Irradiation-induced modifications in the mechanical properties of borosilicate glass

Understanding the evolutions of the mechanical properties of borosilicate glasses under irradiation is crucial for evaluating their performances after long-term interaction with the irradiation environment in the disposal of high level nuclear waste.The variations of the mechanical properties of borosilicate glasses,induced by irradiation have been extensively studied.However,the mechanisms of variations in mechanical properties,induced by irradiation have not been clarified yet,especially when considering the effects of electronic and nuclear processes,respectively.To clarify this issue,a commercial borosilicate glass is investigated through an external irradiation of 5 MeV Xe ions and 1.2 MeV electrons in this paper.The nano-indentation test is used to study the changes of the hardness and modulus.The microstructure evolutions of Xe ion irradiated borosilicate glasses are characterized by Fourier transform infrared (FTIR) spectroscopy to discuss the mechanisms in the evolutions of mechanical properties.The nano-indentation results indicate that the hardness is reduced by 24%,and the modulus is lessened by 7.4% after the glass has been irradiated by Xe ions.Both the hardness and modulus variations reach their stable states when the total deposited energy is around 6.61021 keV/cm3.Although hardness and modulus are also observed to decrease by about 4.7% and 2.9%,resepectively, when the total deposited energy reaches approximately 1.41022 keV/cm3 after the glass has experienced the electron irradiation,the results still emphasize that the nuclear energy deposition is the major factor for the evolutions of the hardness and modulus of the borosilicate glass under ion irradiation.The decreases of hardness and modulus after the glass has experienced ion irradiation can be attributed to the deformation of glass network and volume expansion, which are induced by reducing the average ring size and transforming from[BO4] to[BO3] units.By considering the recovery resistance,it is found that the toughness of the borosilicate glass is significantly strengthened,and therefore the mechanical properties of the borosilicate glass are enhanced after the glass has been irradiated by Xe ions.Compared with the results after ion irradiation,the mechanical properties have negligible changes after electron irradiation.The present work is important for understanding both the irradiation effects on the hardness/modulus and the variations in the mechanical properties during the high level waste disposal.