REBINDER Petr Aleksandrovich (03.H.1898-12.VII.1972), Soviet physicist and chemist, academician of the Academy of Sciences of the USSR since 1946 (corresponding member since 1933), was born in St. Petersburg. Graduated from the Physics and Mathematics Faculty of Moscow University (1924). In 1922-1932. worked at the Institute of Physics and Biophysics of the Academy of Sciences of the USSR and at the same time (in 1923-1941) - at the Moscow State Pedagogical Institute. Liebknecht (since 1923 - professor), since 1935 - head of the department of dispersed systems at the Colloid-Electrochemical Institute (since 1945 - the Institute of Physical Chemistry) of the USSR Academy of Sciences, since 1942 - head of the Department of Colloid Chemistry in Moscow university.

Rebinder's works are devoted to the physical chemistry of dispersed systems and surface phenomena. In 1928, the scientist discovered the phenomenon of a decrease in the strength of solids due to the reversible physicochemical effect of the environment on them (the Rebinder effect) and in the 1930-1940s. developed ways to facilitate the handling of very hard and difficult materials.

He discovered the electrocapillary effect of plasticization of metal single crystals in the process of creep during the polarization of their surface in electrolyte solutions, investigated the features of aqueous solutions of surfactants, the effect of adsorption layers on the properties of dispersed systems, identified (1935-1940) the main patterns of formation and stabilization of foams and emulsions, as well as the process of phase inversion in emulsions.

The scientist has established that the washing action includes a complex set of colloidal-chemical processes. Rebinder studied the processes of formation and structure of micelles of surfactants, developed the concept of a thermodynamically stable micelle of soaps with a lyophobic inner core in a lyophilic medium. The scientist selected and substantiated the optimal parameters for characterizing the rheological properties of dispersed systems and proposed methods for their determination.

In 1956, the scientist discovered the phenomenon of an adsorptive decrease in the strength of metals under the influence of metal melts. In the 1950s. scientists created a new field of science - physical and chemical mechanics. As Rebinder himself wrote: “The ultimate task of physicochemical mechanics is to develop scientific foundations for obtaining solids and systems with given structure and mechanical properties. Consequently, the task of this area is to create an optimally directed technology for the production and processing of essentially all building and structural materials of modern technology - concretes, metals and alloys, especially heat-resistant, ceramics and cermets, rubbers, plastics, lubricants. "

Since 1958, Rebinder has been the chairman of the Scientific Council of the USSR Academy of Sciences on the problems of physical and chemical mechanics and colloidal chemistry, then (since 1967) the chairman of the USSR National Committee at the International Committee on Surfactants. From 1968 to 1972 he was editor-in-chief of the Colloid Journal. The scientist was awarded two Orders of Lenin, had the title of Hero of Socialist Labor (1968), laureate of the USSR State Prize (1942).

Rebinder effect, the effect of the adsorptive decrease in the strength of solids, facilitating the deformation and destruction of solids due to the reversible physicochemical action of the environment. Discovered by P. A. Rebinder (1928) in the study of the mechanical properties of crystals of calcite and rock salt. It is possible when a solid body in a stressed state comes into contact with a liquid (or gaseous) adsorption-active medium. The Rebinder effect is very universal - it is observed in solid metals, ionic, covalent and molecular mono- and polycrystalline solids, glasses and polymers, partially crystallized and amorphous, porous and solid. The main condition for the manifestation of the Rebinder effect is the related nature of the contacting phases (solid and medium) in terms of chemical composition and structure. The form and degree of manifestation of the effect depend on the intensity of interatomic (intermolecular) interactions of the contacting phases, the magnitude and type of stresses (tensile stresses are required), the rate of deformation, and temperature. An essential role is played by the real structure of the body - the presence of dislocations, cracks, foreign inclusions, etc. The characteristic form of the Rebinder effect is a multiple drop in strength, an increase in the fragility of a solid, and a decrease in its durability. So, a zinc plate moistened with mercury does not bend under load, but breaks down brittle. Another form of manifestation is the plasticizing effect of the environment on solid materials, for example, water on gypsum, organic surfactants on metals, etc. The thermodynamic Rebinder effect is due to a decrease in the work of forming a new surface during deformation as a result of a decrease in the free surface energy of a solid under the influence of the environment ... The molecular nature of the effect is to facilitate the breaking and rearrangement of intermolecular (interatomic, ionic) bonds in a solid in the presence of adsorption-active and, at the same time, sufficiently mobile foreign molecules (atoms, ions).

