Effect of atmosphere on the fabrication of Si2N2O matrix composites

Abstract

Si 2 N 2 O matrix composites were fabricated by solid/gas reaction in air or N 2 atmosphere. The effects of atmosphere on the phase and microstructure of the composites were investigated. The reaction mechanism of Si 2 N 2 O system was discussed by analysing the variation of the Gibbs free energy with temperature. The effect of N 2 and air on sintering of Si 2 N 2 O matrix composites was discussed in relation to observed kinetics and thermodynamic calculations. The results showed that gradient structure of Si 2 N 2 O matrix composites were obtained in N 2 atmosphere. While high N 2 concentration was useful for the formation of the pure β-Si 3 N 4 ceramics, low N 2 concentration was proposed to form the pure Si 2 N 2 O ceramics. However, in the air atmosphere, structure of the Si 3 N 4 /SiO 2 composites is homogeneous without the gradient structure appearing. Its composition is a little different as the O 2 concentration changes.