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Single Crystal Growth Theory

Hangzhou JWG Technology Co.Ltd | Updated: Apr 22, 2017

Single crystal growth theory

Crystals are formed in the case of phase transition. There are three kinds of phases, namely, gas phase, liquid phase and solid phase. Only a crystal is a solid. From the gas phase, liquid phase into solid phase to form crystals, the solid phase can also be directly transformed.

The general process of crystal formation is the formation of crystals, and then gradually grow up. It is generally believed that there are three stages in the growth of crystals from liquid phase or gas phase. The medium is over saturated and over cooled.

In a medium system, the appearance of supersaturation and supercooling does not mean the simultaneous crystallization of the whole system. In the system, there are all kinds of transient fine crystalline particles. At this time due to local changes in temperature or concentration of the external impact, or some impurity particles influence, will lead to the system of local supersaturation, a high degree of cooling area, the crystalline particle size reaches the critical value. The formation of crystalline particles is called nucleation.

The particles in the medium system enter into the unstable state at the same time to form a new phase, which is called homogeneous nucleation.

Some local cells in the system first form the nucleus of the new phase, which is called heterogeneous nucleation.

Homogeneous nucleation refers to the fact that the nucleation probability is equal in a system, which is to overcome the considerable surface energy barrier, which requires a considerable degree of supercooling to nucleate.

Heterogeneous nucleation process is due to some heterogeneity exists in the system, such as suspended particles, the vessel wall uneven, they can effectively reduce the surface energy into the nuclear barrier, priority in these heterogeneous nucleation sites. Because of the low degree of supercooling can also be localized into the nucleus.

In unit time, the number of nuclei formed in unit volume is called nucleation rate. It depends on the degree of supersaturation or supercooling. The higher the supersaturation and supercooling degree, the greater the nucleation rate. Nucleation rate is also related to the viscosity of the medium, the viscosity of the general assembly to hinder the diffusion of substances, reduce the nucleation rate. Here are two main theories of crystal growth.

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