TY - JOUR A1 - Cerantola, Valerio A1 - Wilke, Max A1 - Kantor, Innokenty A1 - Ismailova, Leyla A1 - Kupenko, Ilya A1 - McCammon, Catherine A1 - Pascarelli, Sakura A1 - Dubrovinsky, Leonid S. T1 - Experimental investigation of FeCO3 (siderite) stability in Earth's lower mantle using XANES spectroscopy JF - American mineralogist : an international journal of earth and planetary materials N2 - We studied FeCO3 using Fe K-edge X-ray absorption near-edge structure (XANES) spectroscopy at pressures up to 54 GPa and temperatures above 2000 K. First-principles calculations of Fe at the K-edge in FeCO3 were performed to support the interpretation of the XANES spectra. The variation of iron absorption edge features with pressure and temperature in FeCO3 matches well with recently reported observations on FeCO3 at extreme conditions, and provides new insight into the stability of Fe-carbonates in Earth's mantle. Here we show that at conditions of the mid-lower mantle, ~50 GPa and ~2200 K, FeCO3 melts and partially decomposes to high-pressure Fe3O4. Carbon (diamond) and oxygen are also inferred products of the reaction. We constrained the thermodynamic phase boundary between crystalline FeCO3 and melt to be at 51(1) GPa and ~1850 K. We observe that at 54(1) GPa, temperature-induced spin crossover of Fe2+ takes place from low to high spin such that at 1735(100) K, all iron in FeCO3 is in the high-spin state. A comparison between experiment and theory provides a more detailed understanding of FeCO3 decomposition observed in X-ray absorption spectra and helps to explain spectral changes due to pressure-induced spin crossover in FeCO3 at ambient temperature. KW - Deep carbon cycle KW - siderite KW - decomposition KW - melting KW - spin transition KW - Earth in Five Reactions: A Deep Carbon Perspective Y1 - 2019 U6 - https://doi.org/10.2138/am-2019-6428 SN - 0003-004X SN - 1945-3027 VL - 104 IS - 8 SP - 1083 EP - 1091 PB - Mineralogical Society of America CY - Chantilly ER - TY - JOUR A1 - Benard, Antoine A1 - Klimm, Kevin A1 - Woodland, Alan B. A1 - Arculus, Richard J. A1 - Wilke, Max A1 - Botcharnikov, Roman E. A1 - Shimizu, Nobumichi A1 - Nebel, Oliver A1 - Rivard, Camille A1 - Ionov, Dmitri A. T1 - Oxidising agents in sub-arc mantle melts link slab devolatilisation and arc magmas JF - Nature Communications N2 - Subduction zone magmas are more oxidised on eruption than those at mid-ocean ridges. This is attributed either to oxidising components, derived from subducted lithosphere (slab) and added to the mantle wedge, or to oxidation processes occurring during magma ascent via differentiation. Here we provide direct evidence for contributions of oxidising slab agents to melts trapped in the sub-arc mantle. Measurements of sulfur (S) valence state in sub-arc mantle peridotites identify sulfate, both as crystalline anhydrite (CaSO4) and dissolved SO42- in spinel-hosted glass (formerly melt) inclusions. Copper-rich sulfide precipitates in the inclusions and increased Fe3+/Sigma Fe in spinel record a S6+-Fe2+ redox coupling during melt percolation through the sub-arc mantle. Sulfate-rich glass inclusions exhibit high U/Th, Pb/Ce, Sr/Nd and delta S-34 (+ 7 to + 11%), indicating the involvement of dehydration products of serpentinised slab rocks in their parental melt sources. These observations provide a link between liberated slab components and oxidised arc magmas. Y1 - 2018 U6 - https://doi.org/10.1038/s41467-018-05804-2 SN - 2041-1723 VL - 9 PB - Nature Publ. Group CY - London ER - TY - JOUR A1 - Kutzschbach, Martin A1 - Guttmann, Peter A1 - Marquardt, K. A1 - Werner, S. A1 - Henzler, K. D. A1 - Wilke, Max T1 - A transmission x-ray microscopy and NEXAFS approach for studying corroded silicate glasses at the nanometre scale JF - European journal of glass science and technology / Deutsche Glastechnische Gesellschaft (DGG) and the Society of Glass Technology (SGT). B, Physics and chemistry of glasses N2 - In this study transmission X-ray microscopy (TXM) was tested as a