Thermal behavior of Bi-Ni core-shell nanoparticles with different Ni shell thicknesses: A molecular dynamics study

Abstract

In present work, molecular dynamics study method has been used to explore thermal behavior of Bi-Ni core-shell nanoparticles with different coating layer thicknesses during consecutive heating. Computational total energy curves between 300 K and 2000 K are utilized to confirm the phase transitions of nanoparticles with various Ni shell thicknesses. The thermal physical properties of Bi-Ni core-shell nanoparticles with various Ni shell thicknesses are different. The results show that the Ni shell has an inhibitory effect on the volatilization of Bi core for Bi-Ni core-shell nanoparticles with a particle radius of 40 Å during the heating from 300 to 2000 K, which effect increases with the Ni shell thickness. Structural changes of nanoparticles during heating have been discovered by the common neighbor analysis, the mean square displacement and the radial distribution function. The research demonstrates that when the thickness of Ni shell layer is greater than 20 Å, the Bi atoms are perfectly bound in the Ni shell and the volatilization of Bi elements is null. The Ni shell can effectively increase the yield of Bi elements. For Bi-Ni core-shell nanoparticles with Ni shell thickness less than 20 Å, the Ni shells rupture and the rupture temperature increases with the increase of Ni shell thickness when the temperature has not yet reached 2000 K. In addition, for Bi-Ni core-shell nanoparticles with Ni shell thickness over 20 Å, the Ni shell does not rupture when the temperature is within 2000 K with the total energy jumping twice. Furthermore, the first energy jump temperature is the melting temperature of the Ni shell, which is almost the same for all nanoparticles. The second energy jump temperature is the liquid-gas phase transition temperature of the Bi core, which increases with the increase of Ni shell thickness.