Radiation effects on structure and mechanical properties of borosilicate glasses

Borosilicate glass is a candidate material for solidification of high-level radioactive waste (HLW). During disposal of HLW, the glass will be subjected to irradiation, especially the heavy ion irradiation related to alpha decay is expected to affect the properties of the glasses over billions of years. Therefore, it is important to understand the stability of borosilicate glasses upon irradiation. In this work, we study a series of sodium borosilicate glasses as well as the International Simple Glass (ISG) and subject them to irradiation with 5 MeV Xe ions. The radiation effects on the glasses include variations of macroscopic characteristics such as nano-hardness, modulus, volume change and crack initiation resistance (CR). We found that hardness, modulus, and volume changes of the glasses saturate at a certain irradiation dose, above which no further change is observed. The saturated values of hardness and modulus are found to be the same for glasses with different composition, while the saturated volume change depends on the glass composition. In addition, CR of the glasses increases dramatically upon irradiation. Meanwhile, we also studied the structure changes upon irradiation for both borosilicate and ISG glasses using Raman and infrared spectroscopies, showing an apparent transformation of BO₄ to BO₃ groups in borosilicate glasses irradiated with heavy ions. We thus this structural change in relation to the changes of mechanical/elastic properties. Our findings suggest that boron structures play an important role in controlling the macroscopic radiation effects.