Aluminum oxide droplet collisions: Molecular dynamics study

In this work, the induced coalescence mechanism and dynamic contact behavior of alumina (Al2O3) droplets at different impact velocities were investigated for the first time from a microscopic point of view by molecular dynamics (MD) methods through the analysis of axial speed, shrinkage, neck radius ratio, contact force, temperature, kinetic energy, surface energy, and the amount of change in the internal energy of the droplets. The results show that the minimum speed at which collisional coalescence of Al2O3 droplets occurs is 30 m/s. When the speed is lower than 30 m/s, the droplets undergo bounce phenomena due to the Coulomb force. Under the high-speed impact, the inertia force of Al2O3 droplets acts less than the surface tension and viscous resistance. The droplets don't get squashed in the whole collision process. For the different initial velocities, the magnitude of the contact force on a unilateral droplet during the collision process does not always increase with speed. When the collision speed is not higher than 400m/s, the contact force on the droplets eventually stabilizes at about 0.28Kcal/(mol & sdot;& Aring;), whereas this value is about 0.36Kcal/(mol & sdot;& Aring;) and about 0.5Kcal/(mol & sdot;& Aring;) for the intervals from 500m/s to 700m/s and from 800m/s to 1000m/s, respectively. The increase of the droplet's initial speed has a limited contribution to the temperature of the system after the collision, and the amount of loss of the total energy (the sum of kinetic energy, surface energy, and internal energy changes) becomes more pronounced, even up to about 20% when the speed reaches 900m/s. At the same time, we predicted the Al2O3 melting point and compared it with the standard melting point with an error of 2%, proving the accuracy of the model. This work can strengthen our understanding of the industrial processes with applications in high-energy nanomaterials, rocket propellants, rocket structure design and performance optimization.