Name: crystal formation through supersaturation
Uploaded: 2025-05-22T09:05:36.000Z
Duration: 1 min 25 s
Channel: JoVE

结晶是一种相变过程，晶体从饱和溶液等来源中形成，通常伴随着溶液的冷却。
结晶过程始于初级成核，即从不含任何预先存在的晶体以促进该过程的澄清溶液开始。初级成核分为同质成核和异质成核两种类型。
在异相成核过程中，晶体在尘埃颗粒等成核表面上形成。相比之下，均相成核则发生在不含任何异相微粒的澄清溶液中。
在二次成核过程中，晶体的生长是由于引入的晶种等母体晶体所导致的。
达到临界簇尺寸的成核簇会生长并形成更大的晶体，而半径较小的成核簇则会发生溶解。
当溶质在溶剂中的浓度与溶解度之比，即过饱和度比值 S，超过1时，便会发生晶体生长。通过溶剂蒸发提高溶质浓度，或通过降低温度减小溶质的溶解度，均可增大 S 的值。
结晶法常用于制造活性药物成分。&#160;

晶体生长：结晶原理

Crystal Growth: Principles of Crystallization

结晶是一种相变的过程，其中晶体会从过饱和溶液中沉淀出来或从其他的来源形成。在结晶的过程中，原子或分子能够将自身排列为明确的刚性晶格，从而能够以最大限度来减少能量。

引发的结晶通常会涉及到控制溶质的浓度和溶液的温度。由于当溶质在溶剂中的浓度与溶解度之比（过饱和度 S）超过 1 时就会使晶体发生生长，因此溶液必须浓缩，并且温度必须足够低。当结晶活跃时，通过溶剂蒸发来增加溶质浓度或通过降低温度来降低溶质的溶解度，由于这会增加 S 值，从而对该过程是有利的。晶体生长的另一个重要因素是冷却速率，它对晶体的尺寸和形态起着至关重要的作用。缓慢冷却会产生较大的晶体，而快速冷却则会产生较小的晶体。

结晶的物理过程包括两个步骤：成核和晶体生长。在成核的过程中，溶剂会引发溶质分子的随机积累并形成簇，最终会形成核或种子的第一个晶体。如果晶核是由不含预先存在的晶体的溶液所形成的，则它们被称为初级成核。初级成核通常会通过同质或异质机制发生。在异质成核的过程中，晶体会像灰尘颗粒一样在活性剂的表面上形成。另一方面，均匀成核通常发生在透明的溶液中，并且没有任何异质颗粒。在二次成核中，生长是从母晶体（如通过晶种引入的晶体）开始的。在结晶的第二阶段——晶体生长，便会有越来越多的溶质分子加入到晶种的刚性晶格结构中，最终能够将晶体的尺寸增加到宏观尺度。一旦晶体形成且溶液冷却至室温，则可以使用真空过滤来过滤溶液，并将分离到的晶体干燥并储存。

结晶通常用作制药和化学工业中的分离和纯化步骤。它也经常在食品工业中用于制造糖、盐、人造甜味剂和其他的结晶调味料。

结晶是一种相变过程，晶体从过饱和溶液中析出，或由其他来源形成。在……过程中

crystal-growth-principles-of-crystallization

Education

教育

JoVE Core

Analytical Chemistry

分析化学

Unit 1

第一单元

Introduction to Separation Methods

分离方法导论

KEY TERMS AND CONCEPTS

关键术语与概念

crystal formation through supersaturation

Crystal formation through supersaturation begins when a solution contains more dissolved solute than it can normally hold. In crystallization, atoms or molecules line up into a rigid crystal lattice so the system can lower its energy. To start the process, the solute concentration and the solution temperature must be adjusted so the supersaturation ratio, S, is greater than one.

Supersaturation can be increased in two main ways. One method is to concentrate the solution by evaporating the solvent. Another method is to lower the temperature, which reduces the solubility of the solute. Cooling rate also matters. Slow cooling usually produces larger crystals, while rapid cooling tends to form smaller ones.

Crystallization happens in two stages: nucleation and crystal growth. During nucleation, solute molecules gather into small clusters until the first crystal, called the nucleus or seed, appears. If the nuclei form in a solution with no pre-existing crystals, the process is primary nucleation. Primary nucleation can be homogeneous in a clear solution or heterogeneous on particles such as dust.

