Chemical vapor infiltration

During chemical vapour infiltration, the fibrous preform is supported on a porous metallic plate through which a mixture of carrier gas along with matrix material is passed at an elevated temperature.

The preforms can be made using yarns or woven fabrics or they can be filament-wound or braided three-dimensional shapes.

[4] The infiltration takes place in a reactor which is connected to an effluent-treatment plant where the gases and residual matrix material are chemically treated.

The unreacted reactants along with gases exit the reactor via outlet system and are transferred to an effluent treatment plant.

However, the processing time is typically very long and the deposition rate is slow, so new routes have been invented to develop more rapid infiltration techniques: Thermal-gradient CVI with forced flow – In this process, a forced flow of gases and matrix material is used to achieve less porous and more uniformly dense material.

[7] Silicon Carbide / Silicon Carbide (SiC/SiC) Matrix：CH3SiCl3 (g) → SiC(s)+ 3 HCl(g) Interphase: CH4(g) → C(s)+ 2H2(g) The SiC fibers serve as a preform which is heated up to about 1000 °C in vacuum and then CH4 gas is introduced into the preform as the interlayer between fiber and matrix.

There is very little damage to fibres and to the geometry of the preform due to low infiltration temperature and pressures.