General concept
Sublimation in physics is the process of transition of a substance from a solid to a gaseous state, bypassing the liquid state.
In another way it is called sublimation of the substance. This process is accompanied by the absorption of energy (in physics this energy is called “heat of sublimation”). The process is very important and has wide application in experimental physics. You may be interested in: Here are fresh riddles about vitamins for the prevention of sore throat!
Desublimation, on the contrary, is the process of transition of a substance from a gaseous to a solid state. Another name for this process is “deposition”. It is completely the opposite of sublimation. During deposition, energy is released rather than absorbed, and in very large quantities. Desublimation is also very important, but it is much more difficult to give an example of its targeted use by a person, especially in everyday life.
Sublimation processes
One common example of the sublimation process is the disappearance of snow without melting under the influence of cold, dry wind . Examples of sublimation at room temperatures of naphthalene, camphor, benzoic acid, solid carbon dioxide, iodine, ammonia, etc. are also widely known. This explains the pungent odor characteristic of many solid organic compounds. Sublimation is possible for the entire range of pressures and temperatures of coexistence of solid and gaseous phases. This interval also covers low pressures. The temperature at which the saturated vapor pressure of a solid is equal to the external pressure is called the sublimation point .
The process of sublimation corresponds to the reverse process of desublimation , or ablimation , - the direct transition of a substance from a gaseous state to a solid.
The density and pressure of saturated vapor during sublimation, as well as during evaporation, depend on temperature. The pressure of a vapor that is in equilibrium with a solid is a function of temperature and increases with time.
Sublimation
By heating solids, we can observe the process of their melting and then the evaporation of the liquid. When the temperature decreases, the reverse process occurs. However, sometimes with an increase in the temperature of a crystalline substance, it does not melt, but immediately evaporates. An important parameter in this case is not only the temperature, but also the pressure above the surface of the solid.
A solid contains molecules that have sufficient energy to overcome the attraction exerted by other molecules. These “energetic” molecules can break away from the surface of a solid and end up in the surrounding space.
The process of transition of a solid state of a substance into the gaseous phase, without its transition into a liquid, is called sublimation or sublimation.
Sublimation occurs at a certain temperature and pressure and is accompanied by the absorption of heat. Sublimation is a first-order phase transition.
The sublimation process is accompanied by an increase in the internal energy of the system. In crystalline packing, particles oscillate around equilibrium positions. The distances between them correspond to the minimum interaction energy at a given body temperature. During the process of sublimation, the spatial lattice is destroyed, the distances between particles increase, this leads to an increase in the energy of interaction between them.
During sublimation, the energy of each molecule changes, therefore, the more molecules there are in the body, the greater the energy consumption that occurs during the phase transition.
$Q=e_0 N (1).$
$λ=e_0/m_0$ and
$ m=m_0 N (2),$
- $λ$ – specific heat of phase transition (sublimation);
- $ m_0$ is the mass of one molecule of a substance; m is the mass of the entire substance.
The distances between particles during sublimation become approximately ten times greater than in the solid state. Whereas when a substance melts, the distances between the molecules do not change very significantly relative to the distances in the crystalline body. Consequently, the specific heat of fusion is significantly less than the specific heat of sublimation.
As the pressure increases, the sublimation temperature increases.
Desublimation is the reverse process of sublimation. During desublimation, crystallization occurs from a gaseous state without the substance passing into the liquid phase. During desublimation, heat is released.
SUBLIMATION
SUBLIMATION (sublimation, from the Latin sublimo - I lift up), the transition of a substance from a solid state directly (without melting) to a gaseous state. Sublimation obeys the general laws of evaporation. The reverse process is the condensation of a substance from a gaseous state, bypassing the liquid state, directly into the solid state - called. desublimation. Sublimation and desublimation are phase transitions of the first order.
Sublimation-desublimation processes (SD processes) can occur without and with the participation of the so-called. p-residues - inert (not undergoing phase transitions) gaseous or solid components. SD processes with solvents are carried out at atm. or higher pressure, without p-solvents - in a vacuum.
