The above formula, known as Kelvin'

The above formula, known as Kelvin's equation, describes the relationship between critical grain size and solution supersaturation. According to the related crystal theory, only the crystal particles whose size is larger than the critical size can grow in the solution, and the crystal particles whose size is smaller than the critical size can grow in the solution. Otherwise, the crystal will dissolve. In the precipitation reaction, the saturation concentration of the reaction products is very small, which can produce a large degree of supersaturation in an instant. Thus, most nuclei produced by precipitation reactions are homogeneous. A true solution environment must contain some exotic particles. These impurities reduce the nucleation barrier to a certain extent, and promote the formation of Nuclei. Therefore, primary heterogeneous nucleation can occur at a lower level than homogeneous nucleation. At supersaturation. When the degree of supersaturation is high, the primary homogeneous nucleus mainly occurs in the reactive precipitation process. When supersaturation is low, primary heterogeneous nucleation is dominant. Therefore, the total nucleation rate can be roughly expressed as the sum of the two nucleation rates. The process of secondary nucleation in a solution containing solute crystals is called secondary nucleation. Secondary nucleation is also a heterogeneous nucleation process. The origin and formation mechanism of secondary nucleation have been studied by many scholars, and many different mechanisms have been proposed. However, in recent years, it is generally believed that there are two secondary nucleation mechanisms: Shear stress and contact, that is to say, a crystal or crystalline wall, Mixer, etc produced by induction between tiny particles. There were other solid collisions during the second nucleation. In precipitation reaction, secondary nucleation can be neglected because of high supersaturation, large number of Nuclei and small particle size.