Hydration Properties and Interlayer Organization of Water and Ions in Synthetic Na-Smectite with Tetrahedral Layer Charge. Part 1. Results from X-ray Diffraction Profile Modeling

The dehydration of two Na-saturated synthetic saponites with contrasting layer charge was studied by modeling the X-ray diffraction (XRD) patterns recorded along a water vapor desorption isotherm. The interlayer configurations Used to reproduce the XRD data over it large angular range include Na+ cations located in the interlayer midplane and H2O molecules normally distributed about One Or two main positions for mono- and bihydrated layers, respectively. Although Strongly reduced in comparison to natural smectites, hydration heterogeneity wits systematically observed for these synthetic saponites, especially along the transition between two hydration states. Using improved models for the description of the interlayer organization, the influence of layer charge oil the structure of interlayer water call be precisely assessed. In addition, the comparison with water contents obtained from water vapor gravimetry experiments allows discriminating the relative contributions of H2O molecules front 1W and 2W interlayers (crystalline water) and front the pore space network.