Identifying and Quantifying Borate Environments in Borosilicate Glasses: 11 B NMR-Peak Assignments Assisted by Double-Quantum Experiments
Year: 2024
Type: article
Abstract: High Resolution Image Download MS PowerPoint Slide We discuss the prospects for accurate 11 B magic-angle-spinning (MAS) nuclear magnetic resonance (NMR) spectral deconvolutions for reaching beyond the readily extracted borate speciations offered by the integrated resonances of the coexisting B [3] and B [4] species of the respective BO 3 and BO 4 network groups in borosilicate (BS) glasses. We critically review hitherto proposed 11 B [3] and 11 B [4] NMR-peak assignments relating to their neighboring Si, B [3] and B [4] species, as quantified by MAS NMR spectral deconvolution. Guidance to these resonance assignments was offered from double-quantum–single-quantum (2Q–1Q) 11 B MAS NMR experiments that inform about the B [ p ] –O–B [ q ] network linkages. The NMR spectral deconvolutions from two BS glass series with low nonbridging oxygen (NBO) contents and fixed molar ratios n Si / n B = {1.0, 2.0} but variable network-modifying cations of alkali metals and Mg 2+ revealed a dominance of B [4] –O–Si linkages, yet with a significant dependence on the BO 3 population of the glass, which was rationalized by the different propensities for B [4] –O–{Si, B [3], B [4] } linkage formation. For BS glasses with comparable B and Si contents, we recommend three-peak deconvolutions of the 11 B [4] spectral region, whose 11 B [4] ( m Si) sites differ in their (average) numbers of m B [4] –O–Si and 4 – m B [4] –O–B [ p ] bonds, where B [ p ] may assume B [3] or B [4] . We also discuss the structural origin of the two rather arbitrarily classified “ring” and “non-ring” B [3] entities, where 2Q–1Q 11 B NMR suggests the former to primarily constitute BO 3 groups that coexist with BO 4 moieties in (superstructural) ring units largely devoid of bonds to Si, whereas the “non-ring” B [3] sites involve linkages to all of B [3], B [4], and Si, with B [3] –O–Si linkages prevailing. The limitations of 11 B NMR spectral deconvolutions are discussed, including the remaining challenges in analyzing NBO-rich BS glasses.
Authors: Baltzar Stevensson, Peng Lv, Mattias Edén
Institutions: Stockholm University, Lanzhou University
Language: English
Subfield: Ceramics and Composites
Field: Materials Science
Domain: Physical Sciences
Open Access status: hybrid
OpenAlex ID: W4405243054