The formation of filamentous carbon on iron and nickel catalysts : II. Mechanism

Abstract

The mechanism of filamentous carbon growth on iron and nickel catalysts has been studied using a combination of magnetic techniques and temperature-programmed hydrogenation. CO and CH4 were used as carburizing agents. It is concluded that high carbide contents are a prerequisite for the nucleation of filamentous carbon. The presence of a substoichiometric nickel carbide during steady-state growth is established. In the case of iron the hexagonal -Fe2C or ′-Fe2.2C is proposed to be the intermediate in filamentous growth. The driving force for carbon transport can be appreciated considering the presence of a gradient in the carbon content of nonstoichiometric carbides.