Characteristics of Ni-W bimetallic nanoparticle via reactive RF thermal plasma synthesis

Nickel-tungsten binary nanopartide was synthesized by the inductively coupled radio-frequency thermal plasma process which belongs to vapor phase condensation technology. Nanoparticles are nucleated from supersaturated vapor species. Accordingly, vaporization of feedstock micro-powder is the pre-requisite step for nanopartide synthesis. In this context, nickel hydroxide and tungsten trioxide micro-powders were chosen for precursor feedstock of each Ni and W because of their low boiling points. It was confirmed that each feedstock was fully vaporized and mostly reduced by argon-hydrogen thermal plasma as the results of pure nanopartide synthesis from each feedstock. Blended feedstock was prepared by turbulent mixing and the weight fraction of nickel hydroxide in the blended powder was 0.5. Weight fraction of tungsten in the synthesized binary nanopartide was 0.588 and it was well consistent to theoretical one of blended feedstock (0.556). However, chemical composition at the particle level showed a substantial distribution. Full vaporization of each feedstock resulted in coincidence of overall chemical composition, however, particle level chemical composition distribution was due to inhomogeneous condensation of Ni-W vapor mixture. X-ray diffraction and convergent beam electron diffraction revealed that Ni-W binary nanoparticles were composed of gamma-Ni and amorphous phase. Rapid cooling driven co-condensation as well as supersaturating of alloying element and oxygen caused non-equilibrium phase evolution. (C) 2015 Elsevier Ltd. All rights reserved.