Quasi-Elastic Neutron Scattering Studies on Clay Interlayer-Space Highlighting the Effect of the Cation in Confined Water Dynamics

Abstract

It has long been realized that cations play a critical role in the readsorption of water into the interlayer region in clay minerals. To explore possible differences in the water dynamics related to the presence of cations in clays, and to examine the dynamics of its surface water, which plays a prominent role in diffusion of water in clay barriers a comparative study was carried out to highlight differences between water dynamics in montmorillonite and halloysite. Whereas montmorillonite has interlayer cations that interact with interlayer water, and which can rehydrate after dehydration at temperature, halloysite has no interlayer cations. Water is found in both interlayers and on the surface of these clay particles. In this study we show that by combining incoherent inelastic neutron scattering (quasi-elastic and elastic fixed window) and neutron spin echo, it was possible to discriminate the dynamics of surface water (by collapsing the interlayer region by heating and rehydrating the surface layer) from interlayer water. The analysis of the elastic fixed window scans in the temperature range 5−300 K revealed an extension of water dynamics in montmorillonite to lower temperatures than in halloysite. These differences suggested mechanisms that cations (Na+ in this case) in the interlayer regions facilitate water mobility allowing interlayer water to be readmitted to montmorillonite. Finally it was shown that the occurrence of magnetic fluctuations, caused by the presence of paramagnetic Fe3+ ions in the crystalline clay lattice, gave rise to a quasi-elastic contribution that disrupted the evaluation of water diffusion computed from such measurements. Therefore previous estimates of water diffusion coefficients might have been overestimated in recent literature.

Effect of Water Adsorption on Ion Dynamics in Confined Geometry: Na+-Faujasites and Homoionic Alkali Exchanged Montmorillonite

“…2), the observed behavior means that once a sufficiently high amount of water molecules is absorbed there is no more tremendous change into the sample dc conductivity mechanism. Data reported from Neutron Scattering 20,21,22) or from DRS 23) experiments on fully hydrated samples comparable to ours also reveal the occurrence of an abnormal behavior, i.e. Tg-like of super-cooled water, at temperatures comprised between 100 and 250 K depending on the considered materials.…”

Modeling the arrangement of particles in natural swelling-clay porous media using three-dimensional packing of elliptic disks

“…Numerous studies have focused on the dynamical properties of water molecules and cations in the interlamellar space of swelling clay minerals [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18]. However, on larger spatial scales, the presence of strongly anisometric particle shapes and their mutual arrangement in porous media are most often associated with the development of anisotropy in interparticle pore networks [19][20][21].…”

Raman and magnetic susceptibility studies of hexagonal elpasolite Cs2NaAlF6:Cr3+

“…atomic % Cr 3+ The ensemble of our results suggests that chromium ions are not magnetically isolated [30][31][32], however, the chromium content does not exceed the ''percolation threshold'' and longrange magnetic ordering is not observed. Furthermore, the M(H) curves, obtained at 2 K and shown in Fig.…”