method to investigate the chemistry and structure of corroded silicate glasses at the nanometer scale. Three different silicate glasses were altered in static corrosion experiments for 1-336 hours at temperatures between 60 degrees C and 85 degrees C using a 25% HCl solution. Thin lamellas were cut perpendicular to the surface of corroded glass monoliths and were analysed with conventional TEM as well as with TXM. By recording optical density profiles at photon energies around the Na and O K-edges, the shape of the corrosion rim/pristine glass interfaces and the thickness of the corrosion rims has been determined. Na and O near-edge X-ray absorption fine-structure spectra (NEXAFS) were obtained without inducing irradiation damage and have been used to detect chemical changes in the corrosion rims. Spatially resolved NEXAFS spectra at the O K-edge provided insight to structural changes in the corrosion layer on the atomic scale. By comparison to O K-edge spectra of silicate minerals and (hydrous) albite glass as well as to O K-edge NEXAFS of model structures simulated with ab initio calculations, evidence is provided that changes of the fine structure at the O K-edge are assigned to the formation of siloxane groups in the corrosion rim. Y1 - 2018 U6 - https://doi.org/10.13036/17533562.59.1.043 SN - 1753-3562 VL - 59 IS - 1 SP - 11 EP - 26 PB - Society of Glass Technology CY - Sheffield ER - TY - JOUR A1 - Dietrich, Marcel A1 - Behrens, Harald A1 - Wilke, Max T1 - A new optical cell for in situ Raman spectroscopy, and its application to study sulfur-bearing fluids at elevated pressures and temperatures JF - American mineralogist : an international journal of earth and planetary materials N2 - Sulfur is an important component in volcanic gases at the Earth surface but also present in the deep Earth in hydrothermal or magmatic fluids. Little is known about the evolution of such fluids during ascent in the crust. A new optical cell was developed for in situ Raman spectroscopic investigations on fluids allowing abrupt or continuous changes of pressure up to 200 MPa at temperatures up to 750 degrees C. The concept is based on a flexible gold bellow, which separates the sample fluid from the pressure medium water. To avoid reactions between aggressive fluids and the pressure cell, steel components in contact with the fluid are shielded by gold foil. The cell was tested to study redox reactions in fluids using aqueous ammonium sulfate solutions as a model system. During heating at constant pressure of 130 MPa, sulfate ions transform first to HSO4- ions and then to molecular units such as H2SO4. Variation of pressure shows that the stability of sulfate species relies on fluid density, i.e., highly charged species are stable only in high-density fluids. Partial decomposition of ammonium was evident above 550 degrees C by the occurrence of a nitrogen peak in the Raman spectra. Reduced sulfur species were observed above 700 degrees C by Raman signals near 2590 cm(-1) assigned to HS- and H2S. No clear evidence for the formation of sulfur dioxide was found in contrary to previous studies on aqueous H2SO4, suggesting very reducing conditions in our experiments. Fluid-mineral interaction was studied by inserting into the cell a small, semi-open capsule filled with a mixture of pyrite and pyrrhotite. Oxidation of the sample assembly was evident by transformation of pyrite to pyrrhotite. As a consequence, sulfide species were observed in the fluid already at temperatures of similar to 600 degrees C. KW - In situ Raman spectroscopy KW - fluids KW - decompression KW - optical cell KW - sulfur speciation KW - redox reactions Y1 - 2018 U6 - https://doi.org/10.2138/am-2018-6244 SN - 0003-004X SN - 1945-3027 VL - 103 IS - 3 SP - 418 EP - 429 PB - Mineralogical Society of America CY - Chantilly ER - TY - JOUR A1 - Wilke, Max T1 - X-Ray Absorption Spectroscopy Measurements JF - Magmas Under Pressure : Advances in High-Pressure Experiments on Structure and Properties of Melts N2 - An overview is given on the current state of X-ray absorption measurements on silicate melts and glasses. The challenges, limitations, and achievements of analyzing X-ray absorption spectra measured in liquids to determine structural properties of major and minor elements in magmas are described, with particular focus on describing non-Gaussian pair distribution functions in highly disordered glasses and melts, measured at in situ conditions. This includes a discussion on the progress of combining experiments with data from molecular dynamics simulations. For the measurements at conditions of the deep Earth, various experimental approaches and necessities are discussed and two examples are described in more detail. Finally, the achievements and prospects are presented for measuring X-ray absorption spectra indirectly by X-ray Raman scattering. Y1 - 2018 SN - 978-0-12-811274-8 SN - 978-0-12-811301-1 U6 - https://doi.org/10.1016/B978-0-12-811301-1.00006-X SP - 155 EP - 178 PB - Elsevier CY - Amsterdam ER - TY - JOUR A1 - Farges, Francois A1 - de Wispelaere, S. A1 - Rossano, Stephanie A1 - Munoz, Manuel A1 - Wilke, Max A1 - Flank, Anne-Marie A1 - Lagarde, Pierre T1 - Local structures around Si, Al, and Na in hydrated silicate glasses Y1 - 2008 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 - 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 - Nabelek, Peter I. A1 - Labotka, Theodore C. A1 - Helms, Thomas S. A1 - Wilke, Max T1 - Fluid-mediated polymetamorphism related to proterozoic collision of Archean Wyoming and Superior Provinces in the Black Hills, South Dakota Y1 - 2006 ER - TY - JOUR A1 - Wilke, Max A1 - Appel, Karen A1 - Vincze, Laszlo A1 - Schmidt, Christian A1 - Borchert, Manuela A1 - Pascarelli, Sakura T1 - A confocal set-up for micro-XRF and XAFS experiments using diamond-anvil cells N2 - A confocal set-up is presented that improves micro-XRF and XAFS experiment with high-pressure e diamond-anvil cells (DACs) In this experiment a probing volume is defined by the focus of the incoming synchrotron radiation beam and that of a polycapillary X-ray half-lens with a very long working distance, which is placed in front of the fluorescence detector This set-up enhances the quality of the fluorescence and XAFS spectra, and thus the sensitivity for detecting elements at low concentrations. It efficiently suppresses signal from outside the sample chamber, which stems from elastic and inelastic scattering of the incoming beam by the diamond anvils as well as from excitation of fluorescence from the body of the DAC Y1 - 2010 UR - http://journals.iucr.org/s/journalhomepage.html U6 - https://doi.org/10.1107/S0909049510023654 SN - 0909-0495 ER - TY - JOUR A1 - Nabelek, Peter I. A1 - Labotka, Theodore C. A1 - Helms, Thomas S. A1 - Wilke, Max T1 - Fluid-mediated mineral consumption and growth in polymetamorphosed metapelites of the Black Hills, South Dakota Y1 - 2005 SN - 0016-7037 ER - TY - JOUR A1 - Botcharnikov, Roman E. A1 - Koepke, J. A1 - Holtz, Francois A1 - McCammon, C. A1 - Wilke, Max T1 - The effect of water activity on the oxidation and structural state of Fe in a ferro-basaltic melt N2 - Experimental investigations have been performed at T = 1200 degrees C, P = 200 MPa and fH(2) corresponding to H2O-MnO-Mn3O4 and H2O-QFM redox buffers to study the effect of H2O activity on the oxidation and structural state of Fe in an iron-rich basaltic melt. The analysis of Mossbauer and Fe K-edge X-ray absorption nearedge structure (XANES) spectra of the quenched hydrous ferrobasaltic glasses shows that the Fe3+/Sigma Fe ratio of the glass is directly related to aH(2)O in a H-2-buffered system and, consequently, to the prevailing oxygen fugacity (through the reaction of water dissociation H2O <-> H-2 + 1/2 O-2). However, water as a chemical component of the silicate melt has an indistinguishable effect on the redox state of iron at studied conditions. The experimentally obtained relationship between fO(2) and Fe3+/Fe2+ in the hydrous ferrobasaltic melt