Types of diffusion biology. Start in science. Diffusion in nature

The article shows the role of diffuse processes in wounds sutured in the traditional way and in the way proposed by the authors. Theoretically substantiated the improvement of diffuse processes in wounds in the treatment of hardware method.

The problem of wound healing of various etiologies is one of the main branches of medicine that have not lost their significance at the present time. Treatment of this pathology in the shortest possible time without purulent complications is possible only with sufficient provision of medical institutions with modern effective wound healing drugs.

In the wound process, the local and general reaction of the body is directly dependent on the severity and characteristics of damage to tissues and organs. Local and general reactive processes during regeneration processes are in direct and inverse relationship being interdependent and mutually influencing. The basis of wound healing is the ability to control the course of the wound process. This problem is invariably in the field of view of scientists and practicing surgeons.

A large number of used methods of wound treatment belong to the pharmacological group. At the same time, a large number of technical devices for the treatment of wounds were proposed. However, the most common method of suturing wounds is a circular vertical suture.

The human skin, consisting of collagen proteins, is an ideal natural membrane that performs numerous metabolic and protective functions. These processes are mainly due to diffusion. Diffusion (from Latin diffusio - spreading, spreading), mutual penetration of contiguous substances into each other due to the movement of particles of a substance.

Diffusion is a process at the molecular level and is determined by the random nature of the movement of individual molecules. The diffusion rate is therefore proportional to the average velocity of the molecules. Diffusion occurs in the direction of decreasing concentration of the substance and leads to a uniform distribution of the substance over the entire volume it occupies (to equalization of the chemical potential of the substance).

The role of diffuse processes in the pathogenesis and treatment of the wound process is very large. So, for example, in skin transplantation, the thickness of the flaps plays a huge role in the healing of burn wounds, since it has a positive effect on diffuse processes between the graft and the wound surface.

However, the significance of diffuse processes in the wound is practically not studied. The edges of the wound are conductive systems in which diffuse processes should take place under normal conditions. This process is shown schematically in Figure 1.

The schematic drawing shows that the surgical wound (1), sutured with traditional circular vertical sutures according to the classification of Golikov A.N., has certain disadvantages. Surgical suture (2), which is a means for approaching the edges of the wound, provides complete ischemia (5) of tissues, which leads to the formation of "silent areas" for the passage of diffuse processes, which leads to deformation (4) of the diffusion vector (3). As a result, the traditionally used surgical suture leads to the artificial formation of tissue areas that are not involved in the regeneration processes. Moreover, in unfavorable cases, these "tissue defects" are the sources of the formation of foci of the infectious process. Because, in the end, the tissue, deprived of access to nutrients, oxygen, etc., becomes necrotic, which ends with the formation of a scar. Otherwise, necrotic tissue masses are a favorable breeding ground for pathogens.

The security document of the National Institute of Intellectual Property of the Republic of Kazakhstan No. 13864 dated 15.08.2007 was obtained for the hardware method. The main principle of the proposed method is the tight closing of the wound edges to each other using physical and mechanical techniques. A nylon fishing line of sufficient length is applied along the edge of the wound, creating a “ligature arc”, which is fixed with its ends to the ends of the apparatus of the author's design.

The author's apparatus in assembled form has the shape of a frame, in the form of a quadrangular parallelogram, the sides of which are rods, and the ends are movable bars located and fixed to the bars with two nuts at both ends of the pins, holes of the same diameter are drilled on the movable bars for the rods and fixing the threads ligatures (Fig. 2).

regeneration processes. The effectiveness of the apparatus method has been proven experimentally and clinically.

Thus, a rationale for the effectiveness of the proposed hardware method in comparison with traditional methods of suturing wounds has been theoretically proposed. This is due to an increase in pressure on the wound area, which (due to the design features of the device) leads to a local increase in the diffusion rate.

Literature

1. Golikov A.N. Healing of a granulating wound closed with sutures. - Moscow: 1951. - 160 p.
2. Waldorf H., Fewres J. Wound healing // Adv. Derm. - 1995. No. 10. - P. 77–96.
3. Abaturova E.K., Baimatov V.N., Batyrshina G.I. Influence of biostimulants on the wound process // Morphology. - 2002. - T. 121, No. 2–3. – S.6.
4. Kochnev O.S., Izmailov G.S. Methods for suturing wounds. - Kazan: 1992. - 160 p.
5. Kiselev S.I. The value of donor skin resources in the choice of rational surgical tactics in patients with deep burns: Abstract of the thesis. … Candidate of Medical Sciences. Ryazan, 1971. 17 p.

