Nanotechnologies in Construction: A Scientific Internet-Journal @nanobuild-en
Статьи журнала - Nanotechnologies in Construction: A Scientific Internet-Journal
Все статьи: 591
Статья научная
Introduction. The development of methodological monitoring tools to implement building nanomaterials into production is an integral element of designing a mechanism for effective management of the development of business structures. University entrepreneurship and research and educational centers in the ecosystem trend are considered as central actors in the process of creating tools for university transfer of nanobinders for construction purposes. Methods and materials. The process of forming digital competencies among students and teachers in the process of commercialization of scientific developments of a construction university (institute, faculty, department) should be considered as the result of fractal interactions. The development of the innovative ecosystem of the university is achieved by the effective implementation of the process of transferring the results of intellectual activity for the creation of gypsum and ceramic nanocomposites, which are in demand by the regional construction industry. Results. The intellectual and technological potential of universities that train bachelor’s and master’s students for the construction industry determines the prospects for the successful development of the industry in an innovative society. Accelerated promotion of investment developments, requested nanotechnologies of universities, provides universities with additional extrabudgetary funding. On the example of the development of technology for producing small-piece wall and partition products based on nanostructured gypsum binders, they were tested in experimental industrial conditions. Discussion. Effective methodological tools for the transfer of nanotechnological university engineering to the construction industry are: the creation of basic departments at enterprises and the successful functioning of research and educational centers, the participation of employers in educational and industrial practice, etc. From the point of view of laborious commercialization and transfer of scientific developments, the effective way from the idea to the widespread introduction of high-tech products is the real application of the intellectual potential of the teaching staff of the university, institute, departments. Conclusions. The engineering of methodological tools for reliable monitoring of the attractiveness of the regional business ecosystem for the generation and development of transfer processes of popular nanomaterials is an integral element of designing a mechanism for effective management of business structures in construction. Due to the formation of the innovative ecosystem of the university, an effective implementation of the process of commercialization of the results of intellectual activity in the field of nanotechnology, which are in demand by the construction industry of the region, is achieved.
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Статья научная
Introduction. Modification of traditional materials based on mineral binders with fine-dispersed and nano-additives is an essential way to create new functional construction materials with a set of unique characteristics. However, the main difficulty in this process is the method of introducing a finely dispersed component into the cement matrix and the uniformity of its distribution. The homogeneous distribution of the additive particles in the cement composite improves the physical and mechanical characteristics, intensifies the hydration of cement clinker minerals, and is leading to a more durable and dense cement stone structure. The main methods of introducing additives into the cement composition include joint grinding, dry mixing and the introduction of a stabilized suspension of the additive instead of mixing water. Thus, the purpose of this research is to compare the options for the introduction of additives based on the TiO2–Bi2O3 oxide system, which can provide the cement composite with improved physical, mechanical and structural characteristics and the ability to resist mold fouling. The object of this research is the cement compositions modified with an additive based on the TiO2–Bi2O3 system. Materials and methods. The studies were carried out to establish the optimal method of introducing a fine-dispersed additive based on the TiO2–Bi2O3 system. At the first stage, the phase and granulometric composition of the additive was studied, then the additive was introduced into the cement composition in four different ways. The cement stone samples were obtained by dry mixing of the components then mixed with water, by mixing cement powder with water suspension of the additive after ultrasound processing, by mixing a dry mixture of cement and an additive with water-plasticizer solution, and cement powder mixed with water-polymer suspension of the additive after ultrasound processing. After that, the strength characteristics, porosity and ability of the samples to resist fungi fouling were investigated. Results. As a result of the study, the authors concluded that the highest physical and mechanical characteristics of cement stone can be provided by introducing an additive in the form of a stabilized water-polymer suspension. This method contributes to the formation of a more durable and dense structure of cement stone, with an increase in strength of 31; 38 and 44.8% at first day age, 28; 30 and 32% at third day age and 2.4; 9.0 and 14% at 28 days age relative to the control sample containing cement, water and plasticizer. It was found that the highest strength results were shown by a sample containing a stabilized suspension of an additive with a concentration of 50 g/l. The study of the cement stone porosity showed its decrease by 13% at first day age in relation to the control sample with a plasticizer, and by 10% after 28 days of hardening. It was also shown that samples modified with 50 g/l (1.7 wt.%) of the additive demonstrate resistance to bio-fouling. Conclusion. As a result of the research, the authors concluded that the optimal way to introduce a finely dispersed additive based on the TiO2–Bi2O3 system is to mix cement powder with a stabilized water-polymer suspension of the additive, resulting in a more durable and dense structure of cement stone, especially at an early stage of hydration, which can also resist fungi bio-fouling. Thus, the authors came to the conclusion that the cement compositions obtained by this method can be applied as repair compounds and tile grout in damp shaded rooms with favorable conditions for fungi colonization.
