Copper (Cu) -Tin (Sn) Binary Particles Fabrication via Spray Pyrolysis and their Oxidation Behavior
Copper particles are widely used in electronics as conductive pastes, circuits, and packaging materials. However, they are easily oxidized at high temperatures, which prevents their further application. Therefore, numerous efforts have been made to improve Cu oxidation-resistance by doping other metals such as zinc, indium, and silver, etc. Among them, tin seems to be an excellent candidate for the reasons: i) Tin can oxidize forming a layer to protect the copper from further oxidation; ii) Incorporation of tin into copper can occur while still maintaining relatively high conductivity.
Among the various methods have been utilized to generate the metallic particles, spray pyrolysis exhibits its distinct advantages (e.g. controllable particle size and shape, shorter experimental time, and simple experimental equipment) in potential industrial application. However, the common product particles from spray pyrolysis are metal oxides because of the use of aqueous solvent. Recently, metallic copper particles were obtained by adding the ethylene glycol (EG) as a safe reducing agent. By now, plenty of reports have discussed the mechanism for conversion of single salt precursor into final particles. Adding another salt in the precursor solution to make the binary particles greatly increases the complexity of the system. To facilitate further applications, research is needed to explore the factors affecting the morphology, crystallinity, and the distribution of the binary components, as well as how those factors will influence the properties and performance of product particles.
Here, a facile method was reported to synthesize the Cu/Sn particles by spray pyrolysis with Cu(NO3)2 and SnCl2 aqueous solution as the precursor, EG as the reducing agent, N2 as the carrier gas. We found that the particle morphologies, crystallinity, and the copper and tin distribution can be tuned by i) the concentration ratio of Cu(NO3)2 to SnCl2, and EG volume percent in the precursor solution; ii) the spray temperature, and iii) the residence time. By optimizing the conditions, we successfully generated metallic Cu/Sn particles with tin accumulating on the particle surface. Oxidation experiments were also conducted to understand the role of tin when copper was transformed into copper oxides.
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