An approach to TXRF determination of the composition of perovskite nanocomposites of the putative composition CsPbBr₂Cl and CsPbBr₂I is proposed. Sample preparation consists in treatment of hydrophobic samples with dimethylformamide (DMFA) and subsequent dilution of the obtained solutions with water. When using copper solution as an internal standard the reproducibility of the results of TXRF determination of the elements is attained with a Sr no more than 0.05. The validity of the determination of Cs, Pb, Br, and I is confirmed by the results of their determination by ICP-MS in solutions after processing samples in DMFA followed by dilution with 2% HNO₃ for Cs, Pb, Br or tetramethylammonium hydroxide TMAH for Cs, Pb, Br, and I, whereas the determination of chlorides is confirmed by the method of direct potentiometry in diluted solutions. It is shown that lead does not form insoluble chlorides in TMAH solution and does not interfere with the determination. The effect of bromides on the determination of chlorides is characterized by a potentiometric coefficient of 10^–3. The results obtained provide determination of the stoichiometry of the synthesized compounds CsPbBr₂Cl and CsPbBr_2.7I_0.3.

The analytical capabilities of frontal size exclusion chromatography are studied using neutral polystyrene sorbents. When studying the separation of mineral acids and their salts, it is shown that clear separation of the zone of thorium ions and rare-earth elements from the following acid zone is observed on the microporous hypercrosslinked polystyrene sorbents Purolite NN-381 and MN-270. However, separation of the ions of highly charged elements (Zr, Hf, Nb, Ta) from the acid on the studied Purolite sorbents failed. Peaks of significant self-concentration appear in the zone of thorium and rare-earth element release at a concentration of 0.1 – 50 μg/liter. The factors affecting concentration of the analytes were studied. The nature and concentration of the acid, as well as concentration of the analytes, affect the concentration coefficients which attain maximum values in the solutions of nitric acid compared to hydrochloric and phosphoric acids. The degree of analyte concentration depends on the structure of internal pores and dispersion of the sorbent, as well as on the rate of solution passage through the column. Macro-components of seawater are not retained or concentrated on hypercrosslinked polystyrene. Sodium and magnesium at a concentration of 0.1 wt.% do not affect the value of the concentration factor of the target analytes. After chromatographic separation, weakly acidic fractions of the solution with concentrated ions of REE and thorium can be obtained by simple passing of a portion of the test solution through the sorbent layer for 15 – 30 min. The resulting concentrate can be directly introduced into a mass spectrometer. The possibility of combining chromatographic separation and concentration of elements and on-line ICP-MS detection is studied. Optimal conditions for on-line detection have been selected; the accuracy of the developed approach is demonstrated in the determination of rare earth elements in seawater using the spiked test.

An express method for the determination of pilocarpine hydrochloride (PHC) in ophthalmic solutions based on titration of the analyte with photogenerated iodine obtained by irradiation of potassium iodide in the presence of a mixture of sensitizers (sodium eosinate:fluorescein:auramine in a molar ratio of 1:1:1) at pH 5.6 has been developed. The titrant content in the cell was controlled by the voltammetric method (amperometric titration with two polarized electrodes): during the PHC titration a decrease in the current strength in the circuit of the amperometric installation was observed. Stabilization of the current in the circuit of the amperometric installation indicated the completeness of the reaction, and, thus provided the possibility of estimation of the PHC content in a dosage form. The measured generation time required to replenish the loss of titrant upon further irradiation of the solution was also used to calculate the PHC content in the preparation. Testing of the developed technique was carried out on an ophthalmic drug «Pilocarpine, eye drops 1%». Introduction of more than 20.0 g of boric acid used as a preservative agent into the cell resulted in a slight underestimation of the PHC content. The determined PHC content in the sample of series 60918 is 0.93 – 0.94% (measured by generation time) is lower than the tolerance interval set by order of the Ministry of Health of the Russian Federation No. 751n, October 26, 2015 (0.95 – 1.05%). The PHC content in other samples falls within the recommended range, which indicates that the drug quality complies with GMP standards. A linear dependence of the analytical signal on the PHC concentration is observed in the range of 15 – 500 μg. The calculated detection and quantitation limits are 5.6 and 18.6 μg, respectively. The developed photochemical method for PHC determination in the drug «Pilocarpine, eye drops 1%» meets the requirements set forth in the manual for the validation of bioanalytical methods. The method is easy to use and does not require expensive equipment.

