Effect of water vapor on fining and viscosity of soda-lime glass melts

抄録

Fining of soda-lime glass by Na₂SO₄ in a water vapor atmosphere was evaluated via direct observation and viscosity measurement of the melt. Direct observation of the melt was performed using the hot-thermocouple method, which can capture the behavior of bubbles in the melt in a water vapor atmosphere. When the moisture concentration in the atmosphere was high, a reduction in the bubble generation temperature and an increase in the number of generated bubbles were observed. In addition, the viscosity of the sample melt was measured using the rotation cylinder method. The viscosity at a water vapor partial pressure of 98 kPa was 14–16 % lower than that at 2 kPa at 1400–1600 °C. To evaluate fining, the bubble floating velocity was calculated using direct observation of the melt and the viscosity measurement results. At 1400 °C, the bubble emergence rate at P_H2O = 98 kPa was approximately six times faster than that at P_H2O = 2 kPa. These findings suggest that an increase in the moisture concentration in the atmosphere reduces the temperature at which bubbles are generated by Na₂SO₄, thereby promoting fining at a lower level than in air.