The influence of the mineral composition of water on the results of silicon determination by high-resolution atomic absorption spectrometry with a continuous spectrum source (HR-CS-ETAAS) and electrothermal atomization technique using a contrAA 700 spectrometer has been studied. The study was conducted using samples of natural water from different regions of the Russian Federation and model solutions. A low degree of silicon atomization was recorded when analyzing samples with a complex matrix against the background of a strong absorption signal of matrix components. The reason for the non-selective absorption of the sample matrix by chemical compounds has been demonstrated using a water sample with the most complex composition and a total hardness of about 2000 °dH. The effect of soluble salts of Ca (II) and Mg (II) in the presence of macrocomponents — alkali metal ions K (I) and Na(I) — on the determination of silicon in water has been proved. It is shown that at the values of the total stiffness less than 15 °dH there is no dependence of the analytical signal on the content of matrix components. An assumption is made about the strong influence of calcium compounds on the determination of the analyte due to the formation of a carbide coating on the surface of a graphite furnace, the appearance of a «memory effect» and an increase in the background signal during subsequent atomization cycles. The best results of the silicon determination were obtained with tungsten, iron, magnesium, and palladium present as chemical modifiers. A method of diluting the sample solution was used to reduce the level of background absorption during electrothermal atomization of mineral water. Conditions for eliminating the influence of matrix components for real samples of mineral water and calibration solutions are proposed. A method for determination of the dissolved forms of silicon in water samples with a complex matrix has been developed. The correctness of the results of silicon determination in the samples of natural underground water in the case of a strong matrix effect was confirmed by an independent method of analysis. The results of the study reveal the entirely new prospects of using the method of high-resolution electrothermal atomic absorption spectrometry with a continuous spectrum source for the determination of silicon in natural water.

Results of a comparative study of the electroanalytic properties of solid contact sensors (tubular and planar) in cefuroxime (Cefur), cefotaxime (Ceftx), cefixim (Cefix), and amoxicillin (Amox) solutions are presented. Tetraalkylammonium associates — tetradecylammonium (TDA) and dimethyldistearylammonium (DMDSA) — with complex compounds silver (I) — β-lactam [Ag(β-lac)₂] TAA; ZnO modifiers, polyaniline, and polyaniline nanotubes are used as electrode active components (EAC). The studied sensors based on [Ag(Cefur)2] TDA and [Ag(Amox)₂] DMDSA in solutions of cefotaxime, cefuroxime, cefixime, and amoxicillin are characterized by a short response time: for tubular 20 – 25 sec (unmodified), 12 – 17 sec (modified); for planar – 20 – 25 sec (unmodified), 10 – 15 sec (modified). Modifiers stabilize electrode potential and perform a function of a mediator of electron transfer, which leads to improvement of electroanalytic characteristics of sensors. The linear range of electrode functions in antibiotic solutions is 1 × 10^–4 – 1 × 10^–2 M, the detection limit ranges between 2.5 × 10^–5 – 8.9 × 10^–5 M for unmodified and 5.6 × 10^–6 – 7.5 × 10^–5 M for modified sensors, and 4.2 × 10^–5 – 7.2 × 10^–5 M for planar sensors. The potential drift is 8 – 12 mV/day for unmodified and 5 – 7 mV/day for modified planar sensors; service life is 1.5 – 2 months. The advantage of planar sensors is the possibility of using them in microassay detection, which is relevant in the analysis of biological media. Application of solid-contact sensors for determination of the antibiotics under study in model aqueous solutions, medicinal preparations, oral fluid, blood serum in various infectious diseases is demonstrated.

A method for prompt and reliable control of low oxygen content in aluminum nitride powder using a modern gas analyzer «Metavak-AK» operating in automatic mode and never used previously for this object is presented. Aluminum nitride was obtained under conditions of pilot production at ISMAN by the method of self-propagating high-temperature synthesis (SHS). A program for operation of a «Metavac-AK» analyzer has been developed for oxygen determination in AlN samples and optimal conditions of analysis were specified: reductive melting of a sample in a graphite crucible at a furnace temperature of 2700°C in the presence of a combined Sn/Ni flux in a helium flow. The total oxygen content in aluminum nitride powders and the relative standard deviation ranged within 1.01 – 1.18% and 1.75 – 9.87%, respectively.