Zharalardy emdeu biology syndagy diffusion

Tuyin Makalada әdettegi әdіspen zhane maқala avtorlarymen ұsynylyp otyrғan apparatuses аdіstің zhalalardy emdeudegі diffusion processer turaly aitylgyn. Zharalarda diffusion of the processterdin apparatty adistin zhaksargany theory zhuzinde daleldip korsetildі.

DIFFUSION INBIOLOGYHealing

Abstract The article shows the role of diffuse processes in wounds sutured in the traditional way and the method proposed by the authors. The diffuse processes in wounds have been justified theoretically.

Esirkepov M.M., Nurmashev B.K., Mukanova U.A.

South Kazakhstan State Medical Academy, Shymkent

The text of the work is placed without images and formulas.
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Introduction

The relevance of the work. Diffusion is a fundamental phenomenon of nature. It underlies the transformations of matter and energy. Its manifestations take place at all levels of organization of natural systems on our planet, starting from the level of elementary particles, atoms and molecules, and ending with the geosphere. It is widely used in technology, in everyday life.

The essence of diffusion is the movement of particles of the medium, leading to the transfer of substances and the equalization of concentrations or to the establishment of an equilibrium distribution of particles of a given type in the medium. The diffusion of molecules and atoms is due to their thermal motion.

Diffusion is also a fundamental process that underlies the functioning of living systems at any level of organization, from the level of elementary particles (electronic diffusion) to the biospheric level (circulation of substances in the biosphere).

It plays a huge role in nature, in human life and in technology. Diffusion processes can have both positive and negative effects on the life of humans and animals. An example of a positive impact is the maintenance of a homogeneous composition of atmospheric air near the Earth's surface. Diffusion plays an important role in various fields of science and technology, in processes occurring in animate and inanimate nature. It influences the course of chemical reactions.

With the participation of diffusion or in violation and change of this process, negative phenomena can occur in nature and human life, such as extensive pollution of the environment by products of human technical progress.

Objective: To study the features of diffusion in gases, liquids and solids and to find out the use of diffusion by man and the manifestation of diffusion in nature, to consider the influence of diffusion processes on the ecological balance in nature and the influence of man on diffusion processes.

Essence of diffusion

Demonstrates diffusion in gases by spraying deodorant in the corner of the classroom. The spread of odor is explained by the movement of molecules. This movement is continuous and erratic. Colliding with the molecules of gases that make up the air, the deodorant molecules change the direction of their movement many times and, moving randomly, scatter throughout the room.

The process of penetration of particles (molecules, atoms, ions) of one substance between particles of another substance due to chaotic motion is called diffusion(from lat. diffusio - spreading, spreading, scattering). Thus, diffusion is the result of the chaotic movement of all particles of matter, of any mechanical action.

The movement of particles during diffusion is completely random, all directions of displacement are equally probable,

Since particles move in gases, liquids, and solids, diffusion is possible in these substances. Diffusion is the transfer of a substance due to the spontaneous alignment of an inhomogeneous concentration of atoms or molecules of various types. If portions of various gases are let into the vessel, then after a while all gases are uniformly mixed: the number of molecules of each type per unit volume of the vessel becomes constant, the concentration levels out. Diffusion is explained as follows. First, between the two bodies, the interface between the two media is clearly visible (Fig. 1a). Then, due to their movement, individual particles of substances located near the boundary exchange places.

The boundary between substances blurs (Fig. 1b). Having penetrated between the particles of another substance, the particles of the first begin to exchange places with the particles of the second, which are in ever deeper layers. The interface between substances becomes even more vague. Due to the continuous and random movement of particles, this process eventually leads to the fact that the solution in the vessel becomes homogeneous (Fig. 1c).

Fig.1. Explanation of the phenomenon of diffusion.

Diffusion in nature

With the help of diffusion, various gaseous substances spread in the air: for example, the smoke of a fire spreads over long distances.

The result of this phenomenon may be the equalization of the temperature in the room during ventilation. In the same way, air pollution occurs with harmful industrial products and vehicle exhaust gases. The natural combustible gas we use at home is colorless and odorless. In the event of a leak, it is impossible to notice it, therefore, at distribution stations, the gas is mixed with a special substance that has a sharp, unpleasant odor that is easily felt by a person.

Due to the phenomenon of diffusion, the lower layer of the atmosphere - the troposphere - consists of a mixture of gases: nitrogen, oxygen, carbon dioxide and water vapor. In the absence of diffusion, stratification would occur under the action of gravity: at the bottom there would be a layer of heavy carbon dioxide, above it - oxygen, above - nitrogen - inert gases.

