Why is it that the higher the concentration, the finer the precipitated crystals

You can understand this question this way.

The first condition for the crystallization of solute is that there must be a certain degree of supersaturation, and the magnitude of this supersaturation has the most important influence on the final appearance size, particle size distribution and yield of the crystalline product.

The microscopic process of crystallization is like this, firstly, the spontaneous formation of crystal nuclei in the solution that reaches a certain degree of supersaturation, the number of crystal nuclei formed is determined by the size of the supersaturation, the large supersaturation forms a relatively large number of crystal nuclei, after the formation of crystal nuclei, the supersaturation of the solution is reduced to a relatively stable area, and the formed crystal nuclei continue to grow under the impetus of the concentration difference, and finally grow into a crystal body of a certain geometric shape and size.

In order to obtain large crystals, it is necessary to maintain a relatively stable and relatively low supersaturation, because low supersaturation will not spontaneously form crystal nuclei, but can only grow on the original crystal nuclei (or crystals) until they grow to the required crystal size.

The solubility of the solute is small, which means that the saturation range of the "relatively stable" mentioned above is very narrow, and a slight change in environmental conditions will seriously affect the stability of the system.

If the solution evaporates too quickly, it means that the solution is highly supersaturated, and crystallization is a slow process, and too much supersaturation promotes the formation of more crystal nuclei, so the final product will also be dominated by fine crystals.

To get a big crystal, in general, there are two words: "slow".

For more specifics, you can refer to the book "Industrial Crystallization".

That's what it's going on ...

The process of crystallization is also called the process of crystal growth.

Like decimal growth, it is slower ... And the older you get, the slower you grow.

The concentration of the solution is large, the solubility is small, and other conditions all lead to the rapid precipitation.

The speed of precipitation is too fast, and it is too late to crystallize into very large grains, so the grains are very small.

The process of precipitating crystals from the melt is used for single crystal preparation, the process of precipitating crystals from gas is used for vacuum coating, and the process of precipitating crystals from solution is commonly encountered in chemical production. According to the characteristics of liquid-solid equilibrium, the crystallization operation can not only obtain solid solutes from the solution, but also realize the separation of solutes and impurities, so as to improve the purity of the wild trapped products produced in the cave. More than 5,000 years ago, people began to use solar energy to evaporate concentrated seawater to produce table salt.

Can the crystal size of the liquid crystallization be adjusted to be finer, yes, it can be adjusted to be finer and smaller, our high-quality process of crystal inhibitor can make the crystals of the liquid that have crystallized from large to small, from small to fine, and can prevent the further precipitation of the crystals.

The reason for the crystallization of liquid fertilizer is that in autumn and winter, due to the low temperature, liquid fertilizer contains inorganic elements such as potassium and sodium or other electrolytes, and it is easy to precipitate inorganic salts at low temperature (less than 15), forming liquid fertilizer thick or precipitate, and even forming particles like industrial coarse salt, which is the crystalline body we see. The following products can be used: anti-crystallization agent, crystal inhibitor, crystallization control agent, crystallization inhibitor, anti-crystallization agent, crystal particle size regulator, crystallization adjuster, this product has two types: liquid and powder.

Liquids are acidic and solids are neutral. Non-flammable and explosive, no damage to liquid fertilizers and biomass systems. The amount of liquid added is 5 8/1000 of the weight of liquid fertilizer and biomass, that is, 5 10 grams of liquid fertilizer or biomass is added to 1kg, and it can be fully stirred after addition.

Due to the difference of each system, the addition amount can be determined by observing the above experiments, that is, the formation of smaller or fewer crystalline crystals at low temperatures, that is, the economic addition amount. The usual amount is 6 parts per thousand. The commonly used addition amount of powder crystal inhibitor is 3 6 thousandths, that is, 1kg of liquid fertilizer or biomass system, add 3 6 grams of this product, fully stir and dissolve to form a homogeneous crystal inhibitor system, which can be added in the process of fertilizer cooling, without affecting the use effect of fertilizer or biomass, and will not bring damage to the soil.

The crystallization process of pure metals takes place within horizontal segments on the cooling curve. Experiments show that when metal crystallizes, a batch of crystalline cores are spontaneously formed from liquid metals, and at the same time, some foreign refractory pointers can also act as crystal nuclei to form non-spontaneous crystal nuclei. Over time, the formed nuclei grow and grow and continue to produce new nuclei until all the liquid metals disappear and the crystals come into contact with each other.

Therefore, the process of knowing the crystal is the process of continuous terrain nucleus and crystal nucleus continuous growth.

The concentration of the solute in the solution exceeds the value of its saturated solubility). There are three forms of crystal nucleus: primary homogeneous nucleation, primary heterogeneous differential nucleation and secondary nucleation.

At high supersaturation, the process by which the solution spontaneously generates crystal nuclei is called primary homogeneous nucleation; The process by which a solution is induced by foreign substances (such as dust in the atmosphere) to form crystal nuclei is called primary heterogeneous nucleation. And the process of nucleation in a solution containing solute crystals is called secondary nucleation. Secondary nucleation is also a heterogeneous nucleation process, which occurs under the induction of tiny grains produced between crystals or when crystals collide with other solids (vessel walls, stirrers, etc.).

The requirement of crystallization operation is to produce pure crystals with a certain particle size distribution. The particle size and distribution of crystal products mainly depend on the crystal nucleus formation rate (the number of crystal nuclei produced per unit volume of solution per unit time), the crystal growth rate (the increase in a certain linear size of the crystal per unit time) and the average residence time of the crystal in the crystallizer. The supersaturation of the solution is related to the crystal nucleation rate and crystal growth rate, so it has an important impact on the particle size and distribution of the crystalline product.

In a solution with low supersaturation, the ratio of the crystal growth rate to the nucleus formation rate is larger (see figure), resulting in larger crystals and more complete crystal shapes, but a slow crystallization rate. In the industrial crystallizer, the supersaturation is usually controlled in the metastable zone, and the crystallizer has a higher production capacity than the orange bi, and a certain size of crystal products can be obtained.