The search for effective radio-absorbing materials is an urgent task in solving the problems of electromagnetic compatibility, electromagnetic pollution, as well as stealth and stealth technologies. We present the results of studying the electrophysical and radio-absorbing characteristics of ferrite-polymer composites depending on the structure and magnetic properties of the ferrite filler, as well as the dielectric properties of the polymer matrix. The radio absorbing characteristics of composites F-42/Mn-Zn-ferrite, F-42/Ni-Zn-ferrite, F-42/yttrium iron garnet, F-42/BaFe₁₂O₁₉, F2M/LiMnZn-spinel, PS525/Mn-Zn -ferrite, PVA/Mn-Zn ferrite, and PVA/Ni-Zn ferrite have been studied. Experimental data on the reflection coefficient, determined on a metal plate in a frequency range of 0.1 – 7 GHz showed that spinel ferrites and composites containing them are effective radio absorbing materials. Analysis of the spectra of complex dielectric and magnetic permeability revealed that composites with spinel ferrites and yttrium iron garnet are characterized by a dispersion of the magnetic permeability, which arises as a result of resonance processes of the motion of domain boundaries and natural ferromagnetic resonance. Moreover, the electrical properties of ferrites can affect the high-frequency spectra of the permittivity and permeability. It is shown that the use of electroactive polymers as matrices makes it possible to increase dielectric losses in the high-frequency range and obtain the maximum attenuation of electromagnetic radiation within 25 – 40 dB with a width of 10 dB up to 2.5 GHz in 2 – 7 GHz range. The results obtained can be used in further study of the functional properties of radio-absorbing materials in the high-frequency range.

Products based on silicon carbide are widely used in different industrial applications due to a high level of their mechanical, thermal, and operational properties. When the reaction sintering procedure is used to obtain silicon carbide materials, the preformed porous samples consisting of silicon carbide powders, carbon filler, and coke binder are subjected to liquid-phase silicizing (silicon melt infiltration (MI) in a vacuum furnace. We present the results of studying samples of reaction-bonded silicon carbide (RBSC) using visual-optical and radiographic methods of non-destructive control. Silicizing of carbon-silicon carbide materials can result in formation of defects on their surface and in the bulk of the material. The visual-optical method is shown to be rather simple and extremely informative procedure which ensures the detection of surface defects in the form of pores, cracks, chips, shells, and can also provide indirect indications of possible presence of internal defects in the form of underimpregnated areas. The samples silicized with a larger number of silicon drops on their surface exhibit a higher density and a smaller number of underimpregnated areas which can be detected using radiographic control. X-ray control carried out for several exposures differing in the angle of sample rotation by 90° provided 95%-probability of detecting internal volumetric and planar defects. The results obtained can be used in the manufacture of RBSC-based parts of tribotechnical duty, shut-off valves and other wear-resistant products.

It is noted that calculations of the rated strength for bearing elements of extremely loaded structures, including nuclear power plants allow inelastic deformation of the materials of these elements. At the same time calculations of the low cycle fatigue require taking into account factors that are not observed under single loading including, i.e., kinetics of cyclic strains, cyclic creep, change of the mode of inelastic cyclic deformation upon normal operation. Moreover, the materials can be of different types: cyclically hardening, softened or stable. For the first type of materials at a soft loading with constant amplitude of stresses in cycles, the range of strains decreases with an increase in the number of cycles, but increases for the second one. Under a hard mode of loading with constant amplitude of strains the maximum stresses in a cycle for the hardening material increase, and, on the contrary, decrease for softened material. Moreover, the soft loading of softened material results in one-sided accumulation of plastic strains as the number of loading cycles increases. These circumstances must be taken into account both in the analytical description of the kinetics of deformation diagrams and in the corresponding calculation equations used in the strength standards. It is noted that at early stages of forming computation methods developed for these conditions, calculation of stresses was carried out in the assumption of ideal elasticity of the material. The use of such approach was attributed to the lack of available methods for addressing the problem of an inelastic cyclic deformation, complicated on the statement. The subsequent evolution of the theory of cyclic elastoplastic deformation, analytical and numerical solutions of cyclic boundary-value problems, developing of numerical methods of computation and powerful computer packages fundamentally changed the situation providing the possibility of analysis and modeling of physically and geometrically nonlinear deformation processes. It is shown that transition from the elastic adaptability (with an elastic deformation of the structure in a stable cycle) to a sign-variable flow is smooth and continuous, similar to the transition from the elastic to plastic deformation under a single loading. Such a mechanism is similar to conditional boundary of the transition from low cycle to high-cycle fatigue under a cyclic strain. At the same time, we offer to use in calculations the existing rather simple models and experimentally determined parameters of cyclic deformation diagrams of materials. In the modern statement of the problems under consideration, taking into account both the kinetics of cyclic and unilaterally accumulated deformations, with allowance for the manifestation of creep effects in cycles is of fundamental importance. This approach also makes it possible to take into account the acceleration of unsteady cyclic creep due to previous plastic deformation of a different sign, which can be rather significant.

