The Experts below are selected from a list of 258 Experts worldwide ranked by ideXlab platform
Dominique Massiot - One of the best experts on this subject based on the ideXlab platform.
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the role of al3 on rheology and structural changes in sodium silicate and aluminosilicate glasses and melts
Geochimica et Cosmochimica Acta, 2014Co-Authors: Charles Le Losq, Daniel R Neuville, Dominique Massiot, Pierre Florian, Grant S HendersonAbstract:Abstract Because of their importance in both the geosciences and the glass-making industry, alkali aluminosilicate melts have been the focal point of many past studies, but despite progress many problems remain unresolved, such as the complex behaviour of the thermodynamic properties of aluminium-rich alkali silicate melts. This paper presents a study of Na2O–Al2O3–SiO2 glasses and melts, containing 75 mol% SiO2 and different Al/(Al + Na) ratios. Their structure has been investigated by using Raman spectroscopy, as well as, 23Na, 27Al and 29Si 1D MAS NMR spectroscopy. Results confirm the role change of Na+ cations from network modifier to charge compensator in the presence of Al3+ ions. In addition, polymerization increases with increase of the Al/(Al + Na) ratio. These structural changes explain the observed variations in the viscosity of these melts. The viscosity data in turn allow us to calculate the configurational entropy of melts at the glass transition temperature [the Sconf(Tg)]. The variations of the Sconf(Tg) are strongly nonlinear, with sharp increases and decreases depending on the Al/(Al + Na) ratio. More importantly, a strong increase of the Sconf(Tg) is observed when a few Al2O3 is added to sodium silicate melt. A strong decrease is observed after crossing the Tectosilicate join, when Al/(Al + Na) > 0.5 and when Al3+ ions are present in fivefold coordination, Al[5], in the glass. Furthermore, in situ 27Al NMR spectra of the peraluminous melt show a clear increase of the Al[5] concentration with increasing temperature. When considered in combination with melt fragility and heat capacity, our data demonstrate that Al[5] is clearly a transient unit at high temperature in highly polymerized Tectosilicate and peraluminous melts. However, when present in glasses, Al[5] increases the stability of the aluminosilicate network, hence the Tg of glasses. This could be explained by the ability of Al[5] to carry threefold coordinated oxygen atoms in its first coordination shell, as observed in minerals. Localisation of threefold coordinated oxygen atoms on Al[5] implies an increase of the medium-range order in the glass, an hypothesis that is in agreement with the low Sconf(Tg) of peraluminous glasses.
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al environment in Tectosilicate and peraluminous glasses a 27al mq mas nmr raman and xanes investigation
Geochimica et Cosmochimica Acta, 2004Co-Authors: Daniel R Neuville, Laurent Cormier, Dominique MassiotAbstract:Tecto-aluminosilicate and peraluminous glasses have been prepared by conventional and laser heating techniques, respectively, in the CaO-Al2O3-SiO2 system. The structure of these glasses were studied using Raman spectroscopy, X-ray absorption at the Al K-edge and 27Al NMR spectroscopy with two different high fields (400 and 750 MHz). Raman spectroscopy and X-ray absorption are techniques sensitive to the network polymerization and, in particular, show different signal as a function of silica content. However, these two techniques are less sensitive than NMR to describe the local aluminium environment. For Tectosilicate glasses, aluminium in five-fold coordination, [5]Al, was found and a careful quantification allows the determination of a significant amount of [5]Al (7% in the anorthite glass). The proportion of [5]Al increases for the peraluminous glasses with small amounts (<2%) of six-fold coordination, [6]Al. The presence of [5]Al agrees with previous observations of the existence of nonbridging oxygens (NBOs) in Tectosilicate compositions. However, the proportion of [5]Al in the present study indicates that no major proportion of triclusters (oxygen coordinated to three (Si,Al)O4 tetrahedra) is required to explain these NBOS.
Daniel R Neuville - One of the best experts on this subject based on the ideXlab platform.
