An investigation was made of the self-diffusion of H2O in synthetic Na-P zeolite using an isotope-exchange technique. There was a marked increase in the rate of self-diffusion during its progress (table 27). The sudden change in rate was attributed to a low-energy structural change in the zeolite under the hydrothermal conditions. Diffusion in the two regions was described by:

slow:     D(cm2/s) = 8.44 x 10-3exp[-22.6(kcal/mol)/RT]

fast:     D(cm2/s) = 4.78 x 10-9exp[-8.2(kcal/mol)/RT]

Mobility of Water in Zeolites. Self-Diffusion of Water in Synthetic Na-P Zeolite. A.Dyer, A.Molyneux: Journal of Inorganic and Nuclear Chemistry, 1968, 30[10], 2831–40

Table 27

Diffusion of H2O in Na-P Synthetic Zeolite