Department of Chemical Engineering, Indian Institute of Science, Bangalore 560012, Karnataka, India.
J Chem Phys. 2013 May 7;138(17):174503. doi: 10.1063/1.4802777.
In this study, the free energy barriers for homogeneous crystal nucleation in a system that exhibits a eutectic point are computed using Monte Carlo simulations. The system studied is a binary hard sphere mixture with a diameter ratio of 0.85 between the smaller and larger hard spheres. The simulations of crystal nucleation are performed for the entire range of fluid compositions. The free energy barrier is found to be the highest near the eutectic point and is nearly five times that for the pure fluid, which slows down the nucleation rate by a factor of 10(-31). These free energy barriers are some of highest ever computed using simulations. For most of the conditions studied, the composition of the critical nucleus corresponds to either one of the two thermodynamically stable solid phases. However, near the eutectic point, the nucleation barrier is lowest for the formation of the metastable random hexagonal closed packed (rhcp) solid phase with composition lying in the two-phase region of the phase diagram. The fluid to solid phase transition is hypothesized to proceed via formation of a metastable rhcp phase followed by a phase separation into respective stable fcc solid phases.
在这项研究中，使用蒙特卡罗模拟计算了在具有共晶点的系统中均匀晶体成核的自由能势垒。研究的系统是一种具有 0.85 直径比的二元硬球混合物。对整个流体组成范围内的晶体成核进行了模拟。发现自由能势垒在共晶点附近最高，几乎是纯流体的五倍，这将成核速率降低了 10(-31)倍。这些自由能势垒是使用模拟计算得出的最高值之一。对于大多数研究的条件，临界核的组成对应于两种热力学稳定固相之一。然而，在共晶点附近，形成具有组成位于相图两相区的亚稳六方最密堆积(rhcp)固相的成核势垒最低。假设流体到固相的转变是通过形成亚稳 rhcp 相然后分离成各自稳定的面心立方(fcc)固相来进行的。
