Determination of iodine in urine is an important methodology in the assessment of thyroid disorders. This indicator is often used in epidemiological studies of the state of iodine nutrition of the population, since the widespread prevalence of human iodine deficiency diseases is directly related to the lack of iodine intake with food and water. A method for the iodide ion determination in urine has been developed based on preliminary preservation of the sample in the presence of a buffer solution containing 4.28 %wt. H₂O₂ at pH 6.8 – 7.5 and measurements of the potential of the iodide selective electrode directly in the preserved sample solution without separation of the interfering components. After mixing the sample with a buffer solution in a ratio of 1:1, it is preserved after 18 – 24 h and stored for at least 30 days. The interfering effect of macro- and micro-components has been studied. It is shown that the amount of sodium chloride in the sample should be taken into account only in studying the severe iodine deficiency (≤20 μg/liter) and urea does not affect the potential of the electrode. To assess the total effect of the organic components of urine, we compared the results of parallel determinations of iodine in the samples, one of which was preserved, and organics was removed from the second one by alkaline ashing. It is shown that the discrepancies in the results were random and did not exceed 11.3 %. Iodine loss has not been determined, the bias between the concentration of the introduced and found additives was insignificant. Thus, in a buffer solution with hydrogen peroxide, not only the preservation of the urine sample for a long time takes place, but also the interfering influence of inorganic and organic components of the sample matrix on the membrane of the ion-selective electrode is eliminated. Metrological evaluation of the developed methodology was performed, which showed the precision and trueness of the procedure. The method was tested in an experiment on the correction and enrichment of iodine in the diet of schoolchildren. The low cost, convenient and easy to use equipment, the possibility of long-term storage of preserved samples makes the method mobile and suitable for biochemical monitoring of iodine consumption and deficiency during a large-scale population survey.

The goal of the study is to develop a piezoelectric sensor based on a molecularly imprinted polymer (MIP) for the determination of cefotaxime in liquid media. To obtain an antibiotic-selective sensor, the electrode surface of was modified with a molecularly imprinted polymer. A pre-polymerization mixture was prepared using a copolymer of 1,2,4,5-benzoltetracarboxylic acid and 4,4’-diaminodiphenyloxide, and an aqueous solution of cefotaxime in a ratio of 1:1. Then a two-stage thermoimidization was carried out in a drying cabinet at a temperatures of 80 and 120°C. After that, the sensor was cooled to room temperature and placed in distilled water for 24 h. An imprinting factor (IF = 40.9) and a selectivity coefficient were calculated to assess the ability of a sensor with MIP (cefotaxime) to recognize a template molecule. A low selectivity of a MIP sensor with the cefotaxime imprint to other cephalosporin antibiotics is revealed. The experiments were carried out on an original installation including a piezoelectric sensor, a portable generator, and an MP732 USB-frequency meter connected to a computer. Piezoelectric quartz resonators of AT-cut with silver electrodes with a diameter of 5 mm and a thickness of 0.3 mm with a nominal resonant frequency of 4.00 MHz were used as sensors. The determination of antibiotics in model solutions was carried out by the method of calibration schedule. The range of detectable concentrations (0.1 – 1.0 × 10^–4 g/dm³) was experimentally determined. The detection limit of cefotaxime is 1.0 × 10^–5 g/dm^3. The correctness of the cefotaxime determination of in individual and binary model solutions was verified by the «spike-test». It has been shown that a sensor with MIP-cefotaxime is not sensitive to an extraneous antibiotic. The relative standard deviation does not exceed 10 %.

A method for the determination of Fe_tot, SiO₂, P, V₂O₅, TiO₂, Cr₂O₃, Ni, Cu, Zn in iron ore raw materials (i.e., pellets, iron ore agglomerate, aspiration dust and slag component of a scrap) by the method of atomic emission spectrometry with inductively coupled plasma (ICP-AES) has been developed using microwave sample preparation in analytical autoclaves. The composition of the acid mixture for the complete dissolution of the sample component, as well as the parameters of microwave decomposition, excluding the depressurization of the autoclave and the loss of sample elements which form volatile compounds are proposed. The developed method of microwave sample preparation in closed autoclaves makes it possible to decompose iron ore samples using the minimum amount of acid (17 cm³) in 45 min. Conditions for the determination of normalized elements in iron ore samples by the ICP-AES method after microwave sample preparation were determined: the operation parameters of the spectrometer were optimized, the analytical lines of each determined element free from spectral overlaps were selected, the efficiency of using cadmium as an internal standard was experimentally proved. The equations for calibration dependences and the ranges of determinable contents are presented. When using cadmium as an internal standard in the analysis of iron ore, a decrease in the value of the standard deviation from 0.17 to 0.04 is observed when determining Cr₂O₃; from 0.02 to 0.004 when determining Fe; from 0.03 to 0.002 when determining SiO₂; from 0.015 to 0.008 when determining TiO₂; and from 0.17 to 0.02 when determining V₂O₅. The correctness of the determination of the standardized elements by the developed method is evaluated, using certified reference samples (CRS) similar in composition to the analyzed material. The results of determining the standardized elements according to the developed methodology were compared with the data obtained using GOST-approved methods of analysis, and then checked in accordance with the Recommendations of RMG 76–2014. The developed ICP-AES technique is characterized by a wider linear range of the determined concentrations than that in GOST-approved techniques, thus providing determination of the components in iron ore raw materials that could not be controlled before. 