In the sky, we also observe this phenomenon. Scattering clouds are also an example of diffusion, and how exactly F. Tyutchev said about this: “Clouds are melting in the sky ...”

In liquids, diffusion proceeds more slowly than in gases, but this process can be accelerated by heating. For example, in order to quickly pickle cucumbers, they are poured with hot brine. We know that sugar dissolves more slowly in cold tea than in hot tea.

In the summer, watching the ants, I always thought about how they, in the world that is huge for them, find out the way home. It turns out that this mystery is also opened by the phenomenon of diffusion. Ants mark their path with droplets of odorous liquid.

Thanks to diffusion, insects find their food. Butterflies, fluttering between plants, always find their way to a beautiful flower. The bees, having found a sweet object, storm it with their swarm.

And the plant grows, blooms for them, too, thanks to diffusion. After all, we say that a plant breathes and exhales air, drinks water, and receives various microadditives from the soil.

Carnivores also find their prey by diffusion. Sharks smell blood at a distance of several kilometers, as well as piranha fish.

The ecology of the environment is deteriorating due to emissions into the atmosphere, into the water of chemical and other harmful substances, and this all spreads and pollutes vast territories. But trees release oxygen and absorb carbon dioxide through diffusion.

The mixing of fresh water with salt water at the confluence of rivers into the sea is based on the principle of diffusion. The diffusion of solutions of various salts in the soil contributes to the normal nutrition of plants.

In all the examples given, we observe the mutual penetration of molecules of substances, i.e. diffusion. Many physiological processes in the human and animal body are based on this process: such as respiration, absorption, etc. In general, diffusion is of great importance in nature, but this phenomenon is also harmful in relation to environmental pollution.

2.1 Diffusion in the plant world

K.A. Timiryazev said: “Whether we talk about the nutrition of the root due to substances in the soil, whether we talk about the air nutrition of the leaves due to the atmosphere or the nutrition of one organ due to another, neighboring one, everywhere we will resort to the same reasons for explanation. : diffusion".

Indeed, the role of diffusion is very important in the plant kingdom. For example, the large development of the leaf crown of trees is explained by the fact that diffusion exchange through the surface of the leaves performs not only the function of respiration, but also partly of nutrition. Currently, foliar top dressing of fruit trees is widely practiced by spraying their crowns.

Diffuse processes play an important role in supplying natural water bodies and aquariums with oxygen. Oxygen enters the deeper layers of water in stagnant waters due to diffusion through their free surface. Therefore, any restrictions on the free surface of water are undesirable. So, for example, leaves or duckweed covering the surface of the water can completely stop the access of oxygen to the water and lead to the death of its inhabitants. For the same reason, narrow-necked vessels are unsuitable for use as an aquarium.

In the process of metabolism, when complex nutrients or their elements are broken down into simpler ones, the energy necessary for the life of the body is released.

2.2 The role of diffusion in plant nutrition.

The main role in diffusion processes in living organisms is played by cell membranes, which have selective permeability. The passage of substances through the membrane depends on:

Molecule sizes;

Electric charge;

From the presence and number of water molecules;

From the solubility of these particles in fats;

From the structure of the membrane.

There are two forms of diffusion: a) dialysis is the diffusion of solute molecules; b) osmosis is the diffusion of a solvent through a semi-permeable membrane. Soil solutions contain mineral salts and organic compounds. Water from the soil enters the plant by osmosis through the semi-permeable membranes of the root hairs. The concentration of water in the soil is higher than inside the root hairs, so there is diffusion from the zone with a higher concentration to the zone with a lower concentration. Then the concentration of water in these cells becomes higher than in the overlying ones - root pressure arises, causing an upward flow of juice through the roots and stem, and the loss of water by the leaves ensures further absorption of water.

Mineral substances enter the plant: a) by diffusion; b) sometimes by active transfer against the concentration gradient, accompanied by energy consumption. There are also turgor pressure is the pressure exerted by the contents of the cell on the cell wall. It is almost always lower than the osmotic pressure of the sap cell, because. outside is not pure water, but a saline solution. Turgor pressure value:

Preservation of the form of a plant organism;

Ensuring growth in young plant cells;

Preservation of plant elasticity (demonstration of cactus and aloe plants);

Shaping in the absence of reinforcing fabric (demonstration of a tomato);

Application of diffusion in medicine.

More than 30 years ago, the German doctor William Kolf used the "artificial kidney" apparatus. Since then, it has been used: for emergency chronic care for acute intoxication; to prepare patients with chronic renal failure for kidney transplantation; for long-term (10-15 years) life support of patients with chronic kidney disease.

