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Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding

Sugie, Casey ; Navrotsky, Alexandra ; Lauterbach, Stefan ; Kleebe, Hans-Joachim ; Mera, Gabriela (2021)
Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding.
In: Materials, 2021, 14 (15)
doi: 10.26083/tuprints-00019459
Article, Secondary publication, Publisher's Version

Copyright Information: CC BY 4.0 International - Creative Commons, Attribution.

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Item Type: Article
Type of entry: Secondary publication
Title: Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
Language: English
Date: 6 September 2021
Place of Publication: Darmstadt
Year of primary publication: 2021
Publisher: MDPI
Journal or Publication Title: Materials
Volume of the journal: 14
Issue Number: 15
Collation: 23 Seiten
DOI: 10.26083/tuprints-00019459
Corresponding Links:
Origin: Secondary publication via sponsored Golden Open Access

Silicon oxycarbides synthesized through a conventional polymeric route show characteristic nanodomains that consist of sp² hybridized carbon, tetrahedrally coordinated SiO₄, 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 SiO₂, 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.

Status: Publisher's Version
URN: urn:nbn:de:tuda-tuprints-194593
Additional Information:

Keywords: silicon oxycarbide; polymer-derived ceramics; nanodomain structure; carbon nanorolls; polysiloxanes; energetics

Classification DDC: 500 Science and mathematics > 540 Chemistry
500 Science and mathematics > 550 Earth sciences and geology
600 Technology, medicine, applied sciences > 620 Engineering and machine engineering
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
Date Deposited: 06 Sep 2021 12:19
Last Modified: 14 Nov 2023 19:04
URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/19459
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