In SD processes with solvents, an inert gaseous substance (carrier gas) serves to transfer vapors of sublimated (desublimable) substances, as well as to cool gas mixtures during desublimation. An inert solid substance is introduced into the system: as a carrier for transferring the desublimation-desublimate product (for example, during fractional sublimation purification of the substance, see below); to intensify heat supply; to ensure uniform induction or high-frequency heating of the starting material, etc.
Desublimation is carried out on solid surfaces or occurs in the volume of the gas phase with the release of solid matter in the form of aerosol particles.
Natural SD processes are known, for example: the formation of gas hydrates, the formation and change of comet nuclei, desublimation of water vapor in the atmosphere, sublimation of ice.
Mechanisms. Sublimation is an endothermic process, and desublimation is an exothermic process. In the case of sublimation when energy is supplied (convective
or contact heating, radiation heating, e.g. laser) an intermolecular rupture occurs. connections. Sublimir. in-va m.b. final products or sent for desublimation, before the cut they can be subjected to intermediate processing, for example. ad-sorbc. cleaning
During desublimation (the process of self-organization), van der Waals bonds arise between individual molecules of a substance with the release of energy, which is directly removed from the desublimate. its contact with a cooled solid surface, interaction. with additional refrigerant introduced, evaporation of liquid (for example, water) added to the gas mixture, and its expansion.
The gas phase most often forms an ideal mixture of components. The solid phase can form systems in which the components are completely mutually insoluble, unlimited mutually soluble, limited mutually soluble. The nature of solid systems is determined mainly by engineering design of SD processes.
Statics.
SD processes, like other processes with first-order phase transitions, are conveniently represented using a three-phase phase diagram (Fig. 1). In this diagram, sublimation. the process is depicted by dotted lines intersecting the curve c at a point below the triple point Tr with increasing temperature and constant pressure or with decreasing pressure and constant temperature.
Rice. 1. Phase diagram for sublimation-desublimation. processes: a. Kommersant c-curves of steam pressure resp. when melting a substance, above a liquid, above a solid phase, TP-triple point; p-pressure; T-abs. t-ra.
In the case of one-component systems, the equation for the curve c is the Clapeyron-Clausius equation for pressure per sat. vapor above the solid phase at the enthalpy of sublimation DHC = const and abs. t-re T:
where A is the constant, R is the gas constant.
For multicomponent systems, the equation for rp is similar in form to equation (1), but depends on the nature of the interaction. components.
During desublimation, the transition from a homogeneous system to a heterogeneous one begins with the formation of individual elements of a new phase - solid nuclei (clusters), which after reaching the critical point. sizes tend to grow unlimitedly. The energy of clusters increases with the number of molecules included in them, tending asymptotically to a limit equal to the heat of phase transition. Thermodynamically, the possibility of SD processes occurring is determined by the relation:
where Gibbs energy DG < 0; DS-change in entropy of the system. At equilibrium, DG = 0. With increasing temperature, the thermodynamic value increases. the likelihood of sublimation occurring. The change in DHC for molecules containing more than 5 atoms is 4-8 kJ/mol. For molecules with a mol. mass M100 change in entropy DS = 120-140, for M > 100 - from 140 to 160 kJ/(mol K).
Kinetics.
Sublimation is a multi-stage process, for which it is necessary to supplement. thermal energy. When it is supplied, particles of the substance migrate to the surface of the solid phase from the state with the maximum. bond strength into a state with lower strength, and then into the gas phase. At the same time, desublimation of particles occurs from it. At equilibrium, the number of particles desublimated on the surface differs from the number of particles striking the surface. The ratio of these flows is determined by the so-called. coefficient of condensation or sublimation a (Oa1). Max. speed of SD processes max. they are simply found when they are carried out in a vacuum according to the Hertz-Knudsen equation;
where pg is the vapor pressure of the substance in the gas phase.
