Single-Source-Precursor Synthesis of SiC-Based Ceramic Nanocomposites for Energy-Related Applications

The present work deals with the synthesis, characterization, and fabrication of Si-M-C-based ceramic nanocomposites (M = B and V). These were produced by the thermal transformation of tailor-made single-source-precursors, which were synthesized by the chemical modification of an allyl-hydrido polycarbosilane with suitable precursors (i.e., borane dimethylsulfide, allyl-functionalized carboranes, vanadium acetylacetonate and vanadium oxytriisopropoxide). The typical approach to this synthesis consists of a pyrolytic ceramization of the precursors, which converted into amorphous single-phase SiMC(O)-based materials. They are further subjected to high temperature treatment for phase separation and crystallization processes to furnish SiC-based ceramic nanocomposites. The preceramic polymer allyl-hydrido polycarbosilane (commercial name SMP-10) and derived SiC-based ceramics were thorougly investigated with respect to cross-linking behavior, polymer-to-ceramic transformation as well as high-temperature phase composition and microstructure. This knowledge served to optimize the processing of the preceramic polymeric precursor to produce dense and crack-free SiC-based monolithic ceramics by pressureless technique. The obtained ceramic monoliths have been shown to exhibits residual porosity of 15-25 vol%, which however can further be reduced by the use of polymer-infiltration and pyrolysis (PIP) to about 0.5 vol%. Boron-containing single-source-precursors were synthesized upon reactions of SMP-10 with borane dimethylsulfide complex (BMS) or with allyl-functionalized carboranes (AFC). In case of BMS-modified SMP-10 (BMS-SiBC), a detailed structural characterization has been done by means of various spectroscopic techniques. The main aspects addressed in case of BMS-modified SMP-10 (BMS-SiBC) are the fate of boron in the prepared SiBC ceramics, which was not been clarified unambiguously so far, and the role of boron in terms of densification of SiC. X-ray diffraction data, corroborated with X-ray photoelectron ...