The most important areas of technical application are the facilitation and improvement of the mechanical processing of various (especially highly hard and difficult to machine) materials, the regulation of friction and wear processes with the use of lubricants, the effective production of crushed (powdery) materials, the production of solids and materials with a given dispersed structure and the required combination of mechanical and other properties by disaggregating and subsequent compaction without internal stresses. An adsorption-active environment can also cause significant harm, for example, reducing the strength and durability of machine parts and materials under operating conditions. Elimination of the factors contributing to the manifestation of the Rebinder effect, in these cases, allows you to protect materials from unwanted environmental influences.

Even the most durable bodies have a huge number of defects, which weaken their resistance to load and make them less durable in comparison with what theory predicts. When a solid is mechanically destroyed, the process begins from the place where microdefects are located. An increase in the load leads to the development of a microcrack at the site of the defect. However, removing the load leads to the restoration of the original structure: the width of the microcrack is often insufficient to completely overcome the forces of intermolecular (interatomic) interaction. Reducing the load leads to the "contraction" of the microcrack, the forces of intermolecular interaction are restored almost completely, the crack disappears. The point is also that the formation of a crack is the formation of a new surface of a solid, and such a process requires an expenditure of energy equal to the surface tension energy multiplied by the area of \u200b\u200bthis surface. Reducing the load leads to the "contraction" of cracks, since the system tends to reduce the energy stored in it. Consequently, for the successful destruction of a solid, it is necessary to cover the resulting surface with a special substance called a surfactant, which will reduce the work of overcoming molecular forces during the formation of a new surface. Surfactants penetrate microcracks, cover their surfaces with a layer only one molecule thick (which makes it possible to use very small amounts of additives of these substances), preventing the “collapse” process, preventing the resumption of molecular interaction.

Surfactants, under certain conditions, facilitate the comminution of solids. Very fine (down to the size of colloidal particles) grinding of solids is generally impossible to carry out without the addition of surfactants.

Now it remains to remember that the destruction of a solid (i.e., the formation of new microcracks) begins exactly from the place where the structural defect of this body is located. In addition, the added surfactant is adsorbed mainly at the locations of defects - thus facilitating its adsorption on the walls of future microcracks. Here are the words of Academician Rebinder: “Part separation occurs precisely at these weak points [location of defects], and, therefore, the fine particles of the body formed during grinding no longer contain these most dangerous defects. More precisely, the smaller its size, the smaller the probability of meeting a dangerous weak point.

If, grinding a real solid of any nature, we reach particles whose dimensions are approximately the same as the distances between the most dangerous defects, then such particles will almost certainly not contain dangerous structural defects, they will become much stronger than large samples of the same the body itself. Consequently, one has only to grind a solid body into small enough pieces, and these pieces of the same nature, of the same composition will be the most durable, almost ideally strong. "

Then these homogeneous, defect-free particles must be combined, made of them a solid (high-strength) body of the required size and shape, make the particles tightly packed and very firmly unite with each other. The resulting machine part or construction part must be much stronger than the original material prior to grinding. Naturally, not as strong as a separate particle, since new defects will appear at the points of association. However, if the particle combining process is carried out skillfully, the strength of the starting material will be surpassed. This requires particularly tight packing of small particles so that intermolecular forces reappear between them. Typically this is done by compressing the particles by pressing and heating. The fine-grained aggregate obtained by pressing is heated without bringing it to melting. As the temperature rises, the amplitude of thermal vibrations of molecules (atoms) in the crystal lattice increases. At the points of contact, the vibrating molecules of two neighboring particles approach and even mix. The adhesion forces increase, the particles contract, leaving practically no voids and pores, the defects of the contact points disappear.

In some cases, the particles can be glued or soldered together. In this case, the process must be carried out in such a mode that the layers of glue or solder do not contain defects.

A fundamental improvement in the process of grinding solids, based on the practical application of the Rebinder effect, has proved to be very useful for many industries. Grinding processes have accelerated significantly, while energy consumption has significantly decreased. Fine grinding made it possible to carry out many technological processes at lower temperatures and pressures. As a result, more high-quality materials were obtained: concretes, ceramic and metal-ceramic products, dyes, pencil masses, pigments, fillers and much more. Facilitates the machining of refractory and heat-resistant steels.

Here is how he himself describes the method of applying the Rebinder effect: “Building parts made of cement concrete can be reliably combined into a monolithic structure by gluing with a vibrocolloid cement glue ... This glue is a mixture of finely ground cement (part of which can be replaced with finely ground sand) with an extremely small amount of water and the addition of a surfactant. The mixture is liquefied by extreme vibration during application to the glued surfaces in the form of a thin layer. After fast hardening, the layer of adhesive becomes the most durable place in the structure. "

The use of Academician Rebinder's ideas regarding the facilitation of the process of grinding solid bodies is of great practical importance, for example, for the development of a method for reducing the strength of minerals in order to increase the efficiency of drilling in hard rocks.

