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

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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.