TY - JOUR A1 - Wilke, Max A1 - Schmidt, Christian A1 - Farges, Francois A1 - Malavergne, Valerie A1 - Gautron, Laurent A1 - Simionovici, Alexandre A1 - Hahn, Matthias A1 - Petit, Pierre-Emanuel T1 - Structural environment of iron in hydrous aluminosilicate glass and melt-evidence from X-ray absorption spectroscopy N2 - 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 Y1 - 2006 U6 - https://doi.org/10.1016/j.chemgeo.2006.01.017 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Welter, E. A1 - Farges, Francois T1 - Redox Reaction In Silicate Melts Monitored By Static In-Situ Fe K-edge XANES Up To 1180 C Y1 - 2007 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Schmidt, C. A1 - Farges, Francois T1 - In-situ study of the iron species in silicate melts Y1 - 2004 SN - 0016-7037 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Farges, Francois T1 - XAFS of iron in silicate melt at high temperature Y1 - 2004 SN - 0024-4937 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Bernhardt, Rita A1 - Lattard, D. T1 - Determination of the iron oxidation state in basaltic glasses using XANES at the K-edge N2 - Fe K-edge X-ray absorption near edge structure (XANES) and Mossbauer spectra were collected on synthetic glasses of basaltic composition and of glasses on the sodium oxide-silica binary to establish a relation between the pre- edge of the XANES at the K-edge and the Fe oxidation state of depolymerised glasses. Charges of sample material were equilibrated at ambient pressure, superliquidus temperatures and oxygen fugacities that were varied over a range of about 15 orders of magnitude. Most experiments were carried out in gas-flow furnaces, either with pure oxygen, air, or different CO/CO2 mixtures. For the most reduced conditions, the samples charges were enclosed together with a pellet of the IQF oxygen buffer in an evacuated silica glass ampoule. Fe3+/SigmaFe x 100 of the samples determined by Mossbauer spectroscopy range between 0% and 100%. Position and intensity of the pre-edge centroid position vary strongly depending on the Fe oxidation state. The pre-edge centroid position and the Fe oxidation state determined by Mossbauer spectroscopy are nonlinearly related and have been fitted by a quadratic polynomial. Alternatively, the ratio of intensities measured at positions sensitive to Fe2+ and Fe3+, respectively, provides an even more sensitive method. Pre- edge intensities of the sample suite indicate average Fe co-ordination between 4 and 6 for all samples regardless of oxidation state. A potential application of the calibration given here opens the possibility of determining Fe oxidation state in glasses of similar compositions with high spatial resolution by use of a Micro-XANES setup (e.g., glass inclusions in natural minerals). (C) 2004 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0009-2541 ER - TY - JOUR A1 - Wilke, Max A1 - Partzsch, G. M. A1 - Bernhardt, Rita A1 - Lattar, D. T1 - Determination of the iron oxidation state in basaltic glasses using XANES at the K-edge N2 - Fe K-edge X-ray absorption near edge structure (XANES) and Mossbauer spectra were collected on synthetic glasses of basaltic composition and of glasses on the sodium oxide-silica binary to establish a relation between the pre- edge of the XANES at the K-edge and the Fe oxidation state of depolymerised glasses. Charges of sample material were equilibrated at ambient pressure, superliquidus temperatures and oxygen fugacities that were varied over a range of about 15 orders of magnitude. Most experiments were carried out in gas-flow furnaces, either with pure oxygen, air, or different CO/CO2 mixtures. For the most reduced conditions, the samples charges were enclosed together with a pellet of the IQF oxygen buffer in an evacuated silica glass ampoule. Fe3+/Sigma Fe x 100 of the samples determined by Mossbauer spectroscopy range between 0% and 100%. Position and intensity of the pre-edge centroid position vary strongly depending on the Fe oxidation state. The pre-edge centroid position and the Fe oxidation state determined by Mossbauer spectroscopy are nonlinearly related and have been fitted by a quadratic polynomial. Alternatively, the ratio of intensities measured at positions sensitive to Fe2+ and Fe3+, respectively, provides an even more sensitive method. Pre- edge intensities of the sample suite indicate average Fe co-ordination between 4 and 6 for all samples regardless of oxidation state. A potential application of the calibration given here opens the possibility of determining Fe oxidation state in glasses of similar compositions with high spatial resolution by use of a Micro-XANES setup (e.g., glass inclusions in natural minerals). (c) 2004 Elsevier B.V. All rights reserved Y1 - 2005 SN - 0009-2541 ER - TY - JOUR A1 - Wilke, Max A1 - Nabelek, Peter I. A1 - Glascock, Michael D. T1 - B and Li in Proterozoic metapelites from the Black Hills, U.S.A. : Implications for the origin of leucogranitic magmas Y1 - 2002 ER - TY - JOUR A1 - Wilke, Max A1 - Farges, Francois A1 - Petit, Pierre-Emanuel A1 - Brown Jr., Gordon E. A1 - Martin, Francois T1 - Oxidation state and coordination of Fe in minerals : an Fe K XANES spectroscopic study Y1 - 2001 ER - TY - JOUR A1 - Wilke, Max A1 - Farges, Francois A1 - Partzsch, G. M. A1 - Schmidt, C. A1 - Behrens, Harald T1 - Speciation of Fe in silicate glasses and melts by in-situ XANES spectroscopy Y1 - 2007 ER - TY - JOUR A1 - Wilke, Max A1 - Behrens, Harald A1 - Burkhard, Dorothee J. M. A1 - Rossano, Stephanie T1 - The oxidation state of iron in silicic melt at 500 MPa water pressure Y1 - 2002 ER -