The rates of sublimation and desublimation are determined primarily by the rate of destruction of crystals during sublimation and the rate of crystallization during desublimation, as well as the rates of mass transfer from the surface of the solid phase to the gas flow. As sublimation and desublimation proceed, the characteristics of the solid phase change (thickness and porosity of the layer, surface roughness, etc.) and accordingly. intensity of heat and mass transfer with the gas phase.
Hardware design and technological diagrams of SD processes.
When implementing them, it is necessary to ensure the input of the solid phase into the system and the supply of energy to it, the movement of steam in the gas phase, and the implementation of basic. purposes (eg, separation of components), removal of thermal energy during desublimation; separation of the product on a solid surface or in the volume of the gas phase, separation of the carrier gas from the product remaining in the form of vapor or aerosol; maintaining the necessary pressure and temperature in the system.
Equipment for carrying out SD processes includes heating and cooling systems, gas flow supply, vacuum, solid phase transportation and process control. Apparatuses for actual sublimation and desublimation are extremely diverse: tubular (without fins and with different fins), shelf-mounted (including with rotating shelves), rotary vortex, column with a fluidized bed, vacuum chambers, etc. The basis for calculating such devices is mat. models including equations for the transfer of mass, heat and momentum in the working volume for the vapor phase and aerosol particles, kinetic. dependencies for the destruction and growth of the solid phase, a description of changes in the porous structure of this phase and its surface roughness.
One of the important parameters of SD processes is the amount of heat supplied (removed). For sublimation, this parameter is determined by the heat of phase transition; in the case of desublimation, the required amount of gas cooling is first found according to the equation:
where f is the degree of capture; DDH—enthalpy of desublimation; rп, rг-density of steam and carrier gas; Cp is the heat capacity of the carrier gas; pp.in is the steam pressure at the entrance to the system, p is the total pressure in it.
Depending on the purpose of SD processes, different technologies are used. schemes for their implementation. Typical examples of cleaning schemes for decomp. in-in. Purification includes simple (single sublimation and desublimation) and fractional sublimation (multistage direct- and countercurrent, as well as zone; see Crystallization methods for separating mixtures): Simple sublimation can be vacuum (Fig. 2, a) or with a carrier gas, to The latter is removed from the system (Fig. 2, b) or recirculated in it (Fig. 2, c). During fractional sublimation, both gaseous and solid carriers can be recirculated (Fig. 2, d), which ensures a counterflow of phases into the sublimation. column. In this scheme, inert solid non-volatile particles are fed into a desublimator-reflux condenser above the sublimator. column at a temperature below the steam desublimation point; here the particles are covered with a thin film of solid desublimate, which creates a reverse flow for the strengthening part of the sublimate. columns. More volatile components are concentrated at the top. The less volatile parts are at the bottom. The counterflow of the vapor phase is carried out under the influence of a temperature gradient (with an increase in temperature from top to bottom) or by introduction into the bottom. part of a column of recirculating inert carrier gas that creates an upward flow of steam.
Rice. 2. Sublimation schemes. purification in-in: a-simple vacuum sublimation; b-sublimation with an inert carrier gas; c-sublimation with recycle of carrier gas; g-fractional sublimation with recycles of carrier gas and solid carrier; 1-sublimator; 2-desublimator-dephlegmator; 3-remaining amount; 4-heat. circuit; 5-food; 6-pairs; 7-valve (for melt sublimation - quasi-sublimation); 8-cooling circuit; 9-mixture of steam and carrier gas; 10, 11, 13 - heated carrier gas and its recycle; 12-mixture of carrier gas and non-process-sublimir. product; 14-evaporator; 15-reverse flow desublimator · 16-solid carrier recycle; 17, 18-strengthening and exhaustive sections.
Application of SD processes.
