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Carbon substitution for oxygen in silicates in planetary interiors

Sen, S. and Widgeon, S. J. and Navrotsky, A. and Mera, G. and Tavakoli, A. and Ionescu, E. and Riedel, R. (2013):
Carbon substitution for oxygen in silicates in planetary interiors.
In: Proceedings of the National Academy of Sciences, 110 (40), pp. 15904-15907, ISSN 0027-8424,
[Online-Edition: http://dx.doi.org/10.1073/pnas.1312771110],
[Article]

Abstract

Amorphous silicon oxycarbide polymer-derived ceramics (PDCs), synthesized from organometallic precursors, contain carbon- and silica-rich nanodomains, the latter with extensive substitution of carbon for oxygen, linking Si-centered SiOxC4-x tetrahedra. Calorimetric studies demonstrated these PDCs to be thermodynamically more stable than a mixture of SiO2, C, and silicon carbide. Here, we show by multinuclear NMR spectroscopy that substitution of C for O is also attained in PDCs with depolymerized silica-rich domains containing lithium, associated with SiOxC4-x tetrahedra with nonbridging oxygen. We suggest that significant (several percent) substitution of C for O could occur in more complex geological silicate melts/glasses in contact with graphite at moderate pressure and high temperature and may be thermodynamically far more accessible than C for Si substitution. Carbon incorporation will change the local structure and may affect physical properties, such as viscosity. Analogous carbon substitution at grain boundaries, at defect sites, or as equilibrium states in nominally acarbonaceous crystalline silicates, even if present at levels at 10–100 ppm, might form an extensive and hitherto hidden reservoir of carbon in the lower crust and mantle.

Item Type: Article
Erschienen: 2013
Creators: Sen, S. and Widgeon, S. J. and Navrotsky, A. and Mera, G. and Tavakoli, A. and Ionescu, E. and Riedel, R.
Title: Carbon substitution for oxygen in silicates in planetary interiors
Language: English
Abstract:

Amorphous silicon oxycarbide polymer-derived ceramics (PDCs), synthesized from organometallic precursors, contain carbon- and silica-rich nanodomains, the latter with extensive substitution of carbon for oxygen, linking Si-centered SiOxC4-x tetrahedra. Calorimetric studies demonstrated these PDCs to be thermodynamically more stable than a mixture of SiO2, C, and silicon carbide. Here, we show by multinuclear NMR spectroscopy that substitution of C for O is also attained in PDCs with depolymerized silica-rich domains containing lithium, associated with SiOxC4-x tetrahedra with nonbridging oxygen. We suggest that significant (several percent) substitution of C for O could occur in more complex geological silicate melts/glasses in contact with graphite at moderate pressure and high temperature and may be thermodynamically far more accessible than C for Si substitution. Carbon incorporation will change the local structure and may affect physical properties, such as viscosity. Analogous carbon substitution at grain boundaries, at defect sites, or as equilibrium states in nominally acarbonaceous crystalline silicates, even if present at levels at 10–100 ppm, might form an extensive and hitherto hidden reservoir of carbon in the lower crust and mantle.

Journal or Publication Title: Proceedings of the National Academy of Sciences
Volume: 110
Number: 40
Uncontrolled Keywords: carbon in silicates, Li-Si-O-C ceramics, deep Earth
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences
Date Deposited: 20 Feb 2014 13:36
Official URL: http://dx.doi.org/10.1073/pnas.1312771110
Identification Number: doi:10.1073/pnas.1312771110
Funders: This study was performed within a National Science Foundation (NSF) Materials World Network collaborative project entitled “Nanostructure and thermodynamics of polymer-derived ceramics” and was supported by NSF Grant MWN-0906070.
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