DIFFUSION OF WATER AND OXYGEN IN QUARTZ - REACTION-DIFFUSION MODEL

A mechanism of diffusion of isotopically tagged water in crystalline q uartz by molecular diffusion and network exchange is compared to previ ous experiments. Three experimental factors are explained by this mech anism. (1) The apparent diffusion coefficient is proportional to the f ugacity of the water vapor in the gas phase. (2) The ratio of apparent diffusion coefficients at 800 degrees C in deuterium-hydrogen exchang e to O-18-O-16 exchange is 4.7(10)(5). (3) Below 700 degrees C the mea sured diffusion coefficients become time dependent. This diffusion-exc hange mechanism is valid for a wide variety of crystalline and amorpho us oxides. (C) 1998 Elsevier Science B.V. All rights reserved.