THE MONTMOR1LLONITE DIFFERENTIAL THERMAL CURVE. H. EFFECT OF EXCHANGE- ABLE CATIONS ON THE DEHYDROXYLAT ION OF NORMAL MONTMORILLONITE

Examination of the differential thermal characteristics of a normal mont-morillonite saturated with a series of monovalent and divalent cations shows that the temperature of the main dehydroxylation peak is in-dependent of valency but is apparently a parabolic function of ionic radius. NH4+, Cs+, Zn~+ and Cd 2'- give anomalous results, but the apparent discrepancy of the former two ions can be fully accounted for. The results are believed to be consistent with evolution of water mole-cules through the hexagonal holes in the sheet surface and diffusion between the layers to Ill(: micelle edge. The significance of variation in the 800-1000'C region of the curve is briefly considered