Decrease in the strength of metals under the influence of metal melts.In 1956, Rebinder discovered the phenomenon of a decrease in the strength of metals under the influence of metal melts. It was shown that the largest decrease in the surface energy of a solid (metal) to almost zero can be caused by molten media that are close to a solid in molecular nature. Thus, the tensile strength of zinc single crystals was reduced by tens of times when a layer of liquid tin metal with a thickness of 1 micron or less was applied to their surface. Similar effects for refractory and heat-resistant alloys are observed under the action of liquid low-melting metals.

The discovered phenomenon turned out to be very important for improving the methods of metal forming. This process is impossible without the use of lubricants. For materials of new technology - refractory and heat-resistant alloys - processing is especially greatly facilitated when using active lubricants that soften thin surface layers of metal (which, in fact, occurs under the action of small amounts of metal melts). In this case, the metal, as it were, lubricates itself - the harmful excess deformation that occurs during processing, which causes the so-called work hardening, is eliminated - an increase in strength interfering with processing. New possibilities for metal processing by pressure at normal and elevated temperatures are opening up: the quality of products increases, the wear of the processing tool decreases, and the energy consumption for processing decreases.

Instead of converting expensive metal into chips in the process of manufacturing a product by cutting, you can apply plastic reshaping: pressure treatment without metal loss. At the same time, the quality of the products is also improved.

A sharp decrease in the strength of the surface layer of metals plays a significant role in improving the operation of friction units. An automatically operating mechanism of wear control arises: if there are random irregularities on the rubbing surfaces (burrs, scratches, etc.), a high local pressure develops in the places of their dislocation, causing the surface flow of metals, significantly facilitated by the action of adsorbed melts (the surface layer wetted by the melt metal loses strength). Rubbing surfaces are easy to grind or polish. The introduced "lubrication" causes an accelerated "wear" of irregularities, the speed of running-in (running-in) machines increases.

Active impurity melts can be used as modifiers of the crystallization process. Being adsorbed on the nucleated crystals of the released metal, they reduce the rate of their growth. Thus, a fine-grained metal structure with higher strength is formed.

The process of "training" metal in a surface-active medium has been developed. The metal is subjected to periodic surface treatments that do not lead to destruction. Due to the facilitation of plastic deformations in the surface layers, the metal in the internal volume is "kneaded", as it were, and the crystal lattice of grains is dispersed. If such a process is carried out at a temperature close to the temperature of the onset of metal recrystallization, a fine-crystalline structure with a much higher hardness is formed in the surface-active medium. And the grinding of metals when obtaining a fine powder is not complete without the use of surface-active melts. Subsequently, products are obtained from this powder by hot pressing (in full accordance with the process of hardening materials from powders described above).

REBINDER EFFECT IN POLYMERS. The outstanding Soviet physicist and chemist, Academician Pyotr Aleksandrovich Rebinder was the first to try to influence the work of destruction of a solid. It was Rebinder who managed to understand how this can be done. Back in the 20s of the last century, he used for this purpose the so-called surface-active, or adsorption-active, substances that are able to effectively adsorb on the surface even at low concentrations in the environment and sharply reduce the surface tension of solids. Molecules of these substances attack intermolecular bonds at the top of a growing fracture crack and, by adsorbing on freshly formed surfaces, weaken them. By picking up special fluids and introducing them onto the surface of the solid to be destroyed, Rebinder achieved a striking decrease in the work of fracture in tension (Fig. 1). The figure shows the deformation-strength curves of a zinc single crystal (plates with a thickness of the order of a millimeter) in the absence and in the presence of a surface-active liquid. The moment of destruction in both cases is marked with arrows. It is clearly seen that if you just stretch the sample, it breaks at more than 600% elongation. But if the same procedure is performed by depositing liquid tin on its surface, destruction occurs only at ~ 10% elongation. Since the work of destruction is the area under the stress-strain curve, it is easy to see that the presence of liquid reduces the work not even several times, but orders of magnitude. It is this effect that was called the Rebinder effect, or the adsorption decrease in the strength of solids.

