Crystal structure and particle orientation in relation to behaviour of clays during drying

3 páginasThe dehydration-rehydration in Mg-vermiculite is a complex phenomenon. The mechanism can be considered as comprising intermediate stages, in which the transition takes place apparently through interstratified phases. There is evidence for this in the literature [1-5], but the existence and/or the formation of interstratified phases have not been checked and confirmed by a suitable calculation method. The formation of interstratified or mixed-layer structures in vermiculites was reported many years ago [1]. Different aspects were studied, such as identification in crystal structures, natural and laboratory weathering products, exchange reactions with inorganic cations and formation of complexes or interaction with organic substances [6-9]. Mixed-layer Mg-vermiculites are interesting to understand the structural and crystalldchemical features, the interaction with inorganic and organic cations in clays, the formation and study of advanced clay " materials, an the study of various geological problems [10]. It is recognized that the hydration state of Mg-vermiculite depends on the water vapor pressure, temperature, and cation species. It has been defined by the number of water layers [n(H20)] in the interlamellar space, with a development corresponding to different phases, such as zero-, one-, and two-water-layer hydration states, with basal spacings at 9.02 A, 11.50 A and 14.40 A, respectively [2,3]. In the present work, the dehydration-rehydration of Mgvermiculite, as large flakes (7x5x0.1 mm) and powder($ 80 )liD), has been studied.Peer reviewe