Effects of La2O3 on structure and mechanical properties of sodium borosilicate glass

What is it about?

To develop rare-earth-doped borosilicate glasses with enhanced mechanical properties, lanthanum sodium borosilicate glasses were successfully synthesized using a fusion method. The glass composition was (mol.%): 55SiO2 - 25B2O3 – (20-x)Na2O - xLa2O3 (x = 1, 2, 3, 4, and 5). The primary aim was to investigate the impact of Na2O substitution by La2O3 on the structural and mechanical characteristics of the glasses. Raman and Fourier-transform infrared spectroscopyindicated a conversion of BO3 to BO4 units. Additionally, differential thermal analysis revealed an increase in both glass transition and crystallization temperatures with higher La2O3 content. The inclusion of La2O3 enhanced the glass density, Vickers hardness, fracture toughness, and Young’s modulus, owing to the larger ionic radius of La3+ compared to other components. In summary, the incorporation of an optimal concentration of La2O3 significantly improves the mechanical properties of these sodium borosilicate glasses, making them more suitable for applications involving the containment of actinides in nuclear fuel reprocessing.

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Why is it important?

Nuclear energy produces extremely harmful radioactive waste, which is generally stored in a glass matrix to ensure long-term retention. Due to their outstanding vitrification characteristics and chemical durability, typical glass matrices are mainly composed of borosilicate glasses and are capable of holding up to 18.5 % of the waste by weight. However, modifications to nuclear fuel cycles raises new challenges, particularly in terms of waste composition. The encapsulation of minor actinides is a crucial function of lanthanum-based borosilicate glasses, serving as vital components in the development of effective nuclear waste storage materials. La can replace trivalent actinides to simulate their chemical environment and behavior during solidification. This helps to improve glass formulations and guarantees lasting protection against radionuclides. The thermal stability of vitrified waste forms is of utmost importance, as these materials must withstand crystallization during the cooling and melting processes employed at an industrial scale. The presence of boron in these glasses significantly enhances thermal stability due to its high neutron absorption cross-section, which improves both thermal and irradiation stability in vitrified forms. In borosilicate glasses, La3+ions can be positioned at sites of high anionic coordination, helping to stabilize the glass network.

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