The Formation Rate of Carbon Filaments on Transition Metals from CO-H_2 Gas Mixtures

摘要

The kinetic behavior of filamentous carbon formed on substrate of the transition metal (Fe, Co or Ni) from CO-H_2 gas mixtures is investigated. The filamentous carbon holds carbide particle on its head point. Experiments for each metal are carried out in the range of 773 approx 973 K with various molefraction of CO, Y_(CO) in the gas mixtures. In the experimental results, the formation rates, r, for Fe-substrate are described by the following equation:R=(KY_(CO)(1-Y_(CO))~1/2)/((1+KY_(CO))), 773K<=T<=873Kwhere k is the rate constant, K is the adsorption equilibrium constant and T is temperature. The values of k and K give 92 kJ/mol and 126 kJ/mol as the apparent activation energy and the adsorption heat, respectively. This rate equation, however, is not applicable to the rates for Co- or Ni-substrate. Those data are explained by assuming the diffusion process of carbon adsorbed on the carbide particle as the determining step.