Thermodynamic and kinetic studies on the deposition of silicon carbon nitride from CH₃SiCl₃-C₃H₆-NH ₃-H₂-Ar and its excellent electromagnetic absorbing property

Thermodynamics phase diagram of co-deposited C, SiC and Si ₃N₄ from precursors of CH₃SiCl ₃-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, [NH ₃]/[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 Si ₃N₄-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.