Influence Of Aggressive Environment Research Articles

Investigation of the structural and phase state of detonation multilayer coatings based on NiCr/NiCr–Al2O3/Al2O3 during high-temperature oxidation

This paper presents a study of the structural and phase state of detonation multilayer coatings under hightemperature oxidation. The experiment aimed to find out the effect of high temperatures on the structuralphase state of coatings and their effectiveness in preventing oxidative processes. As a result of the research, it was found that after high-temperature tests, protective phases such as NiCr2O4, Al2O3, and Cr2O3 are formed in the structure of multilayer coatings. These phases were identified to play a key role in preventing intensive oxidation of the metal surface. It was determined that NiCr2O4 provides stability to the metal layer, and Al2O3 and Cr2O3 are effective barriers protecting the surface from aggressive environmental influences. It is important to note that no signs of fracture or detachment were found in the multilayer coatings during the entire experiment. After the first cycle, the uncoated sample experienced peeling of its oxide film, resulting in a significant loss of mass. It was determined that the uncoated steel experiences significantly higher mass loss, indicating a faster formation of oxides on its surface. The experimental data confirm the effectiveness of coatings in protecting against oxidative processes at high temperatures, thereby maintaining the stability and durability of the material under extreme thermal influences.

Improving the technology of producing seamless hot‑rolled pipes from stainless steel l80 type 13Cr in the tube rolling workshop

The production of seamless hot‑deformed pipes from martensitic stainless steel with a high chromium content, used under the constant influence of aggressive environments, involves overcoming a series of technological challenges. These challenges are due to the metal’s structural features, such as relatively low plasticity, a narrow temperature range for hot deformation, a tendency to defect formation during rolling, and more intense wear on the rolling tools. The article discusses the main stages of research work on mastering the technology of producing seamless hot‑rolled pipes from stainless steel grade L80 type 13Cr at OJSC “BSW – Management Company of Holding “BMC”. It presents the results and complexities of mastering the technology for producing seamless stainless steel pipes, analyzes the results aimed at reducing the cost of finished products by increasing the durability of piercing mandrels, the resistance of disc saws for cutting blanks, eliminating metal adhesion to the piercing mill’s Dishar discs, increasing the productivity of the rolling line and heat treatment process.

Optimization of Aggregate Composition of Asphalt Concrete Mixtures to Ensure Maximum Density

high strength and stability of asphalt concrete, but also at ensuring optimal characteristics of its structure.The main principles for the optimization of the grain composition are based on the parameters of the size and shape of thе stone aggregate particles included in the composition of asphalt concrete mixtures. An in-depth analysis of the grain composition helps to achieve an optimal balance between coarse and fine fractions, which in turn ensures the stability and durability of the asphalt concrete pavement. The maximum density of an asphalt concrete mixture plays a key role, influen-cing its physical and mechanical properties and ability to withstand aggressive environmental influences and traffic loads. In addition, the density of the mixture significantly affects its resistance to static and dynamic loads and deformations, which is important for ensuring road safety. The paper provides an analytical review of the basic principles and methodology for determining the grain composition of fine-grained asphaltic concrete mixtures with grain sizes up to 10 mm in order to achieve their maximum density. Both domestic and foreign methods for optimizing mixture design parameters are considered. Based on the consideration of ideal mathematical curves the grain composition, the main regularity for fine-grained asphalt concrete has been established, which has similar parameters to the mathematical Fourier curve. Understanding and practical application of the principles of constructing the grain composition of asphalt concrete mixtures of maximum density not only improves the quality of road construction, but also contributes to a more efficient use of resources, ensuring the stability and durability of the pavement. This leads to a reduction in road maintenance and repair costs, which is an important aspect in the context of the economic efficiency of infrastructure projects. Thus, improving the methods for investigating and controlling the grain composition of asphalt concrete is important for the sustainable development of road construction.

ШВИДКІСТЬ КОРОЗІЇ НИЗЬКОВУГЛЕЦЕВИХ ТРУБНИХСТАЛЕЙ У РІЗНИХ АГРЕСИВНИХ СЕРЕДОВИЩАХ

Low-carbon steels are the main material for the production of main oil and gas pipelines. Currently, new generation steels of the X70, X80 type are used in global practice, however long-term pipelines are made of 17Г1C steels (X50, X52). Corrosion of the inner and outer parts of pipes is the main factor in the failure of pipelines. The study examines the influence of aggressive environments on the corrosion rate of low-carbon steels of different generations. It was found that for a more aggressive environment the difference in corrosion rate for different steels becomes more significant, and X80 steel showed the best indicators of corrosion resistance in various aggressive environments.

