Studies on SiBN(C)-ceramics: Oxidation- and Crystallization Behavior Lead the Way to Applications

Abstract

ABSTRACTThe 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.