Fig. 1. Dependence of stress on deformation of zinc single crystals at 400 ° С: 1 - in air; 2 - in the tin melt

The Rebinder effect is a universal phenomenon, it is observed when any solid bodies, including polymers, are destroyed. Nevertheless, the nature of the object brings its own characteristics to the destruction process, and polymers are no exception in this sense. Polymer films are composed of large, intact molecules held together by van der Waals forces or hydrogen bonds, which are noticeably weaker than the covalent bonds within the molecules themselves. Therefore, a molecule, even being a member of a team, retains some isolation and individual qualities. The main feature of polymers is the chain structure of their macromolecules, which ensures their flexibility. The flexibility of molecules, i.e. their ability to change their shape (due to deformation of bond angles and rotations of links) under the influence of external mechanical stress and a number of other factors underlies all the characteristic properties of polymers. First of all, the ability of macromolecules for mutual orientation. However, it should be noted that the latter applies only to linear polymers. There are a huge number of substances that have a large molecular weight (for example, proteins and other biological objects), but do not possess the specific qualities of polymers, since strong intramolecular interactions prevent their macromolecules from bending. Moreover, a typical representative of polymers - natural rubber - being "crosslinked" with the help of special substances (vulcanization process), can turn into a solid - ebonite, which does not show any signs of polymer properties at all.

In polymers, the Rebinder effect manifests itself in a very peculiar way. In an adsorption-active liquid, the emergence and development of a new surface is observed not only during destruction, but much earlier, even in the process of polymer deformation, which is accompanied by the orientation of macromolecules.

Fig. 2. Appearance of polyethylene terephthalate samples stretched in air (a) and in an adsorption-active medium (n-propanol) (b).

rebinder polymer metal strength

Figure 2 shows images of two Lavsan samples, one of which was stretched in air and the other in an adsorption-active liquid. It is clearly seen that in the first case a neck appears in the sample. In the second case, the film does not narrow, but it becomes milky white and opaque. The reasons for the observed whitening become clear upon microscopic examination.

Fig. 3. Electron micrograph of a polyethylene terephthalate sample deformed in n-propanol. (Zoom in 1000)

Instead of a monolithic transparent neck, a unique fibrillar-porous structure is formed in the polymer, consisting of filamentous aggregates of macromolecules (fibrils), separated by microvoids (pores). In this case, the mutual orientation of macromolecules is achieved not in the monolithic neck, but inside the fibrils. Since the fibrils are separated in space, such a structure contains a huge amount of microvoids, which intensely scatter light and give the polymer a milky white color. The pores are filled with liquid, so the heterogeneous structure is retained even after the deforming stress is removed. The fibrillar-porous structure appears in special zones and, as the polymer deforms, captures an ever larger volume. Analysis of microscopic images made it possible to establish the features of structural rearrangements in the polymer subjected to crazing (Fig. 4).

Fig. 4. Schematic representation of individual stages of a crazing polymer: I - initiation of crazes, II - growth of crazes, III - broadening of crazes.

Having originated on any defect (structural inhomogeneities), which are abundant on the surface of any real solid, crazes grow through the entire cross section of the stretched polymer in the direction normal to the tensile stress axis, maintaining a constant and very small (~ 1 μm) width. In this sense, they are like true fracture cracks. But when the craze "cuts" the entire cross-section of the polymer, the sample does not disintegrate into separate parts, but remains a single whole. This is due to the fact that the opposite edges of such a peculiar crack are connected by the finest threads of oriented polymer (Fig. 3). The sizes (diameters) of fibrillar formations, as well as of the microvoids separating them, are 1-10 nm.

When the fibrils connecting the opposite craze walls become sufficiently long, the process of their fusion begins (the surface area decreases, Fig. 5). In other words, the polymer undergoes a kind of structural transition from a loose structure to a more compact one, consisting of densely packed aggregates of fibrils, which are oriented in the direction of the tension axis.

Fig. 5. Diagram illustrating the collapse of the polymer structure occurring at high deformation values \u200b\u200bin an adsorption-active liquid at various stages of stretching

There is a method of separating molecules by adsorption from a solution of those of them that are able to penetrate into pores of a given size (molecular sieve effect). Since the pore size can be easily controlled by changing the draw ratio of the polymer in an adsorption-active medium (using the Rebinder effect), selective adsorption is easy to achieve. It is important to note that the adsorbents used in practice are usually a kind of powder or granulate, which is filled with various kinds of containers (for example, a sorbent in the same gas mask). Using the Rebinder effect, it is easy to obtain a film or fiber with a through nanometric porosity. In other words, the prospect opens up to create a structural material with optimal mechanical properties and, at the same time, being an effective sorbent.

Using the Rebinder effect, an elementary way (simple stretching of a polymer film in an adsorption-active medium) makes it possible to make porous polymer films based on almost any synthetic polymers. The pore sizes in such films are easily controlled by changing the degree of polymer deformation, which makes it possible to manufacture separating membranes for solving a variety of practical problems.

