Mechanical methods of obtaining nanoparticles and nanomaterials. Methods of obtaining nanomaterials
To date, numerous methods for obtaining nanomaterials both in the form of nanopowders and in the form of inclusions in porous or monolithic matrices are developed. At the same time, ferro and ferrimagnetics, metals, semiconductors, dielectrics, etc. can act as nanophaza.
According to Fendler, the most important conditions obtain nanomaterials are:
1. Nonequilibrium systems. Almost all nosnosystems are thermodynamically unstable, and they are obtained in conditions that are far from equilibrium, which allows to achieve spontaneous nucleation and avoid growth and aggregation of the formed nanoparticles.
2. Uniformity of nanoparticles. The high chemical homogeneity of the nanomaterial is ensured if the components are separated during the synthesis, both within one nanoparticle and between the particles.
3. Monodisperity of nanoparticles. The properties of nanoparticles are extremely dependent on their size, therefore, for obtaining materials with good functional characteristics, it is necessary to use particles with a sufficiently narrow distribution in size.
In the future, it was shown that these conditions are not always mandatory for execution. For example, solutions of surfactants (micellar structures, Langmuir film - Blucented, liquid crystal phases) are thermodynamically stable, nevertheless, they serve as the basis for the formation of a variety of nanostructures.
All methods for obtaining nanomaterials can be divided into several large groups. The first group includes the so-called high-energy methods based on rapid condensation of vapors in conditions that exclude aggregation and the increase in the resulting particles. The main differences between the individual methods of this group consist in the method of evaporation and stabilization of the resulting nanoparticles. Evaporation can be carried out using plasma excitation (PLASMA-ARK), laser radiation (Laser Ablation), volt arc (carbon ark) or thermal exposure. Condensation is carried out either in the presence of surfactants whose adsorption on the surface of the particles slows down growth (VAPOR TRAPPING); either on a cold substrate when the growth of particles is limited to diffusion rate; Either in the presence of an inert component, which allows you to select nano composite materials with different microstructures. If the components are mutually insoluble, then the size of the nanoparticles can be varied using heat treatment.
The second group includes mechanochemical methods (ball-mill), allowing to obtain nanocomposites with a joint grinding of mutually insoluble components in the planetary mills or during the decay of solid solutions to form new phases under the action of mechanical stresses.
The third group of methods is based on the use of space-limited systems - nanoreactors (micelles, drops, films, etc.). These include synthesis in converted micelles, in Langmür films - Blucented and in adsorption layers. It is clear that the size of the particles generated at the same time cannot exceed the size of the corresponding nanoreactor, therefore the specified methods allow to obtain monodisperse systems. The biomimetic and biological methods of nanoparticles synthesis are also used to be attributed, in which biomolecules (proteins, DNA, etc.) are used as nanoreactors.
The fourth group includes methods based on formation in solutions of ultramicrodissed colloidal particles during polycondensation in the presence of surfactants preventing aggregation.
The fifth group includes chemical methods for obtaining high-art and finely dispersed structures (metals RIKE, RENEY Nickel), based on the removal of one of the components of the microheterogenic system as a result chemical reaction or anodic dissolution. These methods also include a traditional method for producing nanocomposites by hardening the glass or salt matrix with a solvable substance, resulting in crystallization of this substance in the matrix (glass modified by semiconductor or metal nanoparticles). In this case, the introduction of a substance in the matrix can be carried out in two ways: by adding it to the melt (solution), followed by hardening and directly introducing into a solid matrix using ion implantation.
One of the most common chemical methods for producing nano materials is a sol-gel synthesis. With it, homogeneous oxide systems are obtained, whose chemical modification (recovery, sulphidation, etc.) leads to the formation of nanoparticles of the corresponding material in the matrix. It should be noted that the use of a sol-gel method allows to obtain nanomaterials with improved functional properties due to the control of the composition and structure of intermediate products. It is also attractive also its realizability in laboratory conditions. However, this method has serious disadvantages. First, it does not provide particle monodispers. Secondly, it does not allow to obtain two-dimensional and one-dimensional nanostructures, as well as spatially ordered structures consisting of nanoparticles located at the same distance from each other, or from parallel nanoplastin with interlayers of an inert matrix, which can be synthesized in nano reactors. Finally, in some cases, the preparation of the required nanocomposite is impossible due to the chemical interaction of particles with a gelling agent.
It should be noted that the use of free nanoparticles and nanostructures as materials is very difficult due to the metastability of the substance in the nanocrystalline state. As noted above, this is due to an increase in the specific surface of the particles as they decrease their linear dimensions to nanometer, leading to an increase in the chemical activity of the compound and enhance the aggregation processes. To prevent the aggregation of nanoparticles and protect them from external influences (for example, the oxidation of air oxygen), nanoparticles enter into a chemically inert matrix.
An analysis of literature data shows that there are currently dozens of methods of matrix isolation of nanostructures, which can be divided into two groups: obtaining free nanoparticles, followed by inclusion in an inert matrix and direct formation of nanostructures in the volume of the matrix in the process of its chemical modification.
The first group of methods is characterized by simplicity in implementation, but imposes serious restrictions on the possibility of selecting the matrix. As a latter, organic polymer compounds that are not distinguished by high thermal stability and not always possess the necessary physical properties (for example, high optical transparency). In addition, the processes of nanoparticles aggregation processes are not excluded.
The second group of methods allows not only to avoid these shortcomings, but also directly control the parameters of the nanoparticles in the matrix at the formation stage and even change these parameters during the operation of the material. The matrix used for these purposes should contain structural voids that can be filled with compounds, the subsequent modification of which leads to the formation of nanoparticles in these voids. In other words, these voids should limit the reaction zone with the participation of compounds embedded in them, i.e. Act in the role of peculiar nanoreactors. Obviously, choosing compounds with different form of structural voids, a synthesis of nanostructures of various morphology and anisotropy can be carried out.
As an example, the synthesis of nanomaterials using porous oxide matrices are given (usually SiO 2 or AL 2 OZ). However, due to the disorder of the porous structure of such matrices and a sufficiently wide distribution of pores in size with their help it is almost impossible to obtain satisfactory formed nanosystems. Typically, nanocomposites obtained on the basis of porous oxide matrices are used in catalysis, where the requirements for the monodisperse of particles and their morphology are not so high. In addition, the rigid porous structure of such matrices does not allow to change the dimensions and morphology of particles during the synthesis; The latter, as a rule, firmly depend on the size and morphology of pores, i.e. When using one type of matrix, you can only get a very limited circle of nanostructures.
Sometimes for the rapid directional formation of nanoparticles in the matrix, it is resorted to additional physical impacts, such as ultrasound, microwave and laser irradiation.
Introduction
1 emergence and development of nanotechnology
2 Basics of Nanomaterial Technology
2.2 Consolidated Material Technology
2.2.1 Powder technology
2.2.2 Intensive plastic deformation
2.2.3 Controlled crystallising from amorphous state
2.2.4 Technology of films and coatings.
2.3 Technology of polymer, porous, tubular and biological nanomaterials
2.3.1 Hybrid and Supramolecular Materials
2.3.2 Nanoporous materials (molecular sieves)
2.3.3 Tubular materials
2.3.4 Polymer materials
3 General characteristics of nanomaterials
Conclusion
In the past few years, Nanotechnology has become considered not only as one of the most promising branches of high technology, but also as a system-forming factor in the economy of the 21st century - knowledge-based economy, and not on the use natural resources or their processing. In addition to the fact that nanotechnology stimulates the development of the new paradigm of all production activities ("bottom-up" from individual atoms - to the product, and not "top down", as traditional technologies in which the product is obtained by cutting off the excessive material from a more massive workpiece) , she herself is a source of new approaches to improving the quality of life and solving many social problems in post-industrial society. According to the majority of experts in the field of scientific and technical policy and investing funds, the Nanotechnology Revolution will cover all the vital areas of human activity (from the development of space to medicine, from national security - to ecology and agriculture), and its consequences will be extensive and deeper than the computer revolution of the last third of the 20th century. All this puts the tasks and questions not only in the scientific and technical sphere, but also before administrators of various levels, potential investors, education, public administration authorities, etc.
Nanotechnology has been formed on the basis of revolutionary changes in computer technologies. Electronics as a holistic direction arose about 1900 and continued to grow rapidly throughout the last century. An extremely important event in its history was the invention of the transistor in 1947. After that, the era of the heyday of semiconductor techniques began, in which the size of the silicon devices created was constantly decreased. At the same time, the speed and volume of magnetic and optical storage devices continuously increased.