The use of the device "artificial kidney" is becoming more of a therapeutic procedure, the device is used both in the clinic and at home. With the help of the device, the recipient was prepared for the world's first successful kidney transplantation, carried out in 1965 by Academician B.V. Petrovsky.

The device is a hemodialyzer in which the blood is in contact with a saline solution through a semi-permeable membrane. Due to the difference in osmotic pressures, ions and molecules of metabolic products (urea, uric acid), as well as various toxic substances to be removed from the body, pass through the membrane from the blood into the saline solution. The device is a system of flat channels separated by thin cellophane membranes, through which blood and dialysate slowly move in counter flows - a saline solution enriched with a CO 2 + O 2 gas mixture. The device is connected to the patient's circulatory system using catheters inserted into the into the dialysate) and the ulnar (exit) vein. Dialysis lasts 4-6 hours. This achieves blood purification from nitrogenous wastes in case of insufficient kidney function, i.e. blood chemistry is regulated.

Biology teacher: The following message will help you understand and understand the forms of diffusion, osmosis and dialysis.

Application of diffusion in technology and in everyday life

Diffusion finds wide application in industry and everyday life. Diffusion welding of metals is based on the phenomenon of diffusion. The method of diffusion welding without the use of solders, electrodes and fluxes connects metals, non-metals, metals and non-metals, plastics. The parts are placed in a closed welding chamber with a strong vacuum, squeezed and heated to 800 degrees. In this case, intense mutual diffusion of atoms occurs in the surface layers of the contacting materials. Diffusion welding is mainly used in the electronic and semiconductor industries, precision engineering.

A diffusion apparatus is used to extract soluble substances from solid ground material. Such apparatuses are mainly used in sugar beet production, where they are used to obtain sugar juice from beet chips heated together with water.

An essential role in the operation of nuclear reactors is played by neutron diffusion, that is, the propagation of neutrons in matter, accompanied by a multiple change in the direction and speed of their movement as a result of collisions with atomic nuclei. The diffusion of neutrons in a medium is similar to the diffusion of atoms and molecules in gases and obeys the same laws.

As a result of the diffusion of carriers in semiconductors, an electric current arises. The movement of charge carriers in semiconductors is due to the inhomogeneity of their concentration. To create, for example, a semiconductor diode, indium is melted into one of the surfaces of germanium. Due to the diffusion of indium atoms deep into the germanium single crystal, a p-n junction is formed in it, through which a significant current can flow with minimal resistance.

The phenomenon of diffusion is based on the process of metallization - covering the surface of an article with a layer of metal or alloy to impart physical, chemical and mechanical properties to it, different from the properties of the material being metallized. It is used to protect products from corrosion, wear, increase contact electrical conductivity, for decorative purposes, for example, carburizing is used to increase the hardness and heat resistance of steel parts. It consists in the fact that steel parts are placed in a box with graphite powder, which is installed in a thermal furnace. Due to diffusion, carbon atoms penetrate into the surface layer of the parts. The penetration depth depends on the temperature and the exposure time of the parts in the thermal furnace.

Human influence on the course of diffusion in nature.

Unfortunately, as a result of the development of human civilization, there is a negative impact on nature and the processes taking place in it. The diffusion process plays an important role in the pollution of rivers, seas and oceans. For example, you can be sure that detergents drained into sewers, for example, in Odessa, will end up off the coast of Turkey due to diffusion and existing currents. The annual discharge of industrial and domestic wastewater in the world is estimated at tens of trillions of tons. An example of the negative impact of man on the processes of diffusion in nature are large-scale accidents that occurred in the basins of different water bodies. As a result of this phenomenon, oil and products of its processing spread over the surface of the water and, as a result, diffusion processes are disturbed, for example: oxygen does not enter the water column, and fish die without oxygen.

Due to the phenomenon of diffusion, the air is polluted with waste from various factories, because of it, harmful human waste penetrates the soil, water, and then has a harmful effect on the life and functioning of animals and plants. The area of ​​land polluted by emissions from industrial enterprises, etc. is increasing. Over 2,000 hectares of land are occupied by industrial and domestic waste dumps. One of the currently difficult issues to solve is the issue of industrial waste disposal, including toxic ones.

An urgent problem is air pollution by exhaust gases, products of processing of harmful substances emitted into the atmosphere by various factories. Chimneys of enterprises emit carbon dioxide, nitrogen oxides and sulfur into the atmosphere. Currently, the total amount of gas emissions into the atmosphere exceeds 40 billion tons per year. An excess of carbon dioxide in the atmosphere is dangerous for the living world of the Earth, disrupts the carbon cycle in nature, and leads to the formation of acid rain. The diffusion process plays an important role in the pollution of rivers, seas and oceans. The annual discharge of industrial and domestic wastewater in the world is approximately 10 trillion tons.

