Textures of pyrolytic carbon formed in the chemical vapor infiltration of capillaries |
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Authors: | M Guellali MJ Hoffmann KJ Hüttinger |
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Affiliation: | a Institut für Keramik im Maschinenbau, Universität Karlsruhe, Haid-und-Neu-Strasse 7, 76131 Karlsruhe, Germany b Institut für Chemische Technik, Universität Karlsruhe, Kaiserstrasse 12, 76128 Karlsruhe, Germany |
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Abstract: | Capillaries, 1.1 mm in diameter and 17.0 or 32.5 mm in length, were infiltrated at a temperature of 1100 °C 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 1 and the nucleation mechanism in range 2. The carbon texture shows a maximum in range 1 and a minimum in the transition from range 1 to range 2 followed by a clear increase in range 2. The maximum in range 1 corresponds to the particle-filler model describing formation of various textures of carbon by the ratio of aromatic species to C2 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. |
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Keywords: | Pyrolytic carbon Chemical vapor deposition Chemical vapor infiltration Optical microscopy Texture |
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