Ceramics-Silikáty 45 (4) 137-141 (2001)

EVAPORATION OF PbO-SiO₂ AND K₂O-PbO-SiO₂ MELTS

 J. Matoušek, T. Janů

Evaporation of two model glasses, composed of PbO and SiO₂ (molar relation PbO : SiO₂ = 1 : 1) and PbO, K₂O and SiO₂ (9 mol.% PbO, 15.2 mol.% K₂O, 75.8 mol.% SiO₂) was followed by determining of total mass change and change of surface PbO-concentration. Air and carbon dioxide streaming above the melt and saturated by water vapour were applied in order to find their influence on evaporation. Volatilisation losses of the binary and ternary melts increase exponentially in terms of temperature in both dry and moist gases. The time dependence of volatilisation losses was found to be linear in character except ternary melt exposed to high temperatures in dry and moist air. In the latter case the time dependence was parabolic in shape. Concentration of PbO in the surface layer was determined by means of electron microprobe. The concentration value decreases with temperature and time of evaporation. The lowest value of PbO surface concentration was found if evaporation of the ternary melt proceeded in moist atmospheres.

Keywords: Evaporation, Glass melt, PbO