Thermodynamic and kinetic studies on the deposition of silicon carbon nitride from CH3SiCl3-C3H6-NH3-H2-Ar and its excellent electromagnetic absorbing property

Thermodynamics phase diagram of co-deposited C, SiC and Si3N4 from precursors of CH3SiCl3-C3H6-NH3-H2-Ar was investigated by using FactSage software and its embedded database. The yield of condensed phases in the co-deposition process was examined as the functions of the inject reactant ratios of C3H6/MTS, NH3/MTS and H2/MTS, and the temperature at a fixed pressure of 0.01 atm. The thermodynamic study was used to conduct and determine the deposition condition of silicon carbon nitride (SiCN) in the experimental process. The results show that C-SiC, C-SiC-Si3N4 and C-Si3N4 can be co-deposited by adjusting the reactant ratios and temperature in thermodynamics. In kinetics, SiCN ternary phase was successfully deposited in the porous Si3N4 preform by chemical vapor infiltration and chemical vapor deposition when T = 800 °C, P = 0.01 atm, [NH3]/[MTS] = 0.5 and [C3H6]/[MTS] = 0.2-0.6. The surface morphology of the as-prepared SiCN presented the dense convex cell structure, and the rod-like Si3N4 in preform was uniformly covered by SiCN. The dielectric and electromagnetic (EM) properties of Si3N4-SiCN ceramics were evaluated in 8.2-12.4 GHz (X-band). With the increase of [C3H6]/[MTS] in the precursors, the content of carbon element and the intensity of Si-C bond in SiCN gradually increased, which made the permittivity, dielectric loss and EM shielding effectiveness of ceramics gradually increase and the EM reflection coefficient decrease. It is confirmed that the novel and component-designable SiCN ceramics possess the excellent EM absorbing property, offering a great possibility as the high-temperature matrix and coating candidate of ceramics matrix composites combining the structural and functional properties.