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Ramona Langner 1 , Michael Fechtelkord 1 , Erika Palin 2 ,

Ordering of the Al Cation Distribution in the Octahedral Sheets Related to the Ordering of Al in the Tetrahedral Sheets of Phlogopite Investigated by 2D CPMAS NMR and Monte Carlo Simulations. Ramona Langner 1 , Michael Fechtelkord 1 , Erika Palin 2 , Alberto Garcia 3 , Javier López-Solano 4.

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Ramona Langner 1 , Michael Fechtelkord 1 , Erika Palin 2 ,

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  1. Ordering of the Al Cation Distribution in the Octahedral Sheets Related to the Ordering of Al in the Tetrahedral Sheets of Phlogopite Investigated by 2D CPMAS NMR and Monte Carlo Simulations Ramona Langner1, Michael Fechtelkord1, Erika Palin2, Alberto Garcia3, Javier López-Solano4 1 Ruhr-Universität Bochum, Universitätsstraße 150, 44780 Bochum 2 University of Cambridge, Department of Earth Sciences, Cambridge, UK 3 ICMAB-CSIC, Institut de Ciencia de Materials de Barcelona, Spain 4 Universidad del Pais Vasco, Departamento de Fisica de la Materia Condensada, Bilbao, Spain

  2. Phlogopite: one of the few minerals that can incorporate large amounts of F knowledge of how F is incorporated is useful for magmatic petrology (viscosities of magmas, melting temperatures, … ) F-content strongly depends on the Al-content of the phlogopites Ordering of Mg/Al, Al/Si, and OH/F in the phlogopite structure: combination of experimental techniques with computations NMR spectroscopy: information on the local environments of ions and formation of clusters in the structure J-formalism / Monte-Carlo-Simulations: configuration of lowest energy

  3. The Phlogopite Structure after Tateyama et al. (1974) Z. Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie, 139, 196-206.

  4. Phlogopite Synthesis • K(Mg3-xAlx)(Al1+xSi3-xO10) (OH)y(F)2-y • with varying OH/F- ratios: 0.5  y  2.0 • and varying Al- contents: 0.0  x  1.6 • ( VIMg2+ + IVSi4+ VIAl3+ + VIAl3+; Tschermak’s substitution) • Synthesis conditions: T= 600 °C / 800 °C, p = 2 kbar, t ~ 7 d • impurity phases: corundum (a-Al2O3), kalsilite (KAlSiO4), • potassium aluminium hexafluoride (K3AlF6 * 0.5 H2O) • Analysis: 1H, 19F, 27Al, 29Si MAS NMR spectroscopy, • 1D and 2D {1H} -> 29Si CPMAS NMR spectroscopy, • powder XRD, TEM

  5. 29Si MAS NMR spectrum 1H MAS NMR spectrum

  6. The Dipolar Interaction • The resulting magnetic field for the observed nucleus is also influenced by the • magnetic moments of neighbouring nuclei. • The dipolar Hamiltonian for two interacting nuclei i and j depends on • the magnetogyric ratios iand j of the nuclei • the internuclear distance rij  is the angle between the magnetic field direction and the internuclear vector . • homonucleardipolar interaction (i = j): • heteronucleardipolar interaction (i  j) :

  7. {1H}29Si 2D CPMAS NMR Spectrum of Phlogopite with Nominal Composition K(Mg3-xAlx)(Al1+xSi3-xO10)(OH)y(F)2-y, x = 0.6 and y = 1.0 29Si SiOSi3 SiOAlSi2 SiOAl2Si HOMg3 HOAlMg2 1H

  8. The J formalism Example: two cation types A and B in a simple network of sites E = E0 + NAAJ where E0 = constant, and J = EAA + EBB – 2EAB i.e., the energy associated with replacing two like bonds with two unlike bonds • J >0: EAA + EBB > 2EAB • A-B bonds favoured • ordering • J < 0: EAA + EBB < 2EAB • A-A and B-B bonds favoured • exsolution (phase separation) General expression for multiple sites:

  9. Interlayer T-T interactions

  10. T-T, O-O, O-T interactions

  11. Additional interlayer T-T interactions J values

  12. tetrahedral layer, x = 1.0 blue: Si, red: IVAl

  13. T-O-T layer package, x = 1.0 blue: Si, red: IVAl, yellow: VIAl

  14. T-O-T layer package, x = 0.25 blue: Si, red: IVAl, yellow: VIAl, green: Mg

  15. Comparison for x = 0.1 Theory Experiment nominal x: 0.30 estimated x: 0.14 x = 0.1 Si-Si2Al Si-Si2Al Si-SiAl2 Si-SiAl2 Si-Si3 Si-Si3 Si-Al3 Si-Al3

  16. Comparison for x = 0.5 Theory Experiment x = 0.5 theoretical x: 0.80 estimated x: 0.50 Si-Al3 Si-SiAl2 Si-SiAl2 Si-Si2Al Si-Si2Al Si-Si3 Si-Al3 Si-Si3

  17. Conclusions • NMR spectroscopic investigations and Monte-Carlo-simulations both show a clustering of Al in the phlogopite structure • direct neighbourhood of Al in the octahedral and in the tetrahedral • sheets • perfect ordering of ions at x = 1.0 • formation of domains with octAl/tetAl = 1:2, tetAl/Si = 1:1 • x smaller than 1: formation of Al-rich clusters with perfect ordering and • clusters with composition of pure Mg-phlogopite • additional 1D {1H} 29Si CPMAS NMR experiments show: • grouping of OH-groups in the octahedral sheet • formation of Al-rich and OH-rich clusters in the structure • both investigations are in good agreement • but: • problems with higher x-values -> domain size to large? • influence of F still has to be investigated in the calculations

  18. Acknowledgements This presentation is supported by the European Science Foundation (ESF) under the EUROCORES programme EuroMinScI (www.esf.org/eurominsci), through contact No. ERAS-CT-2003-980409 of the European Commission, DG Research, FP6, and by the Deutsche Forschungsgemeinschaft (DFG) under project No. Fe486/6-1.

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