Mechanisms of Chemical Vapor Deposition on Carbon Fibers

Abstract : Deposition of pyrolytic carbon on the surface of carbon substrates, including carbon fibers, was studied at 1000-1100 C using two different systems, a static reactor operating at subambient pressures and a flow reactor operating at atmospheric pressure. The experimental parameters that affect the deposition rates and mechanism are substrate temperature, type of reactor used, total and partial pressure of methane in the static reactor, partial pressure of methane in the flow reactor, flow rate of hydrocarbon above substrate, presence of hydrogen in the deposition medium, and the type of substrate, as well as its surface area. The two main differences between the deposition under flow and static conditions are rates of deposition and characteristics of deposits. While the rate under flow conditions is considerably higher than under static conditions, the deposits in the flow reactor are intact and less porous than those prepared in the static reactor. This is attributed essentially to the presence of hydrogen in the static reactor which lowers the rates of deposition, prevents the growth of intermediate species to large planar molecules, and attacks the carbon deposits.