Note péÉÅá~ä fëëìÉ Äó dìÉëí bÇáíçêëW lêÖ~åáÅ-íç-fåçêÖ~åáÅ`çåîÉêëáçå mêçÅÉëë Ñçê mçäóãÉê-aÉêáîÉÇ`Éê~ãáÅë póåíÜÉëáë~åÇ`Ü~ê~ÅíÉêáò~íáçå çÑ kçîÉä kçålñáÇÉ pçä-dÉä aÉêáîÉÇ jÉëçéçêçìë^ãçêéÜçìë pá-`-k jÉãÄê~åÉë A novel sol-gel-derived preceramic polymer, namely polyorganosilylcarbodiimide, was synthesized for fabrication of thermally stable amorphous Si-C-N membranes. The gelation process as well as the viscosity of the polyorganosilylcarbodiimide was adjusted for spin coating by reacting a mixture of alkyl and dialkyl chlorosilane monomers with bistrimethylsilylcarbodiimide. The polymeric precursor film was successfully fabricated on a porous substrate by solvent-free spin coating, subsequently converted into a mesoporous amorphous Si-C-N thin film by pyrolysis at 1000c C in Ar. SEM observation as well as N 2 sorption isotherm analysis exhibited the formation of meso-pore channels within the amorphous thin layer. These results indicate that the novel polyorganosilylcarbodiimide developed in this study is suitable for fabricating meso-porous amorphous membranes in the ternary Si-C-N system and with high thermal and chemical stability.

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.

A novel non-oxide sol-gel system based on the reaction of bis(trimethylsilyl)carbodiimide with methyltrichlorosilanes has been examined quantitatively with regard to its viscoelastic properties. The chemistry and phenomenology of this process are completely analogous to the well-known oxide solgel process. The changes of the elastic modulus G′ and the viscous modulus G′′ have been measured with low strain amplitude and constant frequency versus time. At the crossover point, i.e., G′ ) G′′, the gel point is reached. The gelation time is independent of the oscillatory frequency ω. The dynamic moduli G′ and G′′ have also been measured versus strain amplitude and shear stress amplitude. A relaxation exponent of n ) 0.65, strength S ) 0.25, and G′ (end of reaction) ) 10 5 Pa‚s have been determined.

B‐trichloroborazene reacts with bis(trimethylsilyl)carbodiimide to form non‐oxide gels (see scheme). The xerogels consist of a polymeric network of borazine rings linked by carbodiimide groups. Pyrolysis at 1200°C provides amorphous ceramics with the composition BC0.23N1.1Si0.05H0.09 ≈ B4CN4. At 2000°C pure B4C is formed.

No abstract

B‐Trichlorborazin reagiert mit Bis(trimethylsilyl)carbodiimid zu nichtoxidischen Gelen (siehe Schema). Die Xerogele bestehen aus Borazinringen, welche durch Carbodiimidgruppen vernetzt sind. Pyrolysen bei 1200°C liefern amorphe Keramiken der Zusammensetzung BC0.23N1.1Si0.05H0.09≈B4CN4. Bei 2000°C entsteht reines B4C.