Direct determination of the content of selenium and tellurium impurities in metallurgical materials by the method of inductively coupled plasma atomic emission spectroscopy (ICP-AES) is difficult due to spectral and non-spectral interference from macrocomponents present in the materials under study. The separation of micro-(Se, Te) and macro-components (Fe, W, Mo, Cr, Cu, Ni, Co) through preliminary precipitation is the goal of the study. The use of barium acetate and sodium fluoride as precipitants are shown to provide an effective separation of Se and Te from Fe, W, Mo, and Cr (the content in the analyzed solution is less than 0.1 wt.% of the original) and partial separation from Cu, Ni, and Co (the content in the analyzed solution from 25 to 55 wt.% of the original). Optimal conditions for the deposition of macrocomponents (Fe, W, Mo, Cr) and inhibition of the process of coprecipitation of selenium and tellurium on sediments of macrocomponents for their subsequent ICP-AES determination were determined. The optimal pH for the precipitation of macrocomponents equals 1. The optimal mass of precipitants (barium acetate and sodium fluoride) is 10 and 3 g, respectively. To inhibit the process of coprecipitation of selenium and tellurium on sediments of macrocomponents, it is proposed to use hydrofluoric acid. The optimal volume of hydrofluoric and hydrochloric acids for inhibiting the process of coprecipitation of analytes on sediments of macrocomponents was determined (3 and 6 cm³, respectively). The developed procedure for separating micro-Se, Te from macro-components was tested on standard samples of alloyed steels using the «spike» method. The technique is characterized by satisfactory accuracy and reproducibility, the limit of determination of analytes after separation of macrocomponents is 10^–3 wt.%.

A two-stage technique for X-ray fluorescence analysis of ceramic samples of composition Y_3–xYb_xNbO₇ (where x = 0 – 3) has been developed. At the first stage, using the method of fundamental parameters (FPM), a rapid semi-quantitative analysis of ceramic samples and products of intermediate synthesis was carried out to determine their preliminary composition. At the second stage, the quantitative composition of the samples was determined using the constructed calibration dependencies. To construct calibration dependencies a series of reference samples containing 3.16 – 56.55% Y, 8.78 – 71.0% Yb, and 12.83 – 19.70% Nb was synthesized using a method similar to that used for preparation of the ceramic samples under study. Analytical lines of elements free from spectral overlaps and XRF conditions (current and voltage of an X-ray tube, exposure time, method of taking into account the background near the analytical line) were selected. The relative standard deviation of the results of Y, Yb, and Nb determination in ceramic samples did not exceed 0.66%, the relative error was no more than 1.63%. The results obtained were compared with the calculated content of analytes in the samples of stoichiometric composition and with the results of ICP-AES analysis of real ceramic samples. The developed technique provides determination of the main components of ceramic samples and can be used for analytical control of synthesis of rare earth paraniobates.

A method for determining polychlorinated biphenyls (PCBs) in water using the method of concentrating analytes through extractive freezing-out under the effect of a centrifugal forces (EFC) has been developed. A mathematical model for analyte extraction using a three-factor Box-Behnken design demonstrated that the content of acetonitrile in the extraction mixture is a significant factor, whereas the degree of PCBs chlorination and the concentration of analytes are insignificant parameters. Analysis of the surface area of the model allowed the determination of the optimal range of the acetonitrile concentration, which fell between 14 and 21%. A 15% content of acetonitrile in the extraction mixture provided maximum extraction efficiency for 7 different PCBs (>92%) across a wide range of analyte concentrations (1.0 – 5000 ng/liter). The relative standard deviations in the repeatability and reproducibility range from 4.2 to 6.8% and 5.3 to 8.1%, respectively, the accuracy of analyte determination being 10 – 15%. Petroleum hydrocarbons were not extracted into the acetonitrile extract and did not interfere with the determination of PCBs, which provided longer operation of the detector without any loss in the sensitivity. Co-extraction of polycyclic aromatic hydrocarbons and chlorinated pesticides did not affect the extraction of PCBs from water (95 – 100%) and did not touch on the metrological indicators of the determination procedure.

