Chemical vapor infiltration of pyrocarbon - II. The influence of increasing methane partial pressure at constant total pressure on infiltration rate and degree of pore filling

Chemical vapor infiltration of pyrocarbon with methane as the carbon source was studied at a total pressure of 20 kPa, a temperature of 1100 degrees C and methane partial pressures from 2.5 to 20 kPa. A cylindrically-shaped porous alumina ceramic, 20 mm in height and 16 mm in diameter, was used as the substrate. The pore entrance diameters of the porous ceramic range from 1 to 36 mu m; the total porosity amounts to 23%. It is shown by the experimental results that an increase of the methane partial pressure effects an increase of the infiltration rate as well as of the degree of pore filling. The results completely agree with a kinetic analysis of the process based on the Weisz modulus, the pore effectiveness factor and Langmuir-Hinshelwood kinetics. (C) 1998 Elsevier Science Ltd. All rights reserved.