Some medical studies have shown a relationship between the incidence of the respiratory system and the upper respiratory tract and the state of the air. There is a direct relationship between the indicator of the level of respiratory diseases and the volume of emissions of harmful substances into the atmosphere. These examples of diffusion have a detrimental effect on various processes occurring in nature.

Pollution of water bodies leads to the fact that life disappears in them, and the water used for drinking has to be purified, which is very expensive. In addition, chemical reactions occur in polluted water with the release of heat. The temperature of the water rises, while the oxygen content in the water decreases, which is bad for aquatic organisms. Due to rising water temperatures, many rivers now do not freeze in winter. To reduce the emission of harmful gases from industrial pipes, pipes of thermal power plants, special filters are installed. Such filters are installed, for example, at a thermal power plant in the Leninsky district of Chelyabinsk, but their installation is very expensive. To prevent pollution of water bodies, it is necessary to ensure that garbage, food waste, manure, and various chemicals are not thrown near the coast.

Considering global warming, it is important to investigate the change in diffusion rate depending on the increase in ambient temperature.

Experimental part.

I experience. Observation of the penetration of particles of one substance between the molecules of another substance .

Target : study the diffusion of solids and draw a conclusion about the rate of diffusion.

Devices and materials : gelatin, potassium permanganate, copper sulfate, Petria dish, tweezers, heating device.

:

Gelatin serves as a solid solution. In order to prepare the solution, it is necessary to dip 1 spoonful of gelatin in cold water for 2 hours so that the powder swells, then heat the mixture and dissolve the gelatin without boiling, then pour it into a Petria dish (Fig. 3). When the gelatin had cooled, in the middle, with a quick movement, a crystal of potassium permanganate was introduced into one glass with tweezers, and copper sulphate in the other. And now we can observe the result of diffusion.

Here we observed the penetration of particles of potassium permanganate and copper sulphate between gelatin molecules. After 24 hours, no diffusion of potassium permanganate was observed (Fig. 4), since potassium permanganate is a strong oxidizing agent.

Thus, diffusion in solids proceeds more slowly. If strong oxidizing agents enter the environment, they lead to its destruction.

II experience. Observation of the dissolution of gouache pieces in water, at a constant temperature (at t = 22 ° C)

They took a piece of orange gouache and a vessel with clean water at a temperature of 22 ° C. They put a piece of gouache in the vessel (Fig. 1) and began to observe what was happening. After 10 minutes, the water in the vessel begins to turn into the color of gouache (solid) (Fig. 2). Water is a good solvent. Under the action of water molecules, the bonds between the molecules of gouache solids are destroyed. 25 minutes have passed since the beginning of the experiment. The color of the water becomes more intense (Fig. 3). Water molecules penetrate between gouache molecules, breaking the forces of attraction. 45 minutes have passed since the beginning of the experiment (Fig. 4). Simultaneously with the forces of attraction between the molecules, repulsive forces begin to act and, as a result, the crystal lattice of a solid substance (gouache) is destroyed. The process of dissolving gouache is over. The duration of the experiment is 2 hours 50 minutes. The water was completely dyed in the color of gouache.

Thus, the phenomenon of diffusion is a long process, which results in the dissolution of solids.

W experience.The study of the dependence of the rate of diffusion on temperature and penetration into food.

Target : study how temperature affects the rate of diffusion.

Devices and materials : thermometers - 2 pcs, clock - 1 pc, glass - 1 pc, iodine, potatoes, magnetic stirrer.

Description of experience and results : they took a glass, put iodine in it and closed the glass with half-cut potatoes at t = 22 ° C. After 15 min from the beginning of the experiment, the diffusion process is not active. Started the heating process after 4 min. The diffusion process began, after 1 min, we see the penetration of iodine into the potato, after 2 min.

From this experience, it can be concluded that the rate of diffusion is affected by temperature: the higher the temperature, the higher the rate of diffusion, which negatively affects food.

Thus, the air is polluted with waste from various factories, vehicle exhaust gases penetrate food, and then have a harmful effect on the life and functioning of humans, animals and plants.

IV experience.The study of the dependence of the rate of diffusion of gaseous substances into water at a constant temperature

Target : to study the rate of diffusion of gaseous substances into water at a constant temperature and draw a conclusion about the rate of diffusion.

Devices and materials : thermometers - 1 pc, clock - 1 pc, flask - 1 pc, water, iodine.

Description of experience and results : water of the same mass and the same temperature (22 ° C) was poured into the flask, then vegetable oil (5 ml) was poured into another flask. Vegetable oil in our experience imitated oil. The flasks were covered with adhesive tape with iodine glued to it. The observation was taken after 45 minutes.

