Modelling and experimental investigations of composition-dependent heat and mass transfer during Cu-Ni alloy nanoparticle synthesis in a transferred arc helium plasma

In the synthesis of alloy nanoparticles (NPs) via arc evaporation and fast quenching, the composition of the synthesized NPs differs significantly from that of the precursor. The properties of the NPs formed following evaporation of a copper-nickel anode by a helium arc are investigated using a nucleation model coupled to the thermal and flow fields derived from a magneto-hydrodynamic simulation of the arc, and experimentally. Results are obtained for three different Cu:Ni precursor compositions, 10:90, 50:50 and 90:10 at%. The synthesized particles are spherical with different size distributions and have a higher concentration of Cu than the precursor in all three cases, in contrast to previous observations, but in accordance with the predictions of the model. Emission spectroscopic measurements of copper and nickel lines indicate that the concentration of atomic copper in the plasma region near the anode is much higher than that of the nickel, in accordance with the predictions of the model. The higher vapour pressure of copper compared to nickel, and its higher activity in the alloy precursor (anode), immersed in a self-consistent thermal and flow field maintained by the transferred arc are found to play a critical role. The thermodynamic, radiative and transport properties of the helium plasma contaminated with evaporated precursor are important in determining the thermal and flow fields.