A serious problem in computer simulation of the stress state of polymer structures is to ensure the adequacy of the mathematical description of the mechanical properties of materials. The structural model of a viscoelastic material has a number of advantages in describing both the rheology of the material and trajectories of the material deformation. In this model, the material is described as a structure consisting of several elements with relatively simple rheological properties. Reproduction of a complex behavior of the material under alternating non-isothermal loading is ensured through the interaction of simple elements. A technique developed for modeling a viscoelastic material is intended for strength calculations of structures made of materials operating under conditions of prolonged repeated thermomechanical exposure using the finite element method. Application of the developed procedure to a polymeric material, polymethyl methacrylate (PMMA), is considered. The results of testing the material under uniaxial compression at a constant temperature are presented. The methodology and results of identification of the developed structural model using a specialized software are described. Formulas for approximation of the deformation characteristics of the material at a constant deformation rate and the time dependence of material deformation during the holding the material at a constant stress level are obtained. Approximation is an important step in identification of the material model which facilitates the systematization of the initial experimental data and their further mathematical processing. The best approximation of the deformation characteristics of a viscoelastic material is given by a hyperbolic tangent function, whereas the logarithmic function provides the best results for deformation upon exposure. Further construction of the structural model was carried out by selection of sequential parameters of bilinear rheological functions of the individual elements the model and iterative refinement of those parameters. The simulation results were compared with the experiments carried out at different strain rates and with exposure at different stress levels. We just present the results of the initial stage of the carried out experimental and theoretical studies.

Theoretical or theoretical-experimental methods are widely used when studying various techniques for processing materials, cutting among them. The physical and mechanical properties of the materials being processed are to be taken into account along with the process parameters (mode, geometric parameters of the machining tool, etc.). The resistance of the material to plastic shear present in the calculated dependences for determination of the force and temperature in the cutting zone and the temperature in the surface layer of the workpiece, as well as for determination of the quality parameters of the surface layer of the part (the residual stresses, degree and depth of work hardening, roughness, and others) and the accuracy of processing is used in all the aforementioned methods in addition to the ultimate tensile strength and the modulus of elasticity of the processed material. Previously, when determining the numerical value of the resistance of the processed material to plastic shear, the latter was considered as a function of the tensile strength of the processed material. However, an increased temperature observed in the cutting area which depends on the combination of the processed and tool materials, the mode of processing, and on the geometry of the cutting part of the tool was not taken into account. The value of the effective cutting force was also ignored though this value is determined by the same parameters which determine the temperature in the cutting zone. The mechanical characteristics of the processed material are known to depend on the temperature. In this regard, the resistance of the processed material to plastic shear was assessed at a certain temperature determined by the technological conditions of processing. The goal of the study is to prove the necessity of determining the resistance of the processed material to plastic shear to be used in theoretical determination of cutting forces, temperature in the cutting zone, and the quality parameters of the surface layer of the part. The dependence is given to determine the value of the resistance of the processed material to plastic shear under optimal processing conditions that ensure the minimum wear of the cutting tool taking into account the parameters of the cutting process and the geometry of the cutting part of the tool. Processing conditions that determine the temperature and force in the cutting zone are taken into account by chip shrinkage in the formula for determining the value of the resistance of the processed material to plastic shear. The use of the proposed technique can improve the accuracy of calculations of the quality parameters of the material of the surface layer of the part and the accuracy of processing.