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the role of al3 on rheology and structural changes in sodium silicate and aluminosilicate glasses and melts
Geochimica et Cosmochimica Acta, 2014Co-Authors: Charles Le Losq, Daniel R Neuville, Dominique Massiot, Pierre Florian, Grant S HendersonAbstract:Abstract Because of their importance in both the geosciences and the glass-making industry, alkali aluminosilicate melts have been the focal point of many past studies, but despite progress many problems remain unresolved, such as the complex behaviour of the thermodynamic properties of aluminium-rich alkali silicate melts. This paper presents a study of Na2O–Al2O3–SiO2 glasses and melts, containing 75 mol% SiO2 and different Al/(Al + Na) ratios. Their structure has been investigated by using Raman spectroscopy, as well as, 23Na, 27Al and 29Si 1D MAS NMR spectroscopy. Results confirm the role change of Na+ cations from network modifier to charge compensator in the presence of Al3+ ions. In addition, polymerization increases with increase of the Al/(Al + Na) ratio. These structural changes explain the observed variations in the viscosity of these melts. The viscosity data in turn allow us to calculate the configurational entropy of melts at the glass transition temperature [the Sconf(Tg)]. The variations of the Sconf(Tg) are strongly nonlinear, with sharp increases and decreases depending on the Al/(Al + Na) ratio. More importantly, a strong increase of the Sconf(Tg) is observed when a few Al2O3 is added to sodium silicate melt. A strong decrease is observed after crossing the Tectosilicate join, when Al/(Al + Na) > 0.5 and when Al3+ ions are present in fivefold coordination, Al[5], in the glass. Furthermore, in situ 27Al NMR spectra of the peraluminous melt show a clear increase of the Al[5] concentration with increasing temperature. When considered in combination with melt fragility and heat capacity, our data demonstrate that Al[5] is clearly a transient unit at high temperature in highly polymerized Tectosilicate and peraluminous melts. However, when present in glasses, Al[5] increases the stability of the aluminosilicate network, hence the Tg of glasses. This could be explained by the ability of Al[5] to carry threefold coordinated oxygen atoms in its first coordination shell, as observed in minerals. Localisation of threefold coordinated oxygen atoms on Al[5] implies an increase of the medium-range order in the glass, an hypothesis that is in agreement with the low Sconf(Tg) of peraluminous glasses.
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al environment in Tectosilicate and peraluminous glasses a 27al mq mas nmr raman and xanes investigation
Geochimica et Cosmochimica Acta, 2004Co-Authors: Daniel R Neuville, Laurent Cormier, Dominique MassiotAbstract:Tecto-aluminosilicate and peraluminous glasses have been prepared by conventional and laser heating techniques, respectively, in the CaO-Al2O3-SiO2 system. The structure of these glasses were studied using Raman spectroscopy, X-ray absorption at the Al K-edge and 27Al NMR spectroscopy with two different high fields (400 and 750 MHz). Raman spectroscopy and X-ray absorption are techniques sensitive to the network polymerization and, in particular, show different signal as a function of silica content. However, these two techniques are less sensitive than NMR to describe the local aluminium environment. For Tectosilicate glasses, aluminium in five-fold coordination, [5]Al, was found and a careful quantification allows the determination of a significant amount of [5]Al (7% in the anorthite glass). The proportion of [5]Al increases for the peraluminous glasses with small amounts (<2%) of six-fold coordination, [6]Al. The presence of [5]Al agrees with previous observations of the existence of nonbridging oxygens (NBOs) in Tectosilicate compositions. However, the proportion of [5]Al in the present study indicates that no major proportion of triclusters (oxygen coordinated to three (Si,Al)O4 tetrahedra) is required to explain these NBOS.
Dimitri Prêt - One of the best experts on this subject based on the ideXlab platform.
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Upscaling the porosity of the Callovo-Oxfordian mudstone from the pore scale to the formation scale; insights from the 3H-PMMA autoradiography technique and SEM BSE imaging
Sedimentary Geology, 2015Co-Authors: J.-c. Robinet, Paul Sardini, Dimitri Prêt, M. Siitari-kauppi, B. YvenAbstract:The Callovo-Oxfordian mudstone (Meuse/Haute-Marne, France) is currently considered as the host rock barrier for a deep geological repository. The intimate relationships between the porosity and mineralogy of this host rock were investigated at the small scale (mu m-mm) and large scale (m-hm). At the small scale, we have adapted the H-3-PMMA autoradiographic method to inap the porosity of the Callovo-Oxfordian mudstone. The H-3-PMMA autoradiographic method was improved in terms of its spatial resolution. H-3-PMMA porosity maps were then compared to-homologous mineral maps (clay minerals, carbonates and Tectosilicates) built from scanning electron microscopy images (using back-scattered electron imaging). Based on an inversion procedure, the specific porosity of each mineral group was estimated from the mineral and porosity maps. We found that the spatial distribution of porosity at the small scale is mainly controlled by the spatial distribution of the clay matrix (the average porosity of the clay matrix is 40-45%), whereas quartz and carbonate mineral grains have low porosities (0-4%). At the geological formation scale, the porosity and mineralogy distributions were determined by logging tool techniques (nuclear magnetic resonance and spectral gamma-ray). The coupled evolution of clay content and porosity with depth was analyzed according to the porosity/mineralogy relationship defined at the small scale. Finally, we modeled the evolution of the porosity of the Callovo-Oxfordian mudstone with depth by considering the clay content and the effect of physical compaction during burial.