Influence of Aggressive Environment in Macro and Microstructural Properties of Bottom Ash Geopolymer Concrete

India generates 759.02 million metric tons of coal ash annually. Part of that quantity is successfully utilized, and the remaining portion of the ash is discarded into a landfill. There also is a need to address pollution. Cement industries are responsible for 7% of global warming. Cement has been replaced entirely by thermal power plant waste, and bottom ash is used as a binder to overcome those issues. A few researchers have carried out strength characterization, but an extensive study needs to be carried out under different environmental exposures. Therefore, the present study investigated macro and micro properties of bottom ash geopolymer concrete (BAGPC) subjected to aggressive ecological exposure conditions such as acid, salt, and sulfate attack. Sodium silicate (Na2SiO3) and sodium hydroxide (NaOH) of eight molarities were used as activators for the bottom ash geopolymer concrete (BAGPC) binder. Further bonding between steel and conventional concrete BAGPC mixes was investigated. The durability of conventional concrete (CC) was taken as the control mix to compare the durability of the optimized mix (B4) of bottom ash geopolymer. The test samples were cured for 28 days under ambient temperature and tested for the effect of MgSO4, NaCl, and HCl. The strength loss and weight loss of the BAGPC B4 mix after 7, 28, 56, 90, and 180 days under aggressive conditions showed better performance than CC. It has been observed that geopolymer concrete has good bonding in nature, and the bond strength results indicate excellent bonding between steel and concrete. Microstructure studies revealed that the BAGPC B4 mix had a strong microstructure and not as much of a porous structure. It is concluded that BAGPC has potential value in the construction industry based on all aspects of the experiment.

Technical and economic assessment of the possibility of using a thermal and moisture protection screen to increase the resistance of the reinforced concrete cooling tower shell to operational conditions

During the operation of chimney-type evaporative cooling towers which are made of monolithic reinforced concrete, the shell is exposed to various aggressive environmental influences and the carried-away part of the recycled process water leading to its premature destruction. This article illustrates a method of protecting the shell tower of a reinforced concrete cooling tower from the aggressive effects of the operating environment using a thermal and moisture protection screen design – a ventilated curtain wall with a cladding of fiberglass sheets. By the finite element method, using the ANSYS PC, a calculated analysis of temperature values and air velocity in the air gap was performed, resulting in the geometry of the air gap. To assess the overall change in the percentage of reinforcement, the corresponding strength calculations of the cooling tower shell were made with and without a thermal and moisture protection screen. Subsequently, the corresponding technical and economic analysis of the proposed design option was carried out. As a result the use of thermal moisture protection screen allows significantly redact capital costs during the construction of new cooling towers and decrease expenses for periodic major repairs in the operational cycle, thereby increasing the durability of the cooling tower.

DEVELOPMENT OF A MATHEMATICAL MODEL FOR STUDYING THE TRANSIENT STARTING PROCESSES OF AN INDUCTION MOTOR WITH AN INDUCTION RHEOSTAT IN THE PHASE ROTOR CIRCUIT

The task of improving the reliability of lifting and handling equipment in today's economic environment remains a pressing one. Crane mechanisms, drawing mills, and rope machines are an incomplete list of equipment used at enterprises in various industries, and, as a rule, they are outdated. Particular attention should be paid to crane lifting and handling mechanisms that operate under shock loads, high vibration, and are exposed to aggressive environmental influences.
 Unfavorable operating conditions of the equipment lead to frequent repairs and systematic downtime. In this regard, a number of requirements are imposed on crane mechanisms: high fault tolerance, ease of maintenance, and reasonable price. These requirements are partially met by electric drives (ED), which are equipped with asynchronous motors with a phase rotor and additional resistances in the rotor circuit. As the latter, complete resistance cells with additional contact equipment are often used.
 Many years of experience in the operation of such installations shows that the use of such ED on crane mechanisms leads to a number of negative consequences: 1) reduction of the reliability of the ED due to the use of power switching equipment; 2) the need to periodically involve repair personnel to maintain contact equipment; 3) increase in the weight and dimensions of the ED.
 In the current situation, improving the reliability of crane equipment is an urgent task that can be solved by using induction rheostats in the phase rotor circuit of the IM. This approach eliminates the contact equipment in the rotor and avoids the use of a stepwise switching system for starting resistances, and, due to the nonlinear electromagnetic parameters of the IR, ensures a smooth start of the IMP with a given current. The resulting power losses in the rotor circuit are carried out beyond the IM volume. In this case, the mechanical characteristic of the IMP acquires the desired excavator type.

