Surface Tension, Density and Viscosity of PbO-Na₂O-SiO₂ Ternary Melt

Abstract

The surface tension, density and viscosity of PbO-Na₂O-SiO₂ melt have been measured over the temperature range 700° to 1200°C by the dipping cylinder method, the Archimedean method and the counter-balanced-sphere method, respectively.
The surface tension decreases with the addition of Na₂O to (PbO·SiO₂), while it increases with increasing Na₂O in the Na₂O-SiO₂ binary system.
The negative deviation from the additivity in molar volume indicates the bond breaking of SiO₂ and production of discrete anions. Enlargement in the expansion of melt, (∂V⁄∂T)_P, with increasing Na₂O indicates that the melt becomes more ionic with the addition of Na₂O.
Logarithm of viscosity, logη, shows a linear relation with 1⁄T² rather than 1⁄T. The apparent activation energy of viscous flow decreases with increasing Na₂O for the (PbO·SiO₂)-Na₂O system. For the (PbO·SiO₂)-(Na₂O·SiO₂) system, the curve of activation energy vs composition shows a minimum at about 10 mol%Na₂O.