Chemical vapor infiltration of carbon — revised: Part II: Experimental results Original Research Article

Capillaries, 1.1 mm in diameter and 17 or 32.5 mm in length, were infiltrated by carbon deposition from methane at temperatures of 1100 and 1125°C, methane pressures ranging from 10 to 30 kPa, and various flow rates of the gas corresponding to residence times of 0.08, 0.2 and 0.5 s. The deposition gradients from the mouth to the depth of the capillaries basically increase, at least as long as gas phase (pyrolysis) reactions of methane before arriving at the mouth of the capillaries are limited by sufficiently low residence times. The increase of the gradient is significantly enhanced by increasing capillary depth, increasing methane pressure and decreasing residence time. These results represent a complete confirmation of the model simulations presented in Part I. Strongly increasing deposition gradients imply the densification of porous structures from the center to the surface and thus improved degrees of densification.