Ceramics-Silikáty 38, (3) 137 - 141 (1994)

Extraction of sodium from the surface of container glass was studied for temperatures of 400 °C and 600 °C in terms of the time of heating (exposure) and the way of dosing (single dose and repeated doses) of ammonium sulphate. The amount of sodium extracted increases with increasing temperature of heating. At the lower dealkalization temperature, the time dependence exhibits a steady increase in the amount of sodium extracted with both the single a repeated dosage of the reactive agent, and shows a parabolic course. At the higher temperature, the amount of sodium extraced increases uniformly only when the dealkalizing agent is supplied continuously to the glass surtace (repeated dosing). The chemical durability of all the dealkalized surfaces is many times higher than that of the original untreated glass. In the case of glass surface dealkalized at the higher temperature with an only limited dose of the reactive agent, the chemical durability of the surface is becoming gradually reduced as a result of the diffusion of sodium from the internal glass layers into the dealkalized surface layer.