What is Sublimation in simple words, examples from life

Sublimation

(
sublimation
), from lat. sublimo – I lift up – the transition of a substance from a solid to a gaseous state, bypassing the liquid stage (first-order phase transition). In the same way, vapors of a substance can condense, bypassing the liquid state, directly forming crystals.

Sublimation is a method of purifying substances in cases where impurities have a different volatility than the substance itself, and replaces long and labor-intensive crystallization. The substance thus purified is free of impurities, so sublimation is often used as the final operation in obtaining samples for analysis. This method is convenient for purifying substances that form solvates and hydrates.

The reason that a solid directly sublimes without first undergoing melting becomes clear when considering Fig.
27. The sublimation pressure curve reflects the dependence of the saturated vapor pressure on the temperature above the crystals. All three curves - sublimation pressure, melting pressure and vapor pressure - converge at the triple point, the only one (according to the phase rule) in which three phases can exist: solid, liquid and gaseous. The pressure corresponding to this point is the lowest at which the liquid phase of a given substance can exist. If the vapor pressure of a given substance (total or partial) at a given temperature is lower than the pressure corresponding to the triple point, then the vapor will not condense, but will directly turn into crystals; the crystals, in turn, will also directly turn into steam under these conditions. To obtain a substance in a crystalline state, it is necessary to cool its vapor below the temperature of the triple point, and to prevent the formation of liquid, the process should be carried out under a pressure less than that corresponding to the triple point. This can be achieved by reducing the total pressure or diluting the vapor of a given substance with an inert gas (thereby reducing the partial pressure of the vapor). The temperature at which the vapor pressure above a solid is equal to the external pressure is called the sublimation temperature

.

Sublimation must be carried out at a temperature lower than the sublimation point, that is, at a temperature where the vapor pressure of the solid is equal to the external pressure, to prevent contamination by crystal cracking. In addition, increasing the sublimation temperature promotes the formation of small and, therefore, less pure crystals.

Sublimation is carried out both at normal pressure and at reduced pressure (vacuum sublimation), as well as in a flow of inert gas.

Sublimation is used only for those solids that have a relatively high vapor pressure at a temperature below the melting point.

Sublimation is usually used for purification from solid, low-volatile impurities or in cases where purification by recrystallization is difficult due to the large amount of resinous or difficult-to-separate impurities.

In organic chemistry, sublimation is used to purify iodine, anhydrous aluminum chloride, benzoic acid ,

-benzoquinone and other substances. The disadvantage of sublimation is the limited use of it and the long duration of the process.

The rate of sublimation is directly proportional to the pressure of the vapor and the surface of the solid and inversely proportional to the external pressure in the device. It is increased by maintaining an optimal temperature, reducing the distances between the place of heating and condensation of the substance, passing a weak current of inert gas, or creating a vacuum.

Sublimation occurs only from the surface, so the substance must be ground very finely.

To sublimate a small amount of a substance, the devices shown in Fig. are used. 28.

In laboratory conditions, two watch glasses of the same size are used (Fig. 28, a).

The simplest device (Fig. 28, b) is a porcelain cup in which the substance to be purified is placed; the cup is covered with a circle of filter paper with small holes so that the sublimate does not fall back onto the substance to be purified. The top of the paper is covered with an inverted glass funnel of slightly smaller diameter, the outlet tube of which is closed with a cotton swab. A strip of damp cloth is placed on the outer surface of the glass funnel. When a porcelain cup is gently heated, vapors of substances enter the cold space through holes in the paper and crystallize on the wall of the funnel.

a B C D E

Rice. 28. Equipment for sublimation:

A

– two watch glasses of the same size;
b
– porcelain cup with a funnel;
c
– on a finger-shaped refrigerator;
d
– on a cooled distillation flask;
d
– with a vertical condenser: 1 – test tube; 2 – round-bottomed glass; 3 – condensation tube; 4 – capillary; 5 – paper filter

For sublimation at atmospheric pressure, the simplest device is used (Fig. 28, d) - a low glass without a spout with a thin layer designed to sublimate the substance at the bottom. The glass is closed with a round-bottomed flask through which water flows. At high sublimation temperatures, the water in the flask may not be flowing. During the sublimation process, the substance must be heated very slowly; usually, various types of baths are used for this purpose.

