Preparation and Characterization of C/Si_3N_4 Composites by Chemical Vapor Infiltration

C/Si3N4 composites were prepared by chemical vapor infiltration methods (CVI) from SiCl4-NH3-H2 system. The element and phases of the as-processed sample were characterized by EDS and XRD. The phase of the as-processed sample is an amorphous silicon nitride. The phase of the sample heat treated at 1350℃ is also an amorphous silicon nitride. The XRD indicates that the formation of α-Si3N4 and β-Si3N4 occurs after heat treatment at 1450℃. The influences of temperature, time and gas flux on densification, weight gain and microstructure were investigated. The results show that the gases infiltrate and react in preforms equably, the carbon preforms can be infiltrated uniformly and the uniform C/Si3N4 composites were prepared when the process parameters are as follows: temperature 900℃, SiCl4 flow 30mL/min, H2 flow 100mL/min, NH3 flow 80mL/min, time 120h and total pressure 1000Pa.