(76f) Phase Separation and Reaction Mechanism During Agcu Particle Formation by Cosolvent Assisted Pyrolysis Technology

The spray pyrolysis process was used for the generation of micron sized metal particles because of its advantages of making adjustable and narrowly distributed particle sizes.  In our process, a copper nitrate and silver nitrate mixture solution was used as the precursor for the generation of AgCu particles, of interest as ingredients in metal pastes and in isotropic conductive adhesives (ICA). Either 40 vol% ethanol or 40 vol% ethylene glycol was used as the cosolvent, to produce a reducing environment inside the reactor, resulting in metallic powder production without additional hydrogen added as a process gas.  XRD and SEM were used for the characterization of AgCu particles. Phase separation was observed during the generation of AgCu particles, and particles mainly consisted of a Ag-rich solid solution phase and a Cu-rich solution phase.  Short residence time experiments were used to investigate the particle formation process. With a cosolvent of ET, Ag precipitated during the evaporation of the solvent, and agglomerated on the surface of the particles. Cu(NO₃)₂ decomposed to Cu₂(OH)₃NO₃ first, then to CuO and Cu₂O. CuO and Cu₂O were reduced to Cu in the reducing atmosphere resulting from the use of the ET cosolvent. When EG was used, nano-sized Ag particles were generated during the evaporation process. Layered structures of Cu₂(OH)₃NO₃ and Cu₂O with embedded Ag particles were observed during the formation of the particles. Understanding the mechanism of bicomponent particle formation, including role of co-solvent, is important for the optimization of the process and to obtain the desired morphology.