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Microstructural analysis of strain-resistant cement designed for well construction
Статья научная
Introduction. The efficiency of oil and gas well construction depends largely on the stage of casing cementing and is completed by checking the quality of its fixing by various methods, most often by geophysical methods. The necessity of highquality cementing and ensuring the quality of technical conditions in the subsequent years of oil and gas well operation is the main task. Materials and methods. Microstructural features of cement slurries and cement stone were analyzed with advance methods. The essential technological properties were developed according to the requirements of GOST 1581-96 and API standards (API spec.10B). Class G cement (PCT-I-G) was used for all formulations. Polypropylene fiber and expanding additive СMA were used to increase impact resistance and to ensure tight contact with the confining surfaces of the obtained plugging stone. Microstructural analysis of the obtained cement stones and developed plugging mortars was carried out by X-ray diffraction (XRD) and scanning electron microscope (SEM). Results and discussion. The results of the study showed that the expanding additive in tandem with polypropylene fiber works effectively to ensure the integrity of the cement ring. Conclusion. Microstructural analysis of plugging stones showed a tight bond between polypropylene fiber and cement stone at a concentration of – 0.25%. The expanding additive is fully hydrated and the obtained cement stone has no expansion cracks at 7 days. The developed grouts with a water-cement ratio of 0.44 showed high compressive strength.
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Modeling flexibility of nanocomposite pipelines
Статья научная
Pipes for oil and gas pipelines made of nanocomposite materials are increasingly used. The most common manufacture of composite piping is by winding fiberglass onto a rotating mandrel. With continuous winding, it is possible to choose the angle of laying the threads – the so-called angle of reinforcement. Depending on its value, as well as on the angle of curvature of the pipeline when its axis deviates from the straight direction, the strength indicators of the pipe change. The article discusses the modeling of the flexibility behavior of a composite pipeline of a curved shape. It is curved pipelines that are in the most difficult operating conditions, accompanied by the manifestation of the Karman effect in the pipe turning angles. As a modeling parameter, a coefficient of increase in the flexibility of the pipe is adopted. Influencing factors are the angle of reinforcement of the composite and the angle of curvature of the axis of the pipeline. An analysis of the results of the calculation performed earlier showed that in the range of reinforcement angles from 0о to 85о the dynamics of the coefficient of increase in pipe flexibility is different. Mathematical models have been developed for two ranges of values for the coefficient of increase in the flexibility of a composite pipe. Modeling error averages no more than 2%.
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Modeling of oil reservoirs heat losses by nanodimensional cellular automata
Статья научная
The oil and gas industry plays a crucial role in the Russian economy. One of the ways to increase its energy efficiency is to reduce unproductive losses. Losses of oil and petroleum products occur at all stages of the oil and gas complex from hydrocarbon extraction to processing and transfer to secondary product consumers. Unavoidable losses in the system are caused by losses of oil and oil products from evaporation during excessive heating by solar radiation during storage in tank farms. In the cold season, intensive external cooling with outside air leads to increased product viscosity and increased cost of electricity for its transfer. To avoid such situations, strict maintenance of the temperature regime of the reservoir by minimizing external heat gains and its own heat losses is re-quired. The article describes the simulation of heat transfer through the heat-insulated wall of the oil reservoir of one of the linear main station of oil pumping. The construction of the temperature graph through the outer fence is performed by the method of nanoscale cells of cellular automaton. The simulation was carried out for three dimensions of the field of cells. It is shown that for the task, the optimal structure is a field of 560 simulation cells.
