Synthesis and high-temperature behavior of Si/B/C/N precursor-derived ceramics without free carbon

For the preparation of carbon-poor Si/B/C/N precursors, Si/C/N/H polymers with Si:C atomic ratios higher than or equal to 1 were synthesized by Wurtz-type coupling and subsequent ammonolysis of ClSiH(Me)NHSiH(Me)Cl and MeSiHCl2 or H2SiCl2. They were reacted with a borane to obtain three different precursors which were transformed into Si/B/C/N ceramic materials by thermolysis at 1400degreesC. Elemental analysis revealed that the crystallized samples should contain less than 6 atom % of free carbon. The high-temperature behavior up to 2150degreesC was investigated by thermogravimetric analysis and XRD of annealed samples. These results were compared with thermodynamic calculations using the CALPHAD approach.