Tracer diffusion in sodium-rubidium borate glasses. An unconventional mixed-alkali effect?.

Schoo U, Cramer C, Mehrer H

Abstract

In mixed sodium-rubidium borate glasses with a const. total content of 30 mol% alkali oxide and various relative concns. of sodium and rubidium, diffusion of 22Na and 86Rb was studied at 673 K using the radio-tracer serial sectioning method. The diffusion coeffs. of sodium and rubidium show a concn. dependence which is at variance with "classical" expectations for mixed-alkali glasses. No cross-over of the diffusivities is obsd. since Na diffusion is always faster than Rb diffusion. Na diffusion passes through a min. near 60% Na2O content whereas Rb diffusion shows a max. near 50% Na2O content. The ionic cond. deduced thereof displays a min. as a function of the relative compn. of sodium and rubidium as in "classical" mixed-alkali glasses. [on SciFinder(R)]