X-ray diffraction methods are indispensable for studying crystalline materials and provide determination of the phase composition, internal stresses and the parameters of unit cells of crystalline phases, as well as the crystalline size, which is related to the average grain size and affects the width of the diffraction peaks. We present the results of evaluating the repeatability of the X-ray diffraction data obtained for silicon nitride powders Si₃N₄ of different particle size and different initial phase ratios α-, β-Si₃N₄. The relative error of measuring the diffraction peaks was determined using the intensity detector and the absolute error of calculating the unit cell parameters was determined by the Rietveld method. The average particle size of the initial powders was analyzed using scanning electron microscopy. X-ray diffraction studies were performed according to the Bragg – Brentano scheme using CuKα radiation (λ = 1.5406 Å). A series of three experiments was performed for each powder. It is shown that the relative error of intensity measurements with a detector does not exceed 2% for peaks corresponding to 3σ criterion, and the absolute error of the determination of the unit cell phase parameters by the Rietveld method is 0.001 Å. The results obtained can be used to assess the stability of the diffractometer both for the samples based on silicon nitride and materials of different composition and structure, especially for submicron samples. In the latter case, the error of the parameters obtained by X-ray phase analysis can be taken into account without resorting to statistical estimates, as in the method of least squares.

When studying the plastic properties of metallic materials under tension, the initial calculated length of the sample which affects the final results is of significant importance. In the case of determining the short-term mechanical properties of the materials of fuel cladding pipes using annular samples, calculation of the initial effective length of their working part is rather difficult since the plastic deformation of the annular sample is unevenly distributed along the perimeter. This feature is taken into account using the deformation deceleration coefficient. We present the results of determining the deformation deceleration coefficient for calculation of the initial effective length of the working part of an annular sample made of fuel cladding. An experimental method for determining the coefficient is proposed, taking into account the measurements of the distribution of plastic deformation in certain areas along the perimeter of the sample. The method consists in stretching annular and ovalized samples with marks on the end surface. It is shown that for annular and ovalized specimens from the fuel cladding of a BN-600 reactor, the values of the deformation coefficient and effective length are k = 0.50 ± 0.04 and l₀ = 6.1 ± 0.4 mm, respectively. Analysis of the actual relative deformation of the working parts and comparison with the relative elongation showed that when the ovalized specimens are stretched, the value of the relative plastic deformation is higher than that for annular specimens. The proposed method and the results obtained can be used in determination of the parameters of the materials used in the cladding pipes of the of fast neutron reactors.

Sample preparation for determination of the chemical and technological properties of coals is carried out using standard methods when coal samples come into contact with air. However, the outer surface of the resulting small particles is inevitably oxidized during grinding by the molecular oxygen present in air. Therefore, the physicochemical properties of the laboratory sample do not match the properties of the original native coal or coal of larger fractions. We present the results of studying the laboratory samples of low- metamorphized coal. Preparation of the native coal sample was carried out in a pure inert atmosphere (nitrogen) of a glove box. Methods of IR- and EPR- spectroscopy, chemical functional analysis of oxygen groups, determination of specific surface area, as well as methods for determining the wettability (determination of the wetting edge angle by a drop of liquid and the rate of absorption of a drop into a coal briquette) were used to characterize changes in the surface of coal particles. It is shown that the method of coal sample preparation significantly affects the functional composition and hydrophilicity of the outer surface of coal particles. The results obtained can be used in determination of the properties of native stratal coals, improvement of the technology of coal sample preparation, as well as in enrichment and processing of coals.

