Leach testing of model glasses containing sodium or potassium ions as a flux

It is known that ancient glasses produced in the Middle East that contain sodium ions as a flux are more stable and more chemically durable against environmental effects than glasses containing potassium ions (known as wood ash glasses) produced much later in Europe and Bohemia. The objective of this work was to study the behavior of model glasses containing sodium or potassium ions in the presence of water and atmospheric humidity. The model glasses were prepared using the molar ratios: 75 mol% SiO2, 15 mol% Na2O or K2O and 10 mol% CaO (glasses A and B) or the weight ratios: 70 wt% SiO2, 20 wt% Na2O or K2O and 10 wt% CaO (glasses C & D). Crushed glass (0.3-0.5 mm) was exposed to distilled water at the ambient temperature, 37 degrees C or 60 degrees C for a period of two weeks and compact glass samples were exposed to drinking water and atmospheric humidity for eight months (at 37 degrees C). It was found that the nature of the flux employed (sodium or potassium ions) has a fundamental influence on the mechanism, but it does not have any influence on the symptoms of glass corrosion, in. that the Na-glass, i.e. Na2O-CaO-SiO2, dissolved incongruently and the K-glass, i.e. K2O-CaO-SiO2, dissolved congruently. The corrosion of glass is closely related to the ratio R2O/(SiO2+CaO) and, surprisingly, even small changes in this ratio significantly change the kinetics of glass corrosion.