The thermal stability of amorphous borosilicon nitride
(Si3B3N7) and borosilicon carbonitride
(SiBN3C) between 1000°C and 2000oC both in air and
under inert conditions is reported. Both materials are derived from
polymerization and subsequent pyrolysis of a “single source” precursor. On
heating in vacuum or nitrogen SiBN3C remains amorphous up to lCWC
whereas Si3B3N7 crystallizes at about
1800°C under these conditions. At about 2000^ the SiBN(C)-materials
decompose into SiC, BN, B4C and N2.
Oxidation studies performed by TEM- and SEM-investigations of oxidized
borosilicon carbonitride grains reveal that an interlayer consisting of B,
N, and only little O is formed between the oxide scale on the surface and
the inner bulk material. The interlayer does not disappear at temperatures
above 1450°C in contrast to the Si2N20-interiayer
observed on oxidized silicon nitride. The oxidation kinetics of the new
ceramics are established in the range from 1000°C to 1600°C indicating a
very high oxidation resistance. Possible applications as matrix materials as
well as materials for fibers and coatings are discussed.