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Статья научная
Introduction. At present, chemical modifiers are widely used in concrete technology, most of which are complex. The development of the theory and practice of high-strength concrete of the new generation has entailed the development and implementation of complex organomineral additives, which include modern superplasticizers (SP) and finely ground mineral fillers. High-strength concretes are multifunctional concretes that combine, along with high strength, other important properties – high frost resistance, water resistance, elastic-plastic properties, etc. Materials and research methods. Achieving high concrete performance is possible through the use of superplasticizers in combination with finely ground microfillers – stone flour, including nanoparticles and dispersed reinforcement. In this article, the main task is to model the development of the microstructure of cement stone with organomineral additives. For this purpose, a model of the development of the microstructure over time was developed taking into account the possible mechanisms of the influence of components on the composition of hydration products and the nature of early structure formation. Results and discussion. It is shown that the analysis of structural topology and modeling of the processes of formation of the microstructure of filled cement compositions, carried out together with the analysis of hydration products and hardening kinetics, allow us to predict possible mechanisms of action of complex additives and, in a certain sense, to predict possible scenarios for the development of the microstructure of cement stone, which largely determines the main physical and chemical properties of concrete and its durability. Conclusion. Experimental studies have shown that the use of a mixture of microfillers made it possible to achieve a concrete compressive strength of more than 115 MPa on the 28th day of normal hardening, and the insertion of calcium silicate hydrous into the concrete mixture increased the early strength of the hardening composite.
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Modeling the Kinetics of Cement Composite Processes Modified with Calcium-Containing Additives
Статья научная
Introduction. Rock wastes from dust collection systems can be used as mineral additives for making artificial conglomerates based on mineral binders. At the same time, the size of waste particles allows them to be used without additional grinding. Such materials may include fine powders of calcium-containing rocks such as limestone, wollastonite, diopside. Waste rock from dust collection systems can be used as mineral additives for manufacturing artificial conglomerates based on mineral binders. The particle size of the waste allows their utilization without additional grinding. Such materials can include finely dispersed powders of calciumcontaining rocks, such as limestone, wollastonite, and diopside. Methods and materials. We used Portland cement CEM II/A-W 32.5F was used as a binder in the study. The selection of additives was determined through a comparative analysis of their thermodynamic properties with those analogous to clinker minerals. Standard research methods were used to study cement composites, as well as mercury porometry, X-ray phase analysis and electron microscopy. Results. The addition of calcium-containing additives makes it possible to strengthen the structure of cement materials. The greatest increase in strength during the initial hardening period can be achieved by adding 2% of limestone. In the late period of strength gain (in 14 days), the greatest hardening of the stone was obtained with the addition of 9% wollastonite or 7% diopside. Discussion. The results of cement stone diffractogram of the control composition and with the use of additives are given. With the addition of additives, there is a decrease in the intensity of calcium hydroxide reflexes and an increase in the intensity of calcium hydrosilicates reflexes. The study of the macrostructure revealed a significant difference in the structure of the stone. The porosity analysis showed that when calcium-containing additives are added into the system, the total pore volume decreases, the number of small pores increases (size 0.003–1.2 μm). Conclusion. The increase in strength up to 48% is due to the close chemical composition and thermodynamic characteristics of the binder and calcium-containing additives. Wollastonite, due to its fibrous structure, creates micro-reinforcement of the system, and diopside, in its turn, having the highest hardness and elastic modulus of the presented additives, leads to the greatest hardening of the stone.
