Viscous Flow Of Sodium Phosphate Glasses From (Formula) Poise

The viscosities of five sodium phosphate glasses, containing from 45 to 65mol% P2O5, were determined from (formula) poise using a beam bending technique, and from (formula) poise using a torsion vibration technique. Activation energies for viscous flow were calculated for the high and low viscosity ranges. A change in the viscous flow mechanism from bond interchange at high viscosities to molecular flow at low viscosities occurred at about (formula) poise.