Sintering Behaviors of Au Nanopowders with Different Particle Sizes: A Real-Time Synchrotron X-ray Scattering Study

We have studied the solid-phase sintering behaviors of Au nanopowders with different particle sizes using real-time synchrotron X-ray scattering and field-emission scanning electron microscopy (FE-SEM) experiments in air. Au powders with large particle size of 173 nm at room temperature showed a defect-free crystal domain size of 47 nm. Most of these powders showed multiple grains within the particle. Solid-phase sintering typically occurred via surface diffusion of Au atoms near the surface of powders at temperatures above 300 degrees C, Au nanopowders with small particle size of 50 nm at room temperature showed a crystal domain size of 43 nm. Most of these powders showed a single grain inside the particle. Solid-phase sintering occurred simultaneously with volume diffusion of Au atoms near the grain boundary inside powders at temperatures above 250 degrees C and surface diffusion near the surface of powders at temperatures above 300 degrees C. Our study revealed that the solid-phase sintering behaviors of Au nanopowders began at temperatures over 250 degrees C, which is much lower than the melting temperature of 1064 degrees C. The thermal analysis results were consistent with the results of real-time synchrotron X-ray scattering and FE-SEM.