COMPARATIVE STUDIES OF THE STRENGTH CHARACTERISTICS OF CONCRETE BLOCKS WITH TITANIUM AND IRON RODS (BARS)

The relevance of the topic of the work was shown by the accident of a multi-storey residential building in Miami, which was caused by corrosion of steel reinforcement in reinforced concrete.There is a need to maintain the bearing capacity of structures for a long time in a humid climate, aggressive environmental influences and temperature fluctuations with a lower consumption of materials used.The use of titanium will allow changing some parameters of titanium concrete structures in comparison with reinforced concrete structures. The protective layer of concrete, which serves to protect the reinforcement from the effects of the external environment, will be significantly reduced. This will help to reduce the mass of concrete structures while maintaining strength properties and will allow you to create lighter structures that can withstand heavy loads.Strength tests were carried out on concrete blocks reinforced with smooth iron or titanium rods Ø10 mm, which showed the prospects of replacing steel reinforcement with titanium reinforcement in reinforced concrete.

Prospects for the use of steel reinforcement with protective coatings in reinforced concrete structures

Introduction. Corrosion of steel reinforcement is one of the main factors of destruction of reinforced concrete structures exposed to aggressive environment. The use of steel reinforcement with protective coatings applied to its surface in factory conditions is one of the important directions in the creation of durable reinforced concrete structures.Aim. To show possible prospects for the use of various reinforcement protective coatings in Russia to increase the durability of reinforced concrete structures under the influence of aggressive environment. To develop proposals on the need to carry out research work to create a regulatory base and introduce into practice the construction of reinforcement with a protective coating.Materials and methods. The determination of the prospects for the use of protective coatings of reinforcement in reinforced concrete structures was carried out by analyzing scientific and technical literature, articles, regulatory and technical documents and information from open sources on the problem under study.Results. The experience of using steel reinforcement with protective coatings in Russia and abroad is given. The most widely used technologies for applying protective coatings to reinforcement in factory conditions are highlighted. The main advantages and disadvantages of reinforcement with a protective coating are shown on the example of studies, both in terms of the durability of the coating itself and in terms of working together with concrete. The state of the domestic and foreign regulatory base differs significantly from each other. In contrast to Russia, an extensive regulatory base has been created abroad that allows the design of reinforced concrete structures with reinforcement with protective coatings. Using the example of foreign experience, the most economically feasible types of protective coatings have been identified. With a certain increase in the cost of reinforcement with protective coatings compared to black reinforcement, economic efficiency is generally achieved by increasing the service life of the reinforced concrete structure.Conclusions. Modern design and construction practice shows that for a number of reinforced concrete structures operating under the influence of aggressive environment, it is necessary to use reinforcement with protective coatings. There are great prospects for the use of reinforcement with protective coatings in Russia, but it is necessary to develop а regulatory and technical base in this direction. Based on the results of the analysis of the issue, proposals are given on the need to carry out research and a list of necessary regulatory and technical documents for the introduction of reinforcement with a protective coating into the practice of construction.

STUDY ON POLYMER CONCRETE DEFORMATIONS IN DIFFERENT ENVIRONMENTS AT HIGH TEMPERATURE

Problem statement. High stability composite materials, such as polymer concrete, play a significant role in modern practice. Due to a continuing demand for the use of building materials resistant to aggressive environments both in Ukraine and globally, as well as their prospective use in construction, metallurgy, and chemical industry, the investigation deals with deformations of polymer concrete in various types of environment at high temperature. The purpose of the research is to find mechanisms to increase the stability of polymer concrete in aggressive environment. The object of the study is polymer concrete based on modified furan resins. The subject of the study is deformation characteristics (namely creep) of polymer concrete in different environments (water, sulfuric acid) at different temperatures. Results. In the course of research of the deformation parameters of polymer concrete in various environments were identified. Conclusions. The deformation parameters of polymer concrete on modified furan resins in hot sulfuric acid solutions were determined. It has been proved that the decrease in strength and deformation properties also depends on the hygroscopicity of benzosulfonic acid. It is shown that under simultaneous influence of aggressive environment and temperature in a stressed state the phenomenon of creep is more intensive and the polymer concrete is destroyed in a short time.

