There are two types of gas-phase carbon fiber manufacturing: the substrate method and the gas-phase flow method.
Substrate Method
A catalyst is pre-sprayed or coated onto a ceramic or graphite substrate. The catalyst-loaded substrate is then placed in a quartz or corundum reaction tube. A mixture of low-carbon hydrocarbons or aromatics and hydrogen is introduced into the reaction tube and passed through the substrate at 1100°C. Carbon filaments formed on the catalyst particles grow at a rate of 30–50 mm/min, yielding carbon fibers with diameters of 1–100 μm and lengths of 300–500 mm. Commonly used catalysts include iron and nickel microparticles and ferric nitrate solution. If a mixture of acetylene and hydrogen is used as raw material, and passed through a nickel plate or nickel powder catalyst at 750°C, helical carbon fibers can be obtained. This method is a batch production process with a very low yield, approximately 10%.
Gas-phase flow method
A ternary mixture system is formed by combining raw materials such as low-carbon hydrocarbons, aromatic hydrocarbons, and alicyclic hydrocarbons with ultrafine iron, cobalt, and nickel particles and hydrogen. At 1100–1400 °C, the iron or nickel particles are reduced by hydrogen to nascent molten metal droplets. Hollow, linear carbon fibers are formed under the iron particle catalyst droplets, while helical carbon fibers are formed under the nickel particle catalyst droplets. This method can produce carbon fibers with diameters of 0.5–1.5 μm and lengths of several millimeters, with tensile strengths reaching 5000 MPa and tensile moduli of 650 GPa.
