Effect of Water Content on the Electrical Conductivity of Sodium Trisilicate Glasses

The effect of variations in water content on the direct-current electrical conductivity of Na₂O · 3SiO₂ glass was measured. Increasing the water content of this glass from 10 to 500 wt ppm of H₂O results in an increase in the resistivity of a factor of 2 to 3. The increase in resistivity is accompanied by an increase in the activation energy for conduction. Increasing resistivity with increasing water content is attributed to decreasing molar volume. Under identical annealing conditions, "wetter" glasses relax to a smaller molar volume (greater density) because of the presence of a larger number of "terminal" hydroxyl species that allow structural relaxation to continue to lower temperatures.