PROTONIC CONDUCTIVITY AND WATER DYNAMICS IN SWELLING CLAYS

Smectites or swelling clays are lamellar minerals made by the stacking of two tetrahedral silica sheets with one octahedral layer inserted o f brucite or alumina type. Conductivity measurements and cation diffus ion coefficient determination on different smectites, with varying wat er content, show that the conductivity is mainly protonic and depends on the water content. Structure and micro dynamics of adsorbed water i s studied by XRD, IR, QENS, NMR spectroscopies. The protonic conductiv ity (10(-4) S cm(-1)) exhibited by these minerals is associated with t he proton diffusional motion (D = 6 x 10(-6) cm(2) s(-1)): its value f its the Einstein relation well with the residence time tau(0) = 10(-10 ) s and the jump length 2.8 Angstrom deduced from high resolution QENS measurements.