Compositions of Lead

Lead exists naturally as four stable isotopes Pb, Pb, Pb, and Pb. Measurable differences in the relative abundances of these four isotopes throughout the environment result from the amounts and radioactive decay of the progenitor isotopes tx/2 = 4.5 X 9 yr), ti/2 = 0.70 X 10 yr), and Th = 1.4 x 10 yr) that form Pb, Pb, and Pb, 

Natural differences in lead isotopic compositions in geological formations persist after the lead has been extracted and processed as industrial lead. This occurs because there is no measurable biological, chemical, or physical fractionation of lead isotopes either in the environment or in industrial processes (Barnes et al. 1978 Flegal and Stukas 1987 Russell and Farquhar 1960). Although stable lead isotopic compositions may vary naturally by as much as 10%-15%, they generally vary less than that. 

There are, however, relatively pronounced regional and temporal differences in the lead isotopic compositions of contaminant leads in the environment. These have often reflected differences in the isotopic compositions of lead alkyl additives in gasolines, as well as differences in other industrial emissions of lead (Elias et al. 1982 Flegal et al. 1989 Patterson and Settle 1987 Manton 1985 Rabinowitz 1987 Rabinowitz and Wetherill 1972 Smith et al. 1990, 1992a Sturges and Barrie 1987 Tera et al. 1985). These 

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The particle size and chemical composition of lead and lead compounds affect the readiness with which lead is absorbed from the lungs and digestive tract (see Lead compounds, industrial toxicology). Larger particles and compounds having low aqueous solubiHty are less hazardous than finely divided particles and compounds of higher solubiHty. 

Lead—silver alloys are used extensively as soft solders these contain 1—6 wt % silver. Lead—silver solders have a narrower free2ing range and higher melting point (304°C) than conventional solders. Solders containing 2.5 wt % silver or less are used either as binary alloys or combined with 0.5—2 wt % tin. Lead—silver solders have excellent corrosion resistance. The composition of lead—silver solders is Hsted in ASTM B32-93 (solder alloys) (7). 

What composition of lead-tin solder is the best choice for joining electronic components Why is this composition chosen ... 

BS 1 1984 Composition of lead and lead alloy sheaths for electri< cahtes... 

Figure 1.44. Isotopic composition of lead in black ore (open symbols) and in yellow ore (closed symbols) in the Hokuroku district. The isotopic fields for black ore from the Fukazawa, Shakanai, and Kosaka deposits are...

Isotopic composition of leads from Kuroko deposits (Fehn et al., 1983)... 

Many scientists thought that Earth must have formed as long as 3.3 billion years ago, but their evidence was confusing and inconsistent. They knew that some of the lead on Earth was primordial, i.e., it dated from the time the planet formed. But they also understood that some lead had formed later from the radioactive decay of uranium and thorium. Different isotopes of uranium decay at different rates into two distinctive forms or isotopes of lead lead-206 and lead-207. In addition, radioactive thorium decays into lead-208. Thus, far from being static, the isotopic composition of lead on Earth was dynamic and constantly changing, and the various proportions of lead isotopes over hundreds of millions of years in different regions of the planet were keys to dating Earth s past. A comparison of the ratio of various lead isotopes in Earth s crust today with the ratio of lead isotopes in meteorites formed at the same time as the solar system would establish Earth s age. Early twentieth century physicists had worked out the equation for the planet s age, but they could not solve it because they did not know the isotopic composition of Earth s primordial lead. Once that number was measured, it could be inserted into the equation and blip, as Patterson put it, out would come the age of the Earth. ... 

In a climax to his sediment studies, Patterson reported tersely that we have found the composition of lead in snow to be very different from the composition of lead which has been deposited on the ocean floors during the past 100,000 years. The lead in Lassen Volcanic National Park had a signature mix of lead isotopes, a characteristic fingerprint identifying it as a... 

A GC-MS method for determining the isotope composition of lead in blood and urine samples is based on preparation of Pb(CgH4F-p)4 using the corresponding Grignard reagent108. 

Gale, N.H. and Mussett, A.E. (1973). Episodic uranium-lead models and the interpretation of variations in the isotopic composition of lead in rocks. Reviews of Geophysics and Space Physics 11 37-86. 