Even slight overheating can contribute to the rapid thermal decomposition of the sublimating substance. This danger can be avoided by carrying out the sublimation in a vacuum. It is also used in cases where the sublimated substances are slightly volatile. To create a vacuum, water jet, oil, and in special cases, diffusion pumps are used.

Devices for sublimation in vacuum are shown in Fig. 29. When opening the device (Fig. 29, a), it is necessary to avoid shaking (warm up the grinding section!), so as not to cause the sublimate to fall off the cooling surface, which should be as little as possible (5-10 mm) removed from the heated space where sublimation occurs . The substance sublimates only from the surface, so the drug must be ground very finely.

A device that allows sublimation of a substance in a stream of dry air or inert gas with high productivity is shown in Fig. thirty.

a b

Rice. 29. Devices for vacuum sublimation:

A --

under vacuum with water cooling: 1 – glass with ground section;
2 – cap with a finger cooler; 3,4 – tubes for water input and output; 4.5 – pipes for connection to the vacuum pump; 6 – sublimable substance; b –
with a horizontal condensation tube: 1 – flask with a substance; 2 – condensation tube; 3 – head with tap

Control questions

1. What is called sublimation (sublimation)?

2. Types of sublimation.

3. Instruments for carrying out the sublimation process.

4. Practical significance of sublimation.

5. What is the relationship between vapor pressure over a solid or liquid and temperature? Show this relationship using the example of water (phase diagram of water).

Date of publication: 2015-11-01; Read: 1311 | Page copyright infringement

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Dry sublimation

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Dry sublimation occurs when the vapors of a sublimated substance are condensed into a solid, hard or brittle. An example is given by sulfur, film vapor and others, which are collected from vapors into solids. [1]

When does dry sublimation occur and its application. [2]

Turpentine is a liquid obtained by dry sublimation of wood. When it gets on the skin, it degreases it and has an irritating effect, which varies depending on the degree of purification, raw materials and method of obtaining turpentine. [3]

Another sanitary and hygienic requirement - limiting the surface temperature of devices - is caused by the phenomenon of decomposition and dry sublimation of organic dust on a heated surface, accompanied by the release of harmful substances, in particular carbon monoxide.

Sublimation (sublimation)

Dust decomposition begins at a temperature of 65 - 70 C and proceeds intensively on a surface with a temperature of more than 80 C. [4]

Another sanitary and hygienic requirement - limiting the temperature of the heating surface of devices - is caused by the phenomenon of decomposition and dry sublimation of organic dust, accompanied by the release of harmful substances, in particular carbon monoxide. Dust decomposition begins at a temperature of 65 - 70 C and proceeds intensively on a surface with a temperature of more than 80 C. [5]

Another sanitary and hygienic requirement - limiting the temperature of the heating surface of devices - is caused by the phenomenon of decomposition and dry sublimation of organic dust, accompanied by the release of harmful substances, in particular carbon monoxide. Dust decomposition begins at a temperature of 65 - 70 °C and proceeds intensively on a surface with a temperature of more than 80 °C. [6]

The target most often is TeO2 dioxide with an enriched tellurium isotope, from which, after irradiation, radioactive iodine is isolated by dry sublimation. [7]

The design of combined heating systems was justified by sanitary and hygienic considerations: when heating heating devices directly with steam at a temperature of 100 and above, intense dry sublimation of organic dust settles on the surface of the devices and air pollution in heated rooms occurs. [8]

As a result of geological movements, these sediments penetrate to great depths, where, under the influence of pressure and high temperature, and possibly under the influence of microorganisms, the process of dry sublimation takes place over millions of years, during which the carbon contained in the sediments, for the most part, transforms into hydrocarbon compounds, while most of the oxygen and other elements migrate. A liquid substance consisting mainly of a mixture of hydrocarbons of different molecular weights can migrate independently, penetrating through the pores and cracks of the earth’s interior. The main components of natural gas are low molecular weight hydrocarbons (primarily methane and ethane), while oil is high molecular weight hydrocarbons. [9]

From a sanitary and hygienic point of view, steam is a less desirable coolant than water, since dust, settling on the surface of heating devices with a temperature of about 100, burns, decomposes and pollutes the air with dry sublimation products. If water flows through the heating devices, then the dust almost does not burn and the air is not polluted. [10]

From a sanitary and hygienic point of view, steam is a less desirable coolant than water, since dust, settling on the surface of heating devices with a temperature of about 100, burns, decomposes and pollutes the air with dry sublimation products. If water flows through the heating devices, then the dust almost does not burn and the air is not polluted. [eleven]

