SiC/WxCy/C ceramic nanocomposites: Single-source-precursor synthesis, phase, and microstructural evolution

In this study, a novel tungsten-containing single-source precursor (SSP) was synthesized by the reaction of bis(tert-butylimino)bis(dimethylamino)tungsten(VI) (BTBMW) and allylhydridopolycarbosilane (SMP-10) for the purpose of obtaining SiC/WxCy/C nanocomposite ceramics, which have application potential in preparation of ultra-high temperature-resistant ceramic monoliths. The synthesized SSP was characterized by Fourier transform infrared spectroscopy, and the characteristic peak (Si-N-W at 592 cm-1) unique to this type of SSP was found. Subsequent pyrolysis of the SSP at 900 degrees C in Ar resulted in the formation of X-ray amorphous SiWC ceramic. X-ray powder diffraction, Raman spectroscopy, and transmission electron microscopy were used to study the phase formation and microstructural evolution of the ceramic at elevated temperatures. The results show that the final ceramics are composed of an SiWC amorphous matrix with embedded polycrystalline SiC, WC, and W2C nanoparticles as well as sp2-hybridized free carbon. The proportion of each phase can be changed by adjusting the annealing temperature and the feed ratio of raw materials to obtain nanocomposite ceramics in the ternary system Si-W-C with different properties. Even at 1700 degrees C, the in situ formed WC and W2C nanoparticles are still uniformly dispersed in the SiWC matrix, and a large amount of sp2-hybridized free carbon exists between these nanoparticles, which also makes the material a potential candidate for application in high-temperature electrically conductive structural ceramics.