Novel stationary phases with various zwitterionic fragments in the structure of the functional layer with different degrees of branching were used for the determination of organic acids, sugars, nucleosides, and vitamins in various samples. A decrease in efficiency with an increase in the branching degree of the resin’s functional layer was observed for all studied classes of analytes. Therefore, the least branched stationary phase obtained using 1,4-butanediol diglycidyle ether (B) and glycine (G) was used for the determination of nucleosides and nucleobases in bacterial nutrient media. Complete resolution of water-soluble vitamins, namely, thiamine and nicotinamide was achieved on a resin with a more branched layer containing taurine in its inner part. It was established for organic acids that the decrease in efficiency with increasing branching degree is compensated by increasing the strength and an amount of acidic groups in the zwitterion structure. As a result, the stationary phase with taurine (T) and iminodiacetic acid (IDA) in the structure of a branched layer was selected for determining organic acids in various beverages exhibiting superior separation capability and exceeding the performance of the known commercially available phases. The use of taurine for creating a hyperbranched layer also positively affected carbohydrate separation due to improved selectivity and increased efficiency. Consequently, the resin with glycine in the inner layer and taurine in the outer layer was used for rapid carbohydrate determination in sweetened beverages. Analyte identification was performed by comparing retention times with those of peaks in standard solutions. The calibration range was chosen based on the expected content in analyzed samples as well as analyte solubility in aqueous-organic mobile phases. Accuracy was evaluated by spike recovery experiment. The concentrations of compounds of different classes found with using novel stationary phases in real samples corresponded to those declared by manufacturers.

For the first time, we suggest a Raman spectroscopic method for rapid evaluation of punicic acid content in pomegranate seed oil. In this contribution, we study Raman spectra of mixtures of pomegranate seed oil and sunflower oil as model systems of pomegranate seed oil with different punicic acid content using two excitation wavelengths (532 and 785 nm). The spectrum of punicic acid, calculated using the density functional theory, is also considered. We found that the ratio I₁₆₂₈/I₁₄₄₂ of the peak intensities of Raman lines at 1628 and 1442 cm^–1 is proportional to the punicic acid content. The line at 1628 cm^–1 is related to the stretching vibrations of double carbon-carbon bonds (C=C) in the sequence of three conjugated bonds in punicic acid molecule. The line at 1442 cm^–1 belongs to the scissoring C–H vibrations in CH₂ groups in molecules of all fatty acids of pomegranate seed oil. We revealed that Raman spectroscopy permits detecting punicic acid even at very low contents (up to 1 wt.%). In addition, we found that the record-ing Raman spectra using excitation wavelength of 532 allows one to detect carotenoids in pomegranate seed oil.

A non-contact method for determining the mass fraction of milk fat in bottled kefir using diffuse reflection of radiation from LEDs with different wavelengths (365, 390, 850, and 880 nm) using a smartphone and a special homemade colourimetric device was proposed. To record the analytical signal we used a smartphone OnePlus 10 Pro, iPhone 14 with PhotoMetrix PRO®, ColorGrab, RGBer, and FTIR spectrometer for the near infrared region (4000 – 10000 cm–1). The experimental data were processed using specialised programs: TQ Analyst, The Unscrambler X, XLSTAT. It was found that the intensities of RGB channels change depending on the fat content of kefir, which indicates that there is a correlation between colour characteristics and milk fat content. The influence of protein and carbohydrate content on the analytical signal was found to be minimal, as their concentration in kefir with different fat content varies insignificantly. These data confirm the possibility of using digital RGB values as an analytical signal for determining the fat content of kefir. It is shown that polyethylene terephthalate packaging has minimal effect on diffuse reflection, which allows analysis without opening the packaging. The mass fraction of milk fat in kefir was estimated using the method of multivariate data calibration — partial least squares regression. The relative standard deviation of the results did not exceed 0.11%, which confirms the high accuracy of the method. The best results were obtained using LEDs with emission wavelengths of 390 and 850 nm, when RMSEC and RMSEP reached maximum values of 0.0901 and 0.887%, respectively. Equivalence of the results obtained was confirmed by FTIR spectroscopy.

One of the methods for controlling the characteristics of composite materials is the formation of a pyrocarbon matrix with the required anisotropy of pyrocarbon. This work presents results assessing the texture of pyrolytic carbon matrices in composite materials using an optical method. The extinction angle —

a quantitative characteristic of texture — was determined by registering the intensity (brightness) of the quadrant of the pyrolytic carbon spherulite around the carbon fiber. The sought-after value was identified as the angle of rotation of the microscope analyser corresponding to the minimum intensity. A series of micrographs depicting the microstructure of the pyrolytic carbon spherulite, acquired at various analyser rotation angles relative to the polariser, were processed within a graphical editor. Subsequently, the mean grey-level values of selected pixels in a defined region were analysed to identify the point of minimum intensity. It was demonstrated that, with appropriate illumination levels, the spectral characteristics of the light source exert a negligible influence on the image processing and brightness measurement when using graded grey levels. Limitations associated with the geometric dimensions of the investigated pyrolytic carbon were assessed. Extinction angle determination for samples incorporating diverse pyrolytic carbon matrices (including a bilayer matrix) revealed that pyrolytic carbon produced via a temperature gradient method exhibits a highly textured structure, whereas material produced via an isothermal method displays a lower degree of texture. The extinction angles for the bilayer pyrolytic carbon matrix were found to differ between the individual layers. The findings are expected to contribute to the refinement of techniques for microstructural analysis of pyrolytic carbon.