The water, covered with a film of vegetable oil, is very weakly colored, it can be judged that it is more difficult for oxygen molecules to penetrate into the water: fish and other aquatic inhabitants lack oxygen and may even die.

Conclusion : the presence of various substances on the water surface disrupts diffusion processes and can lead to undesirable environmental consequences.

Conclusion

We see how great is the importance of diffusion in inanimate nature, and the existence of living organisms would be impossible if this phenomenon did not exist. Unfortunately, we have to deal with the negative manifestation of this phenomenon, but there are many more positive factors and therefore we are talking about the great importance of diffusion in nature.

Nature makes extensive use of the possibilities inherent in the process of diffusion penetration, plays an important role in the absorption of nutrition and oxygenation of the blood. In the flames of the Sun, in the life and death of distant stars, in the air we breathe, everywhere we see the manifestation of the omnipotent and universal diffusion.

Thus, diffusion is of great importance in the life processes of humans, animals and plants. Due to diffusion, oxygen from the lungs penetrates into the human blood, and from the blood into tissues. But, unfortunately, as a result of their activities, people often have a negative impact on natural processes in nature.

Studying diffusion, its role in the ecological balance of nature and the factors influencing its course in nature, I came to the conclusion that it is necessary to draw public attention to environmental problems.

Literature

Alekseev S.V., Gruzdeva M.V., Muravyov A.G., Gushchina E.V. Workshop on ecology. M. AO MDS, 1996

Ilchenko V.R. Crossroads of physics, chemistry and biology. M: "Enlightenment", 1986

Kirillova I.G. A book for reading in physics. M. "Enlightenment", 1986

Peryshkin A.V. Physics textbook Grade 7. M. "Enlightenment", 2005

Prokhorov A.M. Physical Encyclopedic Dictionary. 1995

Ryzhenkov A.P. Physics. Person. Environment. M: Enlightenment, 1996

Chuyanov V.A. Encyclopedic Dictionary of a Young Physicist. 1999

Shakhmaev N.M. and others. Physics 7.M.: Mnemozina, 2007.

Encyclopedia for children.V.19. Ecology: In 33 volumes / Ch. ed. Volodin V. A. - M.: Avanta +, 2004 - 448 p.

Diffusion

An example of diffusion is the mixing of gases (for example, the spread of odors) or liquids (if you drop ink into water, the liquid will become uniformly colored after a while). Another example is connected with a solid body: the atoms of adjoining metals are mixed at the contact boundary. Particle diffusion plays an important role in plasma physics.

Usually, diffusion is understood as processes accompanied by the transfer of matter, however, sometimes other transfer processes are also called diffusion: thermal conductivity, viscous friction, etc.

The diffusion rate depends on many factors. So, in the case of a metal rod, thermal diffusion takes place very quickly. If the rod is made of synthetic material, thermal diffusion proceeds slowly. Diffusion of molecules in the general case proceeds even more slowly. For example, if a piece of sugar is lowered to the bottom of a glass of water and the water is not stirred, it will take several weeks before the solution becomes homogeneous. Even slower is the diffusion of one solid into another. For example, if copper is coated with gold, then diffusion of gold into copper will occur, but under normal conditions (room temperature and atmospheric pressure), the gold-bearing layer will reach a thickness of several microns only after several thousand years.

A quantitative description of diffusion processes was given by the German physiologist A. Fick ( English) in 1855

general description

All types of diffusion obey the same laws. The diffusion rate is proportional to the cross-sectional area of ​​the sample, as well as the difference in concentrations, temperatures or charges (in the case of relatively small values ​​of these parameters). Thus, heat will travel four times faster through a rod two centimeters in diameter than through a rod one centimeter in diameter. This heat will spread faster if the temperature difference per centimeter is 10°C instead of 5°C. The diffusion rate is also proportional to the parameter characterizing a specific material. In the case of thermal diffusion, this parameter is called thermal conductivity, in the case of a flow of electric charges - electrical conductivity. The amount of a substance that diffuses in a given time and the distance traveled by the diffusing substance are proportional to the square root of the diffusion time.

Diffusion is a process at the molecular level and is determined by the random nature of the movement of individual molecules. The diffusion rate is therefore proportional to the average velocity of the molecules. In the case of gases, the average speed of small molecules is greater, namely, it is inversely proportional to the square root of the mass of the molecule and increases with increasing temperature. Diffusion processes in solids at high temperatures often find practical application. For example, certain types of cathode ray tubes (CRTs) use metallic thorium diffused through metallic tungsten at 2000°C.

