Diffusion of 22Na and 45Ca and ionic conduction in two standard soda-lime glasses

Abstract: The tracer diffusivities of 22Na and 45Ca in two high-quality silica glasses produced by the Deutsche Glastechnische Gesellschaft as standard glasses I and II have been measured in the temperature range between 473 K and 783 K. The temperature dependences of the tracer diffusion coefficients in both glasses follow Arrhenius laws. The diffusion of 22Na is more than six orders of magnitude faster than the diffusion of 45Ca. The ionic conductivity was determined by frequency-dependent impedance spectroscopy and the conductivity diffusion coefficient D σ was deduced from the dc conductivity via the Nernst–Einstein relation. The temperature dependences of D σ for both glasses follow also Arrhenius functions. The activation parameters and pre-exponential factors for tracer diffusion and for conductivity diffusion were determined. The activation enthalpy of 22Na and the activation enthalpy of the dc conductivity are equal, showing that the conductivity of standard glasses is due to the motion of Na ions. The viscosity diffusivities D η were determined from available viscosity data using the Stokes–Einstein relation. They are considerably slower than both tracer diffusivities. The Haven ratios HR are temperature independent for both glasses. The diffusivities of 22Na and 45Ca in soda-lime glasses increase with increasing Na2O content. [Copyright &y& Elsevier]