TY  - JOUR
A1  - Farges, Francois
A1  - Djanarthany, S
A1  - de Wispelaere, S
A1  - Munoz, Manuel
A1  - Magassouba, B
A1  - Haddi, A
A1  - Wilke, Max
A1  - Schmidt, C.
A1  - Borchert, Manuela
A1  - Trocellier, P
A1  - Crichton, W
A1  - Simionovici, Alexandre
A1  - Petit, Pierre-Emanuel
A1  - Mezouar, Mohamed
A1  - Etcheverry, M. P.
A1  - Pallot-Frossard, I
A1  - Bargar, John Reeder
A1  - Brown, G. E.
A1  - Grolimund, D
A1  - Scheidegger, A
T1  - Water in silicate glasses and melts of environmental interest : from volcanoes to cathedrals
N2  - In silicate glasses and melts, water acts according to two main processes. First, it can be dissolved in high temperature/high pressure melts. Second, it constitutes a weathering agent on the glass surface. A number of in-situ x- ray absorption fine structure (XAFS) studies for Fe, Ni, Zr, Th and U show that the more charged cations (Zr, Nb, Mo, Ta, Sn, Th and U) are little affected by the presence of dissolved water in the melt. In contrast, divalent iron and nickel are highly sensitive to the presence of water, which enhance nucleation processes, for example, of phyllosilicates at the angstrom-scale. Such information provides additional constraints on the role of water deep in the Earth, particularly in magmatology. By contrast, the weathering of glass surfaces by water can be studied from a durability perspective. Experimental weathering experiments Of nuclear waste glasses performed in the laboratory show a variety of surface enrichments (carbon, chlorine, alkalis, iron) after exposure to atmospheric fluids and moisture. Mn-, and Fe-surface enrichments of analogous glasses of the XIVth century are related to the formation of Mn and Fe oxy/ hydroxides on the surface. The impact on the glass darkening is considered in terms of urban pollution and mass tourism
Y1  - 2005
ER  - 
TY  - JOUR
A1  - Krstulović, Marija
A1  - Rosa, Angelika D.
A1  - Ferreira Sanchez, Dario
A1  - Libon, Lélia
A1  - Albers, Christian
A1  - Merkulova, Margarita
A1  - Grolimund, Daniel
A1  - Irifune, Tetsuo
A1  - Wilke, Max
T1  - Effect of temperature on the densification of silicate melts to lower earth's mantle conditions
JF  - Physics of the earth and planetary interiors
N2  - Physical properties of silicate melts play a key role for global planetary dynamics, controlling for example volcanic eruption styles, mantle convection and elemental cycling in the deep Earth. They are significantly modified by structural changes at the atomic scale due to external parameters such as pressure and temperature or due to chemistry. Structural rearrangements such as 4- to 6-fold coordination change of Si with increasing depth may profoundly influence melt properties, but have so far mostly been studied at ambient temperature due to experimental difficulties. In order to investigate the structural properties of silicate melts and their densification mechanisms at conditions relevant to the deep Earth's interior, we studied haplo basaltic glasses and melts (albite-diopside composition) at high pressure and temperature conditions in resistively and laser-heated diamond anvil cells using X-ray absorption near edge structure spectroscopy. Samples were doped with 10 wt% of Ge, which is accessible with this experimental technique and which commonly serves as a structural analogue for the network forming cation Si. We acquired spectra on the Ge K edge up to 48 GPa and 5000 K and derived the average Ge-O coordination number NGe-O, and bond distance RGe-O as functions of pressure. Our results demonstrate a continuous transformation from tetrahedral to octahedral coordination between ca. 5 and 30 GPa at ambient temperature. Above 1600 K the data reveal a reduction of the pressure needed to complete conversion to octahedral coordination by ca. 30 %. The results allow us to determine the influence of temperature on the Si coordination number changes in natural melts in the Earth's interior. We propose that the complete transition to octahedral coordination in basaltic melts is reached at about 40 GPa, corresponding to a depth of ca. 1200 km in the uppermost lower mantle. At the core-mantle boundary (2900 km, 130 GPa, 3000 K) the existence of non-buoyant melts has been proposed to explain observed low seismic wave velocity features. Our results highlight that the melt composition can affect the melt density at such extreme conditions and may strongly influence the structural response.
KW  - Silicate melts
KW  - Densification
KW  - High pressure and high temperature;
KW  - XANES
KW  - Coordination number
KW  - Ultra-low velocity zones
Y1  - 2022
U6  - https://doi.org/10.1016/j.pepi.2021.106823
SN  - 0031-9201
SN  - 1872-7395
VL  - 323
PB  - Elsevier
CY  - Amsterdam
ER  -