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Статья научная
Introduction. The aim of this study is to investigate the structural behavior and effectiveness of slab foundations reinforced with vertical elements, a technique increasingly employed in civil engineering to improve the performance of foundations on weak, compressible soil. Traditional slab foundations often suffer from excessive settlement and low bearing capacity, especially under high loads from multi-storey buildings. Reinforcement of the soil base provides a viable solution to these challenges by improving stiffness and reducing deformation. Methods and Materials. The study is based on numerical modeling using the finite element method (FEM) in PLAXIS 3D software, applying the Hardening Soil model in accordance with Eurocode 7. A 9-storey building with a monolithic slab foundation was modeled, and different configurations of vertical reinforcing elements were analyzed. The key parameters varied in the simulations included the spacing (2×2 m, 3×3 m, and 5×5 m) and length (2.5 m, 5.5 m, and 9.5 m) of reinforcing elements. Soil properties were derived from site-specific geotechnical investigations. Results and Discussion. The analysis showed that reinforcing the slab foundation significantly reduced deformation (by a factor of three) and bending moments (by up to 60%) compared to the unreinforced case. The most efficient configuration was found to be concrete elements of 9.5 m length with 2×2 m spacing. The use of vertical reinforcement not only increased the bearing capacity of the foundation but also optimized the stress distribution within the soil mass, minimizing differential settlement. Conclusion. Vertically reinforced slab foundations provide a reliable and cost-effective solution for construction on weak soils. The study confirms that optimal design of reinforcing elements – particularly their length and spacing – plays a crucial role in improving foundation performance. These findings can be directly applied to enhance the design and safety of multi-storey building foundations under challenging geotechnical conditions.
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Modern strategies for the creation of polymer coatings. Part I
Статья научная
Introduction. Coatings on hard materials are widely used in many industries. Coating technologies help prevent or reduce corrosion, contamination and biofouling, chemical and structural degradation, and wear and tear of external surfaces due to exposure to the elements and natural environments. The range of materials used for functional coatings is quite wide: from organic polymers to hybrid composites and inorganic nanoparticles, depending on the desired properties and functionality of the final product. Despite the excellent anti-corrosion characteristics of non-polymer coatings, their usage causes environmental damage. Organic coatings are among the most widely used. Such compositions are applied in liquid form; organic solvents are one of the main components. Environmental concerns have encouraged the development of alternative technologies. The main areas for development are availability of raw materials and the cost of environmentally friendly coatings. Results and discussion. The review substantiates the relevance of research on the development of multifunctional polymer-based coatings. The market for polymer coatings is presented. Methods of surface protection, types of coatings formed, their main components, features of the formation of coatings, the influence of various factors on the formation of polymer coatings, including methods of preparation and pre-treatment of the protected surface are presented. Methods for preventing corrosion are discussed in detail, as well as the main directions in the development of anti-corrosion coatings based on various protective mechanisms. The characteristics of the main components of protective coatings are given. The issue of destruction of polymer coatings depending on the operating environment is considered in detail. The types of media, their influence and mechanisms of action on protected objects are considered. Factors and mechanisms of destruction of polymer coatings, methods for preventing degradation of coatings are listed. The latest technologies for the formation of protective polymer coatings are highlighted. Conclusion. Currently, coatings provide a wide range of quality indicators. An important characteristic of modern coatings is minimal negative impact on the environment, which requires an integrated approach to the design and production of coatings.
