SiC/SiC ceramic matrix composites (CMCs) are emerging in the aerospace industry for high-temperature applications to replace nickel-based alloys in aircraft engines. The matrix is mainly manufactured by chemical vapor infiltration (CVI), derived from chemical vapor deposition (CVD), which produces a high purity silicon carbide. Methyltrichlorosilane (MTS) is the common precursor used in industrial processes. However, this gaseous route conducted under isothermal and isobaric conditions induces a high residual porosity (10-15%) which limits the matrix thermal conductivity and strength. It is nowadays complemented by slurry cast of SiC particles and then infiltration of molten silicon (MI) to reduce the residual porosity. Yet, the presence of free silicon in the composite affects thermomechanical performance. A way to develop both dense and pure SiC/SiC composites is to apply a thermal gradient in the fibrous porous preform during its infiltration by the gaseous route using the thermal gradient CVI (TG-CVI) method.

    An experimental kinetic study was carried out in CVD with the SiCl₄/CH₄/H₂ and MTS/H₂ systems to determine and compare the apparent activation energy E_a values obtained at pressures ranging from 5 to 100 mbar and temperatures between 930 and 1200°C. The compositions of the solid coatings were determined by energy dispersive X-ray spectroscopy (EDS) to identify the best conditions to obtain pure SiC. The results obtained were compared with other systems in the literature to select the best candidate and the best conditions for the TG-CVI process.

    The experimental E_a values are introduced in a model for simulating the TG-CVI process. In particular, the feasibility of approaching the existence of an optimal infiltration front progressing from the hot to the cold surface of the porous substrate is discussed.