Acoustic emission transducers (AET) with piezoelectric cells converting acoustic signals into electric ones, are the most important components of the channel for transmitting information about the parameters of acoustic emission (AE) sources. The main AET parameters are determined by different calibration techniques, but the shape of amplitude-frequency characteristics (AFC) largely depends on the calibration method which significantly complicate the choice of AET for control. We present the results of studying the AET parameters taking into account the role of the acoustic-electronic channel and calibration conditions. It is shown that the most complete data on the AET properties are contained in the impulse response, which should be used to measure the AET parameters. In this case, the AFC is of secondary importance. It is preferable to calibrate the AET using longitudinal waves at normal incidence of the wave on the AET (basic scheme). The results obtained can be used when selecting methods of calibration of working transducers used for diagnostics of industrial objects.

Electric spark alloying (ESA) is a traditional method of obtaining protective coatings on the working surfaces of parts and mechanisms. A review of the results of studying the structure and properties of protective coatings obtained by the ESA method using SHS-electrodes is presented. Ceramic and cermet electrodes are obtained by the method of SHS-extrusion carried out under conditions of combustion processes with high-temperature shear deformation. SHS extrusion makes it possible to obtain electrodes with desired structure and properties in tens of seconds in one technological stage. The results on the study and application of electrode materials made of hard alloy materials, intermetallic compounds, materials based on the MAX-phase and ceramic materials with a nanoscale structure are presented. Analysis of the microstructure and properties of the formed alloy layers showed that the protective coating consists of at least two zones. The sizes of the structural wear-resistant components on the coating surface, usually correspond to their sizes in the original electrodes. When going in depth to the substrate, the grain size decreases and amounts to 20 – 100 nm. It is shown that a protective coating is formed on the surface which increases the mechanical and tribological properties. The presented results can be used in comparative tribological tests of hardened coatings, industrial tests of machined parts, etc.

Artificial materials with negative magnetic and dielectric permittivity have unique electrodynamic properties that are not present in natural materials. We present the results of studying of the main magnetic LC resonance induced by a plane electromagnetic wave of GHz range in the linear structures of subwavelength dielectric ring elements with a high relative permittivity. The dielectric constant of the ring material (capacitor ceramics) is 160. Resonant scattering on the main magnetic mode and wave properties of linear structures consisting of subwavelength dielectric elements in the form of flat thin rings were studied. A single ring or ring structures were arranged in such a way that the vectors of the electric and magnetic fields of a plane incident electromagnetic wave were parallel to the plane of the ring, whereas the wave vector was perpendicular to the plane of the ring. Linear structures consisting of two or three rings were oriented along the magnetic vector of the incident wave. The magnetic field probe was placed on the line of the axis of symmetry of the ring and structures relative to the wave vector at the side of the structures most distant from the antenna. The spectra of transmitted radiation were measured during resonant excitation of magnetic fields in a system of dielectric rings in the near (distance — 2 mm) and remote (distance — 30 mm) zones from the ring. It is shown that in the near wave zone, splitting of the resonant frequency occurs due to mutual inductance and interaction of the rings. As the number of rings increases, the number of additional peaks also increases. A bandwidth of ~200 MHz with an amplitude 25 dB greater than the amplitude of the incident electromagnetic wave in the specified spectrum appears between the split levels. In the far zone, the transmitted radiation at the resonance frequency for a single ring practically does not change due to the splitting of this resonance frequency due to the interaction of the rings in the structure. The results obtained can be used in the development of new materials.

