On determining chemical durability of glasses

Glass is relatively durable in acidic to neutral solutions. Durability is often a desirable property, but in some applications some surface dissolution and reactivity are desired, e.g. bioactive glasses. In this work we compare the suitability of three methods; modified ISO 719, dynamic water, and static TRIS-buffered solution tests for establishing fundamental information on the tendency for glass dissolution. All the tested methods gave similar relative order for the durability of glasses. ISO 719 with additional measurements gave indications of the dissolution reaction mechanisms, while the dynamic test setup gave information about reaction kinetics. Glass compositions chosen for this study were from different hydrolytic resistance groups. All glasses dissolved incongruently with alkali ion exchange being dominant within the temperature range from 40 to 98 degrees C corresponding to the conditions required by ISO 719. However, at 98 degrees C network dissolution was considerable. The temperature dependence of the glass dissolution exhibited Arrhenius-type behaviour. The apparent activation energy based on hydrochloric acid consumption was at same level for all the glasses (20-30 kJ/mol) corresponding to values for a diffusion controlled mechanism. However, the apparent activation energy values based on silica concentration suggested a surface controlled reaction mechanism for E-glass and float glass.