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Lead Content (lead + content)
Selected AbstractsEffect of Lead Content on the Structure and Electrical Properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001Huiqing Fan The effects of lead content on the structure and electrical properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 ceramics were investigated. Specimens with various lead concentrations were prepared by the conventional oxide-mixing method. When the lead concentration was slightly less than the stoichiometric amount, a large amount of pyrochlore phase was formed along with the perovskite phase. On the other hand, excessive amounts of lead led to the formation of PbO on the surface of the specimen. These second phases were seriously detrimental to electromechanical properties. The highest piezoelectric properties were observed when an excess of 1 mol% lead was added. By optimizing the specimen composition, excellent piezoelectric and dielectric properties (kp= 0.7, d33= 490 pC/N, and ,m= 15000) were obtained. [source] Characterization of pottery from the Republic of Macedonia I: Raman analyses of Byzantine glazed pottery excavated from Prilep and Skopje (12th,14th century)JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2009Vinka Tanevska Abstract In order to gain some understanding of and to characterize the materials used in Byzantine glazed ceramic finds in the Republic of Macedonia, as well as to obtain information on their manufacturing technology, micro-Raman spectra of 15 representative glazed shards, all dated from 12th to 14th century, were recorded. The elemental composition of the body and glaze of selected shards was obtained by scanning electron microscopy-energy dispersive X-ray spectrometry (SEM-EDXS). At least 17 different minerals in the ceramic body were identified from the Raman spectra, among which were a variety of feldspars (microcline, albite and sanidine) as well as andradite, apatite and forsterite. According to the identified minerals, locations of the used raw materials in the vicinity of the archaeological sites are proposed. There is a good correlation between the polymerization index derived from the Raman spectra and the lead content obtained from the SEM-EDXS analyses, therefore the firing temperature of the analyzed glazes could be assessed. The SEM-EDXS analyses showed the presence of different coloring agents (Cu, Co, Cr, Sb) as well as opacifying (Sb) and fluxing (Pb) agents in the glaze matrix. The content of P2O5 in the glaze of one of the shards is also discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Structural and Dielectric Characterization of Nanocrystalline (Ba, Pb)ZrO3 Developed by Reverse Micellar SynthesisJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 10 2006Tokeer Ahmad Nanocrystalline zirconates of barium and lead have been synthesized using a modified reverse micellar route (avoiding alkoxides). The entire solid solution of Ba1,xPbxZrO3 (0,x,1) has been synthesized for the first time. Powder X-ray diffraction studies show the monophasic nature of the powders after heating at 800°C except minor impurities of ZrO2 (2%,3%) at a higher lead content (x=0.50 and 0.75). The oxides crystallize in the cubic structure till x=0.25; for higher values, they crystallize in the orthorhombic structure. The particle size obtained from X-ray line-broadening studies and transmission electron microscopic studies is found to be in the range of 20,60 nm for all the oxides obtained after heating at 800oC. The grain size of the solid solution of Ba1,xPbxZrO3 (0,x,1) was found to increase with the lead content. The dielectric constant of the solids corresponding to Ba1,xPbxZrO3 (0,x,1) was found to be a maximum at x=0.50. Note that the cubic to orthorhombic transition is also observed between x=0.25 and 0.5. Dielectric properties with respect to variation in frequency and temperature are reported for these nanocrystalline oxides for the first time. [source] Effect of Lead Content on the Structure and Electrical Properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2001Huiqing Fan The effects of lead content on the structure and electrical properties of Pb((Zn1/3Nb2/3)0.5(Zr0.47Ti0.53)0.5)O3 ceramics were investigated. Specimens with various lead concentrations were prepared by the conventional oxide-mixing method. When the lead concentration was slightly less than the stoichiometric amount, a large amount of pyrochlore phase was formed along with the perovskite phase. On the other hand, excessive amounts of lead led to the formation of PbO on the surface of the specimen. These second phases were seriously detrimental to electromechanical properties. The highest piezoelectric properties were observed when an excess of 1 mol% lead was added. By optimizing the specimen composition, excellent piezoelectric and dielectric properties (kp= 0.7, d33= 490 pC/N, and ,m= 15000) were obtained. [source] Determination of lead content in medicinal plants by pre-concentration flow injection analysis,flame atomic absorption spectrometryPHYTOCHEMICAL ANALYSIS, Issue 6 2009Marina M. A. Campos Abstract Introduction , Although medicinal plants are widely used throughout the world, few studies have been carried out concerning the levels of heavy metal contaminants present. Such metals are highly toxic to living organisms even in low concentrations owing to their cumulative effect. The present paper describes the the development of a pre-concentration flow injection analysis-flame atomic absorption spectrometric system to determine the lead content in medicinal plants at the ppb level. Objective , To develop a pre-concentration