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Modern strategies for the creation of polymer coatings. Part II
Статья научная
Introduction. Coatings on hard materials are widely used in many industries. Coating technologies help prevent or reduce corrosion, contamination and biofouling, chemical and structural degradation, and wear and tear of external surfaces due to exposure to the elements and natural environments. The range of materials used for functional coatings is wide enough: from organic polymers to hybrid composites and inorganic nanoparticles, depending on the desired properties and functionality of the final product. Despite the excellent anti-corrosion characteristics of non-polymer coatings, their usage causes environmental damage. Organic coatings are among the most widely used. Such compositions are applied in liquid form; organic solvents are one of the major components. Environmental concerns have encouraged the development of alternative technologies. The main areas for development are availability of raw materials and the cost of environmentally friendly coatings. Results and discussion. The review substantiates the relevance of research on the development of multifunctional polymer-based coatings. The market for polymer coatings is presented. Methods of surface protection, types of coatings formed, their main components, features of the formation of coatings, the influence of various factors on the formation of polymer coatings, including methods of preparation and pre-treatment of the protected surface are presented. Methods for preventing corrosion are discussed in detail, as well as the primary lines in the development of anti-corrosion coatings based on various protective mechanisms. The characteristics of the main components of protective coatings are given. The issue of destruction of polymer coatings depending on the operating environment is considered in detail. The types of media, their influence and mechanisms of action on protected objects are considered. Factors and mechanisms of destruction of polymer coatings, methods for preventing degradation of coatings are listed. The latest technologies for the formation of protective polymer coatings are highlighted. Conclusion. Currently, coatings provide a wide range of quality indicators. An important characteristic of modern coatings is minimal negative impact on the environment, which requires an integrated approach to the design and production of coatings.
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Modern strategies for the creation of polymer coatings. Part III
Статья научная
Introduction. Coatings on hard materials are widely used in many industries. Coating technologies help prevent or reduce corrosion, contamination and biofouling, chemical and structural degradation, and wear and tear of external surfaces due to exposure to the elements and natural environments. The range of materials used for functional coatings is quite wide: from organic polymers to hybrid composites and inorganic nanoparticles, depending on the desired properties and functionality of the final product. Despite the excellent anti-corrosion characteristics of non-polymer coatings, their usage causes environmental damage. Organic coatings are among the most widely used. Such compositions are applied in liquid form; organic solvents are one of the main components. Environmental concerns have encouraged the development of alternative technologies. The main areas for development are availability of raw materials and the cost of environmentally friendly coatings. Results and discussion. The review substantiates the relevance of research on the development of multifunctional polymer-based coatings. The market for polymer coatings is presented. Methods of surface protection, types of coatings formed, their main components, features of the formation of coatings, the influence of various factors on the formation of polymer coatings, including methods of preparation and pre-treatment of the protected surface are presented. Methods for preventing corrosion are discussed in detail, as well as the main directions in the development of anti-corrosion coatings based on various protective mechanisms. The characteristics of the main components of protective coatings are given. The issue of destruction of polymer coatings depending on the operating environment is considered in detail. The types of media, their influence and mechanisms of action on protected objects are considered. Factors and mechanisms of destruction of polymer coatings, methods for preventing degradation of coatings are listed. The latest technologies for the formation of protective polymer coatings are highlighted. Conclusion. Currently, coatings provide a wide range of quality indicators. An important characteristic of modern coatings is minimal negative impact on the environment, which requires an integrated approach to the design and production of coatings.
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Modification of concrete by hydrothermal nanosilica
Статья научная
The paper shows the possibility to use hydrothermal nanosilica as a modifying additive to increase the strength of concrete based on portland cement. The technology of obtaining hydrothermal nanosilica in the form of sols and nanopowders by ultrafiltration membrane concentration and cryochemical vacuum sublimation is proposed. The results of increased strength of concrete under compression by the addition of hydrothermal nanosilica Sol are presented. The experiments were performed on highly mobile concretes (ST = 10–19 cm) on equal-moving mixtures with water-cement ratio W/C = 0.61–0.71 at a dose of SiO2 2 wt.% and the rate of superplasticizer polycarboxylate 0.95±0.05 mas.% by cement. At the initial stage of hardening when the age is 1 day, the increase in the compressive strength of concrete reached 90–128% compared to the control sample. At the age of 28 days the increase in strength was 40%. High chemisorption activity of hydrothermal nanopowder with respect to Ca(OH)2 was determined in the experiment with lime medium. This indicates that the amorphous nanoadditive SiO2, which has a high specific surface area, causes the formation of high-strength hydrates of calcium silicates in the cement (lime) medium as a result of the pozzolan reaction, and this causes an increase in the strength of concrete.
