A molecular dynamics study of high velocity impact of zinc oxide aggregates

Although dry aerosol deposition methods (aerosol deposition, micro cold spray, and vacuum kinetic spraying) for producing films typically utilize fine powders that are agglomerated or aggregated, to date these processes have been modeled using single particle impacts. In this study, molecular dynamics simulations were conducted to study the more realistic scenario where aggregates of ZnO were impacted at a high velocity. For these simulations, aggregates containing six primary particles with a diameter of 10 nm were first annealed at three temperatures (1000 °C, 1300 °C, and 1500 °C) to induce growth of interparticle necks with varying sizes and therefore indirectly affect the strengths of these interparticle necks. The annealed aggregates were then impacted to observe the deformation mechanisms that contribute to film formation. The results suggest that deformation within the aggregates is driven by viscous flow that occurs after solid state amorphization or melting and is driven by large, localized pressures and heating. The size/strengths of the necks, impact velocity, and aggregate orientations affect how deformation is concentrated and whether the aggregate can dissipate sufficient kinetic energy to deposit onto the substrate without fracturing the interparticle necks. • The strength of aggregates is varied by annealing at a range of temperatures. • Higher annealing temperatures strengthen aggregates so that they resist fracture upon impact. • Effects of impact orientation on deposition are more pronounced for weaker aggregates. • Aggregates can be deposited at a much lower velocity compared to single particles. • Deformation mechanisms for aggregate impacts are consistent with single particles.