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Wilke, M., Schmidt, C., Farges, F., Malavergne, V., Gautron, L., Simionovici, A., Hahn, M. & Petit, P. E. (2006) Structural environment of iron in hydrous aluminosilicate glass and melt-evidence from X-ray absorption spectroscopy. Chem. Geol. 229 144–161. 
Added by: Florent Boucher (2016-05-12 13:21:37)
Type de référence: Article
DOI: 10.1016/j.chemgeo.2006.01.017
Numéro d'identification (ISBN etc.): 0009-2541
Clé BibTeX: Wilke2006
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Catégories: IMN
Mots-clés: coordination environment, diamond-anvil cell, dissolution mechanisms, esrf beamline id26, ferric-ferrous ratio, k-edge, molecular-dynamics, natural silicate liquids, near-edge structure, oxidation-reduction equilibria
Créateurs: Farges, Gautron, Hahn, Malavergne, Petit, Schmidt, Simionovici, Wilke
Collection: Chem. Geol.
Consultations : 8/372
Indice de consultation : 2%
Indice de popularité : 0.5%
Résumé     
The iron speciation in hydrous haplotonalitic and haplogranitic silicate glasses was studied using XAFS spectroscopy and transmission electron microscopy (TEM). Spectral features occurring at the main crest of the XANES at the iron K-edge of hydrous glasses indicate contributions to the spectra by iron-moieties present in a more ordered structural environment than found in the dry glass. These differences are also suggested by analysis of the EXAFS. These effects are not completely suppressed even for those samples that were quenched with a higher cooling rate. Strongest differences to the dry glass are observed for a sample that was quenched slowly through the temperature of glass transformation. Crystals (60 to 1500 nm in size) of magnetite, maghemite and another unidentified phase were observed in this sample by TEM, whereas no crystals were found in samples quenched with regular or high cooling rates. In-situ XANES measurements up to 700 degrees C and 500 MPa were performed to reveal the origin (i.e., during synthesis or quench) of the structural differences for those hydrous glasses that do not display any detectable crystallization. The comparison of XANES spectra collected on Fe2+ in water-saturated haplogranitic melt at 700 degrees C and 500 MPa and on Fe2+ in dry melt at 1150 degrees C shows that the local structural environment of Fe2+ in both systems is similar. This indicates that there is no detectable and direct influence of water on the local structure around iron in this type of melt. Hence, the differences observed between hydrous and dry glasses can only be related to artefacts formed during the quench process. (c) 2006 Elsevier B.V. All rights reserved.
Added by: Florent Boucher  
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