超临界水中碳酸钠团簇成核与生长分子动力学模拟

Nucleation and Growth of Na_2CO_3 Clusters in Supercritical Water Using Molecular Dynamics Simulation

应用分子动力学方法研究了碳酸钠颗粒在超临界水中的成核与生长过程.计算了温度为700-1100K、压力在23-30MPa下碳酸钠的团聚过程,计算时间为1ns.对体系结合能与径向分布函数的分析表明,碳酸钠成核过程主要受静电作用的影响.在超临界态下,水分子与Na+和CO2-3之间的静电作用降低,Na+与CO2-3能够很容易碰撞形成Na2CO3小团簇.在Na2CO3整个成核过程中,单个离子的碰撞在前50ps内完成,同时离子碰撞速率达到1030cm-3·s-1.另外,在成核阶段温度的影响比压力更加明显,温度越高,离子碰撞速率越快,形成的初始团簇越多.而压力对Na2CO3团簇的进一步生长影响较大.

The nucleation and growth of Na2CO3 particles in supercdtical water were investigated using molecular dynamics simulation. The clustering process of Na2CO3 was studied for 1 ns at a series of state points, across temperature and pressure ranges of 700 to 1100 K and 23 to 30 MPa, respectively. The binding energy and radial distribution function analysis showed that the electrostatic interaction was the main factor affecting the whole Na2CO3 nucleation process. Under supercritical conditions, the electrostatic interaction of water molecules with Na＋ and CO（3,^（2-）） ions rapidly decreased, allowing Na＋ and CO（3,^（2-）） ions to readily collide with each other to form small Na2CO3 clusters. During the initial Na2CO3 nucleation process, all the single-ion collisions were complete within 50 ps and the ionic collision rates appeared to be of the order of 1030 cm^（-3） S^（-1）. Furthermore, the effect of temperature was found to be more important than that of the pressure at the nucleation stage and a higher temperature led to an enhanced collision rate and the formation of more initial Na2CO3 particles. The further growth of the Na2CO3 particles was more dependent on the pressure.