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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. (Publisher's Version)
In: Materials, 14 (15), MDPI, e-ISSN 1996-1944,
DOI: 10.26083/tuprints-00019459,

Available under: CC BY 4.0 International - Creative Commons, Attribution.

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Item Type: Article
Origin: Secondary publication via sponsored Golden Open Access
Status: Publisher's Version
Title: Structure and Thermodynamics of Silicon Oxycarbide Polymer-Derived Ceramics with and without Mixed-Bonding
Language: English

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.

Journal or Publication Title: Materials
Volume of the journal: 14
Issue Number: 15
Publisher: MDPI
Collation: 23 Seiten
Classification DDC: 500 Naturwissenschaften und Mathematik > 540 Chemie
500 Naturwissenschaften und Mathematik > 550 Geowissenschaften
600 Technik, Medizin, angewandte Wissenschaften > 620 Ingenieurwissenschaften
Divisions: 11 Department of Materials and Earth Sciences > Material Science > Dispersive Solids
Date Deposited: 06 Sep 2021 12:19
Last Modified: 06 Sep 2021 12:19
DOI: 10.26083/tuprints-00019459
Corresponding Links:
URN: urn:nbn:de:tuda-tuprints-194593
Additional Information:

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

URI: https://tuprints.ulb.tu-darmstadt.de/id/eprint/19459
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