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Modification of portland cement with nanoadditives
Статья научная
Introduction. Portland cement slurries (suspensions) used for well cementing have high water-cement ratios (0.45–0.6). They also contain a minimum amount of inert fillers, must have zero water separation and controlled hardening with a minimum time between the start and end of setting. Literature review. Most of the scientific work on the use of nano-additives in binder systems relates to the construction industry. Nanosilicon, nanotitanium, nanocarbonate, nanoclays, carbon nanofibers, etc. were widely used as modifiers of cement systems, which showed an increase in the strength characteristics of the resulting concretes. Literature review showed that there is a very wide range of concentrations of nanoadditives in cement systems from 0.001 to 10.0%. An increase in the strength of cement with high concentrations of additives in a number of publications is explained by a decrease in its capillary porosity due to clogging of the pore space. However, nanoadditives should not play the role of microfillers in the hardened stone. They should work in cement slurry at the stage of cement hydration and cement structure formation at concentrations less than 1.0%. Results and Discussion. The paper presents the results of experimental studies of the rheological properties and early strength of stone based on Portland cement with additives (0.01%) of nanocarbonate and nanoiron. The role of nanoadditives is to increase the rate of cement hydration by reducing the activation energy, and accelerating the dissolution of the solid phase in the liquid. Nanoadditives can be a “substrate” on which two-dimensional nuclei of a new phase are formed. The probability of the appearance of two-dimensional nuclei on the substrate is much higher than for the formation of three-dimensional nuclei of a new phase in the bulk of the solution. Conclusion. The results show an ambiguous effect of additives on the tested parameters, which indicates the need to optimize the amount of additives. One of the reasons for the ambiguity of the results may be high water-cement ratios, which reduce the likelihood of the formation of “constrained” conditions in cement slurries. At the same time, the effects of accelerated cement hydration are “levelled” and the number of contacts between hydration products is reduced.
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Modifying intensification of the hardening of extruded construction gypsum nanocomposites
Статья научная
The processes of controlled hardening of nanomineral gypsum binders and the formation of microstructure that allow obtaining gypsum concrete with specified technological characteristics are analyzed. Innovative approaches to the regulation of strength and water resistance of gypsum nanobinders, the main directions of increasing their durability in concretes and mortars, building constructions and products are considered. Controlled hardening nanogypsum binders is a promising 3-D additive technology. The mechanism of hardening of gypsum nanocomposites based on calcium sulfate dihydrate and semihydrate is proposed. The kinetics of the process of hydration and setting of nanobinders depending on the content of the components is studied. The increase in strength in the process of hardening of pressed gypsum nanobinders is determined by the content of dihydrate and is accompanied by an increase in the size of needle and plate microcrystals with a thickness of less than 100 nm.
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Nanocoatings in modern construction
Статья научная
The review analyzes the state of the nanocoating market, shows main types of nanocoatings, as well as drivers and barriers to their development and application. Modern progress in the field of nanotechnology allows us to attribute nanocoating to high performance materials, the structure and properties of which can be “designed” according to specific functional criteria and the level of environmental impact. They present unique remarkable characteristics compared to conventional coating materials in construction industry. The government’s grandiose plans to commission new housing and road infrastructure, as well as ambitious projects to develop the Arctic and ensure national security, should lead to the growth of the industry as a whole, as well as to an increase in demand for more efficient, innovative building materials, including nanocoatings and nanopaints.
