Paper derived SiC–Si3N4 ceramics for high temperature applications

Biomorphic Si3N4–SiC ceramics have been produced by chemical vapour infiltration and reaction technique (CVI-R) using paper preforms as template. The paper consisting mainly of cellulose fibres was first carbonized by pyrolysis in inert atmosphere to obtain carbon bio-template, which was infiltrated with methyltrichlorosilane (MTS) in excess of hydrogen depositing a silicon rich silicon carbide (Si/SiC) layer onto the carbon fibres. Finally, after thermal treatment of this Si/SiC precursor ceramic in nitrogen-containing atmosphere (N2 or N2/H2), in the temperature range of 1300–1450 °C SiC–Si3N4 ceramics were obtained by reaction bonding silicon nitride (RBSN) process. They were mainly composed of SiC containing α-Si3N4 and/or β-Si3N4 phases depending on the nitridation conditions. The SiC–Si3N4 ceramics have been characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDX) and Raman spectroscopy. Thermal gravimetric analysis (TGA) was applied for the determination of the residual carbon as well as for the evaluation of the oxidation behaviour of the ceramics under cyclic conditions. The bending strength of the biomorphic ceramics was related to their different microstructures depending on the nitridation conditions.