Abstract
The role of the preferential orientation of clay platelets on the properties of a wide range of natural and engineered clay-rich media is well established. However, a reference function for describing the orientation of clay platelets in these different materials is still lacking. Here, we conducted a systematic study on a large panel of laboratory-made samples, including different clay types or preparation methods. By analyzing the orientation distribution functions obtained by X-ray scattering, we identified a unique signature for the preferred orientation of clay platelets and determined an associated reference orientation function using the maximum-entropy method. This new orientation distribution function is validated for a large set of engineered clay materials and for representative natural clay-rich rocks. This reference function has many potential applications where consideration of preferred orientation is required, including better long-term prediction of water and solute transfer or improved designs for new generations of innovative materials.
Highlights
The role of the preferential orientation of clay platelets on the properties of a wide range of natural and engineered clay-rich media is well established
The extent of anisotropy in clay platelet orientation is most often illustrated by global descriptors of the experimental orientation distribution function (ODF; e.g., the width of the distribution or its maximum value expressed as a multiple of random distribution)[8,15,16,17,18,21,22] or by an adjustable spreading parameter of conventional distribution functions (Gaussian, Bingham, etc.18,21,23,24) fitted to the experimental data
Our methodology based on the maximum-entropy method (MEM) to derive this new numerical function contains, within experimental precision, all relevant information on the ODF from the coupling between λ2 and λ4 parameters
Summary
The role of the preferential orientation of clay platelets on the properties of a wide range of natural and engineered clay-rich media is well established. Both effects have considerable influence on retention and anisotropic transfer of water and solutes in clay-rich media, causing clay minerals to play a pivotal role in the exploration and management of critical resources for human beings In sedimentary rocks such as mudrocks or shales, clay minerals are common markers for paleoenvironmental reconstructions[3,4] and the preferred orientation of clay platelets associated with nanometer-sized pores provides low permeability values to the whole clay-rich material. No conventional distribution function has been shown to be applicable for a large set of data This lack of a reference function describing OD for clay minerals leads to significant uncertainties in the prediction of longterm transfers of critical resources in compacted clay-rich systems[5,25] or for driving the design of high-performance engineered materials[26]. Experimental orientation distributions of clay mineral platelets are determined by X-ray scattering (XRS)
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