X-ray Identification of Mixed-Layer Structures: Modelling of Diffraction Effects

Sakharov, B. A.; Lanson, Bruno

doi:10.1016/b978-0-08-098259-5.00005-6

Cited by 34 publications

(21 citation statements)

References 90 publications

(85 reference statements)

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“…In order to further support this interpretation and to provide some quantitative data on the coexistence of hydrated and collapsed layers within the same structures, XRD profile modeling is required based on the physical description of the distribution of layers in crystals using Markovian statistics. 30,69 This method was applied on three selected samples, i.e., the two endmembers Cs-Sap-0.8 and Cs-Sap- (Figure 7a). Such combination leads to an overall 2W/1W/0W layer content of 14/74/12.…”

Section: Resultsmentioning

confidence: 99%

“…28 The layer-to-layer distance was allowed to deviate from its mean value by introducing a variance parameter  z , that was 0.05, 0.14 and 0.10 Å for samples Cs-Sap-0.8, Cs-Sap-1.2 and Cs-Sap-2.0, respectively, to account for this "disorder of the second type". 29,30 The z-coordinates for all atoms within the 2:1 layer framework were set as proposed by Moore and Reynolds. 27 The interlayer configuration used for bihydrated layers (2W, d 001~1 4.5 Å) was initially proposed by Ferrage et al 29 19,31,32 The fitting procedure is detailed elsewhere.…”

Section: X-ray Diffraction Profile Modeling Of 00ℓ Reflectionsmentioning

confidence: 99%

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Influence of Tetrahedral Layer Charge on the Fixation of Cesium in Synthetic Smectite

et al. 2017

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After radionuclides pollution of soils by nuclear power plant accidents, Cs + strongly interacts with swelling clay minerals, which in turn control the fixation or the migration of this pollutant in the natural media. Little is known, however, about the role played by the amount of layer charge and the two-dimensional confinement on Cs + fixation. In this study a series of tetrahedrally charged smectites with structural formula inter [M + x ] oct [Mg 6 ] tet [Si 8−x Al x ]O 20 (OH) 4 with a layer charge (x) varying from 0.8 to 2.0 and with Na + or Cs + as interlayer cation M + were used. While Na + remains fully exchangeable over the entire range of layer charges investigated, the fraction of exchangeable Cs + decreased gradually for samples with x ≥1.4/O 20 (OH) 4. Structure analysis of Cs +-samples in water-saturated or at 80% relative humidity conditions showed a gradual decrease of the layer-to-layer distance. The results were found to qualitatively agree with analysis of the thermodynamics of the clay/water interfaces derived from molecular simulations. Quantitative structure analysis by modeling of 00ℓ reflections on experimental Xray diffraction patterns suggested that exchangeable Cs + can be correlated with the amount of hydrated interlayers, whereas fixed Cs + in these conditions corresponds to the amount of collapsed layers. To describe the coexistence of both exchangeable and fixed Cs + , a toy-model accounting for the presence of heterogeneous charge distribution was used, in agreement with experimental data obtained on these samples. This model successfully interprets the overall reactivity of Cs + towards smectite over a large range of layer charge values and may contribute to an improved description of Cs + mobility in contaminated soil environments. Water density profile Z-position (Å) Sodium density profile Water density profile Z-position (Å) Cesium density profile Water density profile Z-position (Å) Sodium density profile Water density profile Z-position (Å) Cesium density profile a. Na-Sap-0.8 c. Na-Sap-1.8 b. Cs-Sap-0.8 d. Cs-Sap-1.8

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Section: Resultsmentioning

confidence: 99%

Section: X-ray Diffraction Profile Modeling Of 00ℓ Reflectionsmentioning

confidence: 99%

Influence of Tetrahedral Layer Charge on the Fixation of Cesium in Synthetic Smectite

et al. 2017

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“…Advances in Materials Science and Engineering in [41] and detailed later in [42]. e abundances of the diverse layer types (W i ), the mode of stacking of the di erent kinds of layers, and the mean number of layers per coherent scattering domain (CSD) are determined through XRD pro le modeling.…”

Section: Quantitative Xrd Investigationmentioning

confidence: 99%

Discretization of the Water Uptake Process of Na‐Montmorillonite Undergoing Atmospheric Stress: XRD Modeling Approach

Oueslati

Meftah

2018

Advances in Materials Science and Engineering

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This work focuses on the water-montmorillonite interaction under variable atmospheric conditions in order to characterize the interlamellar space (IS) configuration for possible use in the context of geological barrier for radioactive and industrial waste confinement. Atmospheric stress is achieved by applying, for Na-rich montmorillonite, a water sorption/desorption constraint, created at the laboratory scale. This hydrological disturbance allows the “demolition” of the clay history and to highlight the clay hydrous performance. The structural analysis is achieved using modeling of XRD profiles, which allowed us to determine the optimal structural parameters describing the IS configuration along thec∗axis. During the “in situ” XRD analysis, a sorption/desorption cycle is envisaged by variation of the relative humidity rate (%RH) from the saturated condition (94 %RH) towards extremely dry ones (2-3 %RH). Qualitatively, a new hydration hysteresis behavior of the “stressed” sample appears. Structural analysis achieved before and after perturbation allowed us to identify, respectively, the homogeneous hydration states, the hydrous transition domains, and the hydration heterogeneity degree. This latter parameter is characterized, quantitatively, by variable relative abundances of mixed-layer structure (MLS) population discerned over a wide explored RH range. Using the optimum structural parameter, the water molecule distribution versus the applied hydrous strain was quantified.

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“…Detailed analysis of Toarcian shale samples from the Tournemire site (France) revealed minor differences between the illiteesmectite (I-Sm) mixed-layered mineral composition of preserved and oxidized samples, the latter being slightly enriched in Sm layer (Charpentier et al, 2004). The results rely on X-ray diffraction (XRD) pattern deconvolution, and more advanced analytical identification such as multispecimen methods (Lanson et al, 2009;Sakharov and Lanson, 2013) might be used to unambiguously confirm this point. Electron energy-loss spectroscopy measurements indicate an increase in the Fe(III)/total Fe ratio of I-Sm particles.…”

Section: Perturbing the Physicochemical Conditions In The Subsurface:mentioning

confidence: 89%

Stability of Clay Barriers Under Chemical Perturbations

Bildstein

Claret

2015

Natural and Engineered Clay Barriers

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X-ray Identification of Mixed-Layer Structures: Modelling of Diffraction Effects

Cited by 34 publications

References 90 publications

Influence of Tetrahedral Layer Charge on the Fixation of Cesium in Synthetic Smectite

Influence of Tetrahedral Layer Charge on the Fixation of Cesium in Synthetic Smectite

Discretization of the Water Uptake Process of Na‐Montmorillonite Undergoing Atmospheric Stress: XRD Modeling Approach

Stability of Clay Barriers Under Chemical Perturbations

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