Hydration mechanisms and swelling behavior of Na-magadiite

The hydration behavior of synthetic Na-magadiite was studied by combining t hermal analyses, water adsorption gravimetry, X-ray diffraction, and infrar ed spectroscopy under controlled water pressure. Thermal analyses reveal, a t least, two distinct water populations. The water adsorption isotherm exhi bits two steps at low relative pressure. These steps correspond to three we ll-defined interlayer distances on the X-ray diffractograms. Infrared spect ra recorded under various water pressures show distinct water populations. For relative pressures greater than or equal to 0.20, some water molecules (1665 cm(-1)) are doubly hydrogen bonded, likely to surface sites, whereas other (1625 cm(-1)) exhibit a signal similar to that observed for hydrated clay minerals at low relative pressures, suggesting a strong influence of t he interlayer cation. For lower relative pressures, a single water populati on at 1635 cm(-1) is observed, suggesting a dual influence of both the inte rlayer cation and the surface sites.