Interlayer water in vermiculite: thermodynamic properties, packing density, nuclear pulse resonance, and infra-red absorption

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Abstract
Water vapour sorption isotherms on sodium and magnesium vermiculite of high charge density were measured at 25 and 50°C. Heats of immersion at various stages of hydration were measured at 25°C. According to X-ray observations during the sorption process, two discrete interlayer hydrates are obtained with one and two monolayers of water between the unit layers of the crystallites. The derived integral entropy of adsorption indicates a reduced freedom of motion of the interlayer water molecules compared with that for water molecules in the liquid state. Comparison of the apparent density of the hydrated clay with the calculated crystallographic density indicates that interlayer water is slightly more densily packed than liquid water. However, the bulk density of water in a sodium vermiculite suspension is normal for the water in excess of the two hydration layers.Nuclear pulse resonance results obtained on sodium vermiculite shows that water in the one-layer hydrate is organized and some hypotheses are presented regarding this organization. Water molecules in the two-layer complex show the same degree of orientation only below –65°C. Infra-red absorption spectra for hydrated flakes of sodium vermiculite were obtained as a function of angle between the (001) plane of the crystallites and the i.-r. beam. The results indicate orientation of water molecules in the one-layer hydrate at room temperature.

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