Role of alkalis on the incorporation of iodine in simple borosilicate glasses

To understand the influence of alkali elements on incorporation mechanisms and limit iodine in borosilicate glasses used for nuclear waste immobilization, series model with different contents (22 or 35 mol% Na2O, 22 a mixture alkalis: Na substituted by Li, K Cs) were loaded (from 1 000 to 10 ppm at. under form iodide) at 1100 °C. When was reached, iodide crystals observed (e.g., NaI). For oversaturated samples containing two alkalis, analyzed it found that are enriched heavier one relative bulk composition. Crystal-free studied Electron Probe Micro-Analysis measure iodine. A complex variation found. Initial substitution other alkalis (<50%) leads decrease I limit, this being smallest Li largest Cs. >50%, only potassium-bearing system could be studied. In case, non-linear passed through minimum ∼75%. Glass structure determined X-Ray absorption spectroscopy Nuclear Magnetic Resonance, providing evidence local environments rich alkalis. It is concluded high content concentrations Na2O particularly favorable incorporation.