Flame-driven aerosol synthesis of copper-nickel nanopowders and conductive nanoparticle films

We report the continuous one-step synthesis of bimetallic copper-nickel nanostructured coatings by deposition and sintering of metal nanoparticles produced as an aerosol using a flame driven high temperature reducing jet (HTRJ) process. The HTRJ process allows gas-phase (aerosol) formation of metal nanoparticles from low-cost metal salt precursors. These can be collected as discrete powders for subsequent use in formulating conductive inks or for other applications. However, direct deposition of nanoparticles to form coatings allows measurements of electrical conductivity of films of deposited nanoparticles as a function of composition and sintering temperature, without actually formulating and printing inks. This is the approach taken here for the purpose of screening nanoparticle compositions quickly. We characterized the microstructure and composition of both nanopowders and films and found that their composition consistently matched the ratio of metals in the precursor solution. The electrical conductivity was highest (∼10⁴ S/m) for films with 60:40 and 40:60 copper-to-nickel mass ratios. These films maintained their conductivity during extended storage (1 month) under ambient conditions. The oxidation resistance and high conductivity observed here suggest that 60:40 and 40:60 Cu:Ni nanoparticles have promise as lower cost replacements for silver nanoparticles in conductive ink formulations.