Composition effects on mechanical properties of pristine sodium borosilicate glass

Abstract

Sodium borosilicate (NBS) glass is widely used in the disposal of high level nuclear waste nowadays. In order to understand the mechanism of hardness in NBS glass varies with various compositions, nanoindentation experiment and molecular dynamics simulation were carried out. Both experimental and calculated results suggested that, the hardness of glass increased with the ratio of R ([Na 2 O]/ [B 2 O 3 ] in molar percentage) and K ([SiO 2 ]/[B 2 O 3 ] in molar percentage). In the process of hardness increase, the [BO 3 ] units were transformed into [BO 4 ] units, which could lead to the polymerization increase for the glass system, and the transformation was linear to R. The hardness increase was also accompanying with the increase of silica content, which is another cause for polymerization increase. There are many possible factors that may affect the mechanical properties of pristine NBS glass, and polymerization increase should be the main reason for hardness increase, which could be resulted from the two processes above: (a) the transformation of [BO 3 ] into [BO 4 ]; (b) silica content increase. K E Y W O R D S composition effects, hardness, nanoindentation, sodium borosilicate glass

Properties of irradiated sodium borosilicate glasses from experiment and atomistic simulations

“…Our simulations predict a density of ~2.40 – 2.47 g/cm 3 for this class of glasses. This is by 10% larger than the experimental densities reported by Zhao et al 32 However, our result is very close to other experimental and simulation studies by Barlet et al 49 of glass of similar composition, and in general within a density range expected for borosilicate glasses 49 . In order to shed light on this discrepancy, we applied the models of glass densities as a function of composition analyzed by Barlet et al 49 : (M1) Feil and Feller, 50 (M2) Budhwani and Feller 51 and (M3) Inoue et al 52 as the most accurate model.…”

“…We note that the simulated densities are consistent with the model of Inoue et al 52 On the other hand, model of Budhwani and Feller 51 is consistent with the measured densities, but as discussed by Barlet et al, 49 it, in general, underestimates the densities. With these results, we thus suspect that the experimental densities reported by Zhao et al 32 are somehow underestimated or that the real parameters of the investigated glasses were slightly different.…”

“…In the next step, we performed simulations of the series of SNBS G2 glasses investigated by Zhao et al 32 Zhao et al 32 measured and simulated (with the similar force field‐based method) the Young's modulus and hardness of these materials. However, in these simulation studies, the potential of Kieu et al 40 was used, which according to Wang et al 7 cannot correctly capture the density and boron speciation of borosilicate glass.…”

“…We simulated three different series of borosilicate glasses that reflect the measured compositions of: (G1) Wang et al, 7 (G2) Zhao et al, 32 and (G3) Guan et al 19 The exact compositions are given in Table 1. These could be grouped according to the ratio of alkali to boron ( R = [Na 2 O + CaO]/[B 2 O 3 ]): low (G1 and G2) to high (G1 and G3).…”

“…In the last decades, different glasses have been investigated at the atomistic scale by atomistic modeling methods, including molecular dynamics. There are various such studies of nuclear glasses that aim to understand the structural and physical–chemical properties of these materials 1,4,5,7,25–32 …”