Variable-temperature X-ray diffraction and 2H
NMR spectroscopy of the smectite mineral, hectorite,
containing interlayer Na+, K+, Cs+, Mg2+, Ca2+, Sr2+, and
Pb2+ equilibrated at 43% relative humidity (RH) and mixed
with 2H2O to form a paste provide a comprehensive picture of the structural environments and dynamics of interlayer 2H2O and the relationships of these properties to interlayer
hydration state, the hydration energy and polarizability of
the cation, temperature, and the formation of ice-1h in the
interparticle pores. The variation in basal spacing shown by the XRD data correlates well with the 2H NMR behavior, and the XRD data show for the first time in hectorites that
crystallization of interparticle ice-1h causes a decrease in the interlayer spacing, likely due to removal of interlayer 2H2O. The variation of the 2H NMR behavior of all the samples with decreasing temperature reflects decreasing frequencies of motion for the rotation of the 2H2O molecules around their dipoles, reorientation of the 2H2O molecules, and exchange of the 2H2O molecules between interlayer sites coordinated to and not coordinated to the cations.
Revised: April 30, 2020 |
Published: April 28, 2016