The relative influences of Al2O3 and Fe2O3 on the chemical durability of silicate glasses at different pH values

The influence of the pH of aqueous solutions on the chemical durability of two glasses in the system Na2O-FeO-Fe2O3-SiO2 has been compared with that of two glasses in the system Na2O-MgO-Al2O3-SiO2 where equimolar substitution of MgO for FeO and Al2O3 for Fe2O3 have been made. The presence of Fe2O3, and particularly of Al2O3, in glass reduces its alkali extraction in the pH range 4 to 9. The extraction results have been discussed and interpreted in the light of the available standard thermochemical data for the component oxides of these glasses.