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Title: Effects of temperature on the structures of silicate liquids: sup 29 Si NMR results

Abstract

The effect of temperature on the structures of three silicate liquids has been studied by {sup 29}Si NMR spectroscopy on glass samples prepared with different glass transition temperatures. The compositions studied are (Na{sub 2}O){sub .34}(SiO{sub 2}){sub .66} and (CaO){sub .10}(Na{sub 2}O){sub .15}(SiO{sub 2}){sub .75} and (CaO){sub .25}(MgO){sub .25}(SiO{sub 2}){sub .50}. In the first two, the abundance of SiO{sub 4} tetrahedra with four bridging oxygens (Q{sup 4}) increases significantly with temperature. This change results from the disproportionation reaction 2Q{sup 3} {r equilibrium} Q{sup 2} + Q{sup 4} (Q{sup n} is a SiO{sub 4} tetrahedron with n bridging oxygens), with the observed increase in disproportionation at higher temperatures implying increased randomization of the anionic structure. In the (Na{sub 2}O){sub .34}(SiO{sub 2}){sub .66} composition, the temperature dependence of Q{sup 4} abundance enables them to estimate {Delta}H{sup 0} for this reaction to be 30 {plus minus} 15 kJ per mole of Si. Although this reaction thus makes only a minor contribution to the configurational heat capacity of each liquid, it probably has a major influence on the thermodynamic activity of SiO{sub 2}. Widening of the (CaO){sub .25}(MgO){sub .25}(SiO{sub 2}){sub .50} spectral peak with increasing temperature likewise implies increasing randomization of the anionic structure, althoughmore » specific structural contributions to this widening are not identified. Models of melt structures at liquidus temperatures will be limited in accuracy if they assume that the speciation observed in glasses is unaffected by temperature change.« less

Authors:
;  [1]
  1. Stanford Univ., CA (USA)
Publication Date:
OSTI Identifier:
7164124
Resource Type:
Journal Article
Journal Name:
Geochimica et Cosmochimica Acta; (USA)
Additional Journal Information:
Journal Volume: 52:11; Journal ID: ISSN 0016-7037
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; CRYSTAL STRUCTURE; TEMPERATURE EFFECTS; MOLECULAR STRUCTURE; SILICATE MINERALS; PHASE STUDIES; STRUCTURAL CHEMICAL ANALYSIS; AMORPHOUS STATE; CHEMICAL COMPOSITION; CRYSTAL MODELS; CRYSTALLIZATION; CRYSTALLOGRAPHY; GEOCHEMISTRY; LIQUIDS; QUANTITATIVE CHEMICAL ANALYSIS; SPECTROSCOPY; THERMODYNAMIC ACTIVITY; THERMODYNAMIC MOLECULAR MODEL; THERMODYNAMICS; CHEMICAL ANALYSIS; CHEMISTRY; FLUIDS; MATHEMATICAL MODELS; MINERALS; MOLECULAR MODELS; PHASE TRANSFORMATIONS; 580000* - Geosciences

Citation Formats

Brandriss, M E, and Stebbins, J F. Effects of temperature on the structures of silicate liquids: sup 29 Si NMR results. United States: N. p., 1988. Web. doi:10.1016/0016-7037(88)90034-8.
Brandriss, M E, & Stebbins, J F. Effects of temperature on the structures of silicate liquids: sup 29 Si NMR results. United States. https://doi.org/10.1016/0016-7037(88)90034-8
Brandriss, M E, and Stebbins, J F. 1988. "Effects of temperature on the structures of silicate liquids: sup 29 Si NMR results". United States. https://doi.org/10.1016/0016-7037(88)90034-8.
@article{osti_7164124,
title = {Effects of temperature on the structures of silicate liquids: sup 29 Si NMR results},
author = {Brandriss, M E and Stebbins, J F},
abstractNote = {The effect of temperature on the structures of three silicate liquids has been studied by {sup 29}Si NMR spectroscopy on glass samples prepared with different glass transition temperatures. The compositions studied are (Na{sub 2}O){sub .34}(SiO{sub 2}){sub .66} and (CaO){sub .10}(Na{sub 2}O){sub .15}(SiO{sub 2}){sub .75} and (CaO){sub .25}(MgO){sub .25}(SiO{sub 2}){sub .50}. In the first two, the abundance of SiO{sub 4} tetrahedra with four bridging oxygens (Q{sup 4}) increases significantly with temperature. This change results from the disproportionation reaction 2Q{sup 3} {r equilibrium} Q{sup 2} + Q{sup 4} (Q{sup n} is a SiO{sub 4} tetrahedron with n bridging oxygens), with the observed increase in disproportionation at higher temperatures implying increased randomization of the anionic structure. In the (Na{sub 2}O){sub .34}(SiO{sub 2}){sub .66} composition, the temperature dependence of Q{sup 4} abundance enables them to estimate {Delta}H{sup 0} for this reaction to be 30 {plus minus} 15 kJ per mole of Si. Although this reaction thus makes only a minor contribution to the configurational heat capacity of each liquid, it probably has a major influence on the thermodynamic activity of SiO{sub 2}. Widening of the (CaO){sub .25}(MgO){sub .25}(SiO{sub 2}){sub .50} spectral peak with increasing temperature likewise implies increasing randomization of the anionic structure, although specific structural contributions to this widening are not identified. Models of melt structures at liquidus temperatures will be limited in accuracy if they assume that the speciation observed in glasses is unaffected by temperature change.},
doi = {10.1016/0016-7037(88)90034-8},
url = {https://www.osti.gov/biblio/7164124}, journal = {Geochimica et Cosmochimica Acta; (USA)},
issn = {0016-7037},
number = ,
volume = 52:11,
place = {United States},
year = {Tue Nov 01 00:00:00 EST 1988},
month = {Tue Nov 01 00:00:00 EST 1988}
}