Equation (8.47), with t = 0 and the composition of lead from meteoritic troilite used for the initial isotopic ratio of lead, was used by Clair Patterson (1955,1956) to determine the age of the Earth. In the 1950s, the largest uncertainty in determining the age of the Earth was the composition of primordial lead. In 1953, Patterson solved this problem by using state-of-the-art analytical techniques to measure the composition of lead from troilite (FeS) in iron meteorites. Troilite has an extremely low U/Pb ratio because uranium was separated from the lead in troilite at near the time of solar-system formation. Patterson (1955) then measured the composition of lead from stony meteorites. In 1956, he demonstrated that the data from stony meteorites, iron meteorites, and terrestrial oceanic sediments all fell on the same isochron (Fig. 8.20). He interpreted the isochron age (4.55+0.07 Ga) as the age of the Earth and of the meteorites. The value for the age of the Earth has remained essentially unchanged since Patterson s determination, although the age of the solar system has been pushed back by —20 Myr. 

Cumming, G. L., Robertson, D. K., "Isotopic Composition of Lead From... 

Compositions of lead free gasoline with octane qualities equivalent to present day gasoline are shown in Table IV. These compositions represent the sum total of the many different refinery models presented in the API report. 

Lead is of interest us being the terminal product of radioactive decay. Thus, while ordinary lead has the atomic wcighi 207.11 (being composed of I. 47 r oJPb. 26.205, - " Ph. 2(1.H > " Pb and 51.55. . - " Phi. the isotopic composition, and hence the atomic weight, varies somewhat it) lead from meteorites, from deep-sealed rocks and from uranium ores (the last being sonn-vvhat less dense, as would be expected from the fact that ""Ph is the end produei ol the uranium series I. These variations in isotopic composition of lead pcnnii of calculations. it the age ol ihe eanh laud (he metcoritesi. 

H. Brown, G. Tilton, and M. Inghram Concentration of uranium and lead and the isotopic composition of lead in meteoritic material. Physiol. Rev. 92, 1234 (1953). 

Figure 12.7 206Pb/207Pb versus 208Pb/207Pb plot showing the lead isotopic compositions of lead... 

Hopper, J. F., Ross, H. B., Sturges, W. T., and Barrie, L. A. (1991). Regional source discrimination of atmospheric aerosols in Europe using the composition of lead. Tellus 43B, 45—60. 

The results of the quantitative analysis of montmorillonite samples obtained with different Ca-montmorillonite/lead ion ratio and pH are shown in Table 2.14 for the surfaces with even lead distribution. The chemical composition of lead enrichments is shown in Table 2.15. 

In the first row of Table 2.14, the average composition of calcium-montmoril-lonite is given. In the second row, the mean composition of lead-montmorillonite, where lead concentration is even (no enrichments), is provided. The atomic percent of lead in lead-montmorillonite is about equal, within the experimental error of 5% to 10%, of the atomic percent of calcium in calcium-montmorillonite. Since the interlayer cation of the original montmorillonite is calcium ion, lead ions can completely exchange calcium ions. 

As discussed previously in this chapter, there are spots where the lead content (and the elementary composition) is higher and so-called lead enrichments are formed. Table 2.15 shows that the composition of lead enrichments can be rather different in different enrichments. Besides the increase in lead concentration, other changes in elementary composition may also occur. There are examples of lead enrichment (Figure 2.27 Sample 3 in Table 4) where the average composition remains unchanged even though the lead concentration is elevated. However, there are lead enrichments where the increase in lead concentration is accompanied by a simultaneous increase in iron (Sample 4 in Table 2.15), or a simultaneous increase of calcium and lead (Sample 2). Lead enrichment in these cases is likely due to lead coprecipitation reactions with other minerals (iron oxide and other calcium silicate phases) that were present in the sample. 

Fuel, chiefly charcoal, usually has a low lead content and, in many cases, the trees from which it came were growing near the ore deposit and tend to have incorporated lead of the same isotopic composition as the ore deposit. In most cases, the isotope composition of lead in the smelted copper has not been perturbed away from that of lead in the copper ore. Further isotopic comparisons of copper ores and associated Bronze Age copper slags are needed to examine this question more extensively. Comparisons that have already been made bear out the hypotheses just advanced. 

D 215 22.0 22.5 Fig. 28. Evolution of the isotopic composition of lead and sulfur in the Early and Middle Precambrian, as illustrated by a typical section in Central Ukraine (after Tugarinov and Voytkevich). 

Gast P. W., Tilton G. R., and Hedge C. (1964) Isotopic composition of lead and strontium from Ascension and Gough Islands. Science 145, 1181-1185. 

Altliough plagioclase, unlike calcium-rich pyroxene, ilmenite, or zircon, does not readily incorporate uranium or thorium, isotopic compositions of lead in plagioclase are of particular interest. Plagioclase is a dominant mineral phase in the lunar crust and a major constituent of mare basalts that can incorporate lead into cation sites normally occupied by potassium, sodium, or calcium and thereby play an important role in the U-Th-Pb isotopic systematics. 

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