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Статья научная
The short-term existence of the melt in the weld pool and its overheating, a large temperature gradient near the interface and two-dimensional crystallization centers, in the form of fused grains at the weld pool boundary, reduce the probability and rate of formation of crystallization centers in the liquid phase. This leads to the formation of a coarse-grained columnar structure of the weld metal, which, in combination with defects arising during crystallization, is less ductile than the fine-grained rolled metal being welded, and often causes brittle fracture of the structure. Therefore, obtaining a fine-grained structure of the weld metal is a constant problem in the welding industry. It is now generally accepted that the most effective way to obtain a fine-grained weld metal structure is to modify the weld pool. At the same time, micro- or nanoparticles of refractory metals or their chemical compounds (inoculators) are introduced into the weld pool from the outside, as ready-made crystallization centers. In a superheated melt, the rate of formation of crystallization centers, due to the deactivation of particles, decreases. It can be increased in two ways: by slowing down the decontamination process and by increasing the number of modifying particles introduced into the weld pool. The paper analyzes the factors that determine the modifying activity of inoculators and methods for maintaining this activity in the weld pool. To ensure high activity of the inoculator, it is necessary to reduce the time of its residence in the hightemperature zone of the weld pool; the material of the inoculator should have high values of temperature and heats of fusion, but lower values of thermal and thermal diffusivity. A decrease in the rate of heating and melting of the inoculator particles is achieved by introducing them into the weld pool, by passing the arc column and the high-temperature zone of the bath, in combination with metal particulates that act as microcoolers and means of transporting the inoculator to the tail of the bath. Nanoscale inoculators have a high thermodynamic potential and the associated high nucleating activity. Inclusions of oxides, carbides and nitrides, on the basis of which crystallization centers are formed, in the solidified metal have strong interatomic bonds with the matrix, and due to the fact that the coefficients of their thermal expansion are an order of magnitude lower than those of the matrix, after cooling the metal, they experience all-round compression. Therefore, such inclusions are not dangerous, are not concentrators of tensile stresses and centers of crack initiation. It is experimentally shown in this work that the introduction of carbon nanotubes with a specific surface area of more than 270 m2/g into the weld pool contributes to the formation of a fine-grained structure of the weld metal.
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Статья научная
Steel constructions are the most important objects of the construction industry. The main method of connecting individual elements and assemblies of such structures is fusion welding (electric arc, plasma, electron beam). One of the main problems of metal structures is their tendency to brittle fractures that occur suddenly, without noticeable previous deformations, often at below zero temperatures and loads. In this case, 70–80% of such damage is associated with welding. The nature of the destruction depends not only on temperature, but also on the type of crystal lattice. Metals with a body-centered cubic (bcc) lattice (tungsten, molybdenum, α-iron) are plastic at a relatively high temperature, but become brittle when negative. And metals with a face-centered cubic (fcc) lattice (aluminum, nickel, copper and γ-iron) are plastic even at temperatures close to absolute zero. With decreasing temperature, the mobility of dislocations and vacancies decreases, the yield strength σs increases, that is, the ductility of the metal decreases. Using the A.F. Ioffe model showed that the critical temperature of the transition from viscous to brittle fracture with decreasing temperature depends on the rate of increase of σs. In austenitic steels (fcc lattice with a period a = 0.3645 nm), the impurity mobility (paired with a vacancy) through the internode of the lattice is higher, and the growth rate σs is lower than that of low-carbon low alloy steels (bcc lattice with a shorter period a = 0, 2861 nm). Therefore, the low carbon steels from which structures are made are more sensitive to lower temperatures. In addition, resistance to brittle fracture depends on the number and size of metal continuity defects (pores, inclusions, low-plastic phases in the structure, etc.), which are stress concentrators. Welds are the main suppliers of such dangerous defects and sources of crack initiation. During crystallization of the weld pool, a coarse, columnar dendritic structure with reduced ductility is formed. The formation of a fine-grained structure of the weld during crystallization helps to increase its ductility. The grain size in the cast metal (in the weld) depends on the crystal growth rate and the rate of their nucleation. When welding, the most effective way to grind the grain in the seam is to increase the rate of nucleation. The introduction of refractory particles of nanoscale order into the weld pool (nanomodification) allows obtaining a fine-grained weld structure.
