Diffusion of Na,K, Rb and Cs in glasses of albite and orthoclase composition

The measurement of diffusion coefficients for Na, K, Rb and Cs has been realized by the technique of active salt deposits on glasses of albite and orthoclase composition, at normal pressure and in the temperature range 300–1000°C. The values of D are between 10^?6 and 10^?12 cm² s^?1 and, for every type of run, they vary with temperature according to Arrhenius laws, with activation energies ranging from 13 to 68 kcal mole^?1. These important variations are related to the size of the diffusing element (at 700°C in albite glass D_Na/D_K/D_RbD_Cs ～- 10⁷/10⁵/10³/1) and to the size of the major alkali element (for rubidium at 800°C D_or·gl/D_ab·gl ～- 20). By comparison with available data on diffusion in feldspars, we emphasize the influence of the defect density on the diffusion process.