Permeability of vitreous GeO2 to helium in the temperature range 160-610°C

The permeability of vitreous germanium dioxide to helium is studied in the temperature range 160-610 degrees C. The temperature dependences of the permeability (K), diffusion (D), and solubility (s(Os)) coefficients are described by the equations log K = log K-0-(E-K/2.3RT), log D = log D-0-(E-D/2.3RT), log s(Os) = log s(0) - (E-s/2.3RT), with the parameters that depend on the temperature range and thermal history of samples. It is found that the energy E-K increases above the glass transition temperature Tg: In the temperature range below T-g, the permeability of the quenched(at 1300 degrees C) glasses is considerably higher than that of the annealed glasses. The isothermic heat treatment at 430 degrees C leads to a decrease in the K and D coefficients by a factor of 4-5 due to the structural relaxation, which correlates with an increase in density determined by dilatometric technique. Upon isothermic treatments at temperatures above and below T-g, the K coefficients fall on an "equilibrium line." At temperatures above T-g, the activation energy for equilibrium state is close to E-K.