Flame-based Synthesis of Multi-Component Metal Nanoparticles and Conductive Ink

Metal nanoparticles are of significant interest because of their useful chemical, optical, catalytic, and electrical properties. Among the various applications of metal nanoparticles, printed electronics is of particular interest because of its potential for low-cost high-volume fabrication. Currently, silver nanomaterials are widely used for printed electronics due to the high conductivity and oxidation resistance of silver and the moderate conductivity of silver oxide. However, the high cost of silver has made this process expensive and a need for more economical alternatives remains. Alloying of silver with various other conductive materials has potential to reduce cost while maintaining satisfactory performance. In this thesis, we discuss the synthesis of various multi-component metal nanopowders and nano-inks including copper-silver, nickel-silver and copper-nickel using the High Temperature Reducing Jet (HTRJ) process. The (HTRJ) reactor has been developed by our group to enable continuous one-step gas-phase (aerosol) synthesis of alloy metal nanoparticles from metal salt precursors. As a part of this process, an aqueous metal precursor solution is injected into the throat of a converging-diverging nozzle through which the hot combustion products of a fuel-rich hydrogen flame are accelerated. The hot, high-velocity gas stream atomizes the precursor. The resulting precursor droplets evaporate and decompose, initiating nucleation of particles in a reducing environment containing excess H2. At the end of the reaction chamber a quench flow is used to cool the particles immediately to prevent further particle growth and coalescence. Recently, the capabilities of this system have been expanded to include in situ functionalization of the metal nanopowders using organic ligands. In this thesis we demonstrate this approach in detail, supplying an aerosol of short-chain amine molecules at the exit of the reactor, where they evaporate and bind to the surface of the metal nanoparticles. This initiates the gas-surface reaction between the ligands and nanoparticles. The resulting "functionalized" nanopowders are easily dispersed in organic non-polar solvents to form uniform nano-inks. The potential low-cost and scalable nature of the process for producing these nano-inks could make them promising for use in printed electronics and in pen-on-paper applications.