有自由表面的Ni原子团簇的熔化

Melting of Ni Clusters with Free Surface

采用分子动力学模拟技术研究了不同尺寸的Ｎｉ原子团簇的熔化过程．团簇的最初构型为ＦＣＣ结构．研究结果表明，原子团簇的熔化温度与原子团簇中原子的个数有关，团簇的熔化首先从表面开始，当外层原子成为液态后，整个团簇的熔化从液态层开始，直至核心区域．该熔化过程可以被称为非均质熔化，自由表面充当非均质形核位置．作为对比，对无自由表面的大块固态Ｎｉ的熔化过程也进行了模拟，其熔化温度高于实验温度约４００Ｋ．表明对无自由表面的大块固态的熔化过程，液相形成无非均质形核位置．熔化的本质过程受均质形核机理控制．

The melting process of Ni atom clusters with different size has been studied by molecular dynamics simulation. The initial configuration of clusters is the structure of FCC. The results indicate that melting first occurs at the edges of the clusters, and after the outer shells started to form the liquid layer, melting of the whole clusters began from the liquid to core region. The change in the melting temperature of the clusters is size dependent. The melting process can be referred as heterogeneous melting since the free surfaces act as the heterogeneous nucleation site for the liquid phase; for comparison, the melting point of the bulk solid of Ni has been simulated. It can be superheated up to 400 K above the experimental melting point. For system without free surface, there is no effective heterogeneous nucleation site for the liquid phase, melting is an intrinsic process initiated by a spontaneous homogeneous nucleation mechanism.