The Oxidation of Particulate-Reinforced Si sub 3 N sub 4 --TiN Composites

The effect of titanium nitride grain size and content on the mechanism and kinetics of high-temperature (up to 1500 deg C) oxidation of hot pressed silicon nitride (HPSN) was studied in air under isothermal and non-isothermal conditions. Analysis of oxidation products revealed the formation of rutile in the temperature range from 600-1000 deg C and also alpha -cristobalite, beta -Y sub 2 Si sub 2 O sub 7 , yttrialite, mullite and Y sub 2 Ti sub 2 O sub 7 at higher temperatures. The oxidation of Si sub 3 N sub 4 --TiN composites shows different behaviour depending on the temperature. The presence of fine isolated inclusions of titanium nitride ( < 30 mass%) in the silicon nitride matrix does not change the mass gain during oxidation or increases it only slightly, as compared with a titanium nitride-free material. For materials containing a continuous skeleton of titanium nitride ( > 30 mass%) a noticeable increase of the oxidation rate was observed.