Lead, microprobe analysis electron

Soluble pigments The most important pigments in this class are the metallic chromates, which range in solubilities from 17 0 to 0-00005 g/1 CrO . An examination has recently been carried out of the mechanism of inhibition by chromate ions and it has been shown by chemical analysis of the stripped film, Mdssbauer spectroscopy and electron microprobe analysis that the air-formed film is reinforced with a more protective material in the form of a chromium-containing spinel (Chapter 17). The situation is, however, complicated by the possibility that some chromates, particularly the basic ones, may inhibit through the formation of soaps. There is evidence that lead chromate can function in this way. 

Table V summarizes the data on the lead concentration obtained by electron microprobe analysis of the objects. It was not possible to determine any data on lead from x-ray fluorescence, and NAA cannot be used for lead. The sensitivity of the electron microprobe for lead is poor, and the precision was 15%. These data suggest that the lead content in the silver objects is consistently low and that lead ore refining was well developed.

Lead curse tablets from Roman Carthage contain variable amounts of very small metallic inclusions. Electron microprobe analysis confirmed these metallic inclusions were bronze, brass, and a Sn-Sb alloy. This was interpreted as possible evidence of lead metal recycling. Six samples were chosen to represent a range of tablets containing the minimum to the maximum number of inclusions. Thermal ionization mass spectrometry of the Pb isotopes in the curse tablets appear to define a mixing line, with the tablets containing the least number of inclusions plotting closest to the Tunisian lead ore isotope ratios. 

A.D. were found in old mines, and sizable slag deposits suggest at least some level of lead exploitation during Roman times (2). By the careful selection of Roman lead artifacts likely to have been manufactured in Carthage, and the use of lead isotope analysis, it may be possible to confirm the use of Tunisian lead ores during the Roman period. In this preliminary study, analysis of 22 curse tablets by electron microprobe analysis (EMPA) and six tablets by thermal ionization mass spectrometry (TIMS) suggest that these artifacts might be used to better understand Roman lead use and trade. 

For surface structure studies, perhaps the most popular technique has been LEED (373). Elastically diffracted electrons from a monoenergetic beam directed to a single-crystal surface reveal structural properties of the surface that may differ from those of the bulk. Some applications of LEED to electrocatalyst characterization were cited in Section IV (106,148,386). Other, less specific, but valuable surface examination techniques, such as scanning electron microscopy (SEM) and X-ray microprobe analysis, have not been used in electrocatalytic studies. They could provide information on surface changes caused by reaction, some of which may lead to catalyst deactivation (256,257). Since these techniques use an electron beam, they can be coupled with previously discussed methods (e.g. AES or XPS) to obtain a qualitative mapping of the structure and composition of a catalytic surface. 

Having made these qualitative observations on the parameters that control poisoning, we subjected the catalysts to detailed analysis. As in our earlier poisoning study (3), electron microprobe analysis revealed that the poison accumulated almost exclusively at the outer edge of the catalyst pellet. The relative concentrations of lead and sulfur, as well as x-ray diffraction, suggest that the lead was primarily in the form of lead sulfate (3, 6). The findings from a typical microprobe analysis of a poisoned catalyst are presented in Figure 6. 

In the end, it is worth mentioning that another kind of approach could still be undertaken to determine copper and lead forms in soils polluted with metallurgical dust. This is namely the direct electron microprobe analysis (Hiller and Bruemmer 1989 Weber and Kowaliiiski 1987 Weber 1989). However, some attempts to apply this method to the soils from copper smelter neighbour-... 

Figure 12.7 Electron beam microprobe analysis of Pb, Zr, and Ti stoichiometry as a function of heat-treatment temperature for sintered PZT thin films (2 h anneals). Lead loss is enhanced at higher annealing temperatures. (After Reference 49.)...

From an environmental monitoring viewpoint, this method has been used to determine the elemental composition of complex lead particulates [70]. However, the equipment for electron microprobe analysis is expensive, and sample preparation is complex hence, the method is not extensively used. 

The primary methods of analyzing for lead in environmental samples are AAS, GFAAS, ASV, ICP/AES, and XRFS (Lima et al. 1995). Less commonly employed techniques include ICP/MS, gas chromato-graphy/photoionization detector (GC/PID), IDMS, DPASV, electron probe X-ray microanalysis (EPXMA), and laser microprobe mass analysis (LAMMA). The use of ICP/MS will become more routine in the future because of the sensitivity and specificity of the technique. ICP/MS is generally 3 orders of magnitude more sensitive than ICP/AES (Al-Rashdan et al. 1991). Chromatography (GC,... 

The presence of small lead inclusions is easily established by using the x-ray modulation method on the microprobe. We believe that a lineal intercept analysis from pictures taken by this method is probably the most accurate if the electron microprobe is used. 

The previously discussed analysis methods give information only on the total lead content of the analyte. Electron microprobe and X-ray fluorescene analysis can provide some information on the molecular nature of the lead compound, by comparing the ratios of the elements present [70]. There are, however, several tools that... 

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