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effects of mineral distribution at mesoscopic scale on solute diffusion in a clay rich rock example of the callovo oxfordian mudstone bure france
Water Resources Research, 2012Co-Authors: Jean-charles Robinet, Paul Sardini, D. Coelho, Jean-claude Parneix, Dimitri Prêt, Stéphane Sammartino, Elodie Boller, Scott AltmannAbstract:[1] The mesostructure (millimeter to micrometer scale) of clay-rich sedimentary rocks is generally characterized by a connected fine-grained clay matrix embedding coarser nonclay minerals. We use the Callovo-Oxfordian clay-rich rock formation (France) to illustrate how mesostructure influences solute transfer in clay-rich rocks at larger scales. Using micrometer resolution imaging techniques (SEM and micro-CT) major mineral phases (clay matrix, carbonates, Tectosilicates, and heavy minerals) were mapped both in two dimensional (2-D) and three dimensional (3-D) at the mesoscale. Orientation and elongation distributions of carbonate and Tectosilicate grains measured on mineral maps reveal an anisotropic mesostructure relative to the bedding plane, in agreement with the geological history of the sedimentary rock. Diffusion simulations were performed based on the 3-D mineral maps using a random walk method thus allowing direct computation of mesoscopic scale-related diffusion anisotropy and tortuosity. Considering an isotropic clay matrix, simulated diffusion anisotropy (1.11–1.26) was found lower than the one experimentally measured on macroscopic samples (1.5 to 2), due to the anisotropy feature of pores within the clay matrix. The effects of the mineral content variations on diffusion properties were then investigated by numerical modifications of a mineral map combined with diffusion simulations. Evolution of the tortuosity and diffusion anisotropy with the clay matrix content were successfully interpreted by the Koponen percolation/diffusion model, whereas the Archie approach fails to reproduce diffusion properties at low clay contents. A comparison of fitting parameters with those obtained experimentally indicates that diffusion coefficient variations observed at a large scale could be mainly controlled by the mesostructure.
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spatial distribution of porosity and minerals in clay rocks from the callovo oxfordian formation meuse haute marne eastern france implications on ionic species diffusion and rock sorption capability
Applied Clay Science, 2003Co-Authors: S Sammartino, Jean-claude Parneix, Dimitri Prêt, A Bouchet, E TevissenAbstract:Imaging techniques, adapted to clay rocks, combined with mathematical correlations of petrophysical parameters bring a new petrographic description of this clay rock integrating multi-scale data. Rock heterogeneities (mineral and porosity distributions) are studied at the mineral pore, the core and the borehole scale for interpreting diffusion tests. Although the infra-micrometric pores are associated with the clay particles and larger pores are associated with bioclasts and detrital minerals, especially Tectosilicates, relationships between minerals and pores are quite complex at the borehole scale. They are mainly controlled by mineral spatial arrangements and contents, since micro- to macrostructures of centimetric size are encountered in each lithofacies. Effects of surface interactions and pore-constriction electrochemical controls were underscored for a large proportion of the effective porosity. Although the effective porosity is physically interconnected in the rock volume, diffusion and sorption are discussed in terms of structure and accessibility to sorption sites. These data could be the basis for the construction of a quantitative transport model by diffussion taking into account the sample heterogeneities from the mineral pore size to the centimetric core size ranges. The conceptualisation of the organization of the porosity in such low permeability clayey medium, considered together with the analysis of interface-derived effects constitutes an important step forward in understanding the mechanisms affecting the migration of single ionic species. This understanding should help in extrapolating transport parameters obtained at the centimetric scale from laboratory experiments to the geological formation scale.
