Crystallization is the process of directly converting liquids into a solid state. The process of crystallization takes place when the physical parameters such as temperature and pressure are varied or when the chemical parameters such as acidity are altered. The technique of crystallization is typically used for the purpose of purification of naturally occurring impure elements and to extract solid particles dissolved in a solution. It is a type of physical change because the substances only get changed from one physical form to another and no new substance is formed during the process. In other words, crystallization is the process of obtaining crystals from a solution.
Examples of Crystallization
1. Salt Harvesting
Harvesting of salt is one of the best examples of the crystallization process in real life. Initially, the water contained by seas and salty lakes is subjected to solar evaporation. The salt left behind when the water gets converted into water vapours is impure in nature and has small crystals. It is further cleaned and refined for the purpose of purification and to ensure safe consumption.
2. Separation of Alum Crystals
The separation of alum crystals from an impure sample is done with the help of the crystallization process. Alum exists in nature in a number of minerals such as potash. Potash or potassium sulphate is found in minerals such as kalinite, alunite, leucite, etc. To extract potash alum from an impure sample, the solution of the sample is obtained by mixing distilled water with a crude sample. The solution is then heated to properly dissolve the sample in distilled water. The heated solution is further filtered with the help of a funnel and filter paper. The filtrates are concentrated by continuously stirring and mildly heating the filtered solution. The saturated solution is then transferred to an evaporating dish and is cooled by placing the dish in water. The final step is the separation and drying of the crystals.
3. Crystallization of Honey
The honey initially regurgitated by bees is liquid in nature. The sugar molecules of the honey tend to form sugar crystals when stored over time with the help of the crystallization process. The rate of forming sugar crystals in honey can be increased by storing it in a cold environment.
4. Formation of Natural Crystals
Metals, stones, and minerals present in nature are yet another example of crystals in nature. They are formed by subjecting raw carbon, and other elements to extreme temperature and pressure conditions, which is a natural process of crystallization. Also, a number of artificial gems and stones are also extracted with the help of the crystallization process.
5. Snow Flakes
Snow is one of the prime examples of the crystallization process occurring in nature. Snowflakes are formed due to low temperature and the presence of moisture in the environment. Each snowflake act as a tiny ice crystal, which tend to stick to each other and fall to the ground due to heavyweight.
6. Silicon Purification
Silicon is abundantly present on the earth’s surface in form of sand. It is used in a variety of applications such as the formation of solar cells, electronic components, alloys, etc. The process of extraction of silicon from sand involves heating silica in an arc furnace at 1800 degrees Celcius temperature. The silicon formed as a result contains a number of impurities and is known as metallurgical grade silicon. To extract pure silicon, the metallurgical grade silicon is further grounded into a fine powder and is mixed with hydrogen chloride. The mixture is further heated until it gets thoroughly vaporized. The process takes place in a vacuum environment. The crystals of electronic-grade silicon then get deposited on the electrically heated polysilicon rods. The electronic grade silicon crystals deposited on the rod having a purity of over 99.9% are then pulled out forcefully.
Gout is the medical condition under which a person undergoes acute pain due to the deposition of chalkstones in bones and joints. The main cause of such a disease is the crystallization of uric acid. The crystals of the uric acid tend to get deposited in the joints, leading to a significant increase in friction while moving. Thereby, causing pain and discomfort in the joints and bones.
8. Kidney Stones
Kidney or gall bladder stones typically get formed in the body due to the crystallization process. Salt and calcium particles tend to get deposited in the body organs. These deposited crystals of salt and calcium stick to each other and undergo oxidization to form small stones.
9. Photographic Film
Before digital cameras were invented, photographic film was used to capture images. The process of recording images with the help of a photographic film required the execution of multiple chemical reactions. The photographic film consists of a number of different layers such as a scratch-resistant layer, the emulsion layer, the adhesive layer, the antihalation layer, and the film base. The scratch-resistant layer protects the film from being corrupted. The adhesive layer is the firm layer of flexible plastic and is responsible to provide support to the other layers and is responsible to bind them on the top of the film base. The emulsion layer is the light-sensitive layer made up of gelatin that contains silver halide grains. These silver crystals are obtained via the process of crystallization and help to trap light energy and are basically responsible to capture the image.
10. Purifying Iodine
The process of crystallization is typically used to purify elements such as iodine or sulphur. For this purpose, the iodine is placed in a crucible and is covered with a funnel. The end of the funnel is blocked with the help of a cotton ball. The iodine is then heated by placing the set up on a lighted bunsen burner. The iodine undergoes a sublimation process and produces purple coloured fumes. The fumes are unable to escape the set-up and get trapped in the flask. These fumes then get converted to solid-state causing the so formed crystals to stick to the inside of the curved part of the funnel by undergoing the deposition process. The crystals formed during the process are pure in nature.
11. Crystallization of Sugar
Most of the sweeteners are extracted from syrups with the help of the crystallization process. For instance, to extract the table sugar or sucrose, the sugar cane is boiled at a significantly high temperature. This causes most of the water content present in the sugar cane juice to get evaporated leaving behind a thick syrup. The syrup is then placed in a partial vacuum environment and is heated at a comparatively low temperature. Some of the seedings are artificially added to the syrup and are responsible to fasten the process of growth of the sugar crystals. These crystals are then separated with the help of a centrifugal machine.
12. Crystallisation of Carbon
There are basically three allotrophic forms of carbon namely, amorphous carbon, graphite, and diamond. The key difference between the three basic forms of carbon is the amount of pressure and the rate of metamorphosis each form is subjected to. The variation in the pressure difference leads to the crystallization of carbon that helps to improve its structural strength.
13. Formation of Frost
The formation of frost is a prominent example of the crystallization process. One can easily observe a number of tiny ice particles or the frost particles deposited on the leaves, car windows, and other objects on a winter morning. These particles are formed due to the crystallization of water due to low temperature.
14. Formation of Stalactites and Stalagmites
The stalactites and stalagmites are the limestone rocks that are found inside an underground cave. These structures are yet another example of the crystallization process in real life. The stalactites are the sharp structures hanging from the roof, while stalagmites are the rising structures present on the floor of the caves. These are formed in areas where the concentration of limestone rocks is significantly high. Stalactites and stalagmites fall under the category of chemically formed inorganic sedimentary rocks because they are formed as a result of the evaporation of water from the sedimentary limestone rocks. When the water contained by the limestones get evaporated it sticks to the roof of the caves thereby, forming stalactites. The water from the stalactites eventually condenses and gets deposited on the floor of the caves thereby, forming stalagmites.
15. Desalinisation of Water
The process of desalinisation of water is somewhat similar to that of the extraction of salt from saline water. The sample impure water is subjected to high temperature that causes the water to evaporate, leaving behind salt and other impurity particles. The water vapours formed due to evaporation are then subjected to a condensation process and pure water is obtained. The process of separating the impurity particles from pure water is an example of the crystallization process.