The use of wood in structural and finishing materials can significantly reduce the time of building construction, but the high flammability of wood limits its use in the building industry. To increase fire resistance, wooden structures are impregnated with flame retardants and the penetrating ability depends on their structure. We present the results of a small-angle X-ray scattering study of the structure of flame retardants based on ammonium sulfate and phosphate. The radii of inertia of hydrated complexes formed when flame retardants are dissolved in water, their shape and type of chains along which hydrated ions are located are determined. It is revealed that the presence of diffraction maxima indicates the presence of an ordering in the arrangement of hydrated ions. Aqueous solutions of ammonium sulfate and disubstituted ammonium phosphate contain two types of hydrated complexes of the same shape but different radius of inertia. At the same time, hydrated ions in complexes are located along persistent chains, and ordering revealed in the arrangement of ions, depended on their type. The results obtained can be used in developing flame retardants with a reduced radius of inertia, which will increase the penetrating capacity of the processing solution and increase the fire safety of wooden structures.

The dielectric properties of materials when heated at ultrahigh frequencies are determined by methods based on the use of waveguide cavity resonators. However, as the sample is in the closed volume during measurements, the dielectric properties of destructive material thus determined can contain errors attributed filling of the resonator volume and depositing products of the sample decomposition on the internal conducting surfaces of the resonator. We present the results of studying the dielectric properties of destructive materials under heating in waveguide resonator cavity using methods that exclude the impact of destruction products on the accuracy of measurement. To reduce the influence of destructive vapors rising from the surface of the sample during the destruction process, additional thin quartz plates, placed on the sample surface were used. In addition, cuvettes with a lid were also used to prevent destruction products from entering the resonator volume. A method for taking into account the effect of plates and cuvettes in calculating the dielectric constant and dielectric loss tangent of a material sample when heated in a cavity resonator is presented. Changes in the dielectric properties of a composite material consisting of quartz fabric impregnated with an aluminochromophosphate binder and fiberglass laminate made of quartz fabric impregnated with a phenol-formaldehyde binder were studied in a temperature range above the onset of the destruction (up to temperatures at which loss of the structural strength of the material is observed). The developed method can be used in studying the thermophysical properties of destructive materials to assess changes in their dielectric characteristics under operation conditions of high-temperature heating.

The results of accelerated corrosion tests of a pair of austenitic stainless steel — titanium alloy under conditions of elevated temperatures and high concentrations of corrosive agents are presented, conditions for the developing the mechanism of local corrosion being the same. The proposed approach included provoking the appearance of microstress concentrators by three-point loading of test samples with subsequent forced development of local types of corrosion through simultaneous exposure to an increased concentration of corrosive agents and temperatures at a fixed exposure in an autoclave. The results of modeling the corrosion process in a titanium alloy being in contact with stainless steel are assessed proceeding from the data obtained from metallographic studies of the state of surface layers of the metal and the morphology of corrosion products on prepared sections of the surface of templates cut from the samples under study. We considred a pair of steel 08Kh18N10T — titanium alloy VT-5. It is shown that the contact of samples under conditions of accelerated corrosion tests does not lead to a significant development of local types of corrosion of the titanium alloy. On the contrary, analysis of the state of the surface layers of the samples of stainless steel revealed the presence of deep corrosion pits, triggering the intergranular corrosion. In this case, corrosion of austenitic steel, both in the presence and in the absence of contact with titanium, proceeded in three stages: the initiation and fusion of pitting; formation of knife corrosion ulcers; propagation of intergranular cracks into the depth of steel. The proposed methodology of corrosion testing can be used to predict the possible nature of the development of metal corrosion under operating conditions that form local zones of static stresses in structural materials, and for prompt response to extend the design life of the equipment at thermal and nuclear power facilities.

