OXIDATION BEHAVIOR OF ELECTROCONDUCTIVE SI3N4-TIN COMPOSITES

The presence of dispersed TiN particles in an Si3N4 matrix deeply affects the oxidation resistance at low (600-1000°C) and high temperatures. The thermal stability of dense Si3N4TiN composites up to 1350°C in air results in different oxidation regimes: up to 1000°C only the oxidation of TiN to TiO2 (rutile) takes place, where the second-order reaction is likely to be the governing step. From 1000 to 1200°C diffusion (O2 or N2) through a TiO2 layer could be indicated as the rate-limiting step. At T {greater-than or approximate} 1200°C, parabolic oxidation kinetics indicates diffusion mechanisms. The diffusion of yttrium and aluminium cations from the bulk to the reaction interface is believed to govern the process in the baseline matrix; for the composites the structure and composition of the bulk and the development of complex product layers modify the migration mechanisms of the various mobile participants. However, a strong increase in the oxidation rate is associated with the presence of TiN. © 1990.