The advantages of these processes include: a relatively high equilibrium coefficient. divisions; the possibility, in the case of using gas mixtures, to exclude the evaporation of solvents (as opposed to absorption and rectification); lower working temperature (than with distillation); ease of control of the coating process; the ability to obtain target products immediately in commercial form (dispersed particles, single crystals, solid films), high-purity materials, compositions of non-fusion components (whiskers of non-metals in a metal matrix), fine and ultrafine powders of metals and their oxides. Thanks to these and other advantages, SD processes have become widespread (especially since the 70s) in various fields. fields of science and technology.
Sublimation Inorganic is subjected to purification. (HfCl4, A1C13, I2, a number of metals) and org. (anthraquinone, benzoic and salicylic acids, cyanuric chloride, phthalocyanines) substances, materials for microelectronics. In cryogenic technology, SD processes are used to purify gas mixtures (see Air separation). To sublimation Purification also includes the separation of uranium isotopes.
SD processes are used to isolate target products from steam-air mixtures (for example, phthalic and maleic anhydrides), to obtain new substances (technical carbon, diamonds in the form of single crystals or films, etc.).
Sublimation drying (freeze drying) is used in the production of nylon, lavsan and polyethylene; for purification of Sb2O3, CaF2, ZnS, camphor, pyrogallol, salicylic acid, etc.; when receiving antibiotics, food. products, honey drugs (blood plasma, blood substitutes, etc.).
SD processes are used for layer-by-layer analysis of chemicals. composition of solid systems (using the laser evaporation method); for applying protective coatings to microspheres of nuclear fuel, on decomposed surfaces. in-in during manufacturing it is sensitive. sensors (sensors) for the composition and quality of gases, on the surface of carbon fibers and products made from them, as well as on metal. surfaces (for example, chrome plating); in semiconductor and superconductor technology; in the manufacture of light-emitting diodes, optical. optical fibers, etc. in optoelectronics; for recording information on laser optical devices. disks; when creating integrated circuits in microelectronics; for thermal protection of supersonic devices (see Ablative materials); when creating gas-dynamic. flows (processes occurring during the combustion of mixed solid rocket fuels, etc.); for thermal transfer printing (i.e., obtaining prints by transferring dye when heated from a printing plate to fabric, paper, construction and other materials). This method is based, in particular, on the use of video printers to obtain high-quality images. color copies on film media. Electric signals entering the printer from a video system (for example, a display) are supplied to the thermal head, the point elements heat the layer of decomposition dyes applied to the polymer roll film. colors. The dyes are sequentially sublimated (in an amount proportional to the amount of energy supplied to each element of the thermal head) and transferred in the gas phase to the base. image carrier. The method provides the most. the highest image quality among all printers, allowing you to reproduce St. 16 million color shades.
SD processes also occur during gas-phase polymerization, chemical transport reactions, and chemical vapor deposition. When describing these and other processes accompanied by chemical transformations, the literature sometimes uses the terms “chem. sublimation" and "chem. desublimation."
Lit.: Guigo E.I., Zhuravskaya N.K., Kaukhcheshvili E.I., Freeze drying in the food industry, 2nd ed., M., 1972; Evdokimov V.I., Chemical sublimation, M., 1984; Processes of sublimation and desublimation in chemical technology. Overview information, c. 9, M., 1985; Gorelik A.G., Amitin A.V., Desublimation in the chemical industry, M., 1986; Emyashev A.V., Gas-phase metallurgy of refractory compounds, M., 1987; Golovashkin A.I., “J. All chem. about-va them. D. I. Mendeleev”, 1989, v. 34, no. 4, p. 481-92. A. G. Gorelik.
Process description
Almost anything can serve as catalysts for sublimation in physics. Sometimes substances sublimate (that’s what this process is called in physics) when they reach a certain temperature. As a rule, we are talking about temperatures above average, but there are some exceptions when substances “expand” at negative values.
Sometimes oxygen can be a catalyst for this process. In such cases, the substance will change into a gaseous substance upon contact with air. By the way, this technique is often used by directors in science fiction films. Great, isn't it?!
