Surface Tension, Density and Viscosity of PbO-K₂O-SiO₂ Ternary Melts

Abstract

The surface tension, density and viscosity of PbO-K₂O-SiO₂ ternary melts have been measured in the temperature range 800° to 1200°C by the use of the dipping cylinder method, the Archimedean method and the counter-balanced-sphere method, respectively.
In the (PbO·SiO₂)-K₂O pseudo-binary system, the surface tension decreases with the addition of K₂O. The temperature coefficient of surface tension changes from the negative to the positive sign with increasing amount of K₂O. This characteristic phenomenon may be explained in terms of the production of a homopolar Pb-O bond in the melt with the addition of K₂O.
The negative deviation from the additivity in molar volume and the decrement of viscosity with the addition of K₂O indicate the bond breaking of SiO₂ network and the production of descrete anions.
The apparent activation energy for viscous flow decreases with increasing content in the K₂O in (PbO·SiO₂)-K₂O system. For the (PbO·SiO₂)-(K₂O·SiO₂) pseudo-binary system, the activation energy shows a minimum value at about 10 mol%K₂O.