Synthesis, Characterization, and High Temperature Stability of Si(B)CN-Coated Carbon Nanotubes Using a Boron-Modified Poly(ureamethylvinyl)Silazane Chemistry

Carbon nanotubes (CNT) and polymer-derived ceramics (PDCs) are of interest due to their unique multifunctional properties. CNTs, however, tend to lose their well-defined structure and geometry at about 400°C in air. PDCs on the other hand are structureless in X-ray diffraction but show high chemical and thermal stability in air (up to ~1400°C). Herein, we demonstrate synthesis of a composite nanowire structure consisting of polymer-derived silicon boron-carbonitride (Si–B–C–N) shell with a multiwalled carbon nanotube core. This was achieved through a novel process involving preparation of a boron-modified liquid polymeric precursor through a reaction of trimethyl borate and poly (ureamethylvinyl) silazane under normal conditions; followed by conversion of polymer to ceramic on carbon nanotube surfaces through controlled heating. Chemical structure of the polymer was studied by liquid-Nuclear Magnetic Resonance (NMR) while evolution of various ceramic phases was studied by solid-NMR, Fourier transform infrared and X-ray photoelectron spectroscopy. Electron microscopy and X-ray diffraction confirm presence of amorphous Si(B)CN coating on individual nanotubes for all specimens processed below 1400°C. Thermogravimetric analysis, followed by Raman spectroscopy and transmission electron microscopy revealed high temperature stability of the carbon nanotube core in flowing air up to 1000°C.