Approximation of the normalized in-plane shear stress-strain diagrams under the quasi-static loading of a variety of 25 unidirectional and cross-ply reinforced polymer matrix composites was studied. Approximation was carried out with the use of piecewise prescribed functions for two cases of deformation curve splitting into separate sections, i.e., into two and three parts. The first part is linear and corresponds to Hooke’s law. Description of the second and the third nonlinear parts required the development of a number of different functions relatively simple in structure with three or four independent parameters (coefficient) determined from boundary conditions in characteristic points of the in-plane shear stress-strain diagrams of polymer matrix composites. This approach provided using the minimum set of experimental characteristics of the material for approximation of the deformation curve. All the developed functions and their derivatives are continuous on all parts of the stress-strain diagrams. Assessment of the error of approximating functions was carried out by the criteria based on deviations between design and experimental values of the shear stress. The best functions having the smallest approximation error were determined for all considered materials both on average and separately for each material. It is shown that on average the error of approximation over three parts is 2.5 times less than that over two parts, however for some specific materials approximation over two parts appeared more accurate. The examples of approximation of in-plane shear stress-strain diagrams for three of 25 considered materials are presented for the cases of dividing the deformation curve into two or three parts. The approximating functions obtained can be recommended for use in modeling the stress-strain behavior of layered polymer matrix composites with allowance for nonlinearity of in-plane shear strain of the materials by taking into account the minimum required number of experimental characteristics.

The methods of fastening structural elements made of fiber composites to other structural elements are almost the same as those used for metals. With the most common bolting, a hole is drilled in the element, i.e., a part of the material is removed, thus resulting in a stress concentration near the hole. Certain difficulties can thus arise in designing and calculating of bolted joints of metal elements of critical structures. The use of composites is associated with more serious problems. In this case, both the structural element and the material for this element are manufactured simultaneously. Subsequent machining is quite undesirable, since it violates the integrity of the element and, consequently, the bearing capacity of the entire structure. The efficiency of using composites depends on the technology of manufacturing the material of the element by 90%. We present the results of experimental and theoretical study of the effect of holes made by different technologies on the strength and bearing capacity of fiberglass specimens with different fiber laying patterns. The stress concentration coefficient is compared with the strength reduction coefficients for the holes made by drilling and by expanding the fibers without their damage. The results of tensile tests of specially made composite specimens with different reinforcement structures: [0], [0/90], [0/±45/90] and with central holes are presented. The strength reduction factors calculated from the results of the experiment turned out to be significantly lower than the stress concentration factors. The reasons for this effect are considered and an estimate of the characteristic curvature radius formed after «blunting» of a hole in a composite specimen is given. The obtained results of the study made it possible to draw conclusions about the effectiveness of the technology for hole production in composite samples without breaking fibers, as well as about the effect of the number of fiber families on the strength reduction coefficient near the holes.

The main features of the mechanisms of damage during cyclic loading of metal and composite materials have been studied. The results obtained are used to develop the approaches to fatigue and damage tolerance tests of metal-composite (hybrid) structures to confirm their safe operation. It is shown that composites exhibit higher scattering characteristics compared to metals due to their heterogeneity attributed to the anisotropy of the material properties, the presence of technological defects and various natural inhomogeneities in their structure, both in terms of static and fatigue properties. This leads to the necessity of testing two identical full-scale structures: one to confirm the service life of the metal part, and the other of the composite part. The fatigue tests of structures should be carried out for different ranges of variable loads, which differ in the size of the block of variable loads, the levels of «high» and «small» loads and the load enhancement coefficient. To carry out fatigue tests of the composite part of the structure during an acceptable time, it is necessary either to increase the loads of the variable loading spectrum, or to introduce additional «overload» cycles. Proceeding from the condition of the equality of the probabilities of non-destruction for the metal and composite parts of the structure, the relations for determination of the load enhancement coefficient k_σ and the number of «overload» cycles n are obtained. The load enhancement coefficient is determined by the ratio: , where m_c and m_m are the exponents of fatigue curves of the composite and metal, η_c and η_m are the reliability coefficients when testing composite and metal parts. The required number of «overload» cycles is determined by the ratio: where σ_{eq o}, σ_eq are the equivalent stresses of the overload cycle and the spectrum of variable loads.