Carbon Dioxide Electrochemistry: Homogeneous and Heterogeneous Catalysis (Energy and Environment Series)

Abstract

The current study uses a combination of local and/or surface sensitive chemical analysis tools to explore the alloying behavior in multimetallic nanopowders produced from a thermal plasma process. The W–Ni–Fe ternary system is specifically considered in which constituent metals differ substantially in terms of their saturation vapor pressure and have limited mutual solubilities. The preferential formation of ternary alloy particles with a prevailingly spherical morphology was established in this system. The particles contain a crystalline core of W and expose surface alloys for a range of ternary compositions. The high temperatures of particle growth in the thermal plasma lead to enhanced alloying of a refractory base constituent (W) and lower-melting-point additives (Ni, Fe) to form diffuse interfaces and smooth gradations in composition. The compositional inhomogeneity is inherent in this type of nanoparticle alloy and is related to the different condensation pathways of the alloy constituents with different saturation vapor pressures. The experimental observations are consistent with a particle growth scenario in which a preformed W nanocrystal serves as a target for impingement and assimilation of spontaneously nucleated Ni–Fe liquid nanodroplets under rapidly cooling dynamic conditions.