However, as the size of semiconductor devices approaches 1 microns, the quantum-mechanical properties of the substance begin to appear in them, i.e. Unusual physical phenomena (such as tunnel effect). It is safe to assume that, while maintaining the current pace of power development of computers, the entire semiconductor technology is approached by about 5-10 years with problems of a fundamental nature, since the speed and degree of integration into computers will be reached by some "fundamental" borders defined by the laws of physics. Thus, the further progress of science and technology requires researchers a substantial "breakthrough" to new principles of work and new technological techniques.
Such a breakthrough can only be carried out by using nanotechnology that will create whole line fundamentally new production processes, materials and devices, such as nanorobots.
Calculations show that the use of nanotechnology can increase the basic characteristics of semiconductor computing and storage devices by three orders of magnitude, i.e. 1000 times.
However, nanotechnology should not be reduced only to a local revolutionary breakthrough in electronics and computer technology. A number of extremely important results have already been received, allowing to hope for significant progress in the development of other directions of science and technology.
Many facilities in physics, chemistry and biology show that the transition to nano-level leads to the emergence of qualitative changes in the physicochemical properties of individual compounds and systems obtained on them. We are talking about the coefficients of optical resistance, electrical conductivity, magnetic properties, strength, heat resistance. Moreover, according to observations, new materials obtained using nanotechnology are significantly superior in their physical, mechanical, thermal and optical properties analogues of micrometric scale.
Based on materials with new properties, new types of solar panels, energy converters, environmentally friendly products and much more are being created. Highly sensitive biological sensors (sensors) and other devices, allowing to talk about the occurrence of new science - nanobiotechnology and having enormous practical prospects. Nanotechnology offers new features of micro-processing materials and creating new production processes and new products on this basis, which should have a revolutionary impact on the economic and social life of future generations.
2.1 General characteristics
The structure and, accordingly, the properties of nanomaterials are formed at the stage of their manufacturing. The value of the technology is quite obvious to ensuring the stable and optimal performance characteristics of nanomaterials; This is also important in terms of their economy.
For the technology of nanomaterials in accordance with the variety of the latter, the combination is characterized, on the one hand, metallurgical, physical, chemical and biological methods, on the other hand, traditional and fundamentally new techniques. So, if the overwhelming majority of methods for obtaining consolidated nanomaterials are quite traditional, then operations such as manufacturing, for example, "quantum pens" using a scanning tunnel microscope, the formation of quantum dots of atoms of atoms or the use of ion-track technology to create porous structures in polymeric materials based On fundamentally different technological methods.
Methods of molecular biotechnology are very diverse. All this complicates the statement of the basics of nanomaterial technology, given that many technological details ("know-how") the authors describe only in general terms, and often a message is advertising. Then analyzed only the main and most characteristic techniques.
2.2.1 Powder technology
Under the powder understand the combination of individuals in contact solid tel (or their aggregates) of small size - from several nanometers to a thousand microns. With regard to the manufacture of nanomaterials, ultrafine powders are used as a raw material, i.e. Particles are not more than 100 particles, as well as larger powders obtained under intensive grinding conditions and consisting of small crystallites with a size similar to those specified above.
Subsequent operations of powder technology - pressing, sintering, hot pressing, etc. - are designed to provide a sample (product) of specified forms and sizes with the corresponding structure and properties. The combination of these operations is often called, at the proposal of M.Yu. Balshchin, consolidation. In relation to nanomaterials, consolidation should ensure, on the one hand, almost complete seal (i.e., the absence in the structure of macro and micropores), and on the other hand, maintain a nanostructure associated with the initial sizes of the ultrafine powder (i.e. grain size Sintered materials should be as little as possible and in any case less than 100 nm).
Methods for obtaining powders for the manufacture of nanomaterials are very diverse; They can be divided into chemical and physical, basic, of which, indicating the most characteristic ultrafine powders, are shown in Table 1.
Table 1 . Basic methods for producing powders for the manufacture of nanomaterials
| Method | Option method | Materials |
| Physical methods | ||
| Evaporation and condensation | In vacuo or in inert gas | Zn, Cu, Ni, Al, BE, SN, PB, MG, AG, CR, MGO, AL 2 O 3, Y 2 O 3, ZRO 2, SIC |
| In reactionary gas | TIN, ALN, ZRN, NBN, ZRO 3, AL 2 O 3, TIO 2. | |
High-energy destruction | Shredding | Fe-Cr, BE, Al 2 O 3, Tic, Si 3 N 4, Nial, Tial, Aln |
| Detonation treatment | BN, SIN, TIC, FE, Diamond | |
| Electric explosion | Al, Cd, Al 2 O 3, TiO 2. | |
| Chemical methods | ||
| Synthesis | Plasmochemical | Tic, Tin, Ti (C, N), VN, Aln, SiC, Si 3 N 4, BN, W |
| Laser | Si 3 N 4, SiC, Si 3 N 4 -Sic | |
| Thermal | Fe, Cu, Ni, Mo, W, BN, TIC, WC-CO | |
| Self-propagating high temperature | SiC, Mosi 2, Aln, TAC | |
| Mechanochemical | Tic, Tin, Nial, Tib 2, Fe-Cu, W-Cu | |
| Electrochemical | WC, CEO 2, ZRO 2, WB 4 | |
| Solid | MO 2 C, BN, TIB 2, SIC | |
| Cryochemical | AG, PB, MG, CD | |
| Thermal decisions | Condensed precursors | Fe, Ni, Co, SiC, Si 3 N 4, BN, ALN, ZRO 2, NBN |
| Gaseous precursors | ZRB 2, TIB 2, BN | |
Consider some of the methods for producing ultrafine powders.
To date, dozens of methods for creating nanostructured materials are known. In principle, all methods of obtaining nanostructures can be conditionally divided into two large classes - physical and chemical methods . It should be emphasized that the approach "bottom-up" is characterized to a greater extent for chemical methods of obtaining. The processes of obtaining nanomaterials include both the stage of their synthesis and the stage of their stabilization. Given the same way that nanostructures exhibit their unique properties in most cases precisely in a non-equilibrium metastable state. The use of various stabilizers allows not only to synthesize nanostructures, but also use nanomaterials based on them in nanotechnology.
1 group of methods obtaining and studying nanoparticles (condensation at ultra-low temperatures, options for chemical, photochemical and radiation recovery, laser evaporation) does not allow creating new materials.
P Group of Methods It makes it possible to obtain nanoparticles based on nanoparticles and nanocomposites (options for mechanochemical crushing, condensation from the gas phase, plasma chemical methods, etc.)
The structure of nanoparticles of the same size obtained by dispersing and by constructing from atoms may vary. In the first case, the structure of the original sample is preserved in the particle structure. Nanoparticles obtained by aggregation of atoms may have another spatial arrangement of atoms. For example, with a size of 2-4 nm, a decrease in the lattice parameter is observed.
Physical methods.
1. Plasma spraying: plasma, anode, magnetron, etc. Depending on how to create gas environment, precipitated to the substrate or belonging from the reaction zone, for example a gas stream.
2. ion-ray epitaxy.
3. Gas phase compaction.
4. Methods of laser evaporation.
5. Controlled crystallization.
6. Dispersion and grinding.
7. Plastic deformation.
One of the main methods for producing metal nanoparticles is a process based on a combination of metal evaporation into an inert gas stream, followed by condensation in a chamber at a certain temperature.
The evaporation occurs by low-temperature plasma, molecular beams and gas evaporation, cathode spraying, shock wave, electrical inspection, laser electrocondition, supersonic jet, various mechanical dispersion methods.
At the initial stage, the initial substance evaporates, applying suitable heating methods. Couples of substances are diluted with a large excess flow of inert gas. Usually use argon or xenon. The obtained pair-gas mixture is directed to the surface of the sample (substrate), cooled to low temperatures (usually 4-77 K). The formation of nanoparticles on the surface of the substrate is a non-equilibrium process depends on a number of factors, for example: the temperatures of the cooled substrate, the degree of dilution of the inert gas, the speed of reaching the surface of the substrate, the speed of condensation, etc. The preparation of nanoparticles by the method of squamation of several substances on the cooled surface makes it easy to enter into their composition various additives, and in the process of controlled heating, increasing the mobility of nanoparticles, carry out a number of new and unusual chemical synthesis.
