Diffusion of Cesium Ions in H 2 O-Saturated Granitic Melt

Abstract

The intrinsic self-diffusion coefficient (D) for cesium-134 in a granitic melt containing 6.1 to 6.3 percent (by weight) of dissolved H₂O is three to four orders of magnitude higher than the values reported for chemically similar but dry granitic glass. For the temperature interval 700° to 800°C and a confining pressure of 2 kilobars, cesium diffusivity is given by D = 7.19 x 10^–5 exp (– 19.52 x 10³/RT), where R is the gas constant and T is the absolute temperature; the activation energy of about 20 kilocalories per mole is less than half the value for H₂O-free glass. The observed increase in ionic mobility that accompanies solution of H₂O implies sharply reduced equilibration times for chemical processes that occur in H₂2O-bearing silicate melts.