Sintering Rate of Nickel Nanoparticles by Molecular Dynamics

Abstract

Nickel nanoparticles (Ni NPs) are widely used in batteries, catalysts, and filters. Properties of Ni NPs strongly depend on their crystal structure and morphology quantified by the state (i.e., solid, transient, or liquid phase) of primary particles (PPs), hard agglomerate (aggregate), and PP size. The growth rate of PPs during gas-phase synthesis is determined by their characteristic sintering time (τs) that is sensitive to temperature, the state, and size of PPs. Here, the crystallinity and sintering of Ni NP dimers (2 nm ≤ dp ≤ 5 nm) between 1000 and 1600 K are investigated by molecular dynamics (MD) simulations using the embedded-atom method (EAM) force field. It is shown that at low temperatures (T ≤ 1400 K) and for large PPs (dp ≥ 4 nm), diffusion of atoms in PPs controls solid-state sintering. However, PP crystallinity quantified by the disorder variable indicates that with increasing temperature or decreasing PP size, atoms become increasingly mobile and disordered starting from the surface of the PPs until the Ni NPs become fully melted and viscous flow sintering becomes dominant. A general formula for the τs of Ni NPs is proposed that is valid for all particle states, and its performance is benchmarked by predicting the evolution of the morphology of Ni agglomerate quantified by its mobility and PP diameters during gas-phase sintering in a flow reactor.