A brief review of known approaches to converting diagrams obtained by indentation into tension diagrams is presented. It is noted that most studies on the transformation of kinetic diagrams of indentation of a spherical indenter into tension diagrams are carried out within the limits of uniform deformation using both computational and experimental approaches including the finite element method (FEM) and neural networks. However, we consider that such a transformation from one diagram to another can be fulfilled successfully when using the proper relationship between indentation and tension deformations. This makes it possible to obtain both more reliable estimation of the mechanical properties from indentation tests and more accurate transformation of these results into the stress-strain curves. A relative indentation diameter is one of the main parameters used in the most frequently used formulas for determining plastic deformation. However, at the same values of the relative indentation diameters and a constant ratio of the average contact pressure (Meyer hardness) to the true tensile stress, the strain values upon indentation and tensile can differ significantly due to different ability of materials to strain hardening. We determined a relationship between the true elastoplastic deformation in tensile tests and the relative depth of unrecovered indent obtained in indentation tests with allowance for strain hardening. A methodology for converting the kinetic indentation diagram into a tension diagram in the region of uniform deformation has been developed with the possibility of determining the yield strength, tensile strength, and ultimate uniform elongation of tested materials. The developed method was verified by testing steels, aluminum, magnesium and titanium alloys which differ greatly in the modulus of normal elasticity, strength characteristics, ductility and strain hardening.

All-Russian Scientific Research Institute of Aviation Materials, 17, ul. Radio, Moscow, 105005 Russia; e-mail: 89639619741@mail.ru

Plastic deformation is a type of material damage which can disrupt the normal operation of the structure. In this regard, the method for assessing the degree of damage to a metal sample has been developed. A corset sample for tensile tests was made from an aluminum alloy of the Al – Zn – Mg – Cu system. The ANSYS finite element complex was used to simulate an inhomogeneous stress state occurred in the sample working zone due to the variable cross-section upon tension. First, the hardness of the corset sample was measured, then it was tested for tension until the onset of necking and the load drop on the deformation diagram. After unloading along the sample working area, the Brinell hardness and surface roughness were measured. The results of the hardness measurements showed that in the areas where the tensile stresses are below the conditional yield stress of the material, the hardness value corresponds to the hardness of the starting material. In the areas where the tensile stresses are higher than the conventional yield stress, the hardness increases and reaches the maximum value in the center of the specimen, i.e., in the zone of the minimum cross-section. Thus, the damageability of the material can be assessed through the change in the hardness and roughness of the surface along the sample length. Proceeding from the results of instrumental spherical indentation, a technique for assessing the mechanical characteristics of the material was developed. The method consists in testing one sample for hardness and tensile strength with subsequent construction of the correlation dependences of tensile and indentation loads using the experimental results to obtain calculated tensile diagrams from the indentation diagrams of the material under study.

Fatigue and survivability tests of full-scale structures play a decisive role in the airframe support system. The main purpose of these tests, usually carried out on one of the first production aircraft is the design certification and development of the methods and procedures of the integrity control for subsequent reproduction of the elaborated regulations and methods of in-operation control. Tests are the main requirement of the airworthiness standards for aircraft and helicopters. The results of full-scale tests determine the quality of the airframe design and the operation safety. The endurance of pressurized compartments of aircraft and, first, the fuselages of high-altitude passenger aircraft, occupies a special place in the problem of fatigue strength of aircraft structures. When flying at high altitude, the pressure difference between the cabin and the external atmosphere is maintained at 0.63 × 10⁵ Pa, which results in large radial loads acting on the aircraft fuselage from the inside. The fuselages are loaded with compressed air (pressurization, pneumatic loading) in laboratory conditions. High requirements for the accuracy of pneumatic loading are determined by the fact that in a number of elements of the fuselage structure, e.g., in the area of window cutouts, the stresses created by external loads are significantly lower than those attributed to the pressurization loads. Hence, the accuracy of loading by excess pressure should be higher than the accuracy of the external loading system not to distort the stress state pattern of the structure. Apart from ensuring high accuracy of pneumatic loading of aircraft fuselages, it is necessary to comply the safety conditions of the tests, since the energy reserve of compressed air accumulated inside the fuselage is equivalent to the energy of several kilograms of TNT and in this regard a sudden explosive depressurization can lead to high consequences: the unsuitability of the damaged object for further testing; the failure of structures surrounding the tested object, etc. We present a method of cyclic loading of aircraft fuselages with excess compressed air pressure during fatigue tests which provides (due to the automatic control of the joint operation of high-precision and low-flow valves) an increase in the accuracy of pneumatic loading, expansion of the range of application of the pressurization system and monitoring of the tightness of the tested products in each loading cycle to prevent sudden destruction of the structure (depressurization).