From a sanitary and hygienic point of view, steam is a less desirable coolant than water, since dust, settling on the surface of heating devices with a temperature of about 100 C, burns, decomposes and pollutes the air with dry sublimation products. In low-pressure systems, the steam temperature hardly changes and is always above 100 C. [12]

From a sanitary and hygienic point of view, steam is a less desirable coolant than water, since dust, settling on the surface of heating devices with a temperature of about 100 C, burns, decomposes and pollutes the air with dry sublimation products. If water flows through the heating devices, then the dust almost does not burn and the air is not polluted. [13]

From a sanitary and hygienic point of view, steam is a less desirable coolant than water. C, burns, decomposes and pollutes the air with dry sublimation products. In low-pressure systems, the temperature of steam does not change and is always above 100 C. The listed disadvantages allow the use of steam as a coolant only for heating industrial and individual communal buildings. [14]

Organic dust, settling in rooms, decomposes and releases unpleasant odors. When organic dust is deposited on hot surfaces with temperatures above 80 C, it undergoes dry sublimation, during which the air is polluted with carbon monoxide. [15]

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Sublimation (sublimation)

Some solids, when heated, can actively evaporate before reaching their melting temperatures. The reverse transition of vapor to the solid state occurs immediately, bypassing the liquid phase. This process is called sublimation or sublimation and is used to purify substances.

Sublimation, even a single one, as a rule, leads to the obtaining of a completely pure product and often replaces several recrystallizations. It can be used both for final purification of the product and for preliminary separation of volatile compounds from non-volatile impurities. Sublimation also differs favorably from recrystallization in its higher yield of pure product (98-99%).

On the other hand, sublimation is a very long process, so it is usually used to purify small quantities of substances. The scope of this method is also limited by the fact that the ability of many solid compounds to sublimate is so insignificant that it cannot be used for preparative purposes.

Since the rate of evaporation is proportional to the total surface area of ​​evaporation, the substance to be sublimated must be ground as finely as possible. One should also not allow the substance to melt during sublimation, since this leads to a drop in the rate of the process due to a sharp decrease in the surface of the substance.

The use of rarefaction, as well as during distillation, reduces the temperature at which substances begin to sublime, so under vacuum it is possible to sublimate many labor-volatile compounds.

When choosing devices for sublimation, preference should be given to designs in which the distance between the sublimated substance and the condensation surface is minimal. As this distance decreases, the rate of sublimation increases.

Rice. 81. Devices (a, b) for sublimation with condensation of vapors on cooled surfaces.

Rice.

How to sublimate effectively and why it is useful

Sublimation is useful because it relieves the psyche, allows a person to take a broader look at the situation and find a safe and positive form of activity to splash out their feelings.

Small instructions:

1. Relax. Life around you does not stop while you are focused on your condition.
2. Try to dream. Go through all the options that come to mind. One day you will catch on to something and realize that this is what you want to strive for.
3. Meditate. Deep meditation, when carried out correctly, will help you get to the bottom of your inner “I” and find out what this “I” wants to do and what solution to problems it will prefer.
4. Fall in love. And remember your condition. With the same feeling of euphoria, you need to start fulfilling your chosen goal.

Sublimation (sublimation)

82. The simplest device for sublimation: 1 - porcelain cup with a substance; 2 - glass funnel; 3—a circle of filter paper with holes; 4 - sand bath; 5 - cotton wool.

To sublimate small quantities of easily sublimated substances, a simple device can be used, consisting of a porcelain cup, a watch glass and an ordinary chemical funnel (Fig. 80). The sublimated substance is heated in a sand bath; the sublimate collects on the cold walls of the funnel, from where it should be periodically cleaned off. To prevent the sublimation crystals from falling back into the cup, the substance is covered with a circle of filter paper or asbestos, with several holes punctured in it.

Rice. 82. A device for sublimation of small quantities of substances in a vacuum.

In many cases it is preferable to conduct condensation onto a cooled surface. Of all the devices proposed for this purpose, the simplest and at the same time providing the minimum distance to the condensation surface are the devices shown in Fig. 81.

A commonly used device for the sublimation of small quantities of substances in a vacuum is shown in Fig. 82. Its disadvantages include the need to periodically turn off the vacuum and disassemble the device to scrape off the sublimation.

