A High-Temperature Reducing Jet Reactor for Flame-Based Metal Nanoparticle Production

Carbon-coated copper nanoparticles were synthesized using a new technique that combines thermal decomposition and hydrogen reduction. The technique uses a fuel-rich hydrogen flame as a source of low-cost energy to initiate particle synthesis. The hot combustion products are drawn through a converging-diverging nozzle. An aqueous precursor solution is injected just downstream of the nozzle throat, where it is atomized by the expanding hot gases. Rapid mixing, evaporation, and precursor decomposition lead to particle nucleation and growth. The sonic nozzle separates the flame region from the particle formation region, which decouples the flame chemistry from the particle formation chemistry. Molar concentration of the aqueous precursor solution, reactor pressure and temperature, and flow rate of combustion gases (hydrogen, oxygen, and nitrogen), were varied to control particle size, size distribution, and morphology. Copper serves here as a prototype for non-oxide materials that are generally difficult to produced in flame-based reactors. This work demonstrates that such materials can be produced in substantial quantities with particle diameters below 50 nm in this new process.