Oxygen in lead

Lead is worked and used in both unalloyed and alloyed form. Hard lead e.g. contains antimony and is used in batteries. 

The oxidizing treatment of molten lead plays an important role in the refining processes, especially to remove traces of antimony, arsenic and tin. The oxides resulting from this process separate slowly because of the small difference in density with liquid lead. When the resting periods are too short, there is a risk that the cast lead contains oxide inclusions. 

Another difficulty results from the tendency of liquid lead to oxidize. 

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). 

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Oxygen in lead Maintaining required oxygen content Galvanic cell (measurement of e.m. F. induced in solid electrolyte with ion conductivity)... 

A typical example of the importance of suitable sample preparation was encountered during the certification - provisional in 1974 (5) and final in 1978 (6) - of oxygen in lead. In the first round, sample preparation was carried out by the participating laboratories which are mainly physically oriented. In the final certification all samples were prepared in the same specialized laboratory after extensive study of the problem. Although in both campaigns samples have been etched between irradiation and measurement, the results differ by a factor of 3 in absolute value and a significant improvement in precision was obtained in the second campaign (Table III-2). 

Table III-2 Results for oxygen in lead obtained by photon and charged particle activation analysis (6)...

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... 

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

Lead Telluride. Lead teUuride [1314-91 -6] PbTe, forms white cubic crystals, mol wt 334.79, sp gr 8.16, and has a hardness of 3 on the Mohs scale. It is very slightly soluble in water, melts at 917°C, and is prepared by melting lead and tellurium together. Lead teUuride has semiconductive and photoconductive properties. It is used in pyrometry, in heat-sensing instmments such as bolometers and infrared spectroscopes (see Infrared technology AND RAMAN SPECTROSCOPY), and in thermoelectric elements to convert heat directly to electricity (33,34,83). Lead teUuride is also used in catalysts for oxygen reduction in fuel ceUs (qv) (84), as cathodes in primary batteries with lithium anodes (85), in electrical contacts for vacuum switches (86), in lead-ion selective electrodes (87), in tunable lasers (qv) (88), and in thermistors (89). 

Analytical Methods. Molybdenum contents in ore concentrates and technical oxide are most accurately deterrnined gravimetricaHy by precipitating lead molybdate. Molybdenum content is usually not determined on pure compounds or metal. Instead, spectrographic methods are used to measure impurity elements that must be controlled. Carbon and oxygen in metal products are measured by standard gas analysis methods. 

Polyamides, like other macromolecules, degrade as a result of mechanical stress either in the melt phase, in solution, or in the soHd state (124). Degradation in the fluid state is usually detected via a change in viscosity or molecular weight distribution (125). However, in the soHd state it is possible to observe the free radicals formed as a result of polymer chains breaking under the appHed stress. If the polymer is protected from oxygen, then alkyl radicals can be observed (126). However, if the sample is exposed to air then the radicals react with oxygen in a manner similar to thermo- and photooxidation. These reactions lead to the formation of microcracks, embrittlement, and fracture, which can eventually result in failure of the fiber, film, or plastic article. 

The stmctures in which SiO tetrahedra share all four oxygen atoms lead to the principal forms of siUca. Replacement of some siUcon atoms by aluminum gives a negatively charged framework of composition, A1 S 02. in which positive ions are accommodated in holes in the stmcture. 

The preparation of triaryknethane dyes proceeds through several stages formation of the colorless leuco base in acid media, conversion to the colorless carbinol base by using an oxidising agent, eg, lead dioxide, manganese dioxide, or alkah dichromates, and formation of the dye by treatment with acid (Fig. 1). The oxidation of the leuco base can also be accompHshed with atmospheric oxygen in the presence of catalysts. 

Replacement of the sulfur atom in the thiosemicarba2one moiety by an oxygen atom leads to a loss of antiviral activity. Methisa2one has no significant effect on vaccinia vims DNA synthesis (14) but seems to inhibit late protein synthesis by a mechanism that remains to be elucidated. 

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