Measurement of Surface Viscosity of Molten Oxides

Abstract

Viscosities of molten oxides in the systems, Na₂O-P₂O₅, BaO-B₂O₃, Na₂O-B₂O₃ and Na₂O-SiO₂ are measured at 1 000°C on the surface as well as in the bulk phase, using a modified rotating viscometer. By the viscometer, existance of highly viscous layer on the surface can be detected when the layer is formed, if the viscosity in the bulk phase is above 5 poise. Most viscous layer on the surface was observed for BaO 17.8 mol% -B₂O₃ 82.2 mol% melt, in which the surface visosity is 2.3 times higher than that in the bulk phase. The highly viscous layer observed on the surface can be expained, assuming that the concentration of surface active component as B₂O₃ on the surface is higher than that in the bulk phase.