Relation Between Mechanical Constraints and The Hydration Behaviour in the Case of Na-Montmorillonite:Structural Analysis and Elastics Properties

The experimental prediction of the mechanical properties of minerals remains difficult because of their small particle size (typically < 2 micrometers). This work aims at examining, the effect of an applied mechanical constraint on the hydration behaviour in the case of Na rich-montmorillonite and its relation with the elastic properties. The mechanical constraint is created, at the laboratory scale, by applying a monoaxial pressure for unstressed host material (i.e. Na rich montmorillonite). The structural analysis before and after stress is achieved using an XRD profile modeling approach. This investigation allowed us to determine several structural parameters related to the nature, abundance, size, position and organization of exchangeable cation and water molecule in the interlamellar space along the c* axis. In order to evaluate the affected elastic properties, the GULP code have been used to study the structure and the interlamellar organization. Indeed, the bulk modulus and elastic constants of montmorilonite have been calculated from first principles within density functional theory (DFT). The obtained Young’s modulus for Na-montmorillonite interlayer varies from 5 GPa to 16 GPa. According to the interlamellar space configuration the calculated elastic constant tensors indicate that the a direction is slightly more flexible than the b direction. The calculated elastic constant tensor along c is much lower than the constants calculated along a and b.

The experimental prediction of the mechanical properties of minerals remains difficult because of their small particle size (typically &lt; 2 micrometers). This work aims at examining, the effect of an applied mechanical constraint on the hydration behaviour in the case of Na rich-montmorillonite and its relation with the elastic properties. The mechanical constraint is created, at the laboratory scale, by applying a monoaxial pressure for unstressed host material (i.e. Na rich montmorillonite). The structural analysis before and after stress is achieved using an XRD profile modeling approach. This investigation allowed us to determine several structural parameters related to the nature, abundance, size, position and organization of exchangeable cation and water molecule in the interlamellar space along the c* axis. In order to evaluate the affected elastic properties, the GULP code have been used to study the structure and the interlamellar organization. Indeed, the bulk modulus and elastic constants of montmorilonite have been calculated from first principles within density functional theory (DFT). The obtained Young’s modulus for Na-montmorillonite interlayer varies from 5 GPa to 16 GPa. According to the interlamellar space configuration the calculated elastic constant tensors indicate that the a direction is slightly more flexible than the b direction. The calculated elastic constant tensor along c is much lower than the constants calculated along a and b.