An in situ time-resolved XRD-PSD investigation into Na-montmorillonite interlayer and particle rearrangement during dehydration

X-ray diffraction with a position-sensitive detector (XRD-PSD) Was used to make a time-resolved study of the dynamics of deposition and dehydration of Na-montmorillonite crystallites on flat substrates from deionized water Suspensions. The static PSD geometry and simultaneous Counting procedure allowed the acquisition of high-resolution data on the dynamics of interlayer and interparticle arrangements during dehydration. Three experimental datasets of Na-smectite dehydration are presented, each one representing different initial sample states (Suspension, slurry and re-wetted thin film). The computer program NEWMOD was used to Simulate one of the three datasets (dehydration of a smectite suspension) and thus obtain the apparent changes in relative proportions of different 001 values as smectite crystallites formed and dehydrated. Two types of diffracting domains formed: water-dispersed 'packets' of 1-2 smectite layers gaining long-range order in the c axis direction as water was lost to evaporation, and smectite layers deposited as hydrated crystallites with variable interlayer water contents. The experimental patterns show the rapid step-wise transition of Na-montmorillonite layers from d values of similar to55 to 18.5, 15.4 and 12.5 Angstrom, with variations that depended upon how the hydrated smectite sample was prepared. The simulations show that there was a wide range of d values whose frequency distribution changed as dehydration proceeded and that transient d Values Occurred between the peaks observed experimentally. The data obtained in this Study illustrate that XRD-PSD instruments have great potential in providing detailed data out the rapid kinetics of interlayer reorganization.