Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
Silicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp<sup>2</sup> hybridized carbon, tetrahedrally coordinated SiO<sub>4,</sub> and tetrahedrally coordinated silicon with carbon substitution for oxygen, calle...
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| author | Casey Sugie Alexandra Navrotsky Stefan Lauterbach Hans-Joachim Kleebe Gabriela Mera |
| author_facet | Casey Sugie Alexandra Navrotsky Stefan Lauterbach Hans-Joachim Kleebe Gabriela Mera |
| author_sort | Casey Sugie |
| collection | DOAJ |
| description | Silicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp<sup>2</sup> hybridized carbon, tetrahedrally coordinated SiO<sub>4,</sub> and tetrahedrally coordinated silicon with carbon substitution for oxygen, called “mixed bonds.” Here we synthesize two preceramic polymers possessing both phenyl substituents as unique organic groups. In one precursor, the phenyl group is directly bonded to silicon, resulting in a SiOC polymer-derived ceramic (PDC) with mixed bonding. In the other precursor, the phenyl group is bonded to the silicon through Si-O-C bridges, which results in a SiOC PDC without mixed bonding. Radial breathing-like mode bands in the Raman spectra reveal that SiOC PDCs contain carbon nanoscrolls with spiral-like rolled-up geometry and open edges at the ends of their structure. Calorimetric measurements of the heat of dissolution in a molten salt solvent show that the SiOC PDCs with mixed bonding have negative enthalpies of formation with respect to crystalline components (silicon carbide, cristobalite, and graphite) and are more thermodynamically stable than those without. The heats of formation from crystalline SiO<sub>2</sub>, SiC, and C of SiOC PDCs without mixed bonding are close to zero and depend on the pyrolysis temperature. Solid state MAS NMR confirms the presence or absence of mixed bonding and further shows that, without mixed bonding, terminal hydroxyls are bound to some of the Si-O tetrahedra. This study indicates that mixed bonding, along with additional factors, such as the presence of terminal hydroxyl groups, contributes to the thermodynamic stability of SiOC PDCs. |
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| institution | Directory Open Access Journal |
| issn | 1996-1944 |
| language | English |
| last_indexed | 2024-03-10T09:13:19Z |
| publishDate | 2021-07-01 |
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| spelling | doaj.art-bc31049d4f2746f2b6a468961ccc9eee2023-11-22T05:51:21ZengMDPI AGMaterials1996-19442021-07-011415407510.3390/ma14154075Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding Casey Sugie0Alexandra Navrotsky1Stefan Lauterbach2Hans-Joachim Kleebe3Gabriela Mera4Department of Chemistry, University of California Davis, Davis, CA 95616, USAPeter A. Rock Thermochemistry Laboratory and NEAT ORU, University of California Davis, Davis, CA 95616, USAInstitut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Schnittspahnstraße 9, D-64287 Darmstadt, GermanyInstitut für Angewandte Geowissenschaften, Technische Universität Darmstadt, Schnittspahnstraße 9, D-64287 Darmstadt, GermanyInstitut für Materialwissenschaft, Technische Universität Darmstadt, Otto-Berndt-Straße 3, D-64287 Darmstadt, GermanySilicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp<sup>2</sup> hybridized carbon, tetrahedrally coordinated SiO<sub>4,</sub> and tetrahedrally coordinated silicon with carbon substitution for oxygen, called “mixed bonds.” Here we synthesize two preceramic polymers possessing both phenyl substituents as unique organic groups. In one precursor, the phenyl group is directly bonded to silicon, resulting in a SiOC polymer-derived ceramic (PDC) with mixed bonding. In the other precursor, the phenyl group is bonded to the silicon through Si-O-C bridges, which results in a SiOC PDC without mixed bonding. Radial breathing-like mode bands in the Raman spectra reveal that SiOC PDCs contain carbon nanoscrolls with spiral-like rolled-up geometry and open edges at the ends of their structure. Calorimetric measurements of the heat of dissolution in a molten salt solvent show that the SiOC PDCs with mixed bonding have negative enthalpies of formation with respect to crystalline components (silicon carbide, cristobalite, and graphite) and are more thermodynamically stable than those without. The heats of formation from crystalline SiO<sub>2</sub>, SiC, and C of SiOC PDCs without mixed bonding are close to zero and depend on the pyrolysis temperature. Solid state MAS NMR confirms the presence or absence of mixed bonding and further shows that, without mixed bonding, terminal hydroxyls are bound to some of the Si-O tetrahedra. This study indicates that mixed bonding, along with additional factors, such as the presence of terminal hydroxyl groups, contributes to the thermodynamic stability of SiOC PDCs.https://www.mdpi.com/1996-1944/14/15/4075silicon oxycarbidepolymer-derived ceramicsnanodomain structurecarbon nanorollspolysiloxanesenergetics |
| spellingShingle | Casey Sugie Alexandra Navrotsky Stefan Lauterbach Hans-Joachim Kleebe Gabriela Mera Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding Materials silicon oxycarbide polymer-derived ceramics nanodomain structure carbon nanorolls polysiloxanes energetics |
| title | Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
|
| title_full | Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
|
| title_fullStr | Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
|
| title_full_unstemmed | Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
|
| title_short | Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
|
| title_sort | structure and thermodynamics of silicon oxycarbide polymer derived ceramics with and without mixed bonding |
| topic | silicon oxycarbide polymer-derived ceramics nanodomain structure carbon nanorolls polysiloxanes energetics |
| url | https://www.mdpi.com/1996-1944/14/15/4075 |
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