Shibuta Yasushi, Suzuki Toshio
Department of Materials Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.
J Chem Phys. 2008 Oct 14;129(14):144102. doi: 10.1063/1.2991435.
The phase transition between liquid and solid phases in body-centered cubic (bcc) metal nanoparticles of iron, chromium, molybdenum, and tungsten with size ranging from 2000 to 31,250 atoms was investigated using a molecular dynamics simulation. The nucleation from an undercooled liquid droplet was observed during cooling in all nanoparticles considered. It was found that a nucleus was generated near one side of the particle and solidification spread toward the other side the during nucleation process. On the other hand, the surface melting and subsequent inward melting of the solid core of the nanoparticles were observed during heating. The depression of the melting point was proportional to the inverse of the particle radius due to the Gibbs-Thomson effect. On the other hand, the depression of the nucleation temperature during cooling was not monotonic with respect to the particle radius since the nucleation from an undercooled liquid depends on the event probability of an embryo or a nucleus.
利用分子动力学模拟研究了铁、铬、钼和钨的体心立方（bcc）金属纳米颗粒（尺寸范围为2000至31250个原子）中液相和固相之间的相变。在所有考虑的纳米颗粒冷却过程中，均观察到过冷液滴的成核现象。发现在成核过程中，一个核在颗粒的一侧附近生成，凝固向颗粒的另一侧扩展。另一方面，在加热过程中观察到纳米颗粒固体核心的表面熔化及随后的向内熔化。由于吉布斯-汤姆逊效应，熔点的降低与颗粒半径的倒数成正比。另一方面，冷却过程中成核温度的降低相对于颗粒半径并非单调变化，因为过冷液体的成核取决于胚胎或核的事件概率。
