Synthesis mechanism of α-Si3N4 whiskers via SiO vapor in reaction bonded Si3N4-SiC composite

An indirect nitridation mechanism was designed to realize a high conversion rate to alpha-Si3N4 whiskers in reaction bonded Si3N4-SiC composite via VS mechanism, in which the dominant vapor-phase source of reactants is SiO vapor produced by the active oxidation of Si. The role played by the temperature-time program and addition of ultra-fine Si powder on the formation of SiO vapor and the resulting Si3N4 whiskers was clarified based on the experimental results and the thermodynamic calculations. The result shows that during sintering, in the presence of trace O2, ultra-fine Si particles preferentially undergo active oxidation and volatilized completely in the form of SiO(g). While an equilibrium of SiO(g) and Si(s) is formed on the surface of the coarse Si particle meanwhile. By stepped holding temperature further, this equilibrium is constantly upgraded, so the coarse Si particles is evaporated as SiO(g) shell layer by layer. Massive alpha-Si3N4 whiskers is formed by SiO(g) nitridation while the stepped holding temperature sintering. A reasonable model of the controllable indirect nitridation mechanism was established.(c) 2023 Published by Elsevier B.V.

Automated summary

An indirect nitridation mechanism was utilized to achieve a high conversion rate of α-Si3N4 whiskers in reaction bonded Si3N4-SiC composite through the VS mechanism. The effects of temperature-time program and ultra-fine Si powder addition on the formation of SiO vapor and resulting Si3N4 whiskers were studied and clarified through experimental results and thermodynamic calculations. The results showed that the controllable indirect nitridation mechanism led to the formation of massive α-Si3N4 whiskers.