Investigation of Lead Borosilicate Glass Structure With 207 Pb and 11 B Solid-State NMR
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Investigation of Lead Borosilicate Glass Structure With 207Pb and 11B Solid-State NMR James M. Gibson, Frederick G. Vogt, Amy S. Barnes and Karl T. Mueller Department of Chemistry, The Pennsylvania State University 152 Davey Laboratory, University Park, PA 16802-6300 ABSTRACT A series of three lead borosilicate glasses were synthesized and analyzed for structural information with both 11B and 207Pb solid-state nuclear magnetic resonance (NMR) spectroscopic methods. Results showed that increasing lead content caused lead to take a more active role in the network as a former and that the populations in these sites can be approximately quantified. 207 Pb phase-adjusted-spinning sidebands (PASS), 11B magic-angle spinning (MAS), and 11B multiple-quantum MAS (MQMAS) experiments were used to determine structural parameters for the two nuclei. The 207Pb PASS experiment showed that at higher lead content, more covalent bonding was present. This principle was demonstrated in both an overall shift of the spectral resonances and a quantitative change in site ratios. The 11B MAS experiment showed that the ratio of BO3 to BO4 units was dependent on the amount of lead and boron, consistent with previous studies. Preliminary 11B MQMAS experiments failed to detect any BO3– units, previously hypothesized to exist in this system. INTRODUCTION Lead borosilicate glasses provide the basis for manufacturing of coatings, enamels, solder glasses, and glass-ceramic cements [1]. From prior analysis of nuclear magnetic resonance (NMR) data, x-ray photoelectron spectroscopy (XPS) results, and measurements of the thermal coefficient of linear expansion (TCLE) of lead silicates [2,3] and lead borosilicates [1,4,5], three major conclusions about lead borosilicate glasses can be drawn. Firstly, there are both BO3 and BO4 units in the glasses, and their ratio depends upon the molar composition of the glasses. Secondly, the lead has a dual structural role, in that it is both a network former and a network modifier within the glass. In small amounts the lead behaves as a modifier, while in greater amounts there is an increase in covalent bonds to lead, meaning that some of the lead is now better classified as a network former. Finally, it has been found that there is a broad immiscibility range where these systems can form two-phase glasses. The goals of this work are primarily to address the first two prior observations with newer solid-state NMR methods, as the resolution of both 207Pb and 11B NMR spectra have been significantly improved upon by techniques developed since the pioneering studies by Kim et al. [4]. One aim of this work is an attempt to quantify the amount of lead in the roles of network former or modifier using 207Pb NMR. Another goal is to perform advanced 11B NMR experiments in order to investigate the possibility of detecting BO3– units that were hypothesized to exist [4], as well as to quantify the ratio of BO3 to BO4 units in a range of glasses. 207 Pb NMR studies of a variety of lead compounds reveal spectral resonances with a w
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