Electron microprobe, lead

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.

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. 

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. 

The most useful tool for the study of penetration is the electron microprobe, which was first used for this purpose by Cannon and Welling (14). They have shown the buildup of relatively thick layers of lead compounds around pellets exposed to exhaust originating from heavily leaded fuels. More recently, penetration profiles in pellets have been published for exhaust produced by fuels with lower amounts of lead. Figure 8 shows such a profile in a pellet exposed to exhaust with 0.5 g Pb/gal for 400 hr. Note, that at the exterior of the pellet, lead concentration (by weight) has... 

The surface of the exposed specimens was examined by the electron microprobe. As the electron-microprobe traces of a few of the experiments indicate (Fig. 23), an enhanced Pb affinity for platinum seems to be, indeed, the case. The lower trace (A) shows that there is much more lead retained on the areas covered by Pd, while the middle trace (B) indicates the same for the areas covered by Pt. This phenomenon recurs at each of the four interfaces between the metal and A1203 segments of the slide. In the experiment, the slides were exposed to approximately 72 hr of treatment (which is equivalent to 2000-2500 miles of simulated vehicle operation), and the fuel contained 0.5 g Pb/gal. In case of the traces (A) and (B), there was no scavenger in the fuel. 

Cocherie A., Legendre O., Peucat J. J., and Kouamelan A. N. (1998) Geochronology of polygenetic monazites constrained by in situ electron microprobe Th-U-total lead determination implications for lead behavior in monazite. Geochim. Cosmochim. Acta 62, 2475—2497. 

The parameters that affect the degradation of supported platinum and palladium automotive exhaust catalysts are investigated. The study includes the effects of temperature, poison concentration, and hed volume on the lifetime of the catalyst. Thermal damage primarily affects noble metal surface area. Measurements of specific metal area and catalytic activity reveal that supported palladium is more thermally stable than platinum. On the other hand, platinum is more resistant to poisoning than palladium. Electron microprobe examinations of poisoned catalyst pellets reveal that the contaminants accumulate almost exclusively near the skin of the pellet as lead sulfate and lead phosphate. It is possible to regenerate these poisoned catalysts by redistributing the contaminants throughout the pellet. 

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-... 

Analytical speciation methods, referred to earher, generally differ from the methods adequate for bulk quantrffcation of lead. As with bulk methods, nonetheless, contaminating levels should not be permitted in interfering amounts. Several lead speciation approaches are X-ray absorption spectrometry, X-ray diffraction, and electron-microprobe microanalyses (U.S. EPA, 2006 Welter et al., 1999). 

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. 

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