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.