For RH>54%: Two peaks  2 well-defined families of pore sizes Osmotic swelling occurs at RH > 80% in interlayer space compared to RH ~ 54% in mesopores HYDRATION SEQUENCE of SWELLING CLAYS EXCHANGED with ALKALI and ALKALI-EARTH CATIONS F. Salles 1, O. Bildstein 2, J.M. Douillard 1, B. Prelot 1, J. Zajac 1, M. Jullien 3 and H. Van Damme 4 (1) ICGM, Université Montpellier – France(2) CEA, DEN, LMTE – Cadarache – St Paul lez Durance – France (3) Ecogeosafe – Aix-en-Provence – France(4) ESPCI – Paris -France Material and Method Introduction and Principle Aim of this study : determination of the cation dependence of the hydration process for samples saturated with alkaline cations and the resulting distribution of water molecules in the interlayer space and mesopores Hydration sequence depends on the nature of the interlayer cation Osmotic swelling in mesopores is evidenced by original use of thermoporometry + free water observed in mesopores only at RH>90% Osmotic swelling occurs in mesopores before crystalline swelling is finished in the interlayer space The interlayer spaces are never completely filled in montmorillonites, except for Cs-sample, but interlayer space water > mesopore water for all cations References: (a) F. Salles, I. Beurroies, O. Bildstein, M. Jullien, J. Raynal, R. Denoyel, H. Van Damme, Appl. Clay Sci., 2008, 39, 186 and (b) F. Salles, O. Bildstein, J.M. Douillard, M. Jullien, J. Raynal, H. Van Damme, Langmuir, 2010, 26, 5028 Purified powder of montmo- rillonites (Mont) from the MX-80 bentonite saturated with a large majority of Na + and Ca 2+ as interlayer cations Exchanged powders of MX-80 bentonites saturated by alkaline or Ca 2+ cations: Li +, Na +, K +, Cs + Upon hydration, the structure of the swelling clays is strongly modified due to interactions between water molecules and the multi-scale clay structure (layers and extra-framework cations, particles and aggregates)  induce a multi-scale swelling: interlayer swelling and and osmotic swelling in the mesopores. In this study, from an original use of the thermoporometry on unsaturated clay samples, the mesopore size distribution is investigated for samples saturated with alkali and alkali-earth compensating cations as a function of the relative humidity. The results are validated by comparison with the pore sizes estimated from N 2 adsorption. The impact of the interlayer cation is thus evidenced and the hydration processes can finally be elucidated by distinguishing the impact of the swelling of the various scales. we determine the distribution of water (interlayer water and mesopore water) present in our samples by the original combination of (1) X-ray diffraction data, (2) the pore size distribution obtained by thermoporometry and (3) recent adsorption isotherm results. Material Thermoporometry Results and Interpretation Evolution of the mesopore size Li and Na-Montmorillonites At RH< 54%  no interpretable signal (mesopores not filled or not enough water?) At RH= 54% 1 peak corresponding to a size of 2.5 nm Good agreement with BJH calculations (N 2 adsorption) Impact of Rp dominant compared to the effect of ions for the phase of water Towards a step by step model for hydration m interlayer water = m water in clay – m water in mesopore m water in clay  from water adsorption isotherm m water in mesopore  from thermoporometry data m theoretical interlayer water =d 001 * (S H2O –S N2 ) with S H2O and S N2 specific surface area as a function of RH* (see poster MR/CI/7) and d 001 the interlayer space opening Thermoporometry = calorimetric technique sensitive to phase transitions of fluid confined in the porosity  2 nm < Pore radius < 50 nm (mesoporosity)  Original practice : DSC on unsaturated and swelling samples (powder / mg) but saturation of studied porosity is necessary Theoretical equation  Brun et Quinson Model fusion-solidification-fusion cycles (2°C/min for a range of temperatures between -80°C and 0°C) RH conditions: 11%, 33%, 54%, 75%, 90%, saturated material Hydration  vapour or liquid water for saturated samples fusion solidification R p estimated from solidification RH = 54% 2.5 nm No free water FREE WATER Osmotic swelling RH = 75% RH = 90% RH = saturated Osmotic swelling in interlayer space Crystalline swelling (2 layers of water) Osmotic swelling in mesopores In the case of K-, Rb-, Cs- and Ca-montmorillonites  no mesopore swelling except at saturation in the case of Ca-montmorillonite Conclusions Na Li Ca Cs K 20%<RH<60% Na Li Maximal water amount in interlayer space - Water present in interlayer space - Water present in mesopore space