CARBON DEPOSITION OVER TRANSITION-METAL ALLOYS .1. GENERATION OF (NICO), (FENI), AND (COFE) PHASE-DIAGRAMS

The non-equilibrium phase diagram approach uses thermodynamic principl es to predict the formation of various solid phases under reaction con ditions. This approach attempts to systematically control the phases i n-situ by controlling the gas-phase potentials and has been applied su ccessfully to investigating carbon deposition over Fe, Co, and Ni. In order to maintain the same gas-phase composition and driving force for carbon deposition over the solid phases, this approach is extended to binary alloys of these metals. The thermodynamic metal activities are determined using excess Gibbs free energy of mixing for the [NiCo], [ FeNi], and [CoFe] alloy systems and the lattice stability parameters f or Fe, Co, and Ni reported by Kaufman and co-workers. The non-equilibr ium phase diagrams for the [NiCo], [FeNi], and [CoFe] alloy systems ha ve been generated. By varying the alloy composition, the catalytic act ivity of the various thermodynamically favored solid phases can be stu died under identical gas phase conditions.