200)(201)(186). The problem has been reviewed in some detail by Adams et al. (202), Nargolwalla and Przybylowicz (203) and by Cornells et al. (204). On condition that a suitable 0-shielding is used, so that no P-rays are detected, systematic errors may... 

Applications Basic methods for the determination of halogens in polymers are fusion with sodium carbonate (followed by determination of the sodium halide), oxygen flask combustion and XRF. Crompton [21] has reported fusion with sodium bicarbonate for the determination of traces of chlorine in PE (down to 5 ppm), fusion with sodium bisulfate for the analysis of titanium, iron and aluminium in low-pressure polyolefins (at 1 ppm level), and fusion with sodium peroxide for the complexometric determination using EDTA of traces of bromine in PS (down to 100ppm). Determination of halogens in plastics by ICP-MS can be achieved using a carbonate fusion procedure, but this will result in poor recoveries for a number of elements [88]. A sodium peroxide fusion-titration procedure is capable of determining total sulfur in polymers in amounts down to 500 ppm with an accuracy of 5% [89]. 

Recent Uses of 14 MeVN.A.A. Espanol and Marafuschi report the use of 14 MeV n.a.a. for the determination of Al/O ratios in sintered alumina powders using the usual 0(n,p) N reaction for oxygen and the Al(n,p) Mg reaction for aluminium determination interferences from F and B are discussed. The analysis of oxygen in electrolytic baths is particularly complicated by the F(n,a) N interference due to the presence of NasAlFs, and a correction is necessary based upon the F also induced in the sample by the F(n,2n) F reaction. The interference can also be eliminated by using a lower-energy neutron flux (say, 12 MeV) the F(n,a) N cross-section is much reduced, whereas the 0(n,p) N cross-section is at a maximum. The interference of F is quite serious Morgan and Ehmann report that 0.1 % F gives a response equivalent to an apparent O content of 0.0415% in meteorites. 

The mole fractions of aluminium and chromium, as well as the molar volumes, can easily be determined. The diffusion coefficients have been chosen from the literature as given in Table 4.1. Only the solubility of oxygen in iron has not yet been measured without uncertainty [21], because even small levels of impurities lead to adulteration of the results by oxide formation. Thus in this work another method has been chosen. The critical value h has been set to 1/3. From [22] the lowest aluminium contents for the formation of a closed alumina layer on Fe-Al binary alloys have been chosen and the oxygen solubility is then calculated. The result is plotted in Fig. 4.1. The three data points are connected by the best fit straight line Xq = ll%e—kt— Compared... 

We synthesized nine silicalites which had different concentrations of defect sites in the zeolite framework determined by isotope exchange method. These silicalites were treated with aluminium trichloride vapor under the same reaction conditions 923 K temperature, 1 h time, 11 kPa aluminium trichloride vapor pressure. Figure 1 shows the plots of the amount of aluminium atoms introduced into the framework against the amount of oxygen atoms on the defect sites. A... 

A1 NMR spectroscopy can also be used for the determination of aluminium coordination environments in solid samples. Examples of spectra from the clay minerals kaolinite and saponite, which show respectively octahedral and tetrahedral coordination of oxygen atoms around their aluminium atoms, are shown in Fig. 3.7. 

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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