Boron-modified poly(propenylsilazane)-derived SI-B-C-N ceramics:: preparation and high temperature properties

Boron-modified poly(propenylsilazanes) [B{C3H6Si(CH3)NH}(3)](n), are synthesized via both ammonolysis of B(C3H6Si(CH3)Cl-2)(3) (monomer route) and hydroboration of [(H2C=CHCH2)Si(CH3)NH](n) (n = 3, 4) (polymer route) and subsequently transformed into ceramic materials by pyrolysis up to 1400 degreesC. Thermogravimetric analysis of the as-obtained materials as well as X-ray diffraction of annealed samples were performed to investigate high temperature properties, revealing the stability of the materials toward thermal degradation up to 1800 degreesC and the presence of silicon nitride at 1800/2000 degreesC. The crystallization is additionally investigated by transmission electron microscopy. SiC crystallization is observed first, followed by the evolution of a composite material which is composed of a turbostratic BNC matrix embedding SiC and Si3N4 nanocrystals. (C) 2002 Elsevier Science Ltd. All rights reserved.