Abstract:

In this paper, the crystallization kinetics of ammonium dihydrogen phosphate(MAP) in water-ethylene glycol system was experimentally discussed, the nucleation mechanism of MAP crystallization was studied by using classical nucleation theory, and the nucleation induction time of MAP at different temperatures and different supersaturation ratios was measured. The influence laws of temperature and supersaturation ratio on critical nucleation free energy (ΔG^* ), crystal interfacial free energy (γ), critical nucleation molecule number (i^* ), and critical nucleation radius (r^* ) were studied, and the growth mechanism was revealed according to nucleation parameters. In addition, the effects of stirring rate (N_P) and supersaturation ratio (S) on the crystallization process were explored. Based on the kinetic data, the nucleation and growth kinetics equations of MAP were fitted by least square method, and Canning-Randolph(C-R) and Abegg-Stevens-Larson(ASL) models fitted the linearly correlated growth kinetics model, revealing the synergistic regulation mechanism of solvent composition on crystallization kinetics. The results showed that when the temperature and supersaturation ratio increased, i^*, r^*, ΔG^* and induction time all decreased, while the primary nucleation rate increased. When the supersaturation ratio was 1.08 and above, homogeneous nucleation became the dominant mechanism, and when the supersaturation ratio was 1.06 and below, heterogeneous nucleation was the main nucleation mode. The surface entropy factor values were all less than 1, and the crystal crystallization mechanism was a continuous growth mechanism. When evaluating different linearly correlated growth models, it was found that the ASL model had higher accuracy in describing the crystal growth behavior. It can be seen from the order of the kinetic model that the supersaturation ratio has the greatest impact on the nucleation growth rate. This study elucidates the response law of MAP crystallization in water-ethylene glycol system, providing a theoretical basis for crystal size control based on mixed solvent design and industrial crystallization process optimization.

Key words: ammonium dihydrogen phosphate, crystallization kinetics, nucleation theory, linear growth model

摘要：

对磷酸二氢铵（MAP）在水-乙二醇体系中的结晶动力学进行了实验探讨，利用经典成核理论研究了MAP结晶的成核机理，测定了在不同温度以及不同过饱和比条件下MAP的成核诱导时间，研究了温度及过饱和比对临界成核自由能（ΔG^* ）、晶体界面自由能（γ）、临界成核分子数（i^* ）、临界成核半径（r^* ）的影响规律，根据成核参数揭示其生长机理；此外，探讨了搅拌速率（N_P）、过饱和比（S）等因素对结晶过程的影响；在动力学数据的基础上，用最小二乘法拟合了MAP的成核及生长动力学方程，使用Canning-Randolph（C-R）及Abegg-Stevens-Larson（ASL）模型拟合线性相关生长动力学模型，揭示了溶剂组成对结晶动力学的协同调控机制。结果表明：温度和过饱和比增大时，i^* 、r^* 、ΔG^* 与诱导时间均减小，而初级成核速率增大；过饱和比在1.08及以上时均相成核成为主导机制，在1.06及以下时非均相成核为主要成核方式；表面熵因子值均小于1，该晶体的结晶机制为连续生长机制；在评估不同线性相关生长模型时发现ASL模型在描述晶体生长行为方面具有更高的准确性，从动力学模型阶数可以看出，过饱和比对成核生长速率的影响最大。本研究阐明了水-乙二醇体系中MAP结晶的响应规律，可为基于混合溶剂设计的晶体尺寸控制与工业化结晶工艺优化提供理论依据。

关键词: 磷酸二氢铵, 结晶动力学, 成核理论, 线性生长模型