Water Structure and Dynamics in Smectites: X-ray Diffraction and H-2 NMR Spectroscopy of Mg-, Ca-, Sr-, Na-, Cs-, and Pb-Hectorite

摘要

Variable-temperature X-ray diffraction and H-2 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 (H2O)-H-2 to form a paste provide a comprehensive picture of the structural environments and dynamics of interlayer (H2O)-H-2 and the relationships of these properties to interlayer hydration state, the hydration energy and polarizability of the cation, temperature, and the formation of ice-lh in the interparticle pores. The variation in basal spacing shown by the XRD data correlates well with the H-2 NMR behavior, and the XRD data show show for the first time in hectorites that crystallizationof interpraticle ice-lh causes a decrease in the interlayer spacing, likely due to removal of interlayer (H2O)-H-2. The variation of the H-2 NMR behavior of all the samples with decreasing temperature reflects decreasing frequencies of motion for the rotation of the (H2O)-H-2 molecules around their dipoles, reorientation of the (H2O)-H-2 molecules, and exchange of the (H2O)-H-2 molecules between interlayer sites coordinated to and not coordinated to the cations.