Is secondary nucleation in crystals beneficial or harmful? ? ?
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As the title suggests, I’m seeking help! ! ! ! When paddle stirring is used in the crystallizer, the higher linear velocity at the edges continuously breaks the crystal grains, which may induce secondary nucleation. I’m very confused – is secondary nucleation in crystals beneficial or harmful? ? ?
I think whether secondary nucleation is beneficial or not depends on the type of crystal you want to obtain. If you want fine crystals, secondary nucleation is advantageous; if you want larger crystals, it is not beneficial, and reducing the stirring speed helps the crystals to grow larger.
I’ll ask again gently: when crystallizing, does a higher rotation speed lead to faster crystallization or a lower rotation speed? ? ?
Upstairs, they might not really understand what secondary nucleation is yet. It should be noted that most industrial crystallization processes rely on secondary nucleation to achieve crystallization. Primary nucleation is difficult to control, leading to uneven crystal size, and it is impossible to achieve in industrial settings. I’m not very familiar with your specific situation; generally, high rotational speeds are used only when a small particle size of the product is desired. Otherwise, a large-blade, low-speed propeller-type stirrer is the preferred choice.
In my opinion, there is no inevitable relationship between the speed of rotation and the speed of crystallization; even when the temperature reaches the level at which crystallization occurs, crystals do not necessarily form, as there is also the issue of supersaturation. Sometimes the crystals formed in a single nucleation event are very fine and invisible to the naked eye; crystallization generally occurs in the metastable region. The size of the crystals is closely related to the rate of cooling; if the cooling is too rapid, the crystals tend to be formed through primary nucleation and remain relatively fine, making them difficult to separate.
Generally speaking, crystal nuclei do not need to be tiny grains formed from a supersaturated solution, as this makes it difficult to control the number of nuclei and affects the size of the resulting crystals. The best method is to add pre-ground seed crystals to the saturated solution, with the quantity and particle size determined according to the requirements of the process.
Thank you, comrades upstairs; I’ve learned something
*Eyang is right; I don’t quite agree with the others.