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Title: Nepheline crystallization in boron-rich alumino-silicate glasses as investigated by multi-nuclear NMR, Raman, & Mössbauer spectroscopies

Abstract

A spectroscopic study was conducted on 6 complex simulant nuclear waste glasses using multi-nuclear NMR, Raman and Mössbauer spectroscopies to explore the role of glass-forming elements Si, Al, B, along with Na and Fe and to understand their connectivity with the goal of understanding melt structure precursors to deleterious feldspathoid nepheline-like crystals formation. NMR showed the appearance of two sites for Al, Si, and Na in the samples which crystallized significant amounts of nepheline, and B speciation changed, typically resulting in more B(IV) after nepheline crystallization. Raman spectroscopy suggested a major part of the glass structure is composed of metaborate chains or rings, thus significant numbers of non-bridging oxygens and a separation of the borate from the alumino-silicate network. Mössbauer combined with Fe redox chemical measurements showed that Fe plays a minor role in these glasses, mostly as Fe3+, but that iron oxide spinel forms with nepheline in all cases. Models of the glass network, speciation of B, and allocation of non-bridging oxygens were computed. The Yun-Dell-Bray model failed to predict the observed high concentration of NBO necessary to explain the metaborate features in the Raman spectra, and it largely over-estimated B(IV) fraction. The model assuming Na-Al-Si moieties and usingmore » experimental B(IV) fraction predicted a large amount of NBO consistent with Raman spectra. An alternative notation for appreciating the glass network is suggested and then used to investigate the changes the glass due to crystallization of sodium nepheline and the residual glass network. From a theoretical standpoint, it may be preferred to picture nuclear waste glasses by the Lebedev theory of glass structure where “microcrystallites” of ordered nuclei (or embryos) exist in the matrix of more disordered glass.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE
OSTI Identifier:
1212237
Report Number(s):
PNNL-SA-103049
Journal ID: ISSN 0022-3093; 46403; 39968; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Non-Crystalline Solids; Journal Volume: 409
Country of Publication:
United States
Language:
English
Subject:
Environmental Molecular Sciences Laboratory

Citation Formats

Mccloy, John S., Washton, Nancy M., Gassman, Paul L., Marcial, Jose, Weaver, Jamie L., and Kukkadapu, Ravi K. Nepheline crystallization in boron-rich alumino-silicate glasses as investigated by multi-nuclear NMR, Raman, & Mössbauer spectroscopies. United States: N. p., 2015. Web. doi:10.1016/j.jnoncrysol.2014.11.013.
Mccloy, John S., Washton, Nancy M., Gassman, Paul L., Marcial, Jose, Weaver, Jamie L., & Kukkadapu, Ravi K. Nepheline crystallization in boron-rich alumino-silicate glasses as investigated by multi-nuclear NMR, Raman, & Mössbauer spectroscopies. United States. doi:10.1016/j.jnoncrysol.2014.11.013.
Mccloy, John S., Washton, Nancy M., Gassman, Paul L., Marcial, Jose, Weaver, Jamie L., and Kukkadapu, Ravi K. Sun . "Nepheline crystallization in boron-rich alumino-silicate glasses as investigated by multi-nuclear NMR, Raman, & Mössbauer spectroscopies". United States. doi:10.1016/j.jnoncrysol.2014.11.013.
@article{osti_1212237,
title = {Nepheline crystallization in boron-rich alumino-silicate glasses as investigated by multi-nuclear NMR, Raman, & Mössbauer spectroscopies},
author = {Mccloy, John S. and Washton, Nancy M. and Gassman, Paul L. and Marcial, Jose and Weaver, Jamie L. and Kukkadapu, Ravi K.},
abstractNote = {A spectroscopic study was conducted on 6 complex simulant nuclear waste glasses using multi-nuclear NMR, Raman and Mössbauer spectroscopies to explore the role of glass-forming elements Si, Al, B, along with Na and Fe and to understand their connectivity with the goal of understanding melt structure precursors to deleterious feldspathoid nepheline-like crystals formation. NMR showed the appearance of two sites for Al, Si, and Na in the samples which crystallized significant amounts of nepheline, and B speciation changed, typically resulting in more B(IV) after nepheline crystallization. Raman spectroscopy suggested a major part of the glass structure is composed of metaborate chains or rings, thus significant numbers of non-bridging oxygens and a separation of the borate from the alumino-silicate network. Mössbauer combined with Fe redox chemical measurements showed that Fe plays a minor role in these glasses, mostly as Fe3+, but that iron oxide spinel forms with nepheline in all cases. Models of the glass network, speciation of B, and allocation of non-bridging oxygens were computed. The Yun-Dell-Bray model failed to predict the observed high concentration of NBO necessary to explain the metaborate features in the Raman spectra, and it largely over-estimated B(IV) fraction. The model assuming Na-Al-Si moieties and using experimental B(IV) fraction predicted a large amount of NBO consistent with Raman spectra. An alternative notation for appreciating the glass network is suggested and then used to investigate the changes the glass due to crystallization of sodium nepheline and the residual glass network. From a theoretical standpoint, it may be preferred to picture nuclear waste glasses by the Lebedev theory of glass structure where “microcrystallites” of ordered nuclei (or embryos) exist in the matrix of more disordered glass.},
doi = {10.1016/j.jnoncrysol.2014.11.013},
journal = {Journal of Non-Crystalline Solids},
number = ,
volume = 409,
place = {United States},
year = {Sun Feb 01 00:00:00 EST 2015},
month = {Sun Feb 01 00:00:00 EST 2015}
}