Carbonate formation on sol-gel bioactive glass 58S and on Bioglassreg; 45S5

摘要

Carbonate formation on a sol-gel synthesized bioactive glass (58S) and on a traditional fused glass (Bioglass® 45S5) has been studied by means of infrared spectroscopy, using water and carbon dioxide as probe molecules to simulate the carbonation process. Silica samples doped with Ca and Na have been also analyzed for comparison. It was observed that both CO_2 and an excess of water vapour are necessary to form carbonates on both bioactive glasses and reference silica systems: this indicates that CO_3~(2-) ions are formed through dissolution of CO_2 in a liquid-like water monolayer on the sample surface, and that they react with Ca~(++) or Na~+ cations, giving rise to ionic carbonates. Carbonates formation at spectroscopically detectable levels also on a very low surface area material such as Bioglass® 45S5 indicates that not only surface cations are involved in the carbonation process, but also some cations belonging to the inner glass layers. This is confirmed by the fact that carbonation increases during time and the proces keeps going for a very long time. Mostly calcium-bound carbonates are formed on 58S bioactive glass, whereas only sodium-bound carbonates are formed on Bioglass® 45S5, even though both sodium and calcium are present in the latter sample. This indicates that the surface layers of Bioglass® are enriched in sodium.