Вплив агресивних середовищ на експлуатаційні характеристики матеріалів несучих конструкцій колісних транспортних засобів

The influence of aggressive environments on the operational characteristics of metal structures of wheeled vehicles was investigated. It has been established that, in comparison with their dry concentrates, solutions of mineral fertilizers nitrogen-phosphorus fertilizer and ammonium sulfate cause local corrosion damage not only to ordinary structural steels, but also to alloyed steels (Steel 25, Steel 45, Steel 1X13). At the same time, the rate of corrosion reaches 0.29...0.33 mm/year, which is up to 3 times higher than the rate of corrosion in rainwater. The specified metal materials have the highest rate of corrosion propagation during the first day, then the intensity of corrosion decreases to values equivalent to the rate of corrosion propagation in rainwater. Stationary potentials of steels have the largest negative value for ammonium sulfate solutions, and corrosion currents, in turn, in nitrogen-phosphorus fertilizer solutions.

Mechanical and durability property dimensions of sustainable bamboo leaf ash in high-performance concrete

This research characterises bamboo leaf ash (BLA), which was obtained by calcining dry bamboo leaves at approximately 600 °C for 2 h in a laboratory-controlled muffle furnace. To understand the pozzolanic potentials of the BLA, X-ray fluorescence (XRF) and scanning electron microscope/energy dispersive x-ray (SEM/EDX) techniques were employed. The BLA was then mixed with Portland cement (PC) to produce high-performance concrete (HPC) at 0, 5, 10, and 15% BLA contents by weight. Fresh HPC samples were evaluated for their workability with slump flow test. After 7, 21, 28, and 60 days of hydration, HPC samples' mechanical (compressive, splitting tensile, and flexural) and durability (water absorption, sorptivity, and influence of aggressive environments) were measured. As determined by XRF, the calcined BLA has pozzolanic properties, whereas the SEM micrograph exhibits irregular and angular morphologies. The incorporation of BLA into the HPC matrix enhanced the mechanical and durability qualities of the evaluated samples, primarily at a substitution rate of 10% PC. Therefore, it can be stated that 10% BLA can substitute cement in an HPC subjected to standard environmental conditions.

Investigation of Corrosion Resistance of Two-Layer Protective Coatings

In this article, the influence of aggressive environments on a two-layer coating was investigated. Modern industry places high demands on quality control methods and coating properties during operation. It was established that the electrical resistance of epoxy composite samples depends significantly on the nature of the filler, the cohesive strength of the coatings, and the ambient temperature. We have determined the initial values of the volume resistance of epoxy composites and the temperature values when the samples lose their dielectric properties. The effectiveness of the use of electrospark water hammer treatment with the subsequent introduction of a bidisperse filler at optimal concentrations, which will increase the resist ance of protective coatings, is shown.

ОЦІНКА ЕПОКСИДНО-БІТУМНОГО КОМПОЗИТУ ДЛЯ ЙОГО ЗАСТОСУВАННЯ В АСФАЛЬТОБЕТОННИХ ТОНКОШАРОВИХ ПОКРИТТЯХ НА АВТОДОРОЖНІХ МОСТАХ