The aim of the study is to develop a methodology for assessing changes in the microstructure of aluminum under dynamic deformation in a rather wide range of the strain rate and strain degree. The distribution of the microstructure and the strength properties in the cross-section of pure aluminum samples (A99) after dynamic deformation according to the Taylor test were studied. The tests were carried out at room temperature using a PG-20 light-gas cannon, at sample throwing speeds of 127 and 165 m/sec. An interference microscope (Leica IM DRM) and a scanning electron microscope (Jeol JSM-6490) were used to study the aluminum microstructure; the microhardness measurements were carried out on an HVS-1000 device to study the uniformity of the strain distribution in samples. It is shown that three characteristic areas can be distinguished in aluminum samples after Taylor test: the elastic deformation zone, the plastic deformation zone, and the zone of severe plastic deformation, which is located in the area of collision of the sample with a steel barrier. It is shown that dynamic deformation reduced the grain structure from 1 – 1.1 mm to 2.5 – 3 μm at high impact velocities. An elongated grain shape is observed in the collision zone. The proposed method provided determination of the critical strain degree necessary for the onset of grain fragmentation and allowed us to explain the formation of zones of weak and severe plastic deformation. It is shown that the critical strain degree corresponding to the beginning of grain fragmentation increases from 0.18 to 0.21 with an increase in the throwing speed of the sample from 127 to 165 m/sec. In the zone of weak deformation, plastic deformation proceeds by intragrain riveting and the initial stages of grain fragmentation. In the zone of severe plastic deformation, a fine-grained microstructure is formed, which leads to an increase in the microhardness of aluminum in accordance with the Hall – Petch equation.

The principles of designing products made of the latest complex-structured polymer composite materials necessitate the need to take into account the large-scale structural effects determined by processes at the supramolecular and molecular levels of the polymer: relaxation, kinetic (breaking and recombination of chemical bonds), recrystallization of supramolecular structures, etc. The development of these processes is described by relaxation functions, which, in turn, can be calculated using the functions of relaxation time spectra. The purpose of the work was to develop a specialized equipment for testing micro-samples with a variable working part for uniaxial stretching along with the experimental technique and computational algorithms for processing the obtained measurement data, and experimental approbation of the developed approach to determining spectral relaxation functions. A method is proposed for estimating relaxation functions not at fixed stress levels within linear elasticity, at secant points of deformation diagrams, at fixed values of the linear elasticity modulus, but within an extended range of the sample deformation up to pre-rupture states. A set of test equipment designed for tensile tests of micro-samples with a thickness of the working part of 0.2 – 1.2 mm has been developed. The tooling can be installed on modern high-precision breaking machines. Tensile tests of polyethylene terephthalate micro-samples with a thickness of 50 and 175 μm were carried out taking into account the scale factor. A tensile test of micro-samples that are technologically stabilized by paper frames of a special shape is described. Diagrams illustrating the kinetics of changes in the spectral relaxation functions of oriented polyethylene terephthalate (PET) are constructed proceeding from the data of testing micro-samples with a constant strain rate. A method for using these diagrams in calculations of empirical relaxation time spectra is described. The results of testing micro-samples of polyethylene terephthalate are presented. Illustrative deformation diagrams of the studied polymer samples and calculated diagrams of functions of relaxation time spectra calculated according to the described method are given.

