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X-ray absorption on light elements (Mg, Si, Al, K, Ca) on silicate melts using in situ high temperature
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Daniel Neuville, IPGP (France)
Dominique De Ligny, LPCML (France)
Laurent Cormier, IMPMC (France)
Anne Marie Flank, SOLEIL-SLS (Switzerland)
Pierre Lagarde, SOLEIL-SLS (Switzerland)
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The structure of silicate and aluminosilicate melts is not well known at high temperature. X-ray absorption spectroscopy is a very specific and interesting way to probe the network structure and more specifically the Al and Si surroundings. Recent developments on X-ray absorption spectroscopy at light K-edges, made on the LUCIA beamline at the Swiss Light Source, enable to measured XANES spectra at high temperature on the Mg, Al, Si, Al, K and Ca K-edges. We have investigated crystal and melts from room temperature up to the liquidus.
Significant change are observed at all K-edges with increasing temperature in particular at the Ca K-edge on anorthite, diopside, and calcium aluminate (C3A and CA) which show an increase of the pre-edge intensity and a decrease of the number of oscillations with increasing temperature.
In Al K-edge spectra, a new peak appears above the mean resonance with increasing temperature for aluminosilicates, which is attributed to an increase of Al in five fold coordination [1].
We followed the Mg and Al environments in spinel (MgAl2O4) with temperature and observed significant change, due to an inverse of the speciation of Mg and Al with temperature.
At the K K-edge important modifications in the XANES appear upon chemical changes and increasing temperature.
All these observations on the XANES at the K-edge of light elements are compared with ab initio simulations using FDMNES code [2], allowing a detailed description and understanding of the XANES spectra.
[1] Neuville et al. (2008) American Mineralogist, 93, 228.
[2] Joly et al. (1999) Physical Review Letters, 82, 2398.
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