B/C/N Materials and B 4 C Synthesized by a Non-Oxide Sol−Gel Process

B -trichloroborazene B 3 N 3 H 3 Cl 3 reacts with bis(trimethylsilyl)carbodiimide Me 3 Si−NCN−SiMe 3 in THF or toluene, or without any solvent, to form non-oxide gels. The xerogels, amorphous B/C/N materials, and (semi)crystalline pyrolysis products were characterized using infrared (FTIR) and Raman spectroscopy, 11 B- and 15 N-nuclear magnetic resonance spectroscopy (NMR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and elemental analysis. In addition, the pyrolysis process was investigated through thermal gravimetry coupled with mass spectrometry (TG−MS). The xerogels consist of a three-dimensional polymeric network of borazene rings linked by carbodiimide groups. Interestingly, the sol−gel transition is phenomenologically analogous to oxide systems and the polymers are almost free of chlorine and trimethylsilyl endgroups. Pyrolysis at 1200 °C provides an amorphous ceramic with the composition BC 0.23 N 1.1 Si 0.05 H 0.09 ≈ B 4 CN 4 . This material starts to crystallize around 1600 °C under evolution of nitrogen, forming nearly pure B 4 C at 2000 °C. Very small amounts of amorphous carbon as well as carbon nanotubes were also present.