Dehydration and rehydration of vermiculites: IV. Arrangements of interlayer components in the 1.43 nm and 1.38 nm hydrates of Mg-vermiculite

Models for the respective arrangements of exchangeable cations and water molecules in the interlayers of the 1.43 nm and the 1.38 nm hydrate of 1 M Mg-vermiculite are proposed. The models are based on experimental data obtained for layer charge, water contents and stacking orders by chemical analysis, thermoanalysis and X-ray powder diffractometry, using the 20-50 mu m particle size fraction of a sample prepared from a 1 M phlogopite (Bamle, Norway). Starting from the approved position of Mg(OH2)(6) octahedra between superimposed oxygen triads of adjacent silicate layers in the 1.43 nm hydrate, the models are developed by optimizing mutual atomic distances and H-O...H bond angles existing between (i) water molecules, octahedrally coordinated to interlayer Mg2+ ions, (ii) interstitial water molecules and (iii) oxygen ions of the silicate surface. The proposed arrangements of interlayer components explain the stability of the two structures at the given water contents as well as their transformations, caused by the observed water losses. Both models agree with the results of onedimensional Fourier analyses, calculated from 17 00l reflections of each of the two hydrates (R-1(43). = 0.047, R-1.38 = 0.051).