If in a mixture of gases the mass of one molecule is four times greater than the other, then such a molecule moves twice as slowly compared to its movement in a pure gas. Accordingly, its diffusion rate is also lower. This difference in diffusion rates between light and heavy molecules is used to separate substances with different molecular weights. An example is isotope separation. If a gas containing two isotopes is passed through a porous membrane, the lighter isotopes permeate the membrane faster than the heavier ones. For better separation, the process is carried out in several stages. This process has been widely used for the separation of uranium isotopes (separation of 235 U from the bulk of 238 U). Since this separation method is energy intensive, other, more economical separation methods have been developed. For example, the use of thermal diffusion in a gaseous medium is widely developed. A gas containing a mixture of isotopes is placed in a chamber in which a spatial temperature difference (gradient) is maintained. In this case, heavy isotopes are concentrated over time in the cold region.

Fick's equations

From the point of view of thermodynamics, the driving potential of any leveling process is the growth of entropy. At constant pressure and temperature, the role of such a potential is played by the chemical potential µ , causing the maintenance of the flow of matter. The flux of substance particles is proportional to the potential gradient

In most practical cases, the concentration is used instead of the chemical potential C. Direct Replacement µ on the C becomes incorrect in the case of high concentrations, since the chemical potential ceases to be related to the concentration according to the logarithmic law. If we do not consider such cases, then the above formula can be replaced by the following:

which shows that the flux density of matter J proportional to diffusion coefficient D[()] and the concentration gradient. This equation expresses Fick's first law. Fick's second law relates spatial and temporal changes in concentration (diffusion equation):

Diffusion coefficient D temperature dependent. In a number of cases, in a wide temperature range, this dependence is the Arrhenius equation.

An additional field applied parallel to the chemical potential gradient breaks the steady state. In this case, diffusion processes are described by the non-linear Fokker-Planck equation. Diffusion processes are of great importance in nature:

• Nutrition, respiration of animals and plants;
• The penetration of oxygen from the blood into human tissues.

Geometric description of the Fick equation

In the second Fick equation, on the left side is the rate of change of concentration over time, and on the right side of the equation is the second partial derivative, which expresses the spatial distribution of concentration, in particular, the convexity of the temperature distribution function projected onto the x-axis.

see also

• Surface diffusion is a process associated with the movement of particles occurring on the surface of a condensed body within the first surface layer of atoms (molecules) or over this layer.

Notes

Literature

• Bokshtein B.S. Atoms wander through the crystal. - M .: Nauka, 1984. - 208 p. - (Library "Quantum", Issue 28). - 150,000 copies.

Links

• Diffusion (video lesson, 7th grade program)
• Diffusion of impurity atoms on the surface of a single crystal

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See what "Diffusion" is in other dictionaries:

- [lat. diffusio distribution, spreading] physical, chemical. the penetration of molecules of one substance (gas, liquid, solid) into another upon their direct contact or through a porous partition. Dictionary of foreign words. Komlev N.G.,… … Dictionary of foreign words of the Russian language

Diffusion- is the penetration into the medium of particles of one substance of particles of another substance, which occurs as a result of thermal motion in the direction of decreasing the concentration of another substance. [Blum E.E. Dictionary of basic metallurgical terms. Yekaterinburg … Encyclopedia of terms, definitions and explanations of building materials

Modern Encyclopedia

- (from Latin diffusio spreading spreading, scattering), the movement of particles of the medium, leading to the transfer of matter and the alignment of concentrations or to the establishment of an equilibrium distribution of concentrations of particles of a given type in the medium. In the absence of… … Big Encyclopedic Dictionary

DIFFUSION, the movement of a substance in a mixture from an area of ​​high concentration to an area of ​​low concentration, caused by the random movement of individual atoms or molecules. Diffusion stops when the concentration gradient disappears. Speed… … Scientific and technical encyclopedic dictionary

diffusion- and, well. diffusion f., German. Diffusion lat. diffusio spreading, spreading. Mutual penetration of adjoining substances into each other due to the thermal movement of molecules and atoms. Diffusion of gases, liquids. BAS 2. || trans. They… … Historical Dictionary of Gallicisms of the Russian Language

Diffusion- (from the Latin diffusio distribution, spreading, scattering), the movement of particles of the medium, leading to the transfer of matter and the alignment of concentrations or the establishment of their equilibrium distribution. Diffusion is usually determined by thermal motion ... ... Illustrated Encyclopedic Dictionary

The movement of particles in the direction of decreasing their concentration, due to thermal motion. D. leads to the alignment of the concentrations of the diffusing substance and the uniform filling of the volume with particles. ... ... Geological Encyclopedia

In the school curriculum in the course of physics (approximately in the seventh grade), students learn that diffusion is a process that is the mutual penetration of particles of one substance between particles of another substance, as a result of which concentrations are equalized throughout the occupied volume. This is a rather difficult definition to understand. To understand what simple diffusion is, the law of diffusion, its equation, it is necessary to study in detail the materials on these issues. However, if a general idea is enough for a person, then the data below will help to obtain elementary knowledge.

