Using synchrotron X-ray scattering to study the diffusion of water in a weakly-hydrated clay sample

TL;DR

This study uses synchrotron X-ray scattering to investigate water diffusion in weakly-hydrated smectite clay, revealing a slow, diffusion-controlled intercalation front with a spatial width under 2mm.

Contribution

It demonstrates a novel in situ method to monitor water diffusion in nano-layered clay using synchrotron X-ray scattering.

Findings

Intercalation front width is less than 2mm.

Front velocity decreases over time.

Water diffuses via mesoporosity in the clay.

Abstract

We study the diffusion of water in weakly-hydrated samples of the smectite clay Na-fluorohectorite. The quasi one-dimensional samples are dry compounds of nano-layered particles consisting of ~ 80 silicate platelets. Water diffuses into a sample through the mesoporosity in between the particles, and can subsequently intercalate into the adjacent particles. The samples are placed under controlled temperature. They are initially under low humidity conditions, with all particles in a 1WL intercalation state. We then impose a high humidity at one sample end, triggering water penetration along the sample length. We monitor the progression of the humidity front by monitoring the intercalation state of the particles in space and time. This is done by determining the characteristic spacing of the nano-layered particles in situ, from synchrotron wide-angle X-ray scattering measurements. The spatial width of the intercalation front is observed to be smaller than 2mm, while its velocity decreases with time, as expected from a diffusion process.