B/C/N Materials and B₄C Synthesized by a Non-Oxide Sol−Gel Process

Abstract

B-trichloroborazene B3N3H3Cl3 reacts with bis(trimethylsilyl)carbodiimide Me3Si−NCN−SiMe3 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, 11B- and 15N-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 BC0.23N1.1Si0.05H0.09 ≈ B4CN4. This material starts to crystallize around 1600 °C under evolution of nitrogen, forming nearly pure B4C at 2000 °C. Very small amounts of amorphous carbon as well as carbon nanotubes were also present.

Polymer derived Si–C–B–N ceramics via hydroboration from borazine derivatives and trivinylcyclotrisilazane

“…The polymerization was attributed to hydroboration via a-or b-addition of the borazine ring to the vinyl group, as evidenced by a reduction in vinyl group levels and by the formation of an alkyl bridge, detected by IR, and 1 H-, 13 C-and 29 Si-NMR. The subsequent transformation of the polymeric phase to the ceramic phase starting at 400 8C was accompanied by thermal decomposition of the organic carbon with a major weight loss up to 700 8C, finally resulting in 75% ceramic yield at 1000 8C.…”

“…In the amorphous ceramic at 900 8C, the band at about 3400 cm (1 due to NÁ/H bonds almost disappeared. It was interesting to observe that the NÁ/H bonds displayed high thermal stability, and they reportedly survived up to 800 8C in a recent literature [13]. Fig.…”

“…1 H-, 13 C-and 29 Si-nuclear magnetic resonance (NMR) spectra were performed in C 6 D 6 with a Bruker DMX600. 13 C-and 29 Si-magic angle spinning (MAS) nuclear magnetic resonance (NMR) experiments were performed on an FT Wide Bore (600MHz) Unityl NOVA600. Tetramethylsilane (TMS) was used as an internal standard.…”

Sol–gel derived Si/C/O/N‐materials: molecular model compounds, xerogels and porous ceramics

“…Owing to the pseudo-chalcogenic character of the carbodiimide group, it adopts the role of the oxygen atom, whereas the trimethylsilyl group can be considered as an analog of the protons in a hydrolytic process. [13,16,17] Several materials in the systems Si/C, [18] B/C/N, [19,20] Si/C/N, [21,22] Si/B/C/N, [23 -25] and Si/Al/C/N [26] possessing high thermal resistance and chemical stability, have been synthesized using this particular kind of sol-gel route. Several further reports on related work on BTSC-derived element carbodimides and their use as precursors for hybrid and ceramic materials have been published.…”

Mesoporous Si-B-N Ceramics from a Single Source Precursor via an Imide Gel

“…13 The preparation of microporous silicon imido nitrides by the pyrolysis of gels, which had been prepared via a hot ammonolysis of tris dimethylamino silylamine, Me 2 N 3 SiNH 2 TDSA in a concentrated solution of CH 3 CH 2 n NH 2 nࢼ11-17, was reported recently by Bradley and coworkers. 9 In a continuation of this work in our group, high-surface-area mesoporous silicon diimide gel has been prepared in a non-oxide sol-gel process by the reaction of TDSA with ammonia in the presence of an acid catalyst.…”