Influence of calcium on sodium aluminosilicate glass leaching behaviour

The dissolution kinetics of (1-x)SiO 2 .xCaO.25Na 2 O.5Al 2 O 3 glass (where x ranges from 0 to 25) are described in aqueous solutions buffered to pH 7 at 90°C. The addition of calcium in this series of glass compositions appreciably modified the dissolution mechanisms, as demonstrated by the characterisation of glass samples altered for 60 min to 4 days in highly dilute media. Resonant nuclear reaction (RNR) and elastic recoil detection (ERD) analyses with energetic ion beams have been used to study hydration and ion exchange processes by measuring the hydrogen and sodium profiles of leached glasses. The hydrated layers were also characterised by scanning electron microscopy analysis, which corroborated the solution analysis and protons consumption results indicating a threshold effect with minimal alteration for about 10-15% CaO. Raman spectroscopy has been used to investigate the pristine glass structure. The increased glass alteration above and below this threshold is discussed according the network polymerisation and the calcium position.