Introduction. In this review, epoxy components, in particular epoxy resin and its hardener (thermoactive polymer additives), are defined as the main component of epoxy-bitumen composite (hereinafter — EBC), which is part of the asphalt concrete mixture. The article is aimed at highlighting the results of research conducted to determine the physical and mechanical properties of thin-layer asphalt concrete pavement with the use of EBC for its use on highway bridges. According to the results of laboratory tests, epoxy asphalt concrete (hereinafter — EAB) can be considered one of the best choices for the next generation of durable materials for the installation of thin-layer coatings on highway bridges due to their excellent mechanical properties and thermal stability, as well as economic viability, taking into account the absence of the need for waterproofing of the bridge deck, excessive maintenance and repair costs and a long service life. Problem statement. One of the main mechanisms of destruction of asphalt concrete coatings on highway bridges, especially with orthotropic slabs, is its constant dynamics from external influences, which causes significant deformations that mercilessly affect the durability of the entire bridge structure. Taking into account the thermoreactive nature of epoxy components, the idea of ​​using them as a bitumen modifier arose in order to minimize deformations of the asphalt concrete coating on bridges, reduce the load from the weight of the bridge deck on span structures, and also increase the resistance of the coating to the influence of aggressive environments. In order to obtain high-quality research results for the further possibility of ensuring the installation of coatings on bridges with the best operational characteristics and the most efficient use of labor and resources, studies of the physical and mechanical characteristics of EAB were carried out according to the Superpave methodology. Objective. The purpose of this article is to present the physical and mechanical characteristics of EAB in comparison with other ordinary asphalt concrete on polymer bitumen for the qualitative assessment of the use of EBC during the manufacture of epoxy-asphalt concrete mixtures (hereinafter — EABS) and to determine the real possibility and level of efficiency of using such mixtures for the installation of bridge pavements on automobile roads roads, taking into account the main goal — to increase its durability at various load frequencies due to the improvement of strength, crack resistance and, of course, rut resistance. To achieve the specified goal, a set of experimental studies was conducted, with a comparison of the characteristics of EAB and a number of Superpave protocols of the tested asphalt concretes on polymer bitumen, such as: limit of compressive strength at temperatures of 50 °С, 20 °С and 0 °С; density and water saturation; limit of tensile strength at splitting; stability, conditional plasticity and index of conditional stiffness according to the Marshall method; resistance to rutting. Particular attention was paid to determining the resistance of EAB to the formation of rutting, because during the implementation of certain stages of research it was found that when positive test results were obtained for other indicators, in particular for strength indicators, it is far from a fact that the material is able to pass the rutting resistance test. After the completion of the corresponding comprehensive field test of the bridge covering with EAB, a quantitative assessment of the effectiveness of its use in comparison with similar types of coverings designed to increase the service life (from 30 to 40 years) is planned. Materials and methods. A thin-layer asphalt concrete coating on bitumen modified with thermoreactive polymer additives for its use on an orthotropic or reinforced concrete slab of the carriageway of a road bridge.

МОРФОЛОГІЯ ТА ТЕРМІЧНА СТІЙКІСТЬ СИНТЕТИЧНОГО ЦЕОЛІТУ, МЕХАНОХІМІЧНО МОДИФІКОВАНОГО КАТІОНАМИ Ca, Zn I Mn(II)

An important direction of new technologies of corrosion protection of metals is the use of inhibitory pigments in the composition of paints and varnishes, which are tolerant to the environment, have high efficiency and can replace chromates. Promising anti-corrosion pigments for paints and varnishes are ion-exchange substances, in particular modified zeolites, which will provide optimal selective resistance to aggressive environmental influences. In this work the dispersion and morphology of complex pigments based on synthetic zeolite and monophosphates of calcium, zinc and manganese are investigated. It was found that the modification of zeolites by metal monophosphates by mechanochemical method in a ball mill for 60 min at a speed of 200 rpm leads to decrease in fraction to 2.0 μm by ~44%… 64% and an increase from 2.0 to 10.0 μm by ~60%. The fraction up to 2.0 μm is represented by particles of irregular globular shape > 10.0 μm - agglomerates. Thermogravimetric studies have shown that all synthesized complex pigments are characterized by thermal stability. Thermolysis is characterized by 4 stages, which correspond to the removal of physically adsorbed water, chemically sorbed water, dehydroxylation of the surface by cleavage of OH groups, and phase transitions. Modification with metal monophosphates increases the thermal stability of pigments in the sequence Na-A: Ca(H2PO4)2 - Na-A: Zn(H2PO4)2 - Na-A: Mn(H2PO4)2. Thermolysis of samples in the temperature range from 15 to 700 °С is took place during four stages, most intensively at temperatures up to 400 °С. During mechanochemical dispersion of zeolites with calcium, zinc and manganese monophosphates, the amount of physically adsorbed water increases by ~18… ~41%, and chemically sorbed water decreases by ~19… ~41%. The specific surface area of zeolite Na-A: Ca(H2PO4)2 increases by ~8%, and Na-A: Zn(H2PO4)2 and Na-A: Mn(H2PO4)2 decreases by ~50% and ~22%, respectively. This may be due to the radii of the metal cations and the fraction content up to 2.0 μm when grinding zeolites. Based on the obtained results, the synthesized zeolites can be recommended for further studies of their inhibitory properties as pigments in the composition of paints and varnishes.