For desublimation, the catalysts are exactly the same, but you need to catch one pattern: all parameters, with the exception of some special chemical reactions, will have a negative sign. That is, if during sublimation the bulk of the processes occur at positive temperatures, then during deposition, on the contrary, low ones will appear.
It is also worth noting that the transition occurs sequentially. Each period of time has its own transition.
You may be interested in:Radical substitution: description of the reaction, features, example
Many scientists even divide it into stages, but this need not be done. Let’s apply this to distillation and to its reverse process. This is what allows physicists to control the process and use it even in everyday life.
Crystal-gas transition diagram
$p=BT^{frac{3}{2}}a^{-frac{alpha{}w_0}{kT}} (3),$ where:
- $w_0$ – sublimation energy;
- $B$ is a constant characterizing the substance.
Here, point $B (T=Θ)$ located on the graph (Fig. 1) corresponds to a two-phase state - saturated vapor located above the crystalline substance. The steam is in a state of dynamic equilibrium with the solid phase.
Figure 1. Graph. Author24 - online exchange of student work
As the temperature increases, the crystal becomes a gas. An increase in pressure causes the gas to desublimate and enter the solid phase. The crystal-gas phase transition diagram is similar to the liquid-gas transition diagram. Points below and to the right of the curve (which correspond to lower pressure and higher temperature) indicate that the substance is in the gas state.
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Sublimation (sublimation)
Details Category:
SUBLIMATION
, sublimation, the transition of a solid into a vapor state and back (from vapor to solid), bypassing the liquid phase. Sublimation is characteristic only of such solid “volatile” bodies, the vapors of which have significant pressure even at a temperature below the boiling point of these bodies. In technology, sublimation is used to clean solids from impurities and contaminants. In view of the fact that high temperature often (especially in the case of complex organic compounds) causes decomposition of the product, tarring and significant loss, the use of a relatively low temperature during sublimation preserves the product and increases its yield; to lower the temperature even further, the sublimation process is usually carried out under reduced pressure and, to speed up the process, often in an atmosphere of some indifferent gas, for example, nitrogen. The process of sublimation itself consists of heating the sublimated body to a temperature at which its vapors begin to be released; from this point on, maintain a constant temperature throughout the process; the released vapors are cooled, and they turn back into a solid product, but already cleared of impurities. Maintaining a constant temperature throughout the entire process is a very important condition for sublimation, since temperature fluctuations have a detrimental effect on the process: lowering it slows down sublimation, and increasing it often leads to decomposition of the product.
Therefore, heating, with very rare exceptions, is carried out not over bare fire, but with the help of some intermediate body (heat transmitter), which makes it easier to regulate the temperature; Such heat transmitters are bodies that do not change from an increase in temperature: sand, oil, heated air, low-melting alloys, cast iron shavings, a concentrated solution of magnesium chloride. In some cases, heating is carried out with steam. Single sublimation does not always immediately give a sufficiently pure product; in such cases they resort to secondary and third V.; each subsequent sublimation is carried out under different temperature conditions and often using other inert gases; That. fractional, or fractionated, sublimation is carried out, similar to the fractionated distillation of liquids. Fractional sublimation achieves a faster and more thorough separation of a mixture of solids.
The main parts of the sublimation apparatus are: 1) a cube in which the raw product is heated and converted into a vapor state, and 2) a chamber in which the vapor is cooled and converted into a solid. The solid mass loaded into the cube is heated unevenly: the particles adjacent to the heating surface of the cube are subject to the most intense heating, while the rest are heated relatively weakly, and, due to the fact that the solid mass b. h is a poor conductor of heat; uneven heating of the entire mass occurs, which is also associated with significant heat consumption. To avoid this, it is necessary to place the solid substance in a low layer in the cube; the cube is equipped with a stirrer, etc. With continuous stirring, a thin layer of the substance is heated quite evenly. The volume of the chamber significantly exceeds the volume of the cube. To speed up the process of turning steam into a solid, they resort to artificial cooling of the vapor by spraying the chamber with water or lowering its temperature with cooled salt brine or cooled air; The method of cooling depends on the ease with which condensation of products from vapor occurs.
