Si/B/C/N/Al precursor-derived ceramics:: Synthesis, high temperature behaviour and oxidation resistance

The Si/B/C/N/H polymer T2(1), [B(C2H4Si(CH3)NH)(3)](n), was reacted with different amounts of (H3AlNMe3)-N-, to produce three organometallic precursors for Si/B/C/N/Al ceramics. These precursors were transformed into ceramic materials by thermolysis at 1400 degreesC. The ceramic yield varied from 63% for the Al-poor polymer (3.6 wt.% Al) to 71% for the Al-rich precursor (9.2 wt.% Al). The as-thermolysed ceramics contained nano-sized SiC crystals. Heat treatment at 1800 degreesC led to the formation of a microstructure composed of crystalline SiC, Si3N4, AlN(+ SiC) and a BNCx phase. At 2000 degreesC, nitrogen-containing phases (partly) decomposed in a nitrogen or argon atmosphere. The high temperature stability was not clearly related to the aluminium concentration within the samples. The oxidation behaviour was analysed at 1100, 1300, and 1500 degreesC. The addition of aluminium significantly improved the oxide scale quality with respect to adhesion, cracking and bubble formation compared to Al-free Si(/B)/C/N ceramics. Scale growth rates on Si/B/C/N/Al ceramics at 1500 degreesC were comparable with CVD-SiC and CVD-Si3N4, which makes these materials promising candidates for high-temperature applications in oxidizing environments. (C) 2003 Elsevier Ltd. All rights reserved.