The determination of oxygen in lead

Reducing fusion and hydrogen reduction are suitable for this analysis, which has to date only been described in relatively few papers. The reaction with hydrogen sulphide at high temperature, leading to the formation of water, has been carried out by Grosheim-Krisko et al. (103). 

This determination can be carried out in a similar way as for unalloyed copper. The conditions specified by Kraft and Kahles (64) are as follows Weight of sample about 5 g argon carrier gas 15-40 1/hour temperature 1250°C open graphite crucible no bath nor flux needed several samples 

In view of the low oxygen concentration of lead (99), the reaction is complete within a few minutes. The detection limit of the method is about 0.5 jug/g. 

According to Kraft et al. (99) the following conditions may be used Weight of sample about 5 g temperature 1150°C graphite capsules or open crucible, although capsules are preferred the capsules are heated at about 1900°C before analysis no bath nor flux needed reaction time a few minutes up to 15 minutes if capsules are used determination of the carbon monoxide formed by gas chromatography. 

The Analytical Group of the European Lead Development Committee (106) described a vacuum process which uses pulsed heating the temperature is between 1350 and 1400°C, a covered graphite crucible is used and carbon monoxide is determined by IR spectrometry. The sample weight is 1 g, the blank value of the apparatus is of the order of 2 Mg, and the sensitivity limit is 1 Mg/g. 

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Another need for the determination of oxygen in lead is deoxidizing treatments which are carried out e.g. for hard lead. If accurate analyses are carried out the addition of deoxidizing agents can be adjusted accurately (2). 

THE DETERMINATION OF OXYGEN IN LEAD AND ITS ALLOYS (PbCuTe, PbSnCd)... 

Hydrogen reduction is probably only suitable for the determination of oxygen in copper alloys in special cases. It is limited to alloys containing no alloying components or impurities which form oxides that cannot be reduced with hydrogen. Initial work in this field has been carried out by Hofmann and Schneider (93), who were able to analyse lead bronzes and tin bronzes successfully. 

F can also be separated by solvent extraction. Faure et al. (223)(224) used solvent extraction with disphenyldichiorosilane in isopropyl ether for the determination of oxygen in molybdenum and lead. The separation of F by solvent extraction using triphenyl antimony (V) derivatives is described by Chermette et al. (225)(226). It is shown that, if fluoride is extracted with an excess of reagent, the extracted salt is triphenyl-antimonyhydroxyfluoride if the pH is not too low. The partition constants of this compound in benzene-water and carbon tetrachloride-water systems are high. The kinetics of the fluoride exchange reaction ... 

F is separated by steam distillation of fluorosilicic acid followed by precipitation of lead chlorofluoride. For helium-3 activation (effective incident energy = 15-18 MeV) no extraction of polonium is required. The results obtained for industrial lead were (0.99 + 0.21) /ig/g (n = 8) for He activation and (0.79 + 0.36) ng/g (n = 8) for He activation. The standard deviations of resp. 21 and 45 % compared to the 10 % obtained when roughly the same analytical technique was applied to the determination of oxygen in copper (213)(245), indicate a less homogeneous distribution of the oxygen in lead. The variance for the He results is significantly... 

Gaines SD, Roughgarden J (1985) Larval settlement rate a leading determinant of structure in an ecological community of the marine intertidal zone. Proc Natl Acad Sci USA 82 3707-3711 Gottlieb OR (1989) The role of oxygen in phytochemical evolution towards diversity. Phytochemistry 28 2545-2548... 

The [4 + 2]-cycloaddition of 02( Ag) to rubrene has been shown to be a simple method for the determination of oxygen concentrations in organic solvents.Irradiation of benzene solutions of tropone (86) in the presence of 9,10-dicyanoanthracene leads to the formation of four products, (87), (88), (89) and (90), and in acetonitrile-dichloromethane there is also an [8 + 4]tc adduct (91) produced. It has been suggested that this latter compound arises by coupling of the radical cation of (86) with the radical anion of the dicyanoanthracene (Scheme 2). Solvent-dependent quenching of the lowest excited state of 9,10-dibromoanthracene by 2,5-dimethylhexa-2,4-diene has been studied and appears to proceed by an exciplex. Flash photolysis investigations have shown that a neutral radical species is an intermediate in the formation of the [4 + 2] adduct which is a dibenzobicyclo[2.2.2]octadiene-type compound. Irradiation of 9,10-dicyanophenanthrene (DCA) in the presence of buta-1,3-diene gives a mixture of the product of [3 + 2]-photo-... 

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... 

Marker experiments made with lead to the determination of oxygen diffusion coefficients via alumina grain boundaries and via the oxide bulk. Taking into consideration the plots of In [ 0] = f(x), the first part of the curve corresponds to the apparent diffusion of oxygen. From the three diffusion regimes, the B regime is usually chosen for the study of intergranular diffusion... 

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