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Title: Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations

Authors:
ORCiD logo [1]; ORCiD logo [1]
  1. Department of Materials Science and Engineering, University of North Texas, Denton, Texas 76203, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1416469
Resource Type:
Journal Article: Publisher's Accepted Manuscript
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 148; Journal Issue: 2; Related Information: CHORUS Timestamp: 2018-02-15 00:10:56; Journal ID: ISSN 0021-9606
Publisher:
American Institute of Physics
Country of Publication:
United States
Language:
English

Citation Formats

Deng, Lu, and Du, Jincheng. Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations. United States: N. p., 2018. Web. doi:10.1063/1.5007083.
Deng, Lu, & Du, Jincheng. Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations. United States. doi:10.1063/1.5007083.
Deng, Lu, and Du, Jincheng. 2018. "Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations". United States. doi:10.1063/1.5007083.
@article{osti_1416469,
title = {Effects of system size and cooling rate on the structure and properties of sodium borosilicate glasses from molecular dynamics simulations},
author = {Deng, Lu and Du, Jincheng},
abstractNote = {},
doi = {10.1063/1.5007083},
journal = {Journal of Chemical Physics},
number = 2,
volume = 148,
place = {United States},
year = 2018,
month = 1
}

Journal Article:
Free Publicly Available Full Text
This content will become publicly available on January 10, 2019
Publisher's Accepted Manuscript

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  • A set of molecular dynamics simulations were performed to investigate the effect of cooling rate and system size on the medium-range structure of melt-derived multicomponent silicate glasses, represented by the quaternary 45S5 Bioglass composition. Given the significant impact of the glass degradation on applications of these materials in biomedicine and nuclear waste disposal, bulk structural features which directly affect the glass dissolution process are of particular interest. Connectivity of the silicate matrix, ion clustering and nanosegregation, distribution of ring and chain structural patterns represent critical features in this context, which can be directly extracted from the models. A key issuemore » is represented by the effect of the computational approach on the corresponding glass models, especially in light of recent indications questioning the suitability of conventional MD approaches (that is, involving melt-and-quench of systems containing ∼10{sup 3} atoms at cooling rates of 5-10 K/ps) when applied to model these glasses. The analysis presented here compares MD models obtained with conventional and nonconventional cooling rates and system sizes, highlighting the trend and range of convergence of specific structural features in the medium range. The present results show that time-consuming computational approaches involving much lower cooling rates and/or significantly larger system sizes are in most cases not necessary in order to obtain a reliable description of the medium-range structure of multicomponent glasses. We identify the convergence range for specific properties and use them to discuss models of several glass compositions for which a possible influence of cooling-rate or size effects had been previously hypothesized. The trends highlighted here represent an important reference to obtain reliable models of multicomponent glasses and extract converged medium-range structural features which affect the glass degradation and thus their application in different fields. In addition, as a first application of the present findings, the fully converged structure of the 45S5 glass was further analyzed to shed new light on several dissolution-related features whose interpretation has been rather controversial in the past.« less
  • /sup 9/Be and /sup 19/F NMR techniques are used to gain information about the short-range order in two beryllium fluoride glasses: A simple BeF/sub 2/ glass and a NaFx2BeF/sub 2/ glass. The magnitude of the average quadrupole coupling constant for /sup 9/Be sites is deduced from the location of the first-order satellites and from low-frequency second-order broadening of the central transition of the /sup 9/Be spectrum. The average quadrupole coupling constant for the binary glass was a factor of 4 larger than for BeF/sub 2/ glass. It is argued that this is consistent with the existence of non-tetrahedrally-coordinated Be ionsmore » in the sodium fluoroberyllate glass. The central transition of the /sup 9/Be NMR spectrum for the nominally pure BeF/sub 2/ glass exhibited an anomalous narrow line which may be due to the presence of Be metallic clusters. The linewidth of the /sup 19/F resonance and the /sup 19/F spin-lattice relaxation time, T/sub 1/, of the two glasses were also studied as a function of temperature. These measurements indicate that there is some motion of the fluorines in the binary sample slightly above its transition temperature of 388 K. The two glasses were simulated by methods of molecular dynamics. It was found that whereas in simple BeF/sub 2/ glass virtually all of the Be ions were tetrahedrally coordinated by four F ions, in multicomponent glasses a large number of Be ions have five F ions in the first coordination shell. This is qualitatively consistent with the experimental observations. Meaningful quantitative predictions of the effective /sup 9/Be quadrupole coupling constants for the two glasses failed, however, because the simulated glasses are more disordered than glasses prepared in the laboratory. There is a broad distribution of F--Be--F angles in the simulated BeF/sub 2/ glass.« less
  • We have performed classical molecular dynamics simulations in order to study the changes under compression in the local and medium range structural properties of three sodium borosilicate glasses with varying sodium content. These glasses have been isostatically compressed up to 20 GPa and then decompressed in order to analyze the different mechanisms that affect densification, alongside with the permanent modifications of the structure after a full compression/decompression cycle. The results show that the atomic packing is the prominent characteristic that governs the amount of densification in the glass, as well as the setup of the permanent densification. During compression, themore » bulk modulus increases linearly up to approximately 15 GPa and more rapidly for higher pressures, a behavior which is reflected on the rate of increase of the average coordination for B and Na. Radial distribution functions at different pressures during the cycle help to quantify the amount of distortions in the elementary structural units, with a pronounced shortening of the Na–Na and Na–O bond lengths during compression. A subsequent decomposition of the glassy matrix into elementary Voronoi volumes verifies the high compressibility of Na-rich regions.« less
  • The structure of iron-bearing sodium borosilicate glasses with up to 10 mol% FeO has been investigated in the range 0.15 ≤ Fe{sup 3+}/SFe ≤ 0.95. According to Moessbauer spectroscopy, Fe{sup 3+} and Fe{sup 2+} are mainly in tetrahedral and octahedral coordination, respectively, although other coordination states exist for both cations. From XANES experiments, we conclude that increasing Fe content and varying redox states have only a minor effect on the relative proportions of BO{sub 3} and BO{sub 4} units. In Raman spectra, a decrease of the proportion of BO{sub 4} species present in danburite-like units (Na{sub 2}O.B{sub 2}O{sub 3}.2SiO{sub 2})more » is found upon increasing iron content and oxidizing state. Whereas the insensitivity of the overall boron speciation to iron content and redox state points to weak interactions between boron and iron, the changes affecting BO{sub 4} species do indicate a more subtle interplay between Fe{sup 3+} and the other tetrahedrally coordinated cations (Si,B) because of the competition between tetrahedral Fe{sup 3+} and B{sup 3+} for charge compensation by Na{sup +}. (authors)« less