can be adequately predicted in the investigated range by the existing empiric and thermodynamic models. The ratio of ferric and ferrous Fe is proportional to the oxygen fugacity to the power of similar to 0.25 which agrees with the theoretical value from the stoichiometry of the Fe redox reaction (FeO + 1/4 O-2 = FeO1.5). The mean centre shifts for Fe2+ and Fe3+ absorption doublets in Mossbauer spectra show little change with increasing Fe3+/Sigma Fe, suggesting no significant change in the type of iron coordination. Similarly, XANES preedge spectra indicate a mixed (C3h, Td, and Oh, i.e., 5-, 4-, and sixfold) coordination of Fe in hydrous basaltic glasses. Copyright (c) 2005 Elsevier Ltd Y1 - 2005 SN - 0016-7037 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 - 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 - THES A1 - Wilke, Max T1 - Untersuchungen zur Eisenspeziation in Mineralphasen unter besonderer Berücksichtigung der Röntgenabsorptionsspektroskopie (XAFS) Y1 - 2006 CY - Potsdam ER - TY - JOUR A1 - Wilke, Max T1 - Fe in magma : an overview N2 - The strong influence of physical conditions during magma formation on Fe equilibria offers a large variety of possibilities to deduce these conditions from Fe-bearing phases and phase assemblages found in magmatic rocks. Conditions of magma genesis and their evolution are of major interest for the understanding of volcanic eruptions. A brief overview on the most common methods used is given together with potential problems and limitations. Fe equilibria are not only sensitive to changes in intensive parameters (especially T and fO(2)) and extensive parameters like composition also have major effects, so that direct application of experimentally calibrated equilibria to natural systems is not always possible. Best estimates for pre-eruptive conditions are certainly achieved by studies that relate field observations directly to experimental observations for the composition of interest using as many constraints as possible (phase stability relations, Fe-Ti oxides, Fe partitioning between phases, Fe oxidation state in glass etc.). Local structural environment of Fe in silicate melts is an important parameter that is needed to understand the relationship between melt transport properties and melt structure. Assignment of Fe co-ordination and its relationship to the oxidation state seems not to be straightforward. In addition, there is considerable evidence that the co- ordination of Fe in glass differs from that in the melt, which has to be taken into account when linking melt structure to physical properties of silicate melts at T and P. Y1 - 2005 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 - Botcharnikov, Roman E. A1 - Koepke, J. A1 - Holtz, Francois A1 - McCammon, C. A1 - Wilke, Max T1 - The oxidation and structural state of Fe in hydrous ferrobasaltic melt Y1 - 2004 ER - TY - JOUR A1 - Kanngiesser, Birgit A1 - Hahn, O. A1 - Wilke, Max A1 - Nekat, B. A1 - Malzer, Wolfgang A1 - Erko, Alexei T1 - Investigation of oxidation and migration processes of inorganic compounds in ink-corroded manuscripts N2 - We studied the oxidation and migration processes of inorganic compounds in iron gall inks with a combination of micro X-ray fluorescence analysis (micro-XRF) and micro X-ray absorption near edge structure spectroscopy (micro-XANES). With elemental mapping by micro-XRF, the correlation of the minor elements in the ink to the major element Fe was investigated. Along concentration profiles of Fe, micro-XANES measurements were carried out in order to determine the oxidation state and the local environment. With the help of model inks, we could show that Cu is a further important element in the paper degradation process due to iron gall ink corrosion. (C) 2004 Elsevier B.V. All rights reserved Y1 - 2004 SN - 0584-8547 ER - TY - JOUR A1 - Nabelek, Peter I. A1 - Wilke, Max A1 - Huff, T. A. T1 - Methane production during metamorphism of graphitic pelites, Black Hills, USA Y1 - 2004 SN - 0016-7037 ER -