Low Pressure evaporation from boron containing glass melts by the transpiration method

Abstract

Glass melting is a well-established process, but it does not seem to be well understood under low-pressure conditions. Melting under low pressure has been suggested as a potential support of the refining process. This makes sense only if the evaporation form the glass melt is kept within acceptable limits. A transpiration apparatus equipped for operation at low pressure, termed low pressure transpiration method, was used to investigate the evaporation from boron containing glass melts. We obtained information on the weight loss as a function of temperature, time, and pressure. We investigated an alkali borosilicate glass with acomposition in mol % of: 79SiO₂,7 Na₂O, 10 B₂O₃, 3 AI₂O₃, 1 minor constituents. At the beginning of glass melting, the evaporation mechanism was detected as surface controlled. Later, a diffusion controlled stationary behaviour was observed. The ratio of sodium oxide to boron oxide in the evaporated gas as determined by chemical analysis ranged from 1.25 to 1.4.