A Simple Model for Gas-Phase Synthesis of Nickel Nanoparticles

Abstract

Gas-phase synthesis of nickel (Ni) nanoparticles by thermal decomposition of nickel tetracarbonyl, Ni(CO)4, is simulated accounting for nucleation, surface growth, coagulation, and sintering. By detailed analysis of phenomenological expressions for sintering, it is shown that surface diffusion (SD) is the dominant sintering mechanism for Ni nanoparticles at low temperatures (T < 700 K) and early stages of sintering, but grain boundary diffusion (GBD) dominates as sintering progresses and at higher temperatures. This is consistent with molecular dynamics simulations of noble metal nanoparticle sintering. Using the average of the above SD and GBD characteristic sintering times for Ni as well as a monodisperse population balance model (MPBM) that accounts for agglomerate morphology, polydispersity, and evolving structure with scaling laws from mesoscale simulations, Ni agglomerate sintering is benchmarked with measurements of agglomerate mobility and primary particle diameters. The MPBM predictions are in good agreement with the measured concentration and sizes of Ni nanoparticles by thermal decomposition of Ni(CO)4 in a hot wall flow reactor.