DEHYDRATION OF VERMICULITES AND MONTMORILLONITES - A TIME-RESOLVED POWDER NEUTRON-DIFFRACTION STUDY

Time-resolved powder neutron diffraction has been used to study, in situ, the structural transformations and changes in the hydrogen-atom content of four ion-exchanged (Ca, K, Mg and Na) vermiculites and two natural (Ca and Na) montmorillonites undergoing dehydration. The loss of interlayer water is shown to occur in steps, revealing the existence of a number of intermediate hydration states. These intermediate states are found to be sensitive to the interlayer cation and the layer charge. The Ca- and Na-montmorillonites are found to contain a maximum of three interlayer sheets of water, whereas the Ca-, Mg- and Na-vermiculites contain a maximum of two interlayer sheets of water. The K-vermiculite was found to exhibit a much lower capacity for hydration.