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 hybridized carbon, tetrahedrally coordinated SiO 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.

Novel 0D-nanocarbon-silica ceramic composites: sol-gel synthesis and high-temperature evolution.

Herein we report the synthesis of novel 0D-nanocarbon-based silicon-containing ceramic composites by a facile salt-free synthesis method followed by polymer-to-ceramic transformation. 0D-nanocarbon-silica composites were synthesized via a one-pot sol-gel process using tetramethyl orthosilicate (TMOS) and functionalized nanodiamonds and converted subsequently via pyrolysis under an argon atmosphere into nanodiamond/silica nanocomposites. The thermal conversion of the nanodiamond phase to a multilayer fullerene phase was carefully investigated by integral and local characterization methods such as vibrational spectroscopy, X-ray diffraction, BET, SEM and HRTEM.

Ceramic Nanocomposites from Tailor-Made Preceramic Polymers.

The present Review addresses current developments related to polymer-derived ceramic nanocomposites (PDC-NCs). Different classes of preceramic polymers are briefly introduced and their conversion into ceramic materials with adjustable phase compositions and microstructures is presented. Emphasis is set on discussing the intimate relationship between the chemistry and structural architecture of the precursor and the structural features and properties of the resulting ceramic nanocomposites.

Carbon substitution for oxygen in silicates in planetary interiors.

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 SiO(x)C(4-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 SiO(x)C(4-x) tetrahedra with nonbridging oxygen.

Characterization of the Materials Synthesized by High Pressure-High Temperature Treatment of a Polymer Derived t-BC₂N Ceramic.

Bulk B-C-N materials were synthesized under static high thermobaric conditions (20 GPa and 2,000 °C) in a multianvil apparatus from a polymer derived t-BCN ceramic. The bulk samples were characterised using X-ray synchrotron radiation and analytical transmission electron microscopy in combination with electron energy loss spectroscopy. Polycrystalline B-C-N materials with a cubic type structure were formed under the applied reaction conditions, but the formation of a ternary cubic diamond-like c-BC₂N compound, could not be unambiguously confirmed.