For the synthesis of nanostructured materials, a number of special cryooractors has been developed by the method of chemical squamation. On cryoractors created in the Russian Federation, the United States and Japan, nanomaterials used as catalysts, ferromagnets, film materials, anti-corrosion coatings are obtained. For example, on one of the plants, two metal evaporates in vacuo and condensed to a substrate cooled by liquid nitrogen. The resulting condensate is pressed at high pressure and is converted to bimetallic nanocomposite.
In the installation of plasma deposition into the plasma zone, together with an inert gas, the carrier is introduced compounds. In the plasma zone, nanoparticles are formed, which, when leaving the plasma zone, is contacted with an organic monomer and form stabilized polymer nanoparticles of oxides, nitrides, metal carbides.
The methods of ion-ray implantation receive ordered nanostructures from quantum dots, called heterostructures. Such heterostructures can be used as sensors, logic devices, new generation laser sources.
In the ion-radial implantation installations, the system from quantum dots is coated with a layer of inert material, and then the main active material of the second layer is again applied. In this second layer, a self-assembly of quantum dots associated with the position in the first layer of active material occurs. Multiple spraying leads to the required heterostructure.
In the gas-phase production of nanomaterials, the particles of metals from crucible - evaporator are sent to the filter from which they are removed by the gas flow. As a result of compaction - the consolidation of nanoparticles is possible serial production of nanoporous materials.
In the case of using a laser evaporation method for coating on various particles, various lasers operating in pulse or continuous modes are used.
Nanomaterials can also be obtained by the upgraded method of Verpel, when the ultralight powder ("powder") of the material being processed is passed through a torch of a combustible gas (hydrogen-oxygen), or plasma of electrodeless high-frequency or electrode discharges. The flame is formed by nanoparticles of metal oxides, which are precipitated in the form of a powder (~ 50 nm) on a cooled substrate. On the basis of such technology, coatings were already obtained, not inferior to diamond hardness, sharply increasing the wear resistance of cutting surfaces, their heat resistance and corrosion resistance.
Chemical methods.The main chemical methods for obtaining nanomaterials are as follows:
· Chemical condensation of vapors;
· Preparation of ash liquid phase recovery (including electrochemical precipitation and synthesis in nanoreactors);
· Radioliz;
· Matrix synthesis.
Getting of golden .
Faraday received aggregative sustainable gravities of gold (with particles 2 - 50 nm) restoration of diluted gold salt with yellow phosphorus.
AUCL 3 + 3H 2 O + P ® AU + P (OH) 3 + 3HCl.
Later, Zigmondi developed methods (classical) synthesis of monodisperse gold as a given degree of dispersion reduction in hydrogen peroxide and formaldehyde.
2 HAUCl 4 + 3H 2 O 2 ® 2 AU + 8HCl + 3O 2,
2 HAUCL 4 + 3HCHO + 11KOH ® 2AU + 3HCOOK + 8KCL + 8H 2 O
The process takes place in two stages. First, the embryos of the new phase are formed, and then in the ash, weak superstruction is created, in which the formation of new embryos is no longer occurs, but only their growth is. In this way, you can get yellow (D ~ 20 nm), red (D ~ 40 nm) and blue (D ~ 100 nm) gold evaluation.
Currently, three solutions are used to obtain gold nanoparticles -
1. Gold-cooler hydrogen acid in water
2. Sodium carbonate in water
3. Hypophosphitis in diethyl ether.
The mixture of solutions of an hour withstand at 70 0 s
Gold particles size - 2-5 nm
Disadvantage: a large number of impurities, reduce which can be restored by hydrogen system.
Chemical reduction is carried out in thermodynamically and kinetically unstable systems. The process of selection of the pair of the oxidizing agent pair, their concentration, temperature, pH of the medium, diffuse and sorption characteristics is influenced.
Now they choose the processes in which the reducing agent simultaneously performs the functions of the stabilizer (N-S-containing surfactants, thiols, nitrate salts, etc.).
Alkali metal tetraborates are most common (MVN 4), which is restored in aqueous media in a wide range of pH, almost all cations (high redox potential - 1.24 V in an alkaline medium). The restoration of metal ions is involved with the participation of complexes with bridging connections ... N ..... This contributes to the subsequent transfer of hydrogen atoms and the rupture of the bridge supply, the redox process and the discontinuity communication inn With the formation of VN 3. The latter is hydrolyzed or catalytically decomposed on the surface of metals particles.
The wide distribution of the method of liquid phase recovery is caused by its relative simplicity. Chemical recovery depends on the nature of the pair of the oxidizing agent pair, so on their concentration, pH of the medium, temperature, solvent properties. Metal meter reducing agents are most often used - borohydrides (for example, NABH 4), aluminohydrides, salts of oxalous and wine acids, formaldehyde in water and non-aqueous media.
For example, silver nanoparticles (AG) of less than 5 nm are obtained by restoring silver nitric acid (AGNO 3) sodium borohydride (NABH 4).
Spherical silver nanoparticles with a size of 3-5 nm are synthesized with the reduction of AGNO 3 sodium borohydride in the presence of quaternary salts of ammonium disulfide when mixing the corresponding solutions at a certain temperature mode:
The obtained particles are characterized by intensive optical absorption in the region of 400 nm, which indicates the metal nature of the particles. At pH \u003d 5-9 in the aqueous medium, the particle is stable during the week. An increase or decrease in the pH leads to rapid aggregation and precipitation of silver particles.
Platinum salts during the restoration of sodium borohydride give particles with a radius of 2-3 nm, with a hydrazine restoration - 40 nm. Polyelectrolytic gels with oppositely charged surfactants were used as nanostructured environments.
Nanoparticles 1-2 nm are obtained when heating hydroxide in ethylene glycol
A promising variety is electrochemical recovery. The electrochemical reduction of metals allows, changing the parameters of electrode processes, in wide limits to vary the properties of the nanoclusters obtained. For example, with cathode restoration of metals:
At platinum cathodes, spherical metal nanoparticles can be formed, and on aluminum cathodes, nanoscier-sized films are formed.
Silver nanoparticles 2-7 nm were obtained with electrochemical dissolution of the anode (silver plate in an aprotic solution of tetrabutylammonium bromide in acetonitrile). With high current densities, particles are formed incorrect form. At current density from -1.35 to - 6.90 mA. CM -2 The diameter of spheres varies from 6 to 1.7 nm. This is a platinum cathode. On the cathode of A1, only films are shaped and deposited
To date, a large number of nanoparticle synthesis methods have been developed .. For example, the hydroxide sol of iron can be obtained by reaction:
FECL 3 + 3H 2 O T (90 - 100º C) "Fe (OH) 3 + 3HCl
In this preparation, it is important to carefully observe the conditions for the reaction, in particular, strict control of the pH and the presence of a number of organic compounds in the system are necessary. Thus, the particle size of Fe 2 O 3, obtained as a result of FECL 3 hydrolysis, depends on the concentration of triethanolamine, isopropylamine and piperazine.
To control the processes of formation and stabilization of nanoparticles use emulsions and micelles and organic substance molecules of large sizes - macromolecules (dendrimers),. Dendrimers, emulsions, micelles can be considered as nanoreactors, allowing the synthesis of the nanoparticles of the desired size and form.
The presence of a large excess energy associated with a highly developed interfacial surface of the section in ultrafaceous systems of a large excess of the interfacial surface of the section is promoting the processes of colloidal particles. To obtain particles of a given dispersion, it is necessary to stop the growth of particles in time. To this end, the surface of the dispersed phase particles inhibit due to the formation of the protective layer from the surfactant or due to the formation of complex compounds on it.
The unique object of chemistry is Pav - organic substances (synthetic and natural), which have limited solubility in water and capable adsorb on the surface of the phase separation, reducing the interfacial tension. These substances have a distillation: a molecule or ion of Pav contains a hydrophobic part and a polar group of one or another nature. The hydrophobic part represents a hydrocarbon radical (C n h 2 n + 1, with n h 2 n - 1, with n h 2 n + 1, C 6 H 4 and others), containing from 8 to 18 carbon atoms. Depending on the nature of the hydrophilic group, the PAV is divided into cationic (they include primary, secondary, tertiary amines and quaternary ammonium bases), anionic (molecules of these compounds contain carboxyl, sulfoester, sulfog groups and others). The specifics of the behavior of the surfactant in aqueous solutions is associated with the peculiarities of the interaction between water molecules and surfactants. According to numerous studies, water at room temperature is a structured liquid, the structure of which is similar to the structure of the ice, but in contrast to ice water has only a neighbor order (R< 0,8 нм). При растворении ПАВ происходит дальнейшее структурирование молекул воды вокруг неполярных углеводородных радикалов ПАВ, что приводит к уменьшению энтропии системы. Поскольку система стремится к максимуму энтропии, то при достижении определённой концентрации, называемой критической концентрацией мицеллообразования (ККМ), молекулы или ионы ПАВ начинают самопроизвольно образовывать ассоциаты, которые называются мицеллами (по предложению открывшего их учёного Мак-Бэна, 1913 г.). Образование мицелл сопровождается высвобождением части структурированной воды, что является термодинамически выгодным процессом, поскольку он приводит к увеличению энтропии системы.
