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AN IN SITU TIME-RESOLVED XRD-PSD INVESTIGATION INTO Na-MONTMORILLONITE INTERLAYER AND PARTICLE REARRANGEMENT DURING DEHYDRATION

¹ Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK
² Department of Mineralogy, The Natural History Museum, Cromwell Road, London SW7 5BD, UK

^* E-mail address of corresponding author: j.cuadros{at}nhm.ac.uk

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 00l 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 ~55 to 18.5, 15.4 and 12.5 Å, 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 on the rapid kinetics of interlayer reorganization.

Key Words: Dehydration • Position-sensitive Detector • Smectite • X-ray Diffraction

This article has been cited by other articles:

				E. Ferrage, C. A. Kirk, G. Cressey, and J. Cuadros Dehydration of Ca-montmorillonite at the crystal scale. Part I: Structure evolution American Mineralogist, July 1, 2007; 92(7): 994 - 1006. [Abstract] [Full Text] [PDF]