Structural and mechanical characterization of carbon fibers grown by laser induced chemical vapor deposition at hyperbaric pressures

Abstract

Laser induced chemical vapor deposition (LCVD) of freestanding carbon fibers from ethylene at hyperbaric pressures was investigated. Relationships between processing conditions, growth behavior, microstructure, and mechanical properties of the carbon fibers were established. It is found that the fiber growth rates are limited by surface reaction kinetics at low temperatures and limited by gas phase nucleation at high temperatures. At higher pressures and intermediate temperatures, growth becomes mass transport limited whereupon the fibers exhibit drastic changes in morphology and microstructure from a core-shell, smooth appearance to nodular formations. The tensile strengths of the carbon fibers grown by LCVD are generally poor due to the nature of graphitic carbon deposits. However, the Weibull modulus among the LCVD grown carbon fibers was found to be very high. Effects of processing conditions and microstructure on the fiber strengths are observed and discussed.