In the vacuum sublimator shown in Fig. 83, the sublimate is collected in a horizontally located refrigerator with a fairly wide inner tube. To avoid premature condensation of the product, the flask with the sublimated substance is immersed up to the neck in a liquid bath heated to the required temperature. A small current of air or inert gas supplied to the flask through a capillary facilitates the effective removal of vapors from the evaporation surface, which dramatically increases the performance of the device.

To prevent the smallest particles of a substance from being carried away with the gas flow into the outlet neck of the flask, it is advisable to solder a porous glass partition, however, with a small gas flow, this measure is not necessary.

Depending on the properties of the substance being purified and its quantity, you can change the design of individual parts of the device without changing the principle of its operation. Thus, the shape of the flask and the method of heating it can be different. An externally cooled two-neck flask is very convenient as a condenser for the sublimation of large quantities of a substance.

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Where else does this term appear?

The term “sublimation” can be found not only in physics and chemistry. It is also relevant in psychology. In this science, its interpretation is completely different: it is a way to “let off steam” by radically changing your type of activity.

The term is also used in the printing industry. In this field of activity, the definition changes: sublimation printing is one of the ways to transfer an image to any surface using paint that goes through a sublimation process. Simply put, it is one of the ways to print on any surface.

what is sublimation in physics

what is sublimation in physics

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Sublimation (sublimation) is the transition of a substance from a solid state directly to a gaseous state, bypassing the liquid state. Since during sublimation the specific volume of a substance changes and energy (heat of sublimation) is absorbed, sublimation is a first-order phase transition. The reverse process is desublimation. A well-known example of desublimation is the appearance of frost on branches during intensifying frost. Sublimation of iodine Sublimation is characteristic, for example, of elemental iodine I2, which under normal conditions does not have a liquid phase: black crystals with a blue tint immediately transform (sublimate) into gaseous molecular iodine (medical “iodine” is an alcohol solution). Sublimation of water Water lends itself well to sublimation, which has determined the widespread use of this process as one of the drying methods. During industrial sublimation, the initial body is first frozen and then placed in a vacuum chamber or a chamber filled with inert gases. Physically, the sublimation process continues until the concentration of water vapor in the chamber reaches a normal level for a given temperature, and therefore excess water vapor is constantly pumped out. Sublimation is used in the chemical industry, in particular, in the production of explosive substances obtained by precipitation from aqueous solutions. Application of sublimation in laboratory technology One of the methods for purifying solids is based on the sublimation effect.

Examples from life

Sasha feels resentment towards his colleagues who dumped all the work on him on Friday evening and went home. Instead of showing aggression, the next day he goes to the stadium and runs 10 kilometers.

Lisa loves Lesha, but instead of flirting with him, she enthusiastically paints pictures in the evenings, sighing heavily for her lover.

Lyosha also loves Lisa and therefore plays online games for days, directing his unspent sexual energy to the excitement of conquering the next kingdom.

Now you know what helps wet towels dry in winter, how freeze-drying is related to instant coffee, and why lovers carry a notebook with poems with them. This is all multifaceted sublimation.

Sublimation (physics)

At a certain temperature, one of the substances in the mixture sublimes at a higher rate than the other. The vapors of the substance to be cleaned condense on the cooled surface. The device used for this cleaning method is called a sublimator. Freeze drying Sublimation is also used in the food industry: for example, fruits after freeze drying weigh several times less and are restored in water. Freeze-dried products are significantly superior to dried products in nutritional value, since only water can be sublimated, and during thermal evaporation many useful substances are lost. Before sublimation of food products, rapid freezing is used (-100 to -190 degrees Celsius), which leads to the formation of small crystals that do not destroy cell membranes. ========================================== A simple sublimation machine. Cold water circulates in the condenser, depositing steam on itself. 1 Cold water inlet 2 Cold water outlet 3 Vacuum/gas line 4 Sublimation chamber 5 Sublimation product 6 Raw material 7 External heating

What is it for?

The process of sublimation, in addition to the fact that it is often found in nature, is widespread in everyday matters. This is due to convenience, as well as the low toxicity of things prone to this process. So, here are some examples of its use in everyday life:

In addition, sublimation is widely used in a variety of physical experiments. It is interesting to note that in chemistry the ability of substances to sublimate is often the fundamental reason for a qualitative reaction.