Ceramics-Silikáty 37, (1) 49 - 55 (1993)

Glasses based on the system SiO₂-B₂O₃-Al₂O₃-Na₂O were prepared from natural aluminosilicate raw materials and their melting behaviour was explained by means of data obtained from DTA, GTA and heating microscope examinations. The viscosities established indicate ready meltability of the glasses in question (1000-1200 °C). A short-term test of chemical resistance to water by the standard leaching method ranks the glasses at the best to the 4th hydrolytic class. The rate of quasicongruent dissolution in distilled water at 95 °C during long-term exposure in the Soxhlett apparatus amounts to 4.1 x 10⁻⁶ g cm⁻² h⁻¹, which corresponds to a boundary shift rate of 4.7 x 10⁻¹⁰ cm s⁻¹. According to the results of long-term static tests at 25 °C, the values are lower by more than one order of magnitude and comparable to the long-term corrosion of industrial glasses. The chemical durability of the glasses decreases in an acid medium.