Formation of micelles is fixed usually by changing any physical Property Salt solution (for example, surface tension, electrical conductivity, density, viscosity, light scattering, etc.), depending on the concentration of surfactants. The value of KKM depends on a number of factors: the nature of the surfactant, the length and degree of branching of the hydrocarbon radical, the presence of electrolytes or other organic compounds, the pH of the solution. However, the main factor is the ratio between hydrophilic and hydrophobic properties of surfactants. So, the longer a hydrocarbon radical and a weaker polar group, the smaller the value of the KKM
At concentrations close to KKM, micelles are approximately spherical formations in which polar groups are in contact with water, and hydrophobic radicals are inside, forming a non-polar core. Molecules or ions included in the micelles are in dynamic equilibrium with the volume of the solution. This is one of the causes of the "roughness" of the outer surface of the micelle. The degree of hydration of polar groups, the structure of the hydrate layer, as well as the structure of the inner core depends on the nature of the surfactant.
With concentrations of surfactants, large KKM, it is possible to form several types of micelles (Fig. 4.1), differing in shape: spherical, cylindrical, hexagonally packaged, lamellar. Thus, micelles can be considered as one-dimensional, two-dimensional and volumetric nanoobjects. Depending on the nature of the surge of the aggregation number ( n.) They may vary from dozens to several hundred, while the dimensions of the micelle will change.
Paving molecules insoluble in water with a long hydrocarbon radical and a weak polar group can be dissolved in non-polar liquid phases. In this case, at a certain concentration of surfactants, a micelles are also observed, which is due to specific interactions between the Pavar Polar Groups. Such micelles are called back. The form of reverse micelles depends on the concentration of surfactants and may be different.
There are two approaches to the description of the micheel formation process. According to the first approach (quasichemical model), micelles are considered from the standpoint of the law of the existing mass. Another approach treats the appearance of micelles as the occurrence of a new phase
One of the important properties of micellar systems is to solubilize their ability to significantly increase the solubility of hydrocarbons in aqueous micellar solutions or, accordingly, polar liquids in reverse micellar systems.
Fig. 4.1 - structures arising in solutions surfactant.
1 - Monomers, 2 - Micelles, 3 - cylindrical micelles, 4 - hexagonally packed cylindrical micelles, 5 - laminar micelles, 6 - hexagonally packed water drops in the reverse micellar system.
As a result of solubilization, thermodynamically stable equilibrium isotropic systems are formed, called microemulsion. The variety of factors affecting solubilization (the nature of contacting phases and surfactants, the presence of electrolytes, temperature), leads to the fact that the maximum solubility of substances in the Micelles of the Pav may vary in very wide limits. It should be noted that the properties of the substance at solubilization are strongly changed, as a result of which the rate of chemical reactions occurring in these systems can also change. This phenomenon known as micellery catalysis is widely used in chemistry, biology, medicine, various technological processes. For example, an increase in the reaction capacity of substances is widely used in the processes of emulsion polymerization and enzymatic catalysis.
Microemulsions are thermodynamically stable isotropic dispersions of two unsuccessful liquids. When mixing such liquids of a drop of one of them, stabilized by the interfacial film of surfactant and co-surfactant, which use low molecular weight alcohols, is distributed to another. Microemulsions relate to lyophilic dispersed systems and can be obtained either by spontaneous dispersion of two unsuccessful liquids as a result of a strong decrease in interfacial tension, or in solubilization process. Thermodynamic stability of microemulsion systems is due to low interfacial tension, which can be 10 - 5 mJ. M - 2 for ion surfactants and 10 - 4 mJ. M - 2 for non-ionic surfactants. Depending on which phase is dispersed, and which continuous, microemulsion can be straight - oil in water (m / c) - or reverse - water in oil (in / m). The term "oil" means non-polar organic liquid. In both cases, the dispersed phase consists of droplets, the size of which does not exceed 100 nm.
As a rule, microemulsions are multicomponent systems consisting of various structures (bilayer, cylindrical, spherical micelles). In the process of micelle formation, in addition to liquid isotropic micellar phases, optically anisotropic micellar phases are formed, for example, layered sophisticated and hexagonal phases consisting of rod-shaped units of infinite length, that is, microemulsions have an internal microstructure. In the case when the water and oil content in the system is comparable, the formation of biscontinual systems is possible.
The properties of microemulsions are largely determined by the size and shape of the particles of the dispersed phase, as well as the rheological properties of interfacial adsorption layers formed by the surfactant. Since microemulsions have great mobility and a large surface of the partition between phases, they can serve as a universal environment, including to obtain solid nanoparticles.
In the microemulsion system, the particle of the dispersed phase is constantly facing, coalesce and destroy again, which leads to a continuous exchange of their contents. The process of a collision of the drops depends on the diffusion of the drops in the oil phase (for the reverse microemulsion system), while the exchange process is determined by the interaction of the adsorption layers of the surfactant and the flexibility of the interfacial surface (the latter circumstance is extremely important when conducting chemical reactions in such systems).
Fig. 4.2 - The reaction scheme flowing in the reverse microemulsion system.
Reverse microemulsion systems are often used to obtain solid nanoparticles. For this purpose, two identical microemulsion systems in / m are mixed, the aqueous phases of which contain substances A and B, which form a difficult-soluble compound S. during the chemical reaction, during coalescence of the drops in them as a result of the metabolism, a new connection is formed (Fig. 4.2). The dimensions of the particles of the new phase will be limited to the size of the polar phase drops.
Metal nanoparticles can also be obtained when introduced into a microemulsion containing a metal salt, a reducing agent (for example, hydrogen or hydrazine) or when gas passes (for example, CO or H 2 S) through the emulsion. It is in this way (the restoration of the salt of the corresponding metal or hydrazine) was first obtained by monodisperse metal particles PT, PD, RH and IR (with a particle size of 3 - 5 nm). A similar method was used to synthesize bimetallic platinum and palladium nanoparticles.
Currently, the deposition reactions in microemulsion systems are widely used to synthesize metal nanoparticles, semiconductors, monodisperse particles of SiO 2, high-temperature ceramics.
Despite the fact that the mechanism of formation of nanoparticles is finally not established, a number of factors affecting the reaction flow can be distinguished. This is primarily the ratio of the aqueous phase and the surfactant in the system (W \u003d / [PAV]), the structure and properties of the solubilized aqueous phase, the dynamic behavior of microemulsions, the average concentration of reacting substances in the aqueous phase. The effect of the dispersed phase also has the influence of the nature of the surfactant, which are stabilizers of a microemulsion system. However, in all cases, the size of the nanoparticles formed in the reaction processes is controlled by the size of the droplets of the initial emulsion. Thus, the size of CDs nanoparticles almost linearly increases with an increase in the ratio W. However, the particle size obtained in the reverse microemulsion system, stabilized di (ethylhexyl) sodium sulfosuccinate (Aerosol OT), turns out to be less than in a system stabilized by non-ionic surfactant Triton X- 100 ( n.-(tert-Ocl) phenyl ether polyethylene glycol with n \u003d 10).
Microemulsion systems are used for hydrolysis reactions. An example is the reaction of tetraeethoxysilane hydrolysis in a reverse micellar system stabilized Aerosol Ot
Si (Oet) 4 + 2H 2 O ® SiO 2 + 4etoh.
Most studies in this area refers to the synthesis of spherical nanoparticles. At the same time, great scientific and practical interest is the preparation of asymmetric particles (threads, discs, ellipsoids) and precise control over their form.
Of great interest is the synthesis of nanocomposites consisting of particles of one material (particle size 50 - 100 nm) coated with a thin layer of another material.
Photo and radiation-chemical recovery.
The method is based on the generation of high-level strong reducing agents of the type of electrons, radicals, excited particles.
