Étude du contenu en eau des saponites et vermiculites sodiques et calciques

Abstract

Two-and one-water layer Na-and Ca-saponites and vermiculites have been studied by hydration isotherm curves, thermogravimetry and differential thermal analyses. The interlayer spaces appear to have fairly well defined structures, their thickness and contents remaining almost constant through quite a wide relative humidity range. This has to be connected with the ordered or semi-random layer stacking of these hydrates. For two-layer hydrates, with a given interlayer cation and layer stacking type, the number of water molecules in a unit-cell remains roughly constant whatever the charge. This suggests that, in the interlayer space, the water molecules constitute a framework the cohesion of which is due to interlayer cation and hydrogen bonds. On the other hand, the one-layer hydrates exhibit a nearly constant number of water molecules per cation. So, in the interlayer space there are many vacancies and hydrated cations form isolated groups.