МОДИФІКОВАНІ СУЛЬФАТОСТІЙКІ ПОРТЛАНДЦЕМЕНТИ З ДОБАВКОЮ ЦЕОЛІТУ

The article shows that one of the ways to increase the sulfate resistance of cements is to use as an additive of pozzolanic action based on highly dispersed zeolite, which increases the corrosion resistance of concrete. Physical-chemical properties of zeolite tuff as a mineral constituent of Portland cements with the addition of pozzolana are presented. The use of modern grinding technology by separate grinding of Portland cement clinker and natural zeolite in mills with separators of the latest generation allows to obtain high quality Portland cement with zeolite CEM II/A-P 42.5 R PJSC "Ivano-Frankivsk Cement", characterized by high early strength. It is shown that the replacement of the clinker component with zeolite leads to a decrease the content of clinker minerals C3S and C3A in cements, which significantly limit the corrosion resistance of cement stone. Highly dispersed zeolite is characterized by increased pozzolanic activity (after 28 days, the absorption of Ca(OH)2 is 200-250 mg/g). Due to pozzolanic reaction with the formation of C-S-H-phases, the content of calcium hydroxide in the paste based on CEM II/A-P 42.5 R is reduced by 2 times compared to Portland cement CEM I 42.5 R. Decrease in the concentration of Ca(OH)2 in cement pastes eliminates the possibility of the formation of a significant amount of ettringite, which causes sulfate corrosion of cement stone. It was found that during the hardening of Portland cement CEM II/A-P 42.5 R under the influence of sulfate and magnesium media, the coefficient of corrosion resistance Ks after 56 days is 1.16 and 0.98, respectively, while for samples based on Portland cement CEM I 42.5 R Ks decreases by 1.2-1.3 times. The results of researches of influence of aggressive environments on corrosion resistance of Portland cement with the increased content of zeolite type CEM ІІ/В-Р 42.5 are resulted. For Portland cement CEM ІІ/В-Р 42.5 the coefficient of corrosion resistance in the conditions of sulphate environment Кс90 = 1.47. Portland cements with zeolite strength class 42.5, modified with superplasticizers of polycarboxylate type, are characterized by high sulfate resistance and should be used for the manufacture of concrete classes C25/30...C50/60 for construction of dams, hydraulic structures, sewers storage of waste from livestock farms, etc. Modified rapid-hardening Portland cements with the zeolite additive provide technical, environmental and economic effects in the manufacture of concrete and reinforced concretes of hydraulic structures.

Optimal design of shell constructions taking into account the evolution of corrosion damage

An algorithm for computer modeling of the evolution of corrosion wear of the surface material of shell elements in the conditions of joint action of mechanical external loads and the impact of aggressive environments has been developed.
 A mathematical model of deformation of shells of rotation with variable as a result of corrosion of external and internal components of wall thickness is constructed.
 The proposed algorithm allows to trace in time the process of corrosion degradation of the surface material of the shells in accordance with arbitrary (existing) mathematical models of corrosion from the initial moment of time to complete destruction due to corrosion loss of material.
 An original algorithm for selecting the optimal parameters of the rotation shells and the study of their durability taking into account the corrosion degradation of the surface material has been developed.The essence of the algorithm is to optimize the design parameters at the end of its durability, further reverse bilateral build-up of the "sacrificial" layer of material and rational refinement of the project according to technological requirements.
 The solution of the problem of weight optimization of the shell under conditions of asymmetric bilateral non-uniformto the surface material, as a result of corrosion damage, is carried out using the necessary conditions of optimality in the form of the principle of maximum L. S. Pontryagin with phase constraints.The problem of satisfying technological requirements at the initial moment of time is formulated as the problem of the best quadratic approximation of the obtained continuous controls in the form of optimally variable thickness of the shell wall with a piecewise constant function.
 Numerical results of computer modeling of corrosion degradation of surface material and selection of optimal parameters of a cylindrical reservoir for storage of petroleum products under conditions of simultaneous action of force loading and influence of aggressive environment are given.