For photochemical reduction (photo gallery), energy is typical of less than 60 EV, for radiolization (radiation-chemical) - 103-104 eV.
Features of photolysis and radiolization:
Non-equilibrium in the distribution of particles by energies,
Overlapping the characteristic times of physical and chemical processes,
Determining value for chemical transformations of active particles,
Multichannel and nonstationarity of processes in reacting systems.
Advantages of photolysis and radiolization before chemical restoration:
Big purity of the resulting nanoparticles,
The synthesis of nanoparticles in solid media at low temperatures is possible.
Photoliz in solutions is often used for the synthesis of particles of noble metals.
Medium - solutions of salts in water, alcohols, organic solvents. In them, acting particles are formed under the action of light
H 2 0 → Hν E - (AQ) + H + OH
Reacting with alcohols, hydrogen atom and hydroxyl radical give alcohol radicals:
H (OH) + (CH 3) 2 Choh → Hν H 2 O (H 2) + (CH 3) 2 COH
The solvated electron interacts with the silver ion and restores it to the metal
AG + + (Dendrimer) -SOO - → Hν AG 0
At the beginning of photoles in the UV absorption spectrum, bands appear at 277 and 430 nm, attributed to AG 4 + clusters and silver nanoparticles with a size of 2-3 nm. With increasing irradiation time, the maxima absorption bands are moved, which indicates a decrease in the average particle size and the flow of the aggregation process (long-wave).
The photographer of silver nitrate in the presence of polycarboxylic acids made it possible to develop ways to control the shape and particle size. Spherical and rod silver particles are obtained.
The synthesis of nanoparticles during radiolism is to effect on the system of high energies, approximately 100 eV. With radio mass in the system, free electrons and radicals are generated. So, in aqueous solutions, hydrated particles and hydroxyl radicals and hydroxyl are obtained from irradiation from water molecule:
H 2 O HV → H 0 + HO 0 + E
Electrons and radicals when interacting with the starting material form nanoparticles. With the use of the radiolization, nanocomposites are obtained consisting of several metals. For example, nickel-silver nanosystem with a diameter of 2-4 nm; Bimetallic particles of AU-NI size of 2.5 nm, applied to amorphous carbon; Trimetallic PD-AU-AG nanoparticles consisting of palladium nuclei and two shells of gold and silver. The resulting multilayer nanocluster materials are supposed to be used for femtosecond electronic devices of a new generation.
Radioliz for the synthesis of metals particles passing in the liquid phase contributes to the synthesis of more narrowly dispersed particles. In the initial radiolism, atoms and small metal clusters are formed, which are then converted into nanoparticles. The initial stages of their formation are charged AG 2 +, AG 4 + clusters.
Nanoparticles are obtained, including two or more metals. Thus, when the hydrogen is reduced by hydrogen, Na 2 PDCl 4 in the presence of sodium citrate as a stabilizer was obtained palladium particles with a diameter of 4 nm. The addition of K 2 AU (CN) 4 to the region of palladium particles in methanol and the subsequent γ-irradiation leads to the restoration of gold ions. All gold is deposited on palladium particles, forming an outer layer. The resulting particles was besieged and a layer of silver. These multilayer clusters are interesting to study femtosecond electronic processes.
Cryochemical synthesis
The high activity of small metal clusters in the absence of stabilizers leads to aggregation without activation energy. The stabilization of active atoms was carried out at low (77k) and ultra low (4-10k) temperatures by the method of matrix insulation: the pairs of atoms are condensed with a thousand-art excess of argon and xenon to the surface cooled to 4-12k.
In the study of the samples obtained by the matrix insulation method, during the heating process, reactions with specially administered chemical compounds are carried out (diagram). Metal, x - chemical compound (ligand). This is a diagram of sequential-parallel competing reactions. Direction 1 reflects the aggregation process and the formation of di-, trimers and nanoparticles; Direction 2 is the interaction of atoms with ligands and the subsequent preparation of complexes or organometallic compounds.
The formation of nanoparticles in the process of cryocondensation is influenced by: the rate of reaching the cooled surface atoms, the ratio of metal ligand, the condensation rate, the speed of the loss of excessive energy atoms, the pressure of the vapor, etc.
M → m m 2 → m m 3 → m m 4 → m Direction 1
↓ x ↓ x ↓ x ↓ x
MX → M m 2 x → m m 3 x → m m 4 x → m
↓ x ↓ x ↓ x ↓ x
MX 2 → M m 2 x 2 → m
Direction 2 Metal atoms can be obtained by applying various methods of their heating:
Alkaline and alkaline earth elements are evaporated with direct heating (using a low-voltage (5V) transformer with 300a.
High-handed metals (CU, AG, AU) are evaporated from Knudsen cell with direct or indirect heating.
Nanoparticles have an increased reactivity. One of the methods for obtaining and stabilizing nanoparticles is the use of matrices with nanofills and channels, the size and geometry of which may vary in the wide range of nanotechnology. Such mesoporous matrices prevent the aggregation of nanoparticles, serve as nanocontainers. Often, porous inorganic materials are used as matrices - zeolites (aluminosilicates), silica gel, hydroxylapatitis. Nanostructures are formed or adsorption of the steam of the starting material in the pores of the matrix, or the chemical transformation of adsorbed in the pores. For example, when using polyethylene as a matrix, metal nanoparticles in the emissions of the matrix are obtained. Metal nanostructures were formed with thermal decomposition of metal-based compounds adsorbed in polyethylene mesoporist.
The size and shape of the nanoparticles of metals depend on the method of obtaining, the ratio of the nucleation rates and the growth of particles (temperature, nature and concentration of metal or ligand, the nature of the stabilizer and the reducing agent)
Silver nanoparticles in the form of spheres and cylinders were obtained in the photochemical reduction of silver salts in the presence of polyacrylic acid, giving with AG + complex, when irradiated with a nanoparticle with a size of 1-2 nm.
In the presence of decarboxylated acid, except the spheres are formed and nanishing up to 80 nm. This acid reduces the effectiveness of stabilization of spherical nanoparticles and facilitates the growth of nanishing.
The size of particles of metals generated in the presence of macromolecules depends on the conditions of formation of the protective shell polymer. If the polymer is not a fairly efficient stabilizer, the growth of the particle can continue and after its binding to the macromolecule. By changing the nature of the monomer and the polymer corresponding to it and the polymer concentration in the solution - the size and shape of nanoparticles are changed. When using ultrasound using silver nitrate in the presence of N (CH 2 COOH) 3, particles are obtained in the form of spheres, rods and dendrites. The form depends on the duration of the ultrasound pulse and concentration of reagents. The spheres had a diameter of 20 nm, the diameter of the rods 10-20 nm. Iron nanoparticles in the form of spheres and rods were obtained with thermal decomposition of iron pentarbonyl in the presence of stabilizers. The spheres had a diameter of 2 nm and were amorphous, during dispersing in the solution turned into a rods with a diameter of 2 nm and a length of 11 nm and had a cubic ICC structure.
Nanoserebro.Navy provide high stability of the resulting disperse system And directly participate in the process of its formation, controlling the size and shape of growing nanoparticles.
Acrylic row polycarboxylic acids have ionized carboxylate groups and interact with silver ions, tying them into a robust complex (1),
Restore them under the action of light right in the complex (2),
Stabilize Small charged clusters and metal nanoparticles (3) sequentially generated during the synthesis:
(1) R-COO - + AG + → R-COO - ● AG +
(2) R-coo - ● AG + → Hν R-coo - ● + AG +
(3) R-coo - ● AG + + AG 0 → R-COO - ● AG + 2 → R-COO - ● AG 2+ 4 → Hν R-COOAG + N
The entire process of formation of nanoparticles proceeds in contact with the polymer matrix.
The binding Ag + polyacrylate anions (Pa) with m \u003d 450000 and 1250000 with the degree of ionization α \u003d 1.0 occurs cooperatively (with an increase in silver content in the solution, the concentration of chains in the limit degree filled with AG + ions is growing.
The irradiation of the mercury lamp of aqueous solution Ag + ● PA causes the photorestation of AG + cations. At the same time, the AG 2 +8 clusters are formed (in the absence of UV light they are stable for several weeks). Further irradiation leads to the formation of AG2 + 14 and silver nanoparticles. This solution is also stable for several weeks. These particles have a spherical shape and size 1-2 nm at m \u003d 450000 and size 4-5 nm at m \u003d 1250000.
