Viscosity and diffusion of barium and fluoride in Na2O/K2O/Al2O3/SiO2/BaF2 glasses

The interdiffusion coefficients of barium and fluoride in glasses, in the system Na2O/K2O/Al2O3/SiO2 with BaF2 additions, were determined from the diffusion profiles using energy dispersive X-ray analysis in a scanning electron microscope. The diffusivities were in agreement with Arrhenius-equation. Diffusion coefficients of fluoride were in the range from 4.5 10 15 m s 1 to 30 10 15 m s 1 at 580 and 640 C, respectively, while those of barium were 0.035 10 15 m s 1 at 600 and 1.3 10 15 m s 1 at 680 C and hence are around two orders of magnitude smaller than the values for of fluoride. During the diffusion of F , the charge compensation is assumed to be predominantly achieved by the simultaneous diffusion of highly mobile alkali ions. The viscosity of the melts decreased with increasing BaF2-concentration. The diffusion coefficients did not obey Stokes–Einstein Law. In the case of the crystallization of BaF2 from silicate glasses, the rate determining step should be the diffusion of barium. 2010 Elsevier B.V. All rights reserved.