Nucleation mechanism and crystallization kinetics of potassium dihydrogen phosphate in ethylene glycol-water system

Potassium dihydrogen phosphate （KH₂PO₄） is a crucial chemical component widely applied in industry, agriculture, and medicine. Although its industrial production has been relatively mature, issues such as inclusions, cracks, and dendritic crystal growth often occur in pure water systems, leading to poor optical uniformity and a low laser damage threshold. To address this problem, this study explored the growth and nucleation kinetics of KH₂PO₄ in an ethylene glycol-water system at a specific ratio.First, by controlling the solution’s supersaturation ratio （S） and temperature, the relationship between the induction period and nucleation rate was analyzed. The results showed that homogeneous nucleation dominated when S>1.08, while heterogeneous nucleation dominated when S<1.06. Regarding nucleation parameters, an increase in the supersaturation ratio significantly reduced the nucleation free energy barrier, critical nucleation radius, and critical number of nucleation molecules, while increasing the primary nucleation rate, which confirmed the important roles of temperature and supersaturation ratio in the nucleation process. Analysis of the surface entropy factor demonstrated that the crystallization of KH₂PO₄ primarily followed a continuous growth mechanism.Second, the effects of rotation speed, supersaturation ratio, and suspension density on particle size, growth rate, and nucleation rate were investigated. The linear growth rate of KDP was fitted and calculated using the two-parameter C-R model and three-parameter ASL model, and the kinetic equations for the growth and nucleation processes were determined. This study provides a reference for solving core issues in industrial KDP synthesis, such as crystal defects, high energy consumption, and unstable processes.