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Nanomodification of cement-based composites in the technological life cycle
Статья научная
The paper reviews the theoretical framework of nanomodification principles of building composites and the conceptual model of the nanomodification from the point of view of the evolutionary model of the solid phase formation depending on the kinetics of heterogeneous processes. According to the route, the main factors of the cement system nanomodifcation were identified for all stages of the technological life cycle. These are associated with the nano-sized particles playing the role of a) structure-forming nuclei, b) substrates for crystallization, c) centers of new formation zoning in the matrix substance of the material, d) nano-reinforcing matrix element. The concepts of the nanomodification and technological tools of the nanomodification of building composites are substantiated. Their hydration kinetics, phase composition, microstructure, rheology and strength characteristics are investigated in order to evaluate the efficiency of the nanomodification principles. It is shown that the use of the nanomodifiers enhances the ductility of cement paste, accelerates cement hydration processes by 9–28 times, and increases strength by 1.5–2 times. This will reduce the cost of flow, casting and hardening processes in the technological life cycle of cement-based composites.
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Nanomodification of epoxy binders
Статья научная
In this work, we studied the effect on the properties of epoxy polymers of domestic nanoproduction – carbon nanotubes produced by NanoTechCenter LLC (RF, Tambov). It has been determined that the modification of functionalized CNTs is the most effective in the composition of epoxy resins, for example, in terms of increasing the adhesive properties of binders, and they can be recommended in the formulations of epoxy adhesives. Modification of CNTs leads to a change in the microstructure of the polymer, depending on the curing conditions.
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Статья научная
Introduction. The article considers the issue of modifying the initial chrysotile fiber and its bundles by the action of hydration products of Portland cement and various acidity value of the treated medium. A brief justification of the relevance of the research topic is provided. It is noted that recently, issues of production of composite materials based on natural and man-made raw materials, which are a promising area of modern economics, have aroused great scientific and practical interest. The availability and low cost of raw materials, as well as low energy, transportation, and overhead costs, contribute to reducing the cost of composite materials. At the same time, the high contractual prices and strong demand in both domestic and foreign markets provide incentives for increasing production volumes. The aim of the research is to study the behavior of the initial chrysotile fibers and their aggregates in the composition of the cement component under the influence of different acidity of the treated medium. Research objective: to investigate the behavior of chrysotile cement dust components under an aggressive environmental condition with electron microscopy examination; calculation of the number and dimensional characteristics of nanofibers and dust particles under the influence of various exposure times of the aggressive factor; microdifraction studies of the nanostructure of the studied samples after exposure to acidic media. Materials and methods. The materials used in the research and their characteristics are given, in particular, chrysotile cement dust containing fibers of commercial chrysotile, acidity of the medium, exposure time, micro- and nanofibers obtained after exposure to aggressive medium. Samples of chrysotile cement dust were taken at the slate production No.1 of JSC “BelACI” and collected at the place of sawing of chrysotile cement products, underwent the stage of dispersion using a centrifugal separator. In the work chrysotile cement dust was used as an object of environmental pollution and its further use in the production of composite chrysotile cement products. Results. The results of studies on the influence of aggressive environment on the components of chrysotile-cement dust, their size characteristics, and structural nano-changes are presented. The studied samples have been examined in a scanning ion-electron microscope at magnifications of 200x, 500x, 5000x, 10000x, and their chemical composition have been analyzed. Discussion. The results of analysis of the obtained experimental data are given. Quantitative composition of fibers and aggregates of fibers in chrysotile cement dust changes after its exposure in acidic medium in comparison with their quantity in initial chrysotile cement dust, and the quantity of separate thin fibers increases, it is explained by the fact that in acidic medium there is not only destruction of cement stone, but also splitting of bundles of chrysotile fibers into micro- and nanofibers. Conclusions. Electron microscopic examination of initial commercial chrysotile fibers and their bundles in cement dust have shown changes in their dimensional and quantitative characteristics, including the products of Portland cement hydration under the influence of the factor of aggressiveness of the environment.
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