Viscosity coefficients of liquid lead silicate and lead borate have been measured in the temperature range from 800° to 1200°C by means of the counterbalanced sphere method. The results obtained are summarized as follows:
\ oindent(1) PbO-SiO₂ system
A linear relation is observed between log viscosity and 1⁄T² isocomposition rather than the Arrhenius type plots between log viscosity and 1⁄T. The activation energy for viscous flow decreases with increasing content of PbO.
\ oindent(2) PbO-B₂O₃ system
A linear relation is observed between log viscosity and 1⁄T² isocomposition as in the case of the PbO-SiO₂ system. The activation energy of viscous flow slowly decreases with increasing content of PbO up to about 33 mole%PbO and then more rapidly with increasing concentration.
The density of liquid lead borate decreases with increasing temperature by a linear relation. At about 33 mole%PbO, a minimum is found in the plots of molar volume and composition.