NMR Characterization of Simulated Hanford Low-Activity Waste Glasses and its use in Understanding Waste form Chemical Du
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and the inherent bond strengths of the constituents in a glass to its chemical durability (e.g., reference [2]). However, in some cases the structural models for the constituents are not complete and the available primary bond strength information may not be applicable for certain structural models as secondary effects, such as partial covalent bonding, are not accounted for. Magic angle spinning nuclear magnetic resonance (MAS-NMR) spectroscopy is a sensitive technique for studying the structure and chemical environment of many of the nuclei contained in LAW glass (11B, 27 AI, 29 Si, 31 P, etc.). Here, we build on our previous structural characterization work [3] to develop a model that predicts the 2 9Si MAS-NMR chemical shift value, 6, for a particular glass which we then use to describe the chemical nature of the glass network. By using 6 as an indicator of the bonding characteristics within a glass network, we take into account the effects of primary bond strengths [2] as well as secondary effects, which are not accounted for in other models. As a potential application of this model, we attempt to predict the boron elemental release, determined by product consistency tests (PCT), for a series of glasses of different composition. In this article, we focus on sodium borosilicate, sodium boro-aluminosilicate, and sodium aluminosilicate glasses as well as more complex, but related, simulated LAW glasses [4]. EXPERIMENTAL Table I summarizes the target compositions for the glasses studied in this work. Based on these compositions, the glass batch material was made by mixing appropriate amounts of dry chemical reagents to yield about 150-200 g of glass and melting the mixture in a Pt-10%Rh crucible at temperatures of 1000-15000 C. Details are described in a previous publication [3]. 337 Mat. Res. Soc. Symp. Proc. Vol. 556
© 1999
Materials Research Society
Table I. Target compositions (in wt% oxide component) for the glass series (Bas-1, B-, Al-, NaSiO-, and L4-) studied in this work. Oxide Component A1203 Na2O Other Glass Sio 2 B2 0 3 Bas- 1 74.0 6.0 20.0 B-3 77.0 3.0 20.0 B-16 64.0 16.0 20.0 B-24 56.0 24.0 20.0 A14 70.0 6.0 4.0 20.0 Al-8 66.0 6.0 8.0 20.0 Al-16 58.0 6.0 16.0 20.0 A1-24 50.0 6.0 24.0 20.0 NaSiO-X 65.9 34.1 NaSiO-5A1 57.3 8.1 34.6 NaSiO-1OA1
49.3
-
15.7
35.0
-
NaSiO-15A1 41.8 22.8 35.4 L4-912 56.8 9.0 12.0 20.0 2.2 a a Other includes K2 0, Cs2O, Cl, F, I, P2 0 5 , SO 3 , Cr 2 O3 , MnO, MoO3 , SrO [4]. Room temperature 29 Si magic angle spinning nuclear magnetic resonance (MAS-NMR) spectra were obtained on a Varian VXR-300 spectrometer at 7.05 T using high-speed probes manufactured by Doty Scientific, Inc. Silicon nitride rotors (5 mm diameter) or sapphire rotors (7 mm diameter) with Vespel polymer end caps were used to spin the samples at -5 kHz. Spectra were collected at 59.59 MHz using a single pulse excitation of 64 ms with a pulse delay of 60 s. The 29 Si NMR peak associated with the Si 3N4 rotor was considerably different in position from that of the glass samples, and was used as an "i
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