МЕТОД ЗАЛИВКИ ЭЛЕКТРОННЫХ ИЗДЕЛИЙ ГЕРМЕТИКОМ ВИКСИНТ У-1-18

Relevance The operating conditions of modern electronic products require a responsible approach to their protection from aggressive environmental influences. The use of imported materials in the production of special equipment is limited, so technologists are forced to look for effective ways to work with domestic materials, many of which were developed in the middle of the twentieth century. The use of Viksint U-1-18 sealant has not lost its relevance, it is widely and effectively used. Aim of research To offer an effective and ready-to-use method for pouring metal joints made of stainless steels, aluminum and titanium alloys, for sealing equipment operating in air at temperatures from minus 60 °C to 300 °C when exposed to vibrations — a method that does not require the use of advanced technological equipment. Research methods Review and analysis of normative and technical documentation and scientific literature, as well as generalization of experience in the use of organosilicon sealants by instrumentmaking and shipbuilding enterprises. Results A method has been developed for pouring the product with Viksint U-1-18 sealant. Documentation on the application of the method includes the following sections: — general provisions; — lists of basic and auxiliary materials, equipment, tools and fixtures; technological operations; — characteristics of the main materials (sealant «Viksint U-1-18», sealing paste U-1, catalyst No. 18, sublayer P 11, water-repellent liquid 136-41, active alumina); — safety precautions (indicating the toxic properties of the materials used and indicators of their fire and explosion hazard). Technological operations include: — preparation of products for pouring; — preparation of sealant «Viksint U-1-18» and paste No. 2; — filling products with sealant; — technical control. The proposed method is intended for small enterprises, workshops and laboratories for which the purchase of expensive technological equipment is unprofitable. The results of this work can be used as a reference tool by specialists of design bureaus and manufacturing enterprises, as well as labor protection units, including for the development of organization standards.

Study of Magnetite Nanoparticles by the Method of Mössbauer Spectroscopy

In this work, we studied the Mössbauer spectra of magnetite samples of various compositions. To protect magnetite from oxidation, the resulting particles are coated with protective shells, among which silanes are promising, which polymerize on the surface of magnetite nanoparticles, forming strong covalent bonds. The coating of nanoparticles protects them from aggressive environmental influences, evens out their size distribution, and also protects the environment from the possible toxic effects of the particles themselves. It was shown that the magnetite phase predominates in the sample of native particles, the coating of native particles with alkoxysilane does not lead to fundamental changes in the phase state of the sample particles, and oxidation with nitric acid leads to the complete transformation of magnetite into maghemite. It is obvious that the reason for the distortions of the relaxation nature in the Mössbauer spectra of the samples is the small sizes of the iron-containing domains, which allows us to consider the description of the spectra within the framework of the model of multilevel superparamagnetic relaxation.

STRESS STATE OF COMPRESSED REINFORCED CONCRETE ELEMENTS CONSIDERING CREEP AND INFLUENCE OF AN AGGRESSIVE ENVIRONMENT

Problems associated with the joint long-term action of load and aggressive environment, both in limiting and over-limiting states, are studied bad. Such a combination leads to degradation of materials and changes in the stress-strain state of reinforced concrete structures over time. In case of joint action, they can have mutually increasing damaging effect. Among the many environmental influences encountered, the most aggressive in relation to concrete on cement binder is the impact of sulfates, and in relation to steel reinforcement – the impact of chlorides. It is shown that the stress-strain state of reinforced concrete compressed elements with regard to creep and influence of aggressive environment is formed in time. The deformation in concrete and reinforced concrete compressed elements depends on the stress level. If the stresses are less than the long-term strength, the deformations in time are attenuated, when the stresses in concrete are greater than the long-term strength, the deformations increase. Reinforcement restrains deformations in concrete, while corrosive medium increases creep deformations. When solving these problems we encounter internally statically indeterminate systems. The degree of static indeterminacy is greater than in the case of calculation of reinforced concrete structures without taking into account the influence of the external environment. When the process of soaking is considered, it is possible to consider the influence of the external environment as not aggressive. A solution to the problem using the theory of elastic heredity has been obtained, but it can be shown that a solution using other theories - the theory of aging or the hereditary theory of aging - is also possible. The above solution is true for reinforced concrete elements exposed to external influences at a sufficiently mature age, which can be considered one year or more from the date of manufacture of the structure.