So Restoration of cations, the growth of particles proceeds inside the macromolecular tangle, which protrudes as a nanoreactor of photochemical synthesis of spherical nanoparticles.
When associating Ag + polyacrylate anion with M \u003d 2000, there is no cooperativeness: with an increase in the content of Ag, the uniform filling of macromolecules is accompanied by an increase in the concentration of AG + ions in solution. Photoliz also leads to the formation and assets and nanoparticles.
The shape of silver nanoparticles is determined by the content in the polymer of ionized carboxylate groups. At γ.< 0,7 происходит формирование стержневидных частиц.
At γ \u003d 0.5, particle aggregates are immediately formed in the form of a nanterine thickness of 20-30 nm and a length of several micrometers.
The reduction of AGNO 3 (6.10-4m) sodium borohydride (1.2.10-3m) in the presence of a photodegraboxylated Pa γ \u003d 0.5 (1.2.10m) leads to a stable product with 6 nm spheres. To turn them into elongated enough irradiation from 363<λ <555нм, т.е. в полосе их поглощения. Усиление диполь-дипольного взаимодействия между частицами и вызывает их фотоиндуцированную агрегацию.
The size, shape and degree of polydispersity of silver nanoparticles formed during the photorestation of ions can be controlled by changing M, the degree of ionization and decarboxylation of polycarboxylic acids.
Nanoreactors. The high activity of clusters and particles of metals is associated with noncompensation of surface ties. The multifactor process M + L competing sequentially - parallel reactions going with the activation energy E \u003d 0 occurs in the formations that can be considered as a nanoreactor. These are non-equilibrium systems. Therefore, the more active particle, the lower the temperature of its stabilization. Atoms of most metals are stabilized at a temperature of 4-10K in inert matrices when diluted, for example, argon 1000 times. This is a method of matrix isolation. The essence of it is in the accumulation of substances under conditions that interfere with reactions. Thus, in a solid inert substance at low temperatures, the matrix prevents diffusion and active particles are practically frozen (stable) in a medium that is not able to react with them.
Melting temperature (in K) for inert gases - matrices
NE AR KR XE atoms
P \u003d 1 atm 25 83 116 161
P \u003d 10-3 mm Hg. Art. 11 39 54 74
ELEMENTS OF THE GROUPS OF THE GROUP: FE, CO, NI, RU, RH, PD, OS, IR, PT. The formation of a palladium cluster with a ligand shell L-1,10-phenanthroline and the OAA group occurs in 2 stages:
PD (OAC) 2 + L + H 2 → (1 / N) N + ACOH,
N + O 2 + ACOH → PD 561 L 60 (OAC) 180 + PD (OAC) 2 + L + H 2 O
The obtained palladium particles belong to the "magic" 13, 55, 147, 309, 561, ... ..
These numbers correspond to the fully filled shells of cuboythedral clusters. The mechanism of the synthesis of particles with a fixed number of atoms is not fully found.
Fulleans are obtained by various methods, among which the arc method is common, production in flame, with laser heating, when evaporation of graphite, focused solar radiation, as well as chemical synthesis.
The most effective way to obtain fulleries is thermal spraying of the graphite electrode in the plasma of the arc discharge, Gelia burning in the atmosphere. There is an electric arc between two graphite electrodes, in which the anode is evaporated. On the walls of the reactor, a soot is deposited containing from 1 to 40% (depending on the geometric and technological parameters) of fullerenes. For the extraction of fullerenes from fullerene-containing soot, separation and purification, liquid extraction and column chromatography are used. Performance is no more than 10% of the weight of the original graphite soot, while in the final product, the ratio of 60: from 70 is 90: 10. To date, all fullerenes presented on the market are obtained by this method. The disadvantages of the method include the complexity of the discharge, cleaning and separation of various fullerenes from carbon soot, the low yield of fullerenes, and, as a result, their high cost.
The most common methods of nanotube synthesis are an electric arc discharge, laser ablation and chemical precipitation from the gas phase.
Using electric arc discharge The intensive thermal evaporation of the graphite anode occurs, and the sediment (~ 90% of the anode mass) is formed on the end surface of the cathode) of a length of about 40 microns. Bunches of nanotubes in a sediment on the cathode are visible even with a naked eye. The space between the beams is filled with a mixture of disordered nanoparticles and single nanotubes. The content of nanotubes in the carbon sediment may reach up to 60%, and the length of the resulting single-axis nanotubes is up to several micrometers at a small diameter (1-5 nm).
The disadvantages of the method include technological difficulties associated with the implementation of the multi-stage cleaning of the product from the particulate inclusions and other impurities. The output of single carbon nanotubes does not exceed 20-40%. Hasive amount of control parameters (voltage, strength and density of current, plasma temperature, general pressure in the system, properties and feed rate of inert gas, the size of the reaction chamber, the duration of the synthesis, the presence and geometry of cooling devices, the nature and purity of the material of the electrodes, the ratio of their geometric sizes , as well as a number of other parameters that are difficult to give a quantitative assessment, for example, the cooling speed of carbon vapors) significantly complicates the process regulation, the hardware design of the synthesis settings and prevents them from reproducing industrial applications. It also interferes with the modeling of arc synthesis of carbon nanotubes.
For laser ablation There is evaporation of a graphite target in a high-temperature reactor with subsequent condensation, while the yield of the product reaches 70%. With the help of this method, it is preferably one-way carbon nanotubes with a controlled diameter. Despite the high cost of the material obtained, laser ablation technology can be scaled to an industrial level, so it is important to consider how to exclude the risk of nanotubes into the atmosphere of the working area. The latter is possible with the full automation of the processes and the exclusion of manual labor at the packaging phase of products.
Chemical precipitation from the gas phase It occurs on the substrate with a layer of catalyst from metal particles (most often nickel, cobalt, iron or mixtures thereof). To initiate the growth of nanotubes to the reactor, two types of gases are introduced: technological gas (for example, ammonia, nitrogen, hydrogen) and carbon-containing gas (acitylene, ethylene, ethanol, methane). Nanotubes begin to grow on particles of metal catalysts. This method is most promoted on an industrial scale due to lower cost, relative simplicity and controlling the growth of nanotubes with a catalyst.
A detailed analysis of the products obtained by chemical deposition in the gas phase showed the presence of at least 15 aromatic hydrocarbons, including 4 toxic polycycle carbon compounds were detected. The most harmful in the composition of by-products of production was recognized by polycyclic benzapine - widely known carcinogen. Other impurities are a threat to the ozone layer of the planet.
Several Russian companies have already begun production of carbon nanotubes. Thus, the Scientific and Technical Center "Pomegranate" (Moscow region) has developed by its own pilot installation of the synthesis of carbon nanomaterials by the method of chemical precipitation with a capacity of up to 200 g / h. OJSC "Tambov Plant" Komsomolets "them. N. S. Artemova "Since 2005, it develops the production of carbon nanomaterial Taunit, which is a multi-line carbon nanotubes obtained by gas-phase chemical deposition on a metal catalyst. The total capacity of reactors for the production of carbon nanotubes of Russian manufacturers exceeds 10 t / g.
Nanopowders of metals and their connectionsare the most common type of nanomaterials, while their production is growing every year. In general, the methods of obtaining nanopowders can be divided into chemical(Plasmochemical synthesis, laser synthesis, thermal synthesis, self-propagating high-temperature synthesis (SVS), mechanochemical synthesis, electrochemical synthesis, precipitation from aqueous solutions, cryochemical synthesis) and physical (evaporation and condensation in an inert or reaction gas, electric explosion explosion (eVP), mechanical grinding, detonation processing). The most promising of them for industrial production are gas-phase synthesis, plasma chemical synthesis, grinding and electric explosion explosion.
For gas phase synthesis The evaporation of solid material (metal, alloy, semiconductor) was carried out at a controlled temperature in the atmosphere of various gases (AR, XE, N 2, not 2, air), followed by intensive cooling of the vary of the resulting substance. At the same time, a polydisperse powder is formed (particle size of 10-500 nm).
The evaporation of the metal can occur from the crucible, or the metal enters the zone of heating and evaporation in the form of wire, metal powder, or in the fluid jet. Sometimes the metal is sprayed with a bunch of argon ions. The supply of energy can be carried out by direct heating, transmitting an electric current through a wire, an electric arc discharge in plasma, induction heating currents of high and medium frequency, laser radiation, electron beam heating. Evaporation and condensation can occur in vacuo, in a fixed inert gas, in the gas stream, including in the plasma jet.