The design of the apparatus depends on the physical and chemical properties of the sublimated body and on the ease with which this body undergoes decomposition, but regardless of this, all types of apparatus used in sublimation can be divided into two large groups: apparatus operating without reduced pressure (old type) , and devices operating under reduced pressure (with vacuum). The latter have currently acquired the greatest importance, because they require less time to purify the product and give a greater yield. In the past, the sublimation of salicylic acid was carried out in cylindrical boilers with a hemispherical bottom, lined with lead, and without a stirrer; as a result, the substance sintered into a thick lump that conducts heat poorly; while the upper parts of this lump did not have time to warm up to the required temperature, the lower parts overheated and decomposed, thereby reducing the yield of the product. The sublimation cube was connected to the cooling chamber by a series of narrow tubes, not insulated on the outside, which caused premature cooling of the vapors in these tubes, the release of solid matter and clogging of the tubes. The chamber itself was small in volume and had a vertical rather than horizontal position. As a result, the products of vapor condensation during cooling were layered on top of each other and did not form clearly visible crystals; the vertical position and insufficient dimensions of the chamber did not provide sufficient circulation of vapors inside the chamber for cooling; as a result, complete condensation was not achieved.
A modern apparatus for the sublimation of salicylic acid (Fig. 1) consists of a cube in
with a flat bottom, equipped with a stirrer
driven
by a transmission;
in the lid of this cube (also flat to prevent vortex movements of rising vapors) a hole is made, surrounded by a funnel (hole )
, through which the substance undergoing sublimation is loaded;
The bottom of the cube is surrounded by a metal jacket, which is filled with a substance that serves as a heat transmitter, so that the bottom of the cube does not come into direct contact with the flame anywhere. An inert gas is admitted into the cube through an annular tube r
.
To monitor and regulate the sublimation process, control instruments are placed in this ring tube: a thermometer to determine the temperature of the cube and a vacuum gauge to determine the degree of vacuum; A wide pipe leads from the cube into chamber d
, which has the shape of a horizontally elongated cylinder.
On the side of the chamber lying opposite the pipe connecting it to the cube, there is a door e
through which purified salicylic acid is removed from the chamber.
The side surface of the chamber is equipped with two square hermetically sealed windows for
monitoring the progress of condensation. Apparatuses for the sublimation of benzoic acid and camphor are constructed similarly. When purifying naphthalene, additional heating of the raw product with superheated water steam is used. Sulfur is purified in two ways: distillation (to obtain sulfur in pieces - cutting sulfur) and sublimation (to obtain sulfur in the form of dust - sulfur color). In practice, usually both cleaning methods are carried out together in the same apparatus; By adjusting the temperature of the process, they direct it towards distillation or sublimation as desired. Lumpy, unrefined sulfur is loaded into a cylindrical boiler heated by a naked fire, where the sulfur melts, heavy impurities settle to the bottom, and liquid sulfur flows through a pipe into a cast-iron horizontally located retort, equipped with its own firebox.
At a temperature not exceeding 144°, liquid sulfur evaporates; the vapor passes through the pipe from the retort into the chamber, where it cools and settles along the walls in the form of a sulfur color. The sulfur deposited on the walls is swept away several times during the process. If the temperature is raised above 144°, then the sulfur collects at the bottom of the chamber in liquid form and flows through the holes into the molds, from where, after cooling, the cutting sulfur is extracted. To purify ammonium chloride, sublimation is also used. The raw, unrefined mass is loaded into an iron cauldron with a flat bottom; the boiler (cube) is lined with refractory bricks from the bottom and sides, and the top is covered with a slightly convex lid made of iron or lead; the boiler is heated with bare fire. The moisture contained in the crude ammonium chloride is removed first, for which purpose, at the beginning of sublimation, a hole is opened in the lid of the cube. When all the water has evaporated and the first vapors of ammonium chloride appear, close the hole and continue heating. Be careful not to heat too much as this may cause organic matter to char and contaminate the product. The sublimation of ammonium chloride takes a long time: a load of half a ton is sublimated within five days. At the end of the process, remove the lid on which sublimated ammonium chloride has been deposited in a layer about 10 cm thick, and remove the pure product.
