Sodium tracer diffusion in glasses of the type (Na2O)0.2(B2O3)y(SiO2)0.8 − y

Sodium tracer diffusion coefficients, D⁎Na, have been measured in sodium borosilicate glasses of the type (Na2O)0.2(B2O3)y(SiO2)0.8−y as a function of temperature and the composition parameter y. At constant temperature, the tracer diffusion coefficient of sodium decreases as y increases. The activation enthalpy derived from sodium tracer diffusion data for temperatures up to about 350 °C increases about linearly with increasing values of y from about 70 to 100 kJ/mol. The pre-exponential factor of the sodium tracer diffusion coefficient as a function of y varies by about one order of magnitude and has a minimum at near y = 0.3.