Thanks to this technology, performance reaches tens of kilograms per hour. In this way, metal oxides (MgO, A1 2 0 3, SIO), some metals (Ni, Al, T1, MO) and semiconductor materials with unique properties are obtained. The advantages of the method include low energy consumption, continuity, single-diet and high performance. The purity of nanopowders depends only on the purity of the feedstock. Traditionally, gas-phase synthesis is carried out in a closed volume at high temperature, therefore the risk of nanoparticles into the working area can be due only to an emergency situation or non-cellionism of operators.
Plasmochemical synthesis It is used to obtain nanopowders of nitrides, carbides, metal oxides, multicomponent mixtures with a particle size of 10-200 nm. In synthesis, the low-temperature (10 5 K) argon, hydrocarbon, ammonium or nitric plasma of various types of discharges (arc, glory, high-frequency and ultrahof-frequency) is used. In such a plasma, all substances decompose to atoms, with further rapid cooling of them, simple and complex substances are formed, composition, structure, and the state of which strongly depends on the cooling rate.
The advantages of the method are high speeds of education and condensation of compounds and great performance. The main disadvantages of plasma chemical synthesis are a wide distribution of particles in size (from tens to thousands of nanometers) and a high content of impurities in powder. The specifics of this method requires processes in a closed volume, therefore, after cooling, the nanopowdroke can enter the atmosphere of the working area only with incorrect unpacking and transportation.
Today, the semi-industrial level is implemented only physical Methods of obtaining nanopowders. This technologies own a very small part of the manufacturers, located, mainly in the United States, Great Britain, Germany, Russia, and Ukraine. Physical methods of obtaining nanopowders are based on the evaporation of metals, alloys or oxides with their subsequent condensation at controlled temperature and atmosphere. Parase transitions "Para-liquid-solid body" or "steam-solid" occur in the volume of the reactor or on a cooled substrate or walls. The starting material evaporates through intense heating, steam with the carrier gas is supplied to the reaction space, which is subjected to rapid cooling. Heating is carried out by plasma, laser radiation, electrical arc, resistance furnaces, induction currents, etc. Depending on the type of starting materials and the resulting product, evaporation and condensation are carried out in vacuo, in the stream of inert gas or plasma. The size and shape of the particles depends on the temperature of the process, the composition of the atmosphere and pressure in the reaction space. For example, in the atmosphere of helium particles have a smaller size than in an atmosphere of heavier gas - argon. The method allows you to obtain powders Ni, Mo, Fe, Ti, A1 with a particle size of less than 100 nm. Advantages, disadvantages and dangers associated with the implementation of such methods will be discussed below on the example of the wire explosion method.
The method is also widespread. grinding materials mechanically In which the ball, planetary, centrifugal, vibration mills, as well as gyroscopic devices, attributes and symoloomers are used. Technique and Disintegration Technology LLC produces fine powders, as well as nanopowders using industrial planetary mills. This technology allows you to achieve performance from 10 kg / h to 1 t / h, is characterized by low cost and high purity of the product controlled by the properties of particles.
Mechanically crossed metals, ceramics, polymers, oxides, fragile materials, and the degree of grinding depends on the type of material. So, for tungsten oxides and molybdenum, the particle size is about 5 nm, for iron - 10-20 nm. The advantage of this method is to obtain nanopowers of alloyed alloys, intermetallic, silicides and dispersed-strengthened composites (particle size of ~ 5-15 nm).
The method is easy to implement, allows to obtain material in large quantities. It is also conveniently that for mechanical grinding methods, relatively simple installation and technologies are suitable, you can grind various materials and obtain alloys powders. The disadvantages include a wide distribution of particles in size, as well as contamination of the product with materials of the abrasive parts of the mechanisms.
Among all the listed methods, the use of choppers involves draining nanomaterials into the sewer after cleaning the devices used, and in the case of manual cleaning of parts of this equipment, the staff is in direct contact with nanoparticles.
- Laser ablation is a method for removing a substance with a surface pulse.
- Atrisors and simoloomers are high-energy grinding devices with a fixed body (drum with stirrers that make movement of balls in it). Atritamimizes vertical location of the drum, simoloomers -Gorizonal. Grinding grinding material with grinding balls, in contrast to other types of grinding devices, occurs mainly not for the runtime, but according to the mechanism of abrasion.
Physical methods:
Mechanical: grinding in various ways,
Mechanosynthesis, mechanical doping
evaporation processes (condensation), phase transitions,
gas-phase nanopowdock synthesis with controlled
temperature and atmosphere; Method of electrical explosion
Wire
Chemical methods of receipt:
precipitation, sol-gel method, thermal decomposition or
Pyrolysis, gas-phase chemical reactions, chemical
Restoration, hydrolysis, electrodeposition, photo-and
Radiation-chemical recovery, cryochemical
synthesis.
Biological - intracellular and extracellular methods
synthesis.
Conditional classification, because In real methods of obtaining nanostructures
Various processes are used. Chemical processes are often used with
physical and mechanical.
3
Processes for obtaining nano-lectures "top - down" and "bottom-up"
"Top-down" (TOP-DOWN)lies in decreasing
Sizes of objects to Nanovelichin
"Bottom-Up)
It is the creation of products
by assembling them from individual
atoms or molecules as well
Elementary atomolecular blocks, structural
Fragments of biological cells and
t. n.
Fig. Two approaches to getting nanoparticles:
at the top - downward (physical), down -
Ascending (chemical).
(From the book of B.Sergeeva "Nanochemistry")
4Examples of the most widely used synthesis methods
Nanoparticles and nanomaterials:
1 - plasma chemical method,
2 - Electric explosion explosion,
3 - the method of evaporation and condensation,
4 - Levitational jet method,
5 - Method of gas phase reactions,
6 - decomposition of unstable compounds,
7 - the method of cryochemical synthesis,
8 - Sol-gel method,
9 - the method of precipitation of solutions,
10 - hydro and solvotermal synthesis,
11 - self-propagating high-temperature synthesis,
12 - MechanoNTEZ,
13 - electrolytic method, 14
14 - microemulsion method,
15 - liquid phase recovery,
16 - shock-wave (or detonation) synthesis,
17 - cavitational and hydrodynamic, ultrasound, vibration methods,
18 - method of producing nanopowders by dispersing volumetric materials by
phase transformation in a solid state,
19 - Methods of exposure to various radiations,
20-technologies of conversion spraying.
5
Powder
technology
Powder CD (Glater Method)
Electrical sintering
Hot pressure processing
Intensive
plastic
deformation
Equal co-channel angular pressing
Deformation torsion
Pressure treatment of multilayer composites
Controlled crystallization from amorphous state
Technologies of films and coatings
6
Methods for obtaining films and coatings
Thermalevaporation
Physical
Activated reactive evaporation
Electron beam heating
Laser processing (laser erosion)
Ionic deposition
Ion-arc spraying
Magnetron sputtering
Ion-radiation processing, implantation
Deposition from
Gas phase
Plasma-plays
and
Plasmoactivated CDV processes
Electronic cyclotron resonance
Thermal
decomposition
Chemical
Gaseous
Precursors
and
condensed
7
Shredding
Grinding is a typical example of type-down technologies.
Grinding in mills, disintegrators, attribors and other
dispersing installations occurs due to crushing, splitting,
cutting, abrasion, sawing, impact or as a result of the combination of these
actions. For provoking destruction grinding is often held in
Low temperatures.
Providing, in principle, acceptable performance, grinding, however, not
leads to the preparation of very thin powders, because there is some limit
Grinding that meets the achievement of a kind of equilibrium between the process
The destruction of particles and their agglomeration. Even when grinding fragile materials size
The obtained particles are usually not lower than about 100 nm; Particles consist of crystallites
The size of at least 10--20 nm. Should be reckoned with the fact that in the process of grinding
Practically, the product is contaminated with the material with balls and lining, and
Also oxygen.
8
Physical methods of obtaining nanoparticles
Batio3 (5-25 nm) LF Boride IronMechanical dispersion
carried out on the basis of:
a) planetary principle (rotation of the balls
in the volume of substance)
b) the vibrational principle (due to
Vibrations of the hull and movement of the balls)
Essence: power contact with foreign bodies
or between the particles themselves
Dispersing can be carried out
explosion, under the action of ultrasound,
electric field spontaneously
9
Physical methods of obtaining nanoparticles
Electric explosionWhen passed through relatively thin wire pulses
104-106 A / mm2 density occurs explosive evaporation of metal with
condensation of its vapors in the form of particles of various dispersion. In action
Metal particles may occur from the environment
(inert media) or oxide (nitride) powders (oxidative or
nitrogen media). Required particle size and process performance
are regulated by the parameters of the discharge circuit and the diameter of the used
Wire. The shape of nanoparticles is predominantly spherical.
