Chemical vapor infiltration of carbon - revised - Part I: Model simulations

Carbon deposition from light hydrocarbons and especially from methane is a homogeneous-heterogeneous process in which complex gas phase reactions in series are competing with complex surface reactions. Models of these deposition processes, proposed for carbon deposition from methane, are used to simulate deposition profiles in capillaries, 1 mm in diameter. The influence of the length of the reaction sequence of the gas phase reactions, the methane pressure, the capillary depth and the residence time of the gas (methane) outside of the capillary were investigated. It is shown that the deposition gradients increase from the mouth to the depth of the capillary as long as gas phase reactions outside of the capillary are limited by a short residence time of the gas. Increasing length of the reaction sequence, increasing methane pressure and capillary depth enhance the gradient. Strongly increasing gradients at short residence times correlate with strongly decreasing (inverse) gradients: at long residence rimes. An experimental confirmation of these results is presented in Part TI of the paper. (C) 2001 Elsevier Science Ltd. All rights reserved.