Kinetics of growth of carbon fibers on an iron catalyst in methane pyrolysis: A measurement procedure with the use of an optical microscope

A procedure was developed for measuring the kinetic parameters of growth of carbon fibers in the catalytic pyrolysis of hydrocarbons. In this procedure, the dependence of the averaged length of grown fibers on growth time is constructed based on the measurements of fiber lengths with an optical microscope. The procedure proposed allowed us to reliably determine the Arrhenius parameters of the rate of fiber growth and the induction period of fiber nucleation in the measurement of carbon fibers 100 nm or more in diameter. The kinetics of growth of carbon fibers from methane-hydrogen mixtures on an iron catalyst was measured over a temperature range of 950–1050°C. It was found that the rate of fiber growth as a function of methane activity in the gas phase exhibited a maximum in the activity range 200–300; the value of this maximum depends on the contribution of the products of gas-phase methane pyrolysis to the growth of fibers. It was also found that the rate of fiber growth dramatically increased as the critical concentration of pyrolysis products in the mixture was reached. This increase was interpreted as a change from one growth mechanism (growth from methane) to another growth mechanism (growth from acetylene). The experimental data explained the high sensitivity of the process of carbon fiber growth from methane to temperature and the residence time of the gas in the reactor.