The Rebinder effect in polymers has great potential for applications. First, by simply drawing the polymer in an adsorption-active liquid, it is possible to obtain a variety of polymer sorbents, separating membranes, and polymer products with a transverse relief, and, secondly, the Rebinder effect gives the process chemist a universal continuous method of introducing modifying additives into polymers.

List of materials used

• 1.www.rfbr.ru/pics/28304ref/file.pdf
• 2.www.chem.msu.su/rus/teaching/colloid/4.html
• 3.http: //femto.com.ua/articles/part_2/3339.html
• 4. Great Soviet Encyclopedia. M .: Soviet encyclopedia, 1975, vol. 21.
• 5.http: //him.1september.ru/2003/32/3.htm
• 6.http: //slovari.yandex.ru/dict/bse/article/00065/40400.htm
• 7.http: //www.nanometer.ru/2009/09/07/rfbr_156711/PROP_FILE_files_1/rffi4.pdf
• 8.http: //ru.wikipedia.org/wiki/Rebinder_Effect

The phenomena of wettability were considered for the equilibrium state of the system. Unstable processes occurring at the interface are observed in reservoir conditions. Due to the displacement of oil by water, a moving three-phase perimeter of wetting is formed. The contact angle changes depending on the speed and direction of the fluid (fluid meniscus, Fig.5.5) in the channels and cracks.

Figure 5.5 - Scheme of changing the contact angles when changing the direction of movement of the meniscus in the capillary channel:  1 - advancing,  2 - receding contact angles during the movement of the water-oil meniscus in a cylindrical channel with a hydrophilic surface ( is the static contact angle)

Kinetic wetting hysteresisit is customary to call the change in the wetting angle when moving on a solid surface of a three-phase wetting perimeter. The amount of hysteresis depends on:

from the direction of movement of the wetting perimeter, i.e. whether displacement occurs from a solid surface of water by oil or oil by water;

the speed of movement of the three-phase interface on a solid surface;

roughness of the solid surface;

adsorption on the surface of substances.

Hysteresis phenomena occur mainly on rough surfaces and are of a molecular nature. On polished surfaces, hysteresis is weak.

5.6 Properties of surface layers of formation fluids

There are various assumptions about the structure of the surface layer.

Many researchers studying the structure and thickness of thin liquid layers associate the formation of near-wall layers with the polarization of molecules and their orientation from the surface of a solid to the inner regions of the liquid with the formation of solvation 1 layers.

Oil layers in contact with rocks of the formation have a particularly complex structure, since the interaction of surfactants with minerals is very diverse.

It is noted, for example, that reagents used in flotation technology can be fixed on the surface of a mineral both in the form of ordinary three-dimensional films that form an independent phase on the surface of mineral particles, and in the form of surface compounds that do not have a specific composition and do not form a separate independent phase.

Finally, the reagents can be concentrated in the diffusion part of the electric double layer, and not at the interface itself.

Surfactant components, apparently, always concentrate not only on the surface, but also in a three-dimensional volume near the interface.

Many researchers have attempted to measure the thickness of the film of various liquids on solids. For example, according to the results of measurements by BV Deryagin and MM Kusakov, the thickness of the wetting films of aqueous salt solutions on various solid flat surfaces is about 10 -5 cm (100 them). These layers differ from the rest of the fluid in structure and mechanical properties - shear elasticity and increased viscosity. It has been established that the properties of the liquid in the surface layer also change due to its compression. For example, the density of water adsorbed by silica gel according to some measurements is 1027-1285 kg / m 3.

Adsorption and associated solvation shells in the phase separations in the oil reservoir also have special properties. Some oil constituents can form gel-like structured adsorption layers (with unusual - anomalous properties) with high structural viscosity, and at high degrees of saturation of the adsorption layer - with elasticity and mechanical shear strength.

Studies show that the composition of the surface layers at the oil - water section includes naphthenic acids, low molecular weight resins, colloidal particles of high molecular weight resins and asphaltenes, paraffin microcrystals, as well as particles of mineral and carbonaceous suspensions. It is assumed that the surface layer at the oil - water section is formed as a result of the accumulation of mineral and carbonaceous particles, as well as paraffin microcrystals under the influence of selective wetting by the aqueous phase of the hydrophilic areas of their surface. Asphalt-resinous substances adsorbed on the same interface and turning into a gel-like state cement the particles of paraffin and minerals into a single monolithic layer. The surface layer thickens even more due to the solvatization of gels of asphalt-resinous substances from the oil phase.