Identification of microstructure defects, which are stress concentrators (SC) during the operation of mechanical engineering products, is an important scientific and practical task relevant for manufacturing enterprises. This problem becomes especially urgent and difficult for critical helicopter parts made of sheet TRIP steel VNS9-Sh (23Kh15N5AM3-Sh) and operating under cyclic loads due to the complex microstructure of the steel and small thickness of strips and sheets. To assess the impact of structural defects on the cyclic strength of products made of the steel under study, the specimens were preliminary sorted proceeding from the results of their testing using the method of metal magnetic memory (MMM) and metallographic studies. The MMM method is a structure-sensitive procedure which provides information about the presence of structural defects that arise during the manufacture. Magnetic anomalies in the form of sharp local changes in the intrinsic stray magnetic field (SSMF) (H) and its gradient |ΔH| along the length of the controlled section Δx, were identified on the surface of sheets cut from five different batches. A conventional classification of the identified anomalies was made according to the magnitude of the magnetic field gradient. The specimens of two types were cut in zones of magnetic anomalies and outside them: type 1 — for cyclic tests and type 2 — for metallographic studies. The geometric parameters and field gradient values of magnetic anomalies on specimens of type 1 and type 2 were the same. Metallographic studies in zones of maximum magnetic field gradient on type 2 specimens revealed defects in the form of a strip at the boundary of different structures, which is a structural stress concentrator (SSC) and a source of the inhomogeneity and changes in the magnetic properties. Type 1 specimens with similar magnetic anomalies and Type 1 specimens cut from sheets outside zones of magnetic anomalies were then selected for cyclic testing. Comparative tests for cyclic strength of the specimens with and without specified SSC were carried out. It is shown that the presence of SSC zones in the specimens reduces the number of cycles to failure during cyclic tests by 1 – 2 orders of magnitude compared to the specimens free of SSC. Based on cyclic tensile tests of specimens, a limiting value of the magnetic field gradient was determined that corresponds to the acceptable level of stress concentration on structural defects. This value is recommended for use as a rejection criterion when examining a new tape by the MMM method.

The theory of fuzziness is an important area of modern theoretical and applied mathematics. The methodology of the theory of fuzziness is a doctrine of organizing activities in the field of development and application of the scientific results of this theory. We discuss some methodological issues of the theory of fuzziness, i.e., individual components of the methodology in the area under consideration. The theory of fuzziness is a science of pragmatic (fuzzy) numbers and sets. The ancient Greek philosopher Eubulides showed that the concepts «Heap» and «Bald» cannot be described using natural numbers. E. Borel proposed to define a fuzzy set using a membership function. A fundamentally important step was taken by L. A. Zadeh in 1965. He gave the basic definitions of the algebra of fuzzy sets and introduced the operations of intersection, product, union, sum, negation of fuzzy sets. The main thing he did was demonstration of the possibilities of expanding («doubling») mathematics: by replacing the numbers and sets used in mathematics with their fuzzy counterparts, we obtain new mathematical formulations. In the statistics of non-numerical data, methods of statistical analysis of fuzzy sets have been developed. Interval and triangular fuzzy numbers are often used specific types of membership functions. The theory of fuzzy sets in a certain sense is reduced to the theory of random sets. We think fuzzy and that is the only reason we understand each other. The paradox of the fuzzy theory is that it is impossible to consistently implement the thesis «Everything in the world is fuzzy». For ordinary fuzzy sets, the argument and values of the membership function are crisp. If they are replaced by fuzzy analogues, then their description will require their own clear arguments and membership functions, and so on ad infinitum. System fuzzy interval mathematics proceeds from the need to take into account the fuzziness of the initial data and the prerequisites of the mathematical model. One of the options for its practical implementation is an automated system-cognitive analysis and the intellectual system «Eidos».

A comparative analysis of the computational complexity of exact algorithms for estimating linear regression equations was conducted using the least absolute deviation method. The goal of the study is to compare the computational efficiency of exact algorithms for descent along nodal lines and algorithms based on solving linear programming problems. For this purpose, the algorithm of gradient descent along nodal lines and algorithms for solving the equivalent primal and dual linear programming problems using the simplex method were considered. The computational complexity of algorithms for implementing the method of least modules in solving direct and dual linear programming problems was estimated. A comparison between the average time for determining the regression coefficients using the primal and dual linear programming problems and the average time for gradient descent along nodal lines was conducted using the Monte Carlo method of statistical experiments. It is shown that both options are significantly inferior behind gradient descent along nodal lines, both in terms of the computational complexity of the algorithms and in terms of computation time, and this advantage increases with the sample size, reaching hundred times or more.