In secondary nucleation, growth begins from parent crystals, such as those added during seeding. During the crystal growth stage, more solute molecules attach to the rigid lattice of the seed, making the crystal larger. After the crystals form and the solution returns to room temperature, the mixture is filtered by vacuum filtration. The crystals are then dried and stored.

This separation method is widely used in the pharmaceutical and chemical industries. It also has major uses in the food industry. Sugar, salt, artificial sweeteners, and other crystalline seasonings are often made this way.

Crystal Formation Through Supersaturation

crystal-formation-through-supersaturation

states of matter and phase changes

Heating and Cooling During Phase Changes

Heating and cooling can change a substance from one state of matter to another. These phase changes depend on internal energy, which is the total kinetic energy of particles and the potential energy from their interactions. In the condensed phases, stronger intermolecular forces and the pressure on the substance affect that internal energy. The internal energy is highest in the gaseous state, lowest in the solid state, and in between for the liquid state. Phase transitions happen when...

distillation: vapor&ndash;liquid equilibria

Distillation and Boiling Point Changes

Distillation separates a miscible liquid mixture by using differences in boiling points. It works best when the two liquids have a significant boiling point gap, usually at least 20°C. In this process, the mixture is heated until the more volatile component reaches its bubble point and begins to vaporize. The vapor then rises into a condenser. A condenser is a glass tube with separate inner and outer sections. Cold water flows through the outer section and cools the vapor in the inner section,...

filtration

Filtration Setup and Filtrate Collection

Filtration separates a solid from a liquid by passing a suspension through a porous medium. The solid stays on the filter, and the liquid, called the filtrate, passes through. This makes filtration a physical separation process, not a chemical change. The filtering medium is chosen for the purpose of the separation, the amount of material, and the nature of the precipitate. A good filter medium should be inert, mechanically strong, nonabsorbent toward dissolved materials, and able to let...

centrifugation

Centrifugation for Separating Particles

Centrifugation separates particles in a liquid by using differences in size and density. The sample is placed in centrifugation tubes and spun at high angular velocity. This creates centrifugal force, which makes the different components move at different rates. After spinning, the supernatant, or liquid above the settled material, is decanted. In some cases, the pellet is kept for further purification. In other cases, the supernatant is kept and may be spun again for additional processing. <br...

sublimation

Sublimation in Separation and Purification

Sublimation is the direct change of a solid into a gas. It skips the liquid state. A common example is solid carbon dioxide, or dry ice, which turns into gaseous carbon dioxide at standard pressure and room temperature. The phase diagram shows when sublimation can happen. This process occurs at the solid-gas boundary. It is not seen above the triple point of a substance. The reverse process is deposition, which is when a gas changes directly into a solid. Sublimation and deposition can help...

recrystallization: solid&ndash;solution equilibria

recrystallization-solidsolution-equilibria

Recrystallization for Purifying Solid Compounds

Recrystallization is a way to purify solid compounds by using differences in solubility. It does not involve a chemical reaction. Instead, it relies on physical properties of the desired compound and the impurities. The process is based on solid-solution equilibrium, also called solubility equilibrium. In this equilibrium, a component is split between the solid phase and the solution phase. At equilibrium, the chemical potential of that component is the same in both phases. To begin...

crystal growth: principles of crystallization

Crystal formation through supersaturation begins when a solution contains more dissolved solute than it can normally hold. In crystallization, atoms or molecules line up into a rigid crystal lattice so the system can lower its energy. To start the process, the solute concentration and the solution temperature must be adjusted so the supersaturation ratio, S, is greater than one. Supersaturation can be increased in two main ways. One method is to concentrate the solution by evaporating the...

precipitation and co-precipitation

Selective Ion Separation by Precipitation

Selective ion separation by precipitation is used to isolate ions from a solution. In qualitative inorganic analysis, ions that form sparingly soluble precipitates with the same reagent can be separated by using differences in their solubility products. A solubility product is the limit at which an ionic solid begins to form from dissolved ions. One example is the separation of Cu(II) and Fe(II) ions as insoluble sulfides. Copper(II) sulfide is first precipitated by adding acidic H2S. The acid...

coagulation

Wastewater Cleanup by Coagulation

Coagulation helps remove colloidal particles from wastewater. Colloids are tiny solid particles suspended in a liquid. They are usually negatively charged, so they attract a compact first layer of positive ions. More counterions gather around them and form an electrical double layer. This charge barrier keeps the particles apart and stabilizes the colloid. These suspended solids can be a problem because they may contain toxins that are hard to remove. Coagulation is used to make the particles...

