Cation field‐strength effects on ion irradiation‐induced mechanical property changes of borosilicate glass structures

Abstract

We examine the impact of the glass network-modifier cation field strength (CFS) on ion irradiation-induced mechanical property changes in borosilicate (BS) glasses for the ternary M 2 O-B 2 O 3 -SiO 2 systems with M = {Na, K, Rb} and the quaternary [0.5M (2) O-0.5Na 2 O]-B 2 O 3 -SiO 2 systems with M = {Li, Na, K, Rb Mg, Ca, Sr, Ba}. 11 B nuclear magnetic resonance (NMR) experiments on the as-prepared BS glasses yielded the fractional population of four-coordinated B species (B [4] ) out of all {B [3] , B [4] } groups in the glass network, along with the fraction of B [4] -O-Si linkages out of all B [4] -O-Si/B bonds. Both parameters correlated linearly with the (average) CFS of the M + and/or {M (2)+ , Na + } cations. Both the nanoindentation-derived hardness and Young's modulus values of the glasses reduced upon their irradiation by Si 2+ ions, with the property deterioration decreasing linearly with increasing M z+ CFS, that is, for higher M z+ ⋯O interaction strength. The irradiation damage of the glass network also increased linearly with the fraction of B [4] -O-Si linkages, which are the second weakest in the structure after the M z+ ⋯O bonds. Our results underscore the advantages of employing BS glasses with high-CFS cations for enhancing the radiation resistance for nuclear waste storage.

Sub-Nanometer-Range Structural Effects From Mg2+ Incorporation in Na-Based Borosilicate Glasses Revealed by Heteronuclear NMR and MD Simulations

“…The weakened B [4] /Si contacts upon Mg 2+ -for-Na + substitution reflect a general trend of a linearly decreasing fraction of B [4] –O–Si linkages (out of all B [4] –O–Si/B bridges) for increasing CFS M , as deduced from 11 B [4] MAS NMR spectra deconvolutions . These CFS effects are also mirrored in the 29 Si MAS NMR spectra of the Na4.0–0.75, MgNa4.0–0.75, and MgNa4.0–2.1 glasses shown in Figure : as expected from amorphous (boro)­silicates, the net 29 Si resonance is broad but consistent with solely 29 SiO 4 groups. ,,− Hence, the 29 Si MAS NMR information content is very limited, at best offering qualitative inferences. , Even for the (almost) NBO-free Na4.0–0.75 and MgNa4.0–0.75 glasses, the net 29 Si NMR peak stems from a plethora of unresolved 29 Si (OB [3] ) p (OB [4] ) q (OSi) 4– p − q resonances.…”

“…We now examine the MD-derived BO/NBO partitioning in the first coordination shells of the Na + and Mg 2+ cations in each BS glass structure, i.e., the distribution of the O [2] /O [1] coordinations of the respective {NaO p } and {MgO p } ensembles presented in Table . Because CFS Ca is intermediate between CFS Na and CFS Mg (Table S1) and the relative preferences for M [ p ] –BO/NBO bonding are strongly CFS-dependent, Table also includes modeled data from R [0.5CaO–0.5Na 2 O]–B 2 O 3 – K SiO 2 glasses, denoted “CaNa K – R ” and discussed in refs , , and . Each NBO and BO fraction in the first coordination shell of an M z + cation is denoted by x ( M –NBO) and x ( M –BO), respectively.…”

“…Owing to its larger number of Si neighbors, the resonance decay of 11 B [4] (4Si) is stronger than that of its 11 B [4] (3Si) counterpart. To adequately deconvolute the 11 B [4] NMR signal region of the two Na4.0–0.75 and MgNa4.0–0.75 glasses, however, it was necessary to also include a minor peak at ≈1.2 ppm from 11 B [4] (2Si) environments (accounting for 9% and 17% out of all B [4] ( m Si) groups, respectively) . These NMR signals are not clearly discernible in the REDOR spectra, but they are expected to decay even slower than the 11 B [4] (3Si) resonance, as is also hinted in Figure .…”

“…Our study involved the eight BS glass compositions listed in Table , encompassing four ternary R Na 2 O–B 2 O 3 – K SiO 2 glasses and four quaternary R [0.5MgO–0.5Na 2 O]–B 2 O 3 – K SiO 2 analogs. They constitute a subset of a large BS glass ensemble examined previously. ,, We adopt the glass nomenclature of ref , where each Na- and Mg/Na-based glass is denoted by Na K – R and MgNa K – R , respectively, with the { K , R } parameters defined by , K = n ( SiO 2 ) / n ( B 2 O 3 ) R = [ n false( MgO false) + n false( Na 2 normalO false) ] / n ( B 2 O 3 ) Each nominal glass composition in Table is expressed in terms of its oxide equivalents and the atomic fraction of each element E in the (Mg)–Na–B–Si–O glass, x E = n E / ( n Mg + n Na + n B + n Si + n O ) where n E is the corresponding stoichiometric amount.…”

BO3/BO4 Intermixing in Borosilicate Glass Networks Probed by Double-Quantum 11B NMR: What Factors Govern BO4–BO4 Formation?

“…For M z + -bearing BS glasses, such a hybrid glass network picture is readily envisaged because the boroxol rings become diluted further by more extended and less ordered network segments that constitute the RN portion. Indeed, by direct extrapolation of the B 2 O 3 scenario, numerous analyses of the 11 B [3] resonance region of MAS NMR spectra employ a (rather arbitrary) deconvolution into two signal components from “ring” and “nonring” sites (e.g., see refs –, , and ). The precise 11 B [3] spectral assignments of these (non)­ring motifs vary among reports, with the perhaps most popular interpretation involving “nonring” BO 3 groups present in − B [3] –O–{B [3] /B [4] /Si}– chains with a significant number of B [3] –O–Si linkages. ,– , Notably, those 11 B [3] resonance assignments to “ring” and “nonring” motifs implicitly invoke a “hybrid” BS glass structure interpretation.…”