Textures of pyrolytic carbon formed in the chemical vapor infiltration of capillaries
Guellali, M; Oberacker, R; Hoffmann, MJ; Zhang, WG; Huttinger, KJ
CARBON, 2003, Band 41, Heft 1, S. 97–104
Textures of pyrolytic carbon formed in the chemical vapor infiltration of capillaries.
Capillaries, 1.1 mm in diameter and 17.0 or 32.5 mm in length, were infiltrated at a temperature of 1100 degreesC and methane pressures from 5 to 30 kPa. Layer thickness and carbon texture were determined at cross-sections of 2, 16 and 32 mm from the open end of the capillaries using polarized light microscopy. Average deposition rates, determined from layer thickness and infiltration time, as a function of methane pressure indicate a rate increase up to a saturation adsorption at pressures between 10 and 15 kPa (range 1) and a strong rate increase above these pressures (range 2). This result implies carbon formations based on the growth mechanism in range I and the nucleation mechanism in range 2. The carbon texture shows a maximum in range I and a minimum in the transition from range 1 to range 2 followed by a clear increase in range 2. The maximum in range I corresponds to the particle-filler model describing formation of various textures of carbon by the ratio of aromatic species to C, species. Increasing texture degrees in range 2 suggest that the nucleation mechanism may lead to high textured carbon provided that the residence time for intramolecular rearrangments of polycyclic aromatic hydrocarbons is sufficient.