The special structural and mechanical properties of the surface layers determine the stabilization of various systems and, in particular, the high stability of some water-oil emulsions.

The existence of adsorption layers at the residual water - oil section, apparently, also has a certain delaying effect on the processes of miscibility of water injected into the reservoir with residual water.

5.7 The wedging action of thin layers of liquid.

Deryagin's experiments. Rebinder effect

A liquid wetting a solid, penetrating into thin cracks, is capable of playing the role of a wedge and pushing its walls apart, i.e. thin layers of liquid have a wedging effect 2. This property of thin layers also manifests itself when solid surfaces immersed in liquid approach each other. According to the research of B.V.Deryagin, the wedging action occurs under the condition that the thickness of the layer h fluid pushing the crack surface is less than a certain value h cr ... When h > h cr the wedging action is zero and at h < h cr it increases with decreasing thickness of the liquid layer, i.e., from the moment h ≤ h cr to bring the surfaces of particles closer together, an external load must be applied to them.

The factors creating the wedging action are the forces of ionic-electrostatic origin and the special state of aggregation of polar liquids near the boundary surfaces.

It was mentioned earlier that the properties of the solvation layer on the surface of a solid differ sharply from the properties of the rest of the liquid. This (solvation) layer can be considered as a special boundary phase. Therefore, when approaching particles to distances less than double the thickness of the solvation layers, an external load must be applied to the particles.

The disjoining pressure of ionic-electrostatic origin arises from changes in the concentration of ions in the layer separating the particles and in the surrounding solution.

According to the results of the experiment, the wedging action is the greater, the stronger the bond between the liquid and the surfaces of the solid. It can be enhanced by introducing surfactants into the liquid that are well absorbed by the surface of the solid. The Rebinder effect is based on this phenomenon. Its essence lies in the fact that small amounts of surfactants cause a sharp deterioration in the mechanical properties of a solid. The adsorptive decrease in the strength of solids depends on many factors. It is intensified if the body is subjected to tensile forces and if the liquid wets the surface well.

The effect of adsorptive strength reduction is used in well drilling. When using solutions containing specially selected surfactants as drilling fluids, drilling of hard rocks is noticeably easier.

In addition to the action of chemical processes that affect the properties of the surface and the frictional interaction between solids, there is an open and investigated by P.A. Rebinder is a similar lubricant due to the purely molecular interaction of the lubricant with solid surfaces, called the "Rebinder effect".

Real solids have both surface and internal structural defects. As a rule, such defects have excess free energy. Due to the physical adsorption of surfactant molecules (surfactant), the level of free surface energy of the solid decreases in the places of their landing. This reduces the work function of dislocations to the surface. Surfactants penetrate into cracks and intercrystalline space, exerting a mechanical effect on their walls and pushing them apart, lead to brittle cracking of the material and a decrease in the strength of the contacting bodies. And if such processes develop only on the protrusions of the contacting bodies, reducing the shear resistance of the irregularities of this material, then in general this process leads to a smoothing of the surface, a decrease in the specific pressure in the contact zone and in general

reducing friction and wear of rubbing bodies. But if the normal loads during friction increase significantly, high specific pressures spread over the entire contour area, the softening of the material occurs over a large area of \u200b\u200bthe surface and leads to its very rapid destruction.

The Rebinder effect is widely used both in the development of lubricants (for this, special surfactants are introduced into the lubricant), and to facilitate the deformation and processing of the material in the manufacture of machine parts (for this, special lubricants and emulsions are used in the form of cutting fluids).

The Rebinder effect appears on a wide variety of materials. These are metals, rocks, glass, elements of machinery and equipment. The medium that causes a decrease in strength can be gaseous and liquid. Molten metals can often act as surfactants. For example, the copper released during melting of a plain bearing becomes a surfactant for steel. Penetrating into cracks and intercrystalline space of carriage axles, this process becomes the cause of fragile destruction of axles and the cause of transport accidents.

Without paying due attention to the nature of the process, we often began to come across examples when ammonia causes cracking of brass parts, gaseous combustion products dramatically accelerate the process of destruction of turbine blades, molten magnesium chloride acts destructively on high-strength stainless steels and a number of others. Knowledge of the nature of these phenomena opens up opportunities to address the issues of increasing the wear resistance and destruction of critical parts and assemblies of machines and equipment in a targeted manner, and with proper use of the Rebinder effect, to increase the productivity of processing equipment and the efficiency of using friction pairs, i.e. to save energy.