B. Yven - One of the best experts on this subject based on the ideXlab platform.
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Upscaling the porosity of the Callovo-Oxfordian mudstone from the pore scale to the formation scale; insights from the 3H-PMMA autoradiography technique and SEM BSE imaging
Sedimentary Geology, 2015Co-Authors: J.-c. Robinet, Paul Sardini, Dimitri Prêt, M. Siitari-kauppi, B. YvenAbstract:The Callovo-Oxfordian mudstone (Meuse/Haute-Marne, France) is currently considered as the host rock barrier for a deep geological repository. The intimate relationships between the porosity and mineralogy of this host rock were investigated at the small scale (mu m-mm) and large scale (m-hm). At the small scale, we have adapted the H-3-PMMA autoradiographic method to inap the porosity of the Callovo-Oxfordian mudstone. The H-3-PMMA autoradiographic method was improved in terms of its spatial resolution. H-3-PMMA porosity maps were then compared to-homologous mineral maps (clay minerals, carbonates and Tectosilicates) built from scanning electron microscopy images (using back-scattered electron imaging). Based on an inversion procedure, the specific porosity of each mineral group was estimated from the mineral and porosity maps. We found that the spatial distribution of porosity at the small scale is mainly controlled by the spatial distribution of the clay matrix (the average porosity of the clay matrix is 40-45%), whereas quartz and carbonate mineral grains have low porosities (0-4%). At the geological formation scale, the porosity and mineralogy distributions were determined by logging tool techniques (nuclear magnetic resonance and spectral gamma-ray). The coupled evolution of clay content and porosity with depth was analyzed according to the porosity/mineralogy relationship defined at the small scale. Finally, we modeled the evolution of the porosity of the Callovo-Oxfordian mudstone with depth by considering the clay content and the effect of physical compaction during burial.
Paul Sardini - One of the best experts on this subject based on the ideXlab platform.
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Upscaling the porosity of the Callovo-Oxfordian mudstone from the pore scale to the formation scale; insights from the 3H-PMMA autoradiography technique and SEM BSE imaging
Sedimentary Geology, 2015Co-Authors: J.-c. Robinet, Paul Sardini, Dimitri Prêt, M. Siitari-kauppi, B. YvenAbstract:The Callovo-Oxfordian mudstone (Meuse/Haute-Marne, France) is currently considered as the host rock barrier for a deep geological repository. The intimate relationships between the porosity and mineralogy of this host rock were investigated at the small scale (mu m-mm) and large scale (m-hm). At the small scale, we have adapted the H-3-PMMA autoradiographic method to inap the porosity of the Callovo-Oxfordian mudstone. The H-3-PMMA autoradiographic method was improved in terms of its spatial resolution. H-3-PMMA porosity maps were then compared to-homologous mineral maps (clay minerals, carbonates and Tectosilicates) built from scanning electron microscopy images (using back-scattered electron imaging). Based on an inversion procedure, the specific porosity of each mineral group was estimated from the mineral and porosity maps. We found that the spatial distribution of porosity at the small scale is mainly controlled by the spatial distribution of the clay matrix (the average porosity of the clay matrix is 40-45%), whereas quartz and carbonate mineral grains have low porosities (0-4%). At the geological formation scale, the porosity and mineralogy distributions were determined by logging tool techniques (nuclear magnetic resonance and spectral gamma-ray). The coupled evolution of clay content and porosity with depth was analyzed according to the porosity/mineralogy relationship defined at the small scale. Finally, we modeled the evolution of the porosity of the Callovo-Oxfordian mudstone with depth by considering the clay content and the effect of physical compaction during burial.
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effects of mineral distribution at mesoscopic scale on solute diffusion in a clay rich rock example of the callovo oxfordian mudstone bure france
Water Resources Research, 2012Co-Authors: Jean-charles Robinet, Paul Sardini, D. Coelho, Jean-claude Parneix, Dimitri Prêt, Stéphane Sammartino, Elodie Boller, Scott AltmannAbstract:[1] The mesostructure (millimeter to micrometer scale) of clay-rich sedimentary rocks is generally characterized by a connected fine-grained clay matrix embedding coarser nonclay minerals. We use the Callovo-Oxfordian clay-rich rock formation (France) to illustrate how mesostructure influences solute transfer in clay-rich rocks at larger scales. Using micrometer resolution imaging techniques (SEM and micro-CT) major mineral phases (clay matrix, carbonates, Tectosilicates, and heavy minerals) were mapped both in two dimensional (2-D) and three dimensional (3-D) at the mesoscale. Orientation and elongation distributions of carbonate and Tectosilicate grains measured on mineral maps reveal an anisotropic mesostructure relative to the bedding plane, in agreement with the geological history of the sedimentary rock. Diffusion simulations were performed based on the 3-D mineral maps using a random walk method thus allowing direct computation of mesoscopic scale-related diffusion anisotropy and tortuosity. Considering an isotropic clay matrix, simulated diffusion anisotropy (1.11–1.26) was found lower than the one experimentally measured on macroscopic samples (1.5 to 2), due to the anisotropy feature of pores within the clay matrix. The effects of the mineral content variations on diffusion properties were then investigated by numerical modifications of a mineral map combined with diffusion simulations. Evolution of the tortuosity and diffusion anisotropy with the clay matrix content were successfully interpreted by the Koponen percolation/diffusion model, whereas the Archie approach fails to reproduce diffusion properties at low clay contents. A comparison of fitting parameters with those obtained experimentally indicates that diffusion coefficient variations observed at a large scale could be mainly controlled by the mesostructure.
