纳米镍团簇表面性质及能量的分子动力学研究

Molecular Dynamics Study on Surface Properties and Energy of Nickel Nanoclusters

在单分散金属纳米粒子制备过程中,金属烧结现象需要尽量避免。烧结与诸多因素有关,其中金属纳米粒子的表面性质和能量对烧结作用有着重要影响。本工作利用分子动力学,以4种不同粒径的金属Ni纳米团簇为研究对象,在COMPASS力场下对不同温度下其表面积、扩散性质、表面能以及比表面能等进行了计算。结果显示,随着温度从300K升至1000K,纳米团簇的表面积稍微增加了约5%,表面层扩散系数显著增加了约3个数量级,表面能量升高了约15%,同时表面层与体相的能量差明显增加了近3倍。比表面能定义为增加单位表面积所引起的表面能的增量。计算结果表明,700K时团簇的比表面能比镍熔点处的表面张力高出约3个数量级,预示着团簇烧结具有强大的推动力。比表面能随温度升高以及粒径增大而下降,与热力学原理相一致。

In the process of preparing monodisperse metal nanoparticles,metal sintering should be avoided as much as possible.Sintering is related to many factors,among which the surface properties and energy of metal nanoparticles have important effects on sintering effect.In this study,molecular dynamics simulation was used to calculate the surface area,diffusion properties,surface energy and specific surface energy of four metal Ni nanoclusters with different particle sizes under the COMPASS force field at different temperatures.The results showed that with the increase of temperature from 300 K to 1000 K,the surface area of the nanoclusters slightly increases about 5% and the diffusion coefficient of nickle atoms in the surface layer significantly increases about three orders of magnitude,meanwhile the surface energy of the nanocluster increases and the energy difference between the surface layer and the bulk phase significantly increases about three times.Specific surface energy is defined as the increment of surface energy caused by increasing unit surface area.The calculated results showed that the specific surface energy is about three orders of magnitude higher than the surface tension at the nickel melting point,which indicates that the cluster sintering has a strong driving force.The specific surface energy decreases with the increase of temperature and particle size,which is consistent with the thermodynamic principle.