Diffusion of water and oxygen in quartz: reaction–diffusion model

A mechanism of diffusion of isotopically tagged water in crystalline quartz by molecular diffusion and network exchange is compared to previous experiments. Three experimental factors are explained by this mechanism. (1) The apparent diffusion coefficient is proportional to the fugacity of the water vapor in the gas phase. (2) The ratio of apparent diffusion coefficients at 800°C in deuterium–hydrogen exchange to 18O–16O exchange is 4.7(10)5. (3) Below 700°C the measured diffusion coefficients become time dependent. This diffusion-exchange mechanism is valid for a wide variety of crystalline and amorphous oxides.