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| Titel |
Monoclinic structure of hydroxylpyromorphite Pb10(PO4)6(OH)2 – hydroxylmimetite Pb10(AsO4)6(OH)2 solid solution series |
| VerfasserIn |
Alicja Giera, Maciej Manecki, Olaf Borkiewicz, Sylwia Zelek, John Rakovan, Tomasz Bajda, Tomasz Marchlewski |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250128329
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| Publikation (Nr.) |
 EGU/EGU2016-8312.pdf |
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| Zusammenfassung |
| Seven samples of hydroxyl analogues of pyromorphite-mimetite solid solutions series were
synthesized from aqueous solutions at 80˚ C in a computer-controlled chemistate: 200 mL
aqueous solutions of 0.05M Pb(NO3)2 and 0.03M KH2AsO4 and/or KH2PO4 were dosed
with a 0.25 mL/min rate to a glass beaker, which initially contained 100 mL of distilled
water. Constant pH of 8 was maintained using 2M KOH. The syntheses yielded
homogeneous fine-grained white precipitates composition of which was close to theoretical
Pb10[(PO4)6−x(AsO4)x](OH)2, where x = 0, 1, 2, 3, 4, 5, 6. High-resolution powder X-ray
diffraction data were obtained in transmission geometry at the beamline 11-BM at the
Advanced Photon Source (Argonne National Laboratory in Illinois, USA). The
structure Rietveld refinements based on starting parameters of either hexagonal
hydroxylpyromorphite or monoclinic mimetite-M were performed using GSAS+EXPGUI
software.
Apatite usually crystallizes in the hexagonal crystal system with the space group P63/m.
For the first time, however, the lowering of the hexagonal to monoclinic crystal
symmetry was observed in the hydroxyl variety of pyromorphite-mimetite solid solution
series. This is indicated by better fitting of the modeled monoclinic structure to the
experimental data. The same is not the case for analogous calcium hydroxylapatite series
Ca5(PO4)3OH – Ca5(AsO4)3OH (Lee et al. 2009). Systematical linear increase of unit cell
parameters is observed with As substitution from a=9.88, b=19.75, and c=7.43 for
Pb10(PO4)6(OH)2 to a=10.23, b=20.32, and c=7.51 for Pb10(AsO4)6(OH)2. A strong
pseudohexagonal character (γ ≈ 120˚ and b ≈ 2a) of the analyzed monoclinic phases was
established.
This work is partially funded by AGH research grant no 11.11.140.319 and partially by
Polish NCN grant No 2011/01/M/ST10/06999.
Lee Y.J., Stephens P.W., Tang Y., Li W., Philips B.L., Parise J.B., Reeder R.J.,
2009. Arsenate substitution in hydroxylapatite: Structural characterization of the
Ca5(PxAs1−xO4)3OH solid solution. American Mineralogist, 94, 666-675. |
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