Rebinder effect

the effect of an adsorptive decrease in the strength of solids, facilitating the deformation and destruction of solids due to the reversible physicochemical action of the environment. Discovered by P. A. Rebinder (1928) in the study of the mechanical properties of crystals of calcite and rock salt. It is possible when a solid body in a stressed state comes into contact with a liquid (or gaseous) adsorption-active medium. R, e. very versatile - it is observed in solid metals, ionic, covalent and molecular mono- and polycrystalline bodies, glasses and polymers, partially crystallized and amorphous, porous and solid. The main condition for the manifestation of R. e. - the related nature of the contacting phases (solid and medium) in chemical composition and structure. Form and degree of manifestation of R. e. depend on the intensity of interatomic (intermolecular) interactions of the contacting phases, the magnitude and type of stresses (tensile stresses are required), the rate of deformation, and temperature. An essential role is played by the real structure of the body — the presence of dislocations, cracks, foreign inclusions, and others. - multiple drop in strength, increase in the fragility of a solid, decrease in its durability. So, a zinc plate moistened with mercury does not bend under load, but breaks down brittle. Another form of manifestation of R. e. - the plasticizing effect of the medium on solid materials, for example, water on gypsum, organic surfactants on metals, etc. Thermodynamic R. e. due to a decrease in the work of formation of a new surface during deformation as a result of a decrease in the free surface energy (see Surface energy) of a solid under the influence of the environment. Molecular nature of R. e. consists in facilitating the breaking and rearrangement of intermolecular (interatomic, ionic) bonds in a solid in the presence of adsorption-active and, at the same time, sufficiently mobile foreign molecules (atoms, ions). The most important areas of the technical application of R. e. - facilitation and improvement of mechanical processing of various (especially highly hard and difficult to machine) materials, regulation of friction and wear processes with the use of lubricants (see Lubrication action), efficient production of crushed (powdery) materials, production of solids and materials with a given dispersed structure (See. Dispersed structure) and the required combination of mechanical and other properties by disaggregation and subsequent compaction without internal stresses (see. (See also Physicochemical Mechanics). An adsorption-active environment can also cause significant harm, for example, reducing the strength and durability of machine parts and materials under operating conditions. Elimination of the factors contributing to the manifestation of R. e., In these cases, allows you to protect materials from the unwanted effects of the environment.

Lit .: Goryunov Yu. V., Pertsov NV, BD Summ, Rebinder effect, M., 1966; Rebinder P. A., Shchukin E. D., Surface phenomena in solids in the processes of their deformation and destruction, "Uspekhi fizicheskikh nauk", 1972, v. 108, v. 1, p. 3.

L. A. Shits.

Great Soviet Encyclopedia. - M .: Soviet encyclopedia. 1969-1978 .

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Reducing the strength of tv. bodies in adsorption active media (surfactant solutions, electrolytes, molten salts, etc.). Discovered by P. A. Rebinder in 1928. It is used to improve the efficiency of dispersion, grinding, cutting materials and ... ... Natural science. encyclopedic Dictionary

hall effect - the appearance of a transverse electric field and a potential difference in a metal or semiconductor through which an electric current passes, when it is placed in a magnetic field, perpendicular to the direction of the current. Opened by American ... ...

mossbauer effect - resonant absorption of γ quanta by atomic nuclei, observed when the source and absorber of γ radiation is a solid, and the energy of the quanta is low (150 keV). Sometimes the M. effect is called resonance, absorption without recoil, or nuclear ... Encyclopedic Dictionary of Metallurgy

seebeck effect - the phenomenon of the emergence of an electromotive force in an electrical circuit consisting of different conductors, the contacts between which have different temperatures; discovered in 1821 by the German physicist T. Seebeck. Electromotive force, ... ... Encyclopedic Dictionary of Metallurgy

bauschinger effect - a decrease in the resistance of a metal or alloy to small plastic deformations (for example, in compression) after preliminary deformation of the opposite sign (in tension). In single crystals of pure metals, the Bauschinger effect ... ... Encyclopedic Dictionary of Metallurgy

Books

• The role of surface phenomena in the structural and mechanical behavior of solid polymers, A. L. Volynsky, N. F. Bakeev. The book presents modern ideas about the role of surface phenomena in the structural and mechanical behavior of amorphous and crystalline polymers. The processes of development and healing are considered ...

where ps is the saturated vapor pressure at a given temperature; steam pressure.

p s - relative

The BET polymolecular adsorption isotherm equation can be easily reduced to a linear form:

by which it is possible to construct a linear dependence in the coordinates / on and determine the constants C and A∞.