The sublimation of iodine presents some features. Unpurified iodine contains 10-25% impurities and water. To purify iodine, cast iron cauldrons of relatively small capacity with a lead lid are used; several such boilers communicate with one ceramic chamber; Ceramic cauldrons with polished lids are more often used; These boilers are heated in a sand bath. The load of each boiler is relatively small - about 10 kg. When heated, iodine sublimes and collects on the lid of the boiler in the form of leaves, which are cleaned from the lids from time to time.
Let us also point out the purification of white arsenic. Sublimation is carried out in an apparatus schematically shown in Fig. 2; white arsenic is loaded into a cast iron boiler
, the capacity of which is designed for 150 kg of crude arsenic anhydride.
The boiler is
equipped with a high, narrow cap
made
of sheet iron and is heated directly in the flame of a coal firebox.
Upon reaching the sublimation temperature, arsenic begins to sublimate and is deposited on the iron cap in the form of a transparent vitreous body - arsenic glass; the other part of the vapor passes through pipe b
into chamber
c
, where it is deposited on the walls in the form of a powder - purified arsenic anhydride.
Source: Martens. Technical encyclopedia. Volume 4 - 1928
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Examples
There are many examples of sublimation in physics, but there are also quite a lot of examples of the reverse process. Both categories are worth considering.
- Dry ice. This is probably the most common example of the process. Surely everyone has seen or held it in their hands at least once. At one time, dry ice was an extremely popular subject for filming videos on YouTube. Almost every person has seen at least one such video. It is worth noting that ice is used not only for entertainment purposes. It also has quite wide application in everyday life.
- Drying clothes in the cold. Absolutely every housewife hangs out her laundry in the cold in winter. It would seem that it should return frozen, but it returns completely dry. This is due to the fact that sublimation of water molecules has occurred. This is the most obvious example of the use of sublimation in physics.
- Frost. This is the most obvious example of desublimation in nature, which absolutely everyone has associated with. The process occurs when there is an extremely sharp cooling and the dew point passes too quickly. This phenomenon is widespread. You can see frost in late autumn and winter. It is most clearly visible in October-November, when there is still very little snow.
- Pattern on the windows in winter. Yes, it turns out that it is desublimation that creates our New Year's atmosphere. Intricate patterns arise due to the huge difference between indoor and outdoor temperatures.
Sublimation
A simple sublimation machine. The substance to be purified condenses from the gas phase on a “finger” refrigerator cooled by water. 1
Cold water inlet
2
Cold water outlet
3
Vacuum/gas line
4
Sublimation chamber
5
Sublimation product
6
Raw material
7
External heating
In industry, sublimation and desublimation are used for the separation of substances from gas streams (for example, phthalic anhydride, uranium hexafluoride), purification of substances, freeze drying (for example, food products), thermal protection of aircraft at supersonic flight speeds, application of protective and functional coatings in manufacturing devices, etc.[1]
Application of sublimation in laboratory technology
One of the methods for purifying solids is based on the sublimation effect. 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
Main article: Lyophilization
Freeze drying
(
otherwise
lyophilization; freeze drying) (
eng.
freeze drying
or
lyophilization) is the process of removing solvent from frozen solutions, gels, suspensions and biological objects, based on the sublimation of a solidified solvent (ice) without the formation of macroquantities of the liquid phase.
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.
Sublimation is also used in the food industry: for example, freeze-dried coffee is obtained from frozen coffee extract through vacuum dehydration. After sublimation, fruits 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.
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.
