A new borazine-type single source precursor for Si/B/N/C ceramics

Abstract

The new borazine derivative [B{CH(CH₃)(SiCl₃)}NH]₃ (TSEB) was prepared by reacting Cl₃Si–CH(CH₃)–BCl₂ (TSDE) with hexamethyldisilazane (hmds) at ambient conditions. TSEB was characterized by infrared spectroscopy (IR), nuclear magnetic resonance (NMR), and by mass spectrometry (MS). The specially designed molecule serves as a single source precursor for the synthesis of a highly durable Si/B/N/C ceramic material via the well known ‘polymer route’. Pursuing this philosophy, polymerization of TSEB with methylamine as the cross-linking reagent has lead to a highly homogeneous pre-ceramic polymer, which was further characterized by spectroscopic methods. Subsequent thermal degradation of the as-obtained polyborocarbosilazane was monitored by means of DTA/TG/MS up to 1400 °C. The resulting amorphous silicon boron carbonitride of the approximate elemental composition Si₃B₃N₅C₄ exhibits an outstanding thermal durability at 2000 °C under inert conditions and is also stable in pure oxygen up to at least 1300 °C. The ceramic material still contains borazine rings from the TSEB precursor molecule embedded in the covalent Si/B/N/C network, acting as rigid structural units which reinforce the ceramic material on an atomic scale.