(667f) Ag/Cu Particle Generation by Cosolvent Spray Pyrolysis: Effect of Cosolvent

A cosolvent spray pyrolysis process was developed for the generation of various single component and multi-component metal particles that require a reducing atmosphere to promote the formation of oxide free metal particles. During the process, a cosolvent was added to a precursor solution, and it decomposed in the furnace.  The original work on the cosolvent process utilized ethanol as the cosolvent.  To make the process amenable to commercialization, other cosolvents were investigated.  Ethylene glycol with a much higher flash point was found to produce oxide free metal particles.  We found some differences when ethylene glycol(EG) was used as the cosolvent versus the use of ethanol(ET).   In order to understand the effect of the cosolvent on the particle properties as well as to elucidate reaction pathways during the pyrolysis process, single component Cu and two component Cu/Ag particles were generated using either ethylene glycol or ethanol as the cosolvent. Residence times were adjusted from 0.2 s to 3 s by changing the carrier gas flow rate from 2.5 L/min to 10 L/min and furnace temperature from 400 ^oC to 1000 ^oC. The powder particles were characterized by SEM, XRD, FTIR and He pycnometry. Experimental results showed that Cu(NO₃)₂ first decomposes to Cu₂(OH)₃(NO₃) and CuO and then is reduced to form pure Cu particles. Higher density particles were generated with the cosolvent of ET rather than with EG.  The use of ET also led to an alternate morphology of product particles. For two component Cu/Ag particle generation, it was observed that pure Ag precipitated out in less than 0.2 s, and promoted the transition from Cu(NO₃)₂ to Cu after the evaporation of solvent. Different phase separation behavior was observed for ET and EG, which can be attributed to the different solubility and reactivity of the nitrates in these solvents.