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Title: Borate melt structure: Temperature-dependent B–O bond lengths and coordination numbers from high-energy X-ray diffraction

Borate melts containing <20 mol% Na 2O have been studied using high-energy synchrotron X-ray diffraction. Temperature dependencies of the mean B–O bond lengths are shown to vary strongly with soda content, by comparison to previous measurements on liquid B 2O 3 and Na 2B 4O 7. Whereas in liquid B 2O 3 linear thermal expansion of the BØ 3 units is observed, with coefficient α BO = 3.7(2) × 10 -6 K -1, this expansion is apparently slightly suppressed in melts containing <20 mol% Na 2O, and is dramatically reversed at the diborate composition. These effects are interpreted in terms of changes in the mean B–O coordination number, where the reaction BØ 4- + BØ 3 ⇌ BØ 3 + BØ 2O- shifts to the right with increasing temperature. The empirical bond-valence relationship is used to convert measured bond lengths, r BO, to coordination numbers, n BO, including a correction for the expected thermal expansion. This method is more accurate and precise than direct determination of n BO from peak areas in the radial distribution functions. Gradients of Δn BO/ΔT = -3.4(3) × 10 -4 K -1 close to the diborate composition, and Δn BO/ΔT = -0.3(1) × 10 -4more » K -1 for a 13(3) mol% Na 2O melt are observed, in reasonable agreement with Raman spectroscopic observations and thermodynamic modeling, with some quantitative differences. These observations go toward explaining isothermal viscosity maxima and changes in fragility across the sodium borate system.« less
Authors:
ORCiD logo [1] ;  [2] ;  [3] ;  [4] ;  [1]
  1. Materials Development, Inc., Arlington Heights, IL (United States); Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS), X-Ray Science Division
  2. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS), X-Ray Science Division
  3. Materials Development, Inc., Arlington Heights, IL (United States); Northwestern Univ., Evanston, IL (United States). Dept. of Materials Science and Engineering, McCormick School of Engineering and Applied Science
  4. Materials Development, Inc., Arlington Heights, IL (United States)
Publication Date:
Grant/Contract Number:
AC02-06CH11357; SC0007564; SC0015241; AC02‐06CH11357
Type:
Accepted Manuscript
Journal Name:
Journal of the American Ceramic Society
Additional Journal Information:
Journal Volume: 101; Journal Issue: 8; Journal ID: ISSN 0002-7820
Publisher:
American Ceramic Society
Research Org:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org:
USDOE Office of Science (SC)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; atomic structure; borates; glassmelting; thermodynamics; X-ray methods
OSTI Identifier:
1480859
Alternate Identifier(s):
OSTI ID: 1429154

Alderman, Oliver L. G., Benmore, Chris J., Lin, Alex, Tamalonis, Anthony, and Weber, J. K. Richard. Borate melt structure: Temperature-dependent B–O bond lengths and coordination numbers from high-energy X-ray diffraction. United States: N. p., Web. doi:10.1111/jace.15529.
Alderman, Oliver L. G., Benmore, Chris J., Lin, Alex, Tamalonis, Anthony, & Weber, J. K. Richard. Borate melt structure: Temperature-dependent B–O bond lengths and coordination numbers from high-energy X-ray diffraction. United States. doi:10.1111/jace.15529.
Alderman, Oliver L. G., Benmore, Chris J., Lin, Alex, Tamalonis, Anthony, and Weber, J. K. Richard. 2018. "Borate melt structure: Temperature-dependent B–O bond lengths and coordination numbers from high-energy X-ray diffraction". United States. doi:10.1111/jace.15529.
@article{osti_1480859,
title = {Borate melt structure: Temperature-dependent B–O bond lengths and coordination numbers from high-energy X-ray diffraction},
author = {Alderman, Oliver L. G. and Benmore, Chris J. and Lin, Alex and Tamalonis, Anthony and Weber, J. K. Richard},
abstractNote = {Borate melts containing <20 mol% Na2O have been studied using high-energy synchrotron X-ray diffraction. Temperature dependencies of the mean B–O bond lengths are shown to vary strongly with soda content, by comparison to previous measurements on liquid B2O3 and Na2B4O7. Whereas in liquid B2O3 linear thermal expansion of the BØ3 units is observed, with coefficient αBO = 3.7(2) × 10-6 K-1, this expansion is apparently slightly suppressed in melts containing <20 mol% Na2O, and is dramatically reversed at the diborate composition. These effects are interpreted in terms of changes in the mean B–O coordination number, where the reaction BØ4- + BØ3 ⇌ BØ3 + BØ2O- shifts to the right with increasing temperature. The empirical bond-valence relationship is used to convert measured bond lengths, rBO, to coordination numbers, nBO, including a correction for the expected thermal expansion. This method is more accurate and precise than direct determination of nBO from peak areas in the radial distribution functions. Gradients of ΔnBO/ΔT = -3.4(3) × 10-4 K-1 close to the diborate composition, and ΔnBO/ΔT = -0.3(1) × 10-4 K-1 for a 13(3) mol% Na2O melt are observed, in reasonable agreement with Raman spectroscopic observations and thermodynamic modeling, with some quantitative differences. These observations go toward explaining isothermal viscosity maxima and changes in fragility across the sodium borate system.},
doi = {10.1111/jace.15529},
journal = {Journal of the American Ceramic Society},
number = 8,
volume = 101,
place = {United States},
year = {2018},
month = {3}
}

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