Physical phenomenon - what is it

Due to the fact that many people confuse or do not know at all what a physical phenomenon is and how it differs from a chemical one, as well as what kind of phenomena diffusion belongs to, it is necessary to understand what a physical phenomenon is. So, as everyone knows, physics is an independent science belonging to the field of natural science, which studies the general natural laws about the structure and movement of matter, and also studies matter itself. Accordingly, a physical phenomenon is such a phenomenon, as a result of which no new substances are formed, but only a change in the structure of the substance occurs. The difference between a physical phenomenon and a chemical one lies precisely in the fact that no new substances are obtained as a result. Thus, diffusion is a physical phenomenon.

Definition of the term diffusion

As you know, there can be many formulations of a concept, but the general meaning should not change. And diffusion is no exception. The generalized definition is as follows: diffusion is a physical phenomenon, which is the mutual penetration of particles (molecules, atoms) of two or more substances to a uniform distribution over the entire volume occupied by these substances. As a result of diffusion, no new substances are formed, therefore it is precisely a physical phenomenon. Simple diffusion is called diffusion, as a result of which particles move from the region of highest concentration to the region of lower concentration, which is due to thermal (chaotic, Brownian) motion of particles. In other words, diffusion is a process of mixing particles of different substances, and the particles are distributed evenly throughout the volume. This is a very simplified definition, but the most understandable.

Types of diffusion

Diffusion can be fixed both when observing gaseous and liquid substances, and solid ones. Therefore, it includes several types:

• Quantum diffusion is the process of diffusion of particles or point defects (local disturbances in the crystal lattice of a substance), which is carried out in solids. Local violations are violations at a certain point in the crystal lattice.

• Colloidal - diffusion occurring throughout the entire volume of the colloidal system. A colloidal system is a medium in which particles, bubbles, drops of another medium, differing in aggregate state and composition from the first, are distributed. Such systems, as well as the processes occurring in them, are studied in detail in the course of colloid chemistry.
• Convective - the transfer of microparticles of one substance by macroparticles of the medium. A special branch of physics called hydrodynamics deals with the study of the motion of continuous media. From there you can get knowledge about the states of the flow.
• Turbulent diffusion is the process of transferring one substance to another, due to the turbulent movement of the second substance (typical for gases and liquids).

The statement is confirmed that diffusion can proceed both in gases and liquids, and in solids.

What is Fick's law?

The German scientist, physicist Fick, deduced a law showing the dependence of the particle flux density through a single area on a change in the concentration of a substance per unit length. This law is the law of diffusion. The law can be formulated as follows: the flow of particles, which is directed along the axis, is proportional to the derivative of the number of particles with respect to the variable plotted along the axis relative to which the direction of the flow of particles is determined. In other words, the flow of particles moving in the direction of the axis is proportional to the derivative of the number of particles with respect to the variable, which is plotted along the same axis as the flow. Fick's law allows you to describe the process of transfer of matter in time and space.

Diffusion equation

When flows are present in a substance, the substance itself is redistributed in space. In this regard, there are several equations that describe this redistribution process from a macroscopic point of view. The diffusion equation is differential. It follows from the general equation for the transfer of matter, which is also called the equation of continuity. In the presence of diffusion, Fick's law is used, which is described above. The equation has the following form:

dn/dt=(d/dx)*(D*(dn/dx)+q.

Diffusion methods

The diffusion method, or rather the method of its implementation in solid materials, has been widely used in recent years. This is due to the advantages of the method, one of which is the simplicity of the equipment used and the process itself. The essence of the method of diffusion from solid sources is the deposition of films doped with one or more elements on semiconductors. There are several other methods for implementing diffusion, in addition to the solid source method:

• in a closed volume (ampoule method). Minimal toxicity is an advantage of the method, but its high cost, due to the disposability of the ampoule, is a significant drawback;
• in an open volume (thermal diffusion). The possibility of using many elements due to high temperatures is excluded, as well as lateral diffusion are big disadvantages of this method;
• in a partially closed volume (box method). This is an intermediate method between the two described above.

In order to learn more about the methods and features of diffusion, it is necessary to study additional literature devoted specifically to these issues.