The growth and formation of quartz stone?
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 it is too cool, it can be locally nucleated.In unit time, the number of nuclei formed in unit volume is called nuclear velocity. It depends on the degree of supersaturation or supercooling of the material. The higher the supersaturation and supercooling, the greater the nucleation rate. The nucleation speed is also related to the viscosity of the medium. The wheel assembly hinders the diffusion of material and reduces the nucleation rate. The nucleation will further develop after the formation of the nucleation. Here are two main theories about crystal growth.
The particles in the medium system enter the unstable state simultaneously and form a new phase, which is called homogeneous nucleation.In some parts of the system, the nucleation of the new phase is first formed, which is called heterogeneous nucleation.Homogeneous nucleation means that in a system, the formation of nuclei is equal to the number of particles, which overcomes considerable surface energy barrier, which requires considerable supercooling to nucleate.
The general process of crystal formation is nucleation, and then growing up gradually. It is generally believed that the growth of crystal from liquid phase or gas phase has three stages: firstly, the medium reaches over saturation and supercooling stage; secondly, nucleation stage; growth phase.In a certain medium system, the appearance of supersaturation and supercooling does not mean simultaneous crystallization of the whole system. Transient fine crystalline particles appear first and everywhere in the system. 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.
Crystals are formed in the case of phase transitions. There are three kinds of phases: gas phase, liquid phase and solid phase. Only crystals are real solids. The crystals form when the gas phase and liquid phase change into solid phase, and the solid phase can also change directly.
