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 (FESEM) 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 °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 °C and surface diffusion near the surface of powders at temperatures above 300 °C. Our study revealed that the solid-phase sintering behaviors of Au nanopowders began at temperatures over 250 °C, which is much lower than the melting temperature of 1064 °C. The thermal analysis results were consistent with the results of real-time synchrotron X-ray scattering and FE-SEM.