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

Krystalizacja to proces przemiany fazowej, w którym kryształy powstają ze źródła, takiego jak chłodzący nasycony roztwór.
Krystalizacja rozpoczyna się od pierwotnego zarodkowania, które rozpoczyna się od klarownego roztworu bez żadnych wcześniej istniejących kryształów, które wspomagają ten proces. Dzieli się na typy jednorodne i niejednorodne.
Podczas zarodkowania heterogenicznego kryształy tworzą się na powierzchniach zarodkujących, takich jak cząsteczki pyłu. Natomiast jednorodne zarodkowanie zachodzi w klarownym roztworze bez żadnych niejednorodnych cząstek.
Podczas zarodkowania wtórnego wzrost następuje z powodu kryształów macierzystych, takich jak te wprowadzone przez zasiew.
Klastry zarodkujące, które osiągają krytyczny rozmiar klastra, rosną, tworząc większe kryształy, podczas gdy te o mniejszych promieniach ulegają rozpuszczeniu.
Wzrost kryształów następuje, gdy stosunek stężenia i rozpuszczalności substancji rozpuszczonej w rozpuszczalniku lub współczynnik przesycenia, S, przekracza jeden. Zwiększenie stężenia substancji rozpuszczonej poprzez odparowanie rozpuszczalnika lub zmniejszenie rozpuszczalności substancji rozpuszczonej poprzez obniżenie temperatury zwiększa wartość S.
Krystalizacja jest powszechnie stosowana do wytwarzania aktywnych składników farmaceutycznych.

wzrost kryształów: zasady krystalizacji

Crystal Growth: Principles of Crystallization

Krystalizacja to proces przemiany fazowej, podczas którego kryształy wytrącają się z roztworu przesyconego lub powstają z innych źródeł. Podczas krystalizacji atomy lub cząsteczki układają się w dobrze określoną, sztywną sieć krystaliczną, aby zminimalizować energię.

Zainicjowanie krystalizacji polega na manipulowaniu stężeniem substancji rozpuszczonej i temperaturą roztworu. Ponieważ wzrost kryształów zachodzi, gdy stosunek stężenia i rozpuszczalności substancji rozpuszczonej w rozpuszczalniku – współczynnik przesycenia S – przekracza jeden, roztwór musi być stężony, a temperatura musi być wystarczająco niska. Ponieważ krystalizacja aktywnie zachodzi, zwiększenie stężenia substancji rozpuszczonej poprzez odparowanie rozpuszczalnika lub zmniejszenie rozpuszczalności substancji rozpuszczonej poprzez obniżenie temperatury zwiększa wartość S, wspomagając proces. Innym ważnym czynnikiem wzrostu kryształów jest szybkość chłodzenia, która odgrywa zasadniczą rolę w wielkości i morfologii kryształów. Powolne chłodzenie prowadzi do większych kryształów, podczas gdy szybkie chłodzenie prowadzi do małych kryształów.

Fizyczny proces krystalizacji składa się z dwóch etapów: zarodkowania i wzrostu kryształów. Podczas zarodkowania rozpuszczalnik inicjuje przypadkową akumulację cząsteczek substancji rozpuszczonej, tworząc skupiska, które ostatecznie tworzą pierwszy kryształ zwany jądrem lub zarodkiem. Jeśli zarodki kryształów powstają z roztworu, który nie zawiera wcześniej istniejących kryształów, nazywa się je zarodkowaniem pierwotnym. Zarodkowanie pierwotne zachodzi poprzez mechanizmy jednorodne lub heterogeniczne. Podczas heterogenicznego zarodkowania kryształy tworzą się na środkach powierzchniowo czynnych, takich jak cząstki pyłu. Z drugiej strony jednorodne zarodkowanie zachodzi w przezroczystym roztworze bez żadnych heterogenicznych cząstek. W przypadku wtórnego zarodkowania wzrost następuje z kryształów macierzystych, takich jak te wprowadzone przez zaszczepianie. Podczas drugiej fazy krystalizacji – wzrostu kryształów – coraz więcej cząsteczek substancji rozpuszczonej przyłącza się do sztywnej struktury siatkowej zarodka, ostatecznie zwiększając rozmiar kryształów do skali makroskopowej. Po utworzeniu się kryształów i ochłodzeniu roztworu do temperatury pokojowej roztwór sączy się za pomocą filtracji próżniowej, a oddzielone kryształy suszy się i przechowuje.

Krystalizacja jest często stosowana jako etap oddzielania i oczyszczania w przemyśle farmaceutycznym i chemicznym. Jest również często używana w przemyśle spożywczym do produkcji cukru, soli, sztucznych słodzików i innych krystalicznych przypraw.

Wzrost kryształów: Zasady krystalizacji

Krystalizacja to proces przemiany fazowej, w którym kryształy wytrącają się z przesyconego roztworu lub powstają z innych źródeł. Podczas...

crystal-growth-principles-of-crystallization

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Analytical Chemistry

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Introduction to Separation Methods

Wstęp do metod rozdziału

KEY TERMS AND CONCEPTS

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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

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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...

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Centrifugation for Separating Particles

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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

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Solvent Partitioning in Chemical Extraction

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Chelate Extraction for Metal Ion Separation

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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

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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

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Crystal Formation Through Supersaturation

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