Molecular dynamics study on wetting characteristics of lead droplet on iron surface at high temperatures

The wetting characteristics of a lead (Pb) droplet on an iron (Fe) surface at high temperatures are vital in reactor-related applications. The wetting characteristics of the lead droplet on the iron surface at different temperatures have been investigated by molecular dynamics with the generalized embedded atom method. The spreading process of the lead droplet can be divided into stages dominated by momentum and surface tension, respectively. For the two stages, the spreading radius R of the precursor film (PF) of the lead droplet increases with time t, but the increase of the latter stage is significantly smaller than that of the former one, and the equations of R vs. t are R similar to t(0.5092) and R similar to t(0.2078), respectively. The contact angle of the lead droplet on the iron surface decreases with the increase of the temperature at the same time. In the stage dominated by momentum, the velocity field of the lead droplet presents an overall trend of downward flow. In the stage dominated by surface tension, the flow velocity in the region near the liquid-vapor interface of the lead droplet is significantly higher than that in its internal region, and the velocity of the PF is extremely small. The atoms of the PF of the lead droplet are regularly distributed in the interstitial positions on the iron surface during the spreading process, and its diffusion mechanism on the iron surface is the surface near-neighbor interstice hopping mechanism. Furthermore, the iron substrate is corroded by the liquid lead during the wetting process, and the corrosion is aggravated with both the increase of the time and the temperature.