flow injection analysis-flame atomic absorption spectrometric system to determine the lead content in medicinal plants at the ppb level. Methodology , A pre-concentration flow system was coupled to a flame atomic absorption spectrometer. The plant samples were analysed after nitroperchloric digestion. The proposed system was optimised by evaluating the following parameters: nature, concentration and volume of the eluent solution, elution flow rate, elution efficiency, pre-concentration flow rate and pre-concentration time. Results , The proposed system exhibited good performance with high precision and repeatability (RSD , 2.36%), excellent linearity (r = 0.9999), low sample consumption (10.5 mL per determination) and an analytical throughput of 55 samples/h. Lead concentrations ranged from 3.37 ± 0.25 to 7.03 ± 0.51 ,g/g in dry material. This concentration interval is greater than that previously published in the literature. Conclusion , The inclusion of a pre-concentration column in the flow manifold improved the sensitivity of the spectrometer. Thus, it was possible to determine the analyte at the ng/mL level in sample solutions of medicinal plants. This is a very important accomplishment, especially when the cumulative effect of heavy metals in living organisms is considered. Copyright © 2009 John Wiley & Sons, Ltd. [source] Problems in determination of skeletal lead burden in archaeological samples: An example from the First African Baptist Church populationAMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 4 2008L.E. Wittmers Jr. Abstract Human bone lead content has been demonstrated to be related to socioeconomic status, occupation and other social and environmental correlates. Skeletal tissue samples from 135 individuals from an early nineteenth century Philadelphia cemetery (First African Baptist Church) were studied by electrothermal atomic absorption spectrometry and X-ray fluorescence for lead content. High bone lead levels led to investigation of possible diagenetic effects. These were investigated by several different approaches including distribution of lead within bone by X-ray fluorescence, histological preservation, soil lead concentration and acidity as well as location and depth of burial. Bone lead levels were very high in children, exceeding those of the adult population that were buried in the cemetery, and also those of present day adults. The antemortem age-related increase in bone lead, reported in other studies, was not evidenced in this population. Lead was evenly deposited in areas of taphonomic bone destruction. Synchrotron X-ray fluorescence studies revealed no consistent pattern of lead microdistribution within the bone. Our conclusions are that postmortem diagenesis of lead ion has penetrated these archaeological bones to a degree that makes their original bone lead content irretrievable by any known method. Increased bone porosity is most likely responsible for the very high levels of lead found in bones of newborns and children. Am J Phys Anthropol, 2008. © 2008 Wiley-Liss, Inc. [source] Geochemical and mineralogical distinctions between Bonnin and Morris (Philadelphia, 1770,1772) porcelain and some contemporary British phosphatic waresGEOARCHAEOLOGY: AN INTERNATIONAL JOURNAL, Issue 7 2001J. Victor Owen The major element compositions of 15 ceramic sherds from the Bonnin and Morris factory site were determined by electron microprobe. Thirteen samples are phosphatic; the others consist of (a) "soapstone" (magnesian/plombian) and (b) true porcelain, and are interpreted as exotic artifacts, as is one compositionally distinct (relatively SiO2 -poor, P2O5+CaO-rich) phosphatic sample. Although long considered to be virtually indistinguishable from Bow porcelain (London: ca. 1747,1776), the phosphatic Philadelphia wares have a relatively low mean CaO/P2O5 ratio (3.3 versus 3.8; molecular proportions) and high alumina content (6.6 versus 5.4 wt % Al2O3). Furthermore, unlike Bow, the Bonnin and Morris samples contain calcic plagioclase (bytownite), and in some instances, an orthoclase-rich ternary feldspar. The preservation of calcic plagioclase indicates that Philadelphia porcelain was fired at (rather than above) the thermal minimum in the An-SiO2 -C3P system, although the presence of Na (and other fluxes) in these wares precludes the exact determination of the maximum firing temperature from this phase diagram. These wares are also distinctive insofar as the phosphate and melt phases can contain small amounts of lead; they have bulk lead contents of approximately 0.1,1.2 wt % PbO. This component has not been detected in the body of Bow or other contemporary British phosphatic porcelains. Their principal similarity lies in the fact that both wares contain sulfate. In addition, the glazes on Bonnin and Morris porcelain (e.g., PbO , 35,50 wt %; SnO2 , 1,2%) compositionally resemble those used at Bow. If feldspar is formed at all, then Al-poor phosphatic porcelain (or those with low CaO/P2O5 ratios) will have comparatively low modal calcic plagioclase contents, thereby allowing the rapid depletion of this mineral via resorption by the melt phase during vitrification. Such appears to have been the case for analyzed Bow porcelain, which is therefore interpreted to have been overfired (sensu lato) relative to its Philadelphia counterpart. Conceivably, calcic plagioclase could be preserved in low-Al wares that were fired only briefly at vitrification temperatures. Given the role of firing history in governing the mineralogy of porcelain, compositional criteria are more reliable for distinguishing these wares. © 2001 John Wiley & Sons, Inc. [source] |