The BET theory, like the Langmuir theory, points the way for determining the specific surface area of \u200b\u200bthe adsorbent. Having found А∞ for vapors of simple substances at low temperatures and knowing the area occupied by the adsorptive molecule, it is easy to calculate the specific surface area of \u200b\u200bthe adsorbent.

Inert gases (nitrogen, argon, krypton, etc.) are used as adsorbates, which are characterized by weak intermolecular interaction on the surface of the adsorbent, which is in accordance with the initial assumptions of the theory, and this ensures the reliability of the results obtained. To increase the adsorption of such gases, it is carried out at low temperatures, hence the frequent name of the BET method - the low-temperature adsorption method.

13 Adsorption reduction in strength. Rebinder effect

Many technological processes start with crushing and grinding. This is one of the most massive and energy-intensive operations of modern technology. Grind grain, turning it into flour, grind ore, coal, rocks necessary for the production of cement, glass. Every year they grind billions of tons of raw materials, spending an enormous amount of electricity.

The phenomenon of the adsorption effect of the medium on the mechanical properties and structure of solids - rebinder effect- was discovered by an academician Peter Alexandrovich Rebinderin 1928. The essence of this phenomenon lies in facilitating the deformation and destruction of solids and the spontaneous occurrence of structural changes in them as a result of a decrease in their free surface energy upon contact with a medium containing substances capable of adsorption on the interface. Many phenomena observed in nature, technology, and scientific research practice are based on the Rebinder effect.

Depending on the chemical nature of the solid and the medium, the conditions of deformation and destruction of the structure of the solid, the Rebinder effect can manifest itself in various forms: adsorptive plasticization (facilitating plastic deformation), adsorptive decrease in strength, or spontaneous dispersion of the solid structure. Despite the variety of manifestation forms, a number of common features characteristic of the Rebinder effect can be distinguished:

1) The action of media is very specific: only a few specific media act on each given type of solid.

2) The change in the mechanical properties of solids can be observed immediately after establishing contact with the medium.

3) For the manifestation of the action of the environment, very small amounts of it are sufficient.

4) The Rebinder effect manifests itself only under the combined action of the medium and mechanical stresses.

5) A peculiar reversibility of the effect is observed: after removal of the medium, the mechanical properties of the initial material are completely restored.

These features are the difference between the Rebinder effect from other possible cases of the influence of the medium on the mechanical properties of solids, in particular, from the processes of dissolution and corrosion, when the destruction of the body under the influence of the medium can occur in the absence of mechanical stresses. In the latter case, exposure to significant quantities of an aggressive environment is usually necessary.

The adsorption decrease in strength (ADS) is observed in the presence of media that cause a strong decrease in the surface energy of solids. The strongest effects are caused by liquid media that are close to solids in molecular nature. So, for solid materials such media are melts of more low-melting metals; for ionic crystals and oxides - water, electrolyte solutions and salt melts; for molecular non-polar crystals - hydrocarbons. Among numerous media of the same molecular nature, a significant decrease in the strength of solids is often caused by substances that form a simple eutectic diagram with a solid with a low solubility in the solid state; this corresponds to a small positive energy of mixing of the components. In systems with a low intensity of interaction of the components (mutual insolubility), as well as in the case of a very high mutual affinity, especially if the components enter into a chemical reaction, APP is usually not observed.

In brittle fracture, the relationship between strength P and surface energy is described by the Griffiths equation:

, (13.1)

where E is the modulus of elasticity of a solid, l is the characteristic size of defects existing in it or arising during preliminary plastic deformation - nucleation cracks of destruction. In accordance with the Griffiths relation, which is valid under brittle fracture conditions, the ratio of the strengths of the material in the presence of P A and in the absence of the medium P 0 is equal to the square root of the ratio of the corresponding surface energies: P A / P 0 \u003d (A / 0) 1/2. When solids are destroyed in the presence of mixtures of two liquid components differing in adsorption activity, the strength decreases the more the higher the concentration of the more active component, which is predominantly adsorbed on the fracture surface.

Comparing the Griffiths relation with the Gibbs adsorption equation (at low concentrations) Г \u003d - (RT) -1 d / dlnc, one can directly relate adsorption to the strength P:

The Rebinder effect made it possible to reduce energy consumption by 20-30%, as well as to obtain ultrafine grinding materials, for example, cement with special properties. The Rebinder effect is also used in metal machining, when surfactants are added to the cooling lubricant, which reduce the strength in the cutting zone. Surfactants are widely used in the food industry: for

decrease in strength when crushing grain, to improve the quality of baked bread, slow down the process of its staleness; to reduce the stickiness of pasta, to increase the plastic properties of margarine; in the production of ice cream; in the production of confectionery, etc.

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