electrodeposition

Electrodeposition for Metal Ion Separation

Electrodeposition separates metal ions from a solution by using an electric current and an electrolytic cell. The cell has an anode and a cathode. When current flows, oxidation happens at the anode. At the cathode, metal ions gain electrons, undergo reduction, and deposit on the large metal surface. This method works well when metals have very different reduction potentials. Copper and nickel in the same solution can be separated this way. First, the solution is made acidic. Then current is...

extraction: partition and distribution coefficients

extraction-partition-and-distribution-coefficients

Solvent Partitioning in Chemical Extraction

Solvent partitioning in chemical extraction describes how a solute spreads between two immiscible solvents. Immiscible solvents do not mix, such as an aqueous phase and an organic phase. The distribution law, also called Nernst's distribution law or the partition law, explains how that solute is shared at a constant temperature and equilibrium. At equilibrium, the ratio of solute concentrations in the two solvents stays constant. For extraction from water into an organic solvent, this...

extraction: effects of ph

pH Control in Liquid Extraction

pH control in liquid extraction changes how amines and acids move between organic and aqueous phases. The pH of the aqueous phase affects the charge on acidic and basic solutes. The charged form is usually more soluble in the aqueous phase. For a weak base such as an amine, the neutral form is called B. Its partition coefficient, K, describes how the neutral molecule distributes between the two liquids. If the conjugate acid of the amine is soluble only in the aqueous phase, while the base...

extraction: advanced methods

Chelate Extraction for Metal Ion Separation

Chelate extraction is a way to separate metal ions by using an organic ligand, or chelating agent, to form an uncharged metal complex. The chelating agent needs hydrophobic groups, and it must act as a weak acid so it can lose a proton and bind to the metal. Most organic ligands used for this method are not stable in water or are insoluble in the aqueous phase. For that reason, the chelating agent is first placed in the organic phase. It then moves into the aqueous phase, where the...

chromatography: introduction

Chromatography: Separation by Polarity

Chromatography separates compounds by how they divide between a stationary phase and a mobile phase. The stationary phase is the material that holds the compounds for a time. The mobile phase is the solvent that carries the solutes to be analyzed. In column chromatography, a mixture flows through the stationary phase. The compounds separate based on their structure and polarity. Solutes that interact weakly with the stationary phase move faster through the column and exit first. Solutes that...

dialysis

Dialysis Separation by Diffusion

Dialysis separates small molecules from larger ones by diffusion through a semipermeable membrane. It is a purification method used to remove unwanted ions or small organic molecules from a sample while keeping larger analytes in place. The membrane is usually made of cellulose acetate or cellulose nitrate. Its pores are typically about 1 to 5 nm wide. Molecules such as chloride, sodium, and glucose can pass through these pores. Larger molecules, including proteins, hormones, and enzymes, are...

volatilization

Mass Loss in Gravimetric Analysis

Volatilization gravimetry is a way to measure mass loss in a sample by driving off a volatile substance. It helps estimate how much volatile material is present. In this method, a known amount of sample is heated to a high temperature in a crucible or another suitable vessel. As the sample heats, the volatile substance evaporates. The vapor is then completely removed from the crucible, either by continued heating or by bubbling an inert gas through the vessel. The non-volatile part stays...

ion exchange

Ion Exchange Resins and Charged Molecules

Ion exchange chromatography separates charged molecules from a solution by swapping them with mobile, or active, ions on a stationary phase. It is used to separate ions, soften and deionize water, and purify solutions. The method depends on a solid column made of high-molecular-weight, chemically stable polymers that are crosslinked to make them porous and essentially insoluble. These polymers are functionalized with either acidic or basic groups. When acidic groups are present, the resin is a...

key terms and concepts

Learn how supersaturation, cooling rate, nucleation, and crystal growth shape crystal formation, and why crystallization is used to separate and purify materials.

Crystal Formation Through Supersaturation | JoVE K12

analytical chemistry

JoVE Core Analytical Chemistry simplifies complex chemical principles by breaking them down into clear, engaging animations, making topics from SI Units to NMR spectroscopy more accessible and straightforward. Additionally, the scientist-in-action videos highlight the application of these concepts in real-world research conducted in laboratories globally.

Crystal Formation Through Supersaturation

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