The viscosities of sodium borosilicate slags containing lead oxide were measured with a Brookfield Rotational Viscometer at temperatures in the range of 950–1000°C. Increasing additions oflead oxide produced a marked decrease in viscosity. Also, the viscosity decreased as the borax to silica ratio in the melt increased, at constant lead oxide contents. The role of lead oxide and sodium oxide in rupturing the rigid silica network and effectively depolymerizing the melt is discussed and a mechanism is proposed which explains the observed changes.

The effect of copper oxide on the viscosity of sodium borosilicate slags was studied in the temperature range 950-1000-degrees-C with a Brookfield rotational viscometer. Increasing additions of copper oxide reduced viscosity dramatically. At constant copper oxide concentration an increasing borax/silica ratio in the melt also lowered viscosity. The role of copper oxide and sodium oxide in depolymerizing the melt is discussed.