The influence of iodide on glass transition temperature of high-pressure nuclear waste glasses

The glass transition temperature (T-g) is a key parameter to investigate for application in nuclear waste immobilization in borosilicate glasses. T-g for several glasses containing iodine (I) has been measured in order to determine the I effect on T-g. Two series of glass composition (ISG and NH) containing up to 2.5 mol% I and synthesized under high pressure (0.5 to 1.5 GPa) have been investigated using differential scanning calorimetry (DSC). The I local environment in glasses has been determined using X-ray photoelectron spectroscopy and revealed that I is dissolved under its iodide form (I-). Results show that T-g is decreased with the I addition in the glass in agreement with previous results. We also observed that this T-g decrease is a strong function of glass composition. For NH, 2.5 mol% I induces a decrease of 24 degrees C in T-g, whereas for ISG, 1.2 mol% decreases the T-g by 64 degrees C. We interpret this difference as the result of the I dissolution mechanism and its effect on the polymerization of the boron network. The I dissolution in ISG is accompanied by a depolymerization of the boron network, whereas it is the opposite in NH. Although ISG corresponds to a standardized glass, for the particular case of I immobilization it appears less adequate than NH considering that the decrease in T-g for NH is small in comparison to ISG.

Automated summary

The glass transition temperature (T-g) was investigated for borosilicate glasses used in nuclear waste immobilization with different levels of iodine (I) added. The results showed that the addition of I decreased T-g, with a stronger effect observed in ISG compared to NH glass compositions. The difference in T-g decrease was attributed to the dissolution mechanism of I and its impact on the boron network polymerization.