Nanopowder γ-δ-al2o3,
obtained by the method
Elektrolov
10
Physical methods of obtaining nanoparticles
Levitation and Inkjet Method (Flowing Gas Evaporation Technique)Evaporation of metal in the stream of inert gas, for example from continuous
fed and warmed by high-frequency electromagnetic field
Liquid metal drops. With increasing gas flow rate medium
The particle size decreases from 500 to 10 nm, while the particle size distribution
The size is narrowed.
NP manganese with particle size (rhombic form) from 20 to
300 nm, antimony with amorphous structure and medium particle size of 20 nm and
Other np.
11
Physical methods of obtaining nanoparticles
Condensation methodThis is one of the main methods for producing metal nanoparticles. The process is based
on the combination of metal evaporation into the stream of inert gas followed
condensation in the chamber at a certain temperature. Stages:
1) Homogenic or heterogeneous nucleation of the embryos.
2) Metal evaporation by low-temperature plasma, molecular beams
and gas evaporation, cathode spraying, shock wave, electric visiting,
Laser electrodesiss, supersonic jet, various methods of mechanical
Dispersing.
3) Couples of substances are diluted with a large excess of the flow of inert gas.
Usually use argon or xenon. The resulting vapor mixture is sent to
Sample surface (substrate), cooled to low temperatures (usually 4-77
TO).
Currently, the condensation method was modified to obtain
Ceramic nanopowders. The evaporator is a tubular reactor in which
The metallic precursor is mixed with the carrier inert gas and
decomposes. Forming continuous cluster flow or nanoparticles falls
from the reactor to the working chamber and condenses on the cold rotating
Cylinder.
Precessor - chemical, source component or intermediate member
Reactions in the synthesis of any substance.
12
Physical methods for obtaining nanoparticles (condensation method)
1 stage of the condensation process - heating of the substance andFormation of gas flow
2 Stage - Phase transition
3 Stage - Condensation until the formation of the LF
13Method of epitaxy
Epitaxy (Epi + Greek. Τάχις - Location) - Process
growing thin monocrystalline layers (basic
semiconductor structures) on monocrystalline
Substrates. Growing thin layer often inherits type
Crystal lattice substrate
Growing the epitaxial layer of the same composition and
Structures - homoepitaxia, autoepitakia
Growing the epitaxial layer of another composition and
Structures - heteroepitaxia. Determined by the condition
conjugation of the crystal lattice of the applied layer and
Substrate
The formation of quantum dot
Mechanisms of self-organized growth of thin
layer on the surface of the single crystal:
a - two-dimensional (layered),
b - three-dimensional (island),
B - an intermediate growth mechanism (mechanism
Stropean and Krasstanov) (Karpovich I.A. Quantum
engineering. Self-organizing quantum dots //
Coolant 2001, No. 7. P. 102-108.)
14Lithography method
Lithography (from Greek. Lithos - Stone, and Grapho - I write) - the oldest way
Flat printing, in which the printed form was manufactured on the stone (on limestone).
In the process of growth in the AlgaAs semiconductor, impurity atoms are introduced.
Electrons from these atoms go to the GaAs semiconductor, that is, in the region
with less energy. But not too far, because they are attracted to
Powered by them atoms of impurities that received a positive charge.
Almost all electrons focus on the heterobrict itself
From the side of GaAs and form a two-dimensional gas.
A number of masks are applied to the surface of AlgaAs (photoshamis), each of
which has a circle form. After that, the deep
etching at which the entire layer of AlgaAs is removed and partially layer
GaAs, as a result, the electrons turn out to be locked in the resulting
cylinders.
Quantum dots formed in
Two-dimensional electronic gas at the border
two semiconductors.
15
Methods for obtaining consolidated nanomaterials
Powder CDObtained by the condensation nanoparticle
deposited on the surface, a special scraper is removed and
Collector collected. After pumping inert gas in vacuum
preliminary (under pressure of approximately 1 GPa) and
final (under pressure up to 10 gp) pressing
nanocrystalline powder. As a result, plates get
with a diameter of 5-15 and a thickness of 0.2-3.0 mm with a density of 70-90% of
theoretical material (up to 97% for
nanocrystalline metals and up to 85% for nanocheramic).
In general, to obtain compact nanocrystalline
Materials, especially ceramic, promising
pressing with subsequent high-temperature sintering
Nanoporoshkov When implementing this method, it is necessary to avoid
Enlarges of grains at the sintering stage of compressed samples. it
possible at high density of presses when processes
sintering proceeds quite quickly, and with relatively low
Temperature.
16
Methods for obtaining consolidated nanomaterials
Intensive plastic deformationVery attractive way to create compact
Super farm materials with medium grain size 100
Nm is intense plastic deformation. Based on
This method of obtaining nanomaterials is the formation of
The score of large deformations is strongly fragmented and
a disoriented structure that preserves residual signs
Recrystallized amorphous state. For achievement
Large material deformations are used by various methods:
Cutting under quasi-hydrostatic pressure, equal
Corner pressing, rolling, comprehensive forging. Essence of them
lies in multiple intense plastic
Deformation of the shift of the material being processed. Using
Intensive plastic deformation allows you to stay with
reducing medium grain size to make massive
samples with practically a unpaved material structure, which is not
It will be possible to achieve the compactir-type of highly RMS powders.
17
Methods for obtaining consolidated nanomaterials
Laser evaporation methods (laser erosion)The action of the mechanism of this method is as follows:
Sour surface layer of metal during the impact of laser
radiation of moderate power density is heated to temperatures,
large boiling temperatures and the resulting vapor bubbles,
Blowing, supply particles of the liquid phase into the erosion torch of the metal.
According to theoretical estimates conducted for media that are not
have microdefects, as well as medium media, process
volume vaporization is essential at densities
Power of large 108 W / cm2. In real conditions, the process of volumetric
Steaming begins with much less power densities.
In this case, the resulting particles move along the normal surface
targets involved in pairs of target material. If on the way like this
Particle beam Place the captive medium (liquid, substrate,
Polymer matrix) - It is possible to form substrates containing
Nanoparticle material target.
18
Methods for obtaining consolidated nanomaterials
Controlled crystallization of amorphous materialsAccording to this method, the nanocrystalline structure is created in
amorphous alloy by crystallization in sintering processes
amorphous powders, as well as hot or warm pressed or
extrusion. The size of crystals arising inside amorphous
Material is regulated by the process temperature. The method is promising
For materials of various purposes (magnetic,
heat-resistant, wear-resistant, corrosion-resistant, etc.) and on the most
Different bases (iron, nickel, cobalt, aluminum). Disadvantage
The method is that obtaining a nanocrystalline state
It is less likely to be microcrystalline.
19
Methods for obtaining consolidated nanomaterials
Deposition on the substratePrecipitation on the cold or heated surface of the substrate
Films and coatings are obtained, i.e. continuous layers of nanocrystalline
material. In this method, in contrast to gas-phase synthesis, education
nanoparticles occurs directly on the surface of the substrate, and not in
The volume of inert gas near the chilled wall. Thanks
formation of compact layers of nanocrystalline material
There is no need to press.
Deposition on the substrate can occur from vapor, plasma or
Colloidal solution. When departing from vapors, the metal evaporates in
vacuum, in oxygen or nitrogen-containing atmosphere and metal pairs or
The resulting compound (oxide, nitride) is condensed to
Substrate. Crystallite size in the film can be adjusted by change
The speed of evaporation and temperature of the substrate. More often everything in this way
Get nanocrystalline films of metals. When deposition is
Plasma for maintaining an electrical discharge is used inert
gas.
20
Methods for obtaining consolidated nanomaterials
Technology for receiving Langmuir-Brojett films,This is the technology of obtaining mono- and multimolecular films by
Transfer to the surface of a solid substrate of Langmur films
(monolayers of amphiphilic compounds - PAV, formed on
liquid surface)
21
Methods for obtaining consolidated nanomaterials
Technology for obtaining Langmuir-Brojett films (continued)Types (x, y, z) formed layered structures when transferring several
Monosloev on the substrate (hydrophilic (y) or hydrophobic (x, z))
