过饱和液相内析出-长大行为的蒙特卡罗模拟

摘要

The precipitation-growth progress in the supersaturated liquid was simulated by the Monte Carlo method. The simulation rules were established to simulate the micro-processes of solute diffusion, solute precipitation, and particle dissolution. The critical nucleus and the relationship between the critical nucleus size and liquid concentration were considered for analyzing the simulation data. The results show that during prolonging the simulation time, the liquid concentration and supersaturation ratio show rapid decrease, and slow decrease up to equilibrium sequentially. With decreasing simulation temperature, the equilibrium concentration decreases and the time to attain equilibrium becomes longer, and the solute lattices precipitate to form more smaller aggregations in the graphic results. Ostwald ripening growth occurs by prolonging the simulation time, in which the average precipitated particle radius increases parabolically. This growth is promoted by raising the simulation temperature. The particle growth exponents of 0.320-0.332 have only a tiny fluctuation when changing the simulation temperature. The simulation results are consistent with the temperature-decreasing and time-prolonging experiments of NiFe2O4-KCl molten salt system and SrMoO4 supersaturated solution, and the Ostwald ripening theory based on the diffusion-controlled kinetics.%采用蒙特卡罗方法模拟过饱和液相体系内的析出-长大行为，其中针对溶质扩散、溶质析出以及颗粒溶解等微观过程分别制定模拟规则，并在分析模拟数据时引入临界晶核，考虑液相析出浓度与临界形核尺寸之间的关联性。模拟结果表明，随着模拟时间延长，液相浓度和过饱和度均呈现出急剧下降、缓慢下降、最后趋于平衡稳定的变化趋势。模拟温度越低，则平衡浓度越低，达到平衡浓度所需时间越长，并且在图形模拟结果中形成更多、更小的溶质格点聚集析出微区。在延长模拟时间的过程中，会发生Ostwald熟化长大，并且平均析出颗粒半径呈抛物线增加，提高模拟温度则会引起更快的析出长大行为，各种模拟温度下得到的颗粒长大指数在0.320~0.332之间，不随模拟温度变化发生较大波动。上述模拟结果与NiFe 2 O 4-KCl熔盐体系和SrMoO 4过饱和溶液体系在降低温度和延长保温时间过程中的实验现象以及在扩散过程控制下的Ostwald熟化长大理论较为吻合。