Carbon deposition over Fe, Ni, and Co foils from CO-H₂-CH₄-CO₂-H₂O, CO-CO₂, CH₄-H₂, and CO-H₂-H₂O gas mixtures: I. Morphology

Nonequilibrium C-H-O phase diagrams have been used to systematically investigate the effect of the gas composition on the type(s) and relative amounts of carbon formed over Fe, Ni, and Co foils. Filamentous and "amorphous" carbon, and graphite platelets were observed to form from the catalytic decomposition of five-component gas mixtures of CO, H₂, CH₄, CO₂, and H₂O, binary gas mixtures of CO-CO₂ and CH₄-H₂, and ternary gas mixtures of CO-H₂-H₂O over Fe, Ni, and Co foils at 900 K and 1 atm. A gas-phase carbon activity of 10 was used for all carbon deposition experiments. The carbon formed over Ni foils was found to be primarily filamentous in nature, and these filaments were generally well formed. The type of carbon deposited on Fe and Co foils was found to have a greater dependency on the gas composition; well-formed filaments with little co-existing platelet and "amorphous" carbons were deposited over Fe and Co foils if the P_H2 P_CO ratio of the gas mixture was greater than 1.9. Poorly formed filaments with larger amounts of co-existing platelet and "amorphous" carbon were observed when the P_H2 P_CO ratio was less than 1.9.