The active development of telecommunication systems operating at frequencies from 30 GHz and above (including 5G systems) requires the development and creation of materials with a dielectric constant of less than 2.2 compatible with printed circuit board technology. Technological approaches to manufacturing such materials are based on the formation of air cavities in the initial dielectric matrix and require control of their microwave parameters (primarily the dielectric constant and the tangent of the dielectric loss angle) in a given frequency range. The paper presents the results of a study of the electrophysical properties of a composite dielectric material with a low dielectric constant. Sealed dielectric plates with a predetermined volume distribution of air cavities were produced using mechanical perforation and additive 3D printing technology. The microwave parameters of the obtained samples were determined using a detachable cylindrical resonator at a frequency of ~10 GHz. Samples with a minimum dielectric constant of 1.75 were examined. It has been established that the use of additive 3D printing technologies, due to several features, leads to a distortion of the geometric dimensions of the forming air cavities, which in turn affects the electrophysical properties of the samples. The results obtained can be used in the development of new microwave materials.

Moscow obl., 142717, Russia; *e-mail: R_Vagapov@vniigaz.gazprom.ru

The impact of hydrogen sulfide contained in hydrocarbons extracted at oil and gas facilities on steel equipment and pipelines is dangerous not only due to corrosion damage, but also due to hydrogen penetration into carbon and low-alloy steels. However, such a negative impact on the durability and properties of structural materials has previously been studied mainly for liquid conditions typical of oil fields. The paper presents the results of a study of internal corrosion processes at gas fields. The patterns and features of the composition and properties of deposits formed in gas pipelines during the interaction of H₂S-containing gas with steel were analyzed. Using the X-ray diffraction method, it was determined that the main corrosion product is iron sulfides (tetragonal and cubic), formed in the gaseous and liquid phases. The forms of hydrogen sulfide corrosion product crystals formed on the steel surface were studied using scanning electron microscopy. The effect of differences in their phase composition and crystalline forms on general corrosion losses and hydrogenation of steels was revealed. In addition, the lack of continuity in the iron sulfide film can lead to the formation of local corrosion defects on steel structures. The results obtained can be used to assess the degree of danger of hydrogen sulfide corrosion on steel equipment in gas fields and pipelines, as well as to select anti-corrosion protection agents (e. g., corrosion inhibitors).

A method for assessing the survivability of a pipeline at a distance from a transverse weld with a longitudinal surface semi-elliptical mode I crack is proposed, taking into account the biaxial constraint along its front. A literature review has shown that there are currently no works in which the forecast of the growth of such crack is carried out taking into account the T_xx- and T_zz-stresses, which are nonsingular terms in the Williams expansion for stresses at the crack tip. To model the growth of a fatigue crack, a modified Paris formula is used, in which the range of the effective stress intensity factor (SIF) is substituted instead of the span of the usual SIF. In this case, in addition to the usual SIF, the expression for the effective SIF includes the T_xx- and T_zz-stresses. The proposed two-parameter approach allows taking into account the constraint in the crack plane in the direction perpendicular to the front, due to the introduction of T_xx-stresses into the expression for the effective SIF, and in the longitudinal direction due to the introduction of T_zz-stresses. The expression for the effective SIF was previously obtained by the authors by improving the fracture criterion of maximum tangential stresses. It is assumed that tangential stresses in the fracture process zone are equal to the local strength of the material. In this case, the size of the fracture process zone and the local strength of the material are determined taking into account the T_xx- and T_zz-stresses. Numerical simulation was performed in the finite element environment of ANSYS Workbench. To construct a mathematical model of a pipe with a semi-elliptical crack, three types of finite elements (FE) were used: 10-node tetrahedral elements SOLID187; 20-node hexahedral FE SOLID186 and 15-node wedge FE degenerated from SOLID186. The latter of which singular FEs have a built-in function for calculating the SIF and T_xx-stresses. Special macros were written in the APDL programming language to calculate the T_zz-stresses and the effective SIF along the crack front. It is shown that the use of a one-parameter approach based on the Paris formula does not allow taking into account the biaxiality of the stress state when assessing the survivability of an oil pipeline, since, unlike the effective SIF, the usual SIF for a longitudinal semi-elliptical crack depends only on circumferential stresses. It is established that for cracks of the same initial depth, the durability decreases with an increase in half-length. It is revealed that the durability predicted using the usual one-parameter Paris formula is approximately 30% underestimated, compared to the results of a two-parameter analysis.

The article presents an assessment of the structural heterogeneity and mechanical properties of the turbine runners of hydroelectric power plants in the presence of operational defects based on the hardness measurements. The article presents the design features and structure of the turbine runner’s metal. The chemical composition of the steel was determined by laser spark emission spectrometry using a portable laser steeloscope. The mechanical properties were determined based on the static tension testing of the samples using an tensile testing machine. The impact work and impact toughness characteristics were obtained based on the impact bending testing of samples with a U-shaped concentrator using a pendulum impact test machine in the temperature range from +20 to –30°C. The crack resistance characteristics were obtained based on the crack resistance testing of samples using a testing machine. The samples for all tests were cut from a fragment of the turbine runner’s blade. The metal hardness values were obtained using the dynamic portable hardness tester by measuring the Brinell hardness on four blades from the non-pressure side in the areas of cavitation damage. The main problems of hydraulic turbine operation associated with cavitation damage to the metal are described. The division of the turbine runner’s blades into zones according to the degree of cavitation damage is shown. Based on the results of Brinell hardness measurements, the characteristics of mechanical properties — the yield strength and tensile strength — were calculated. Based on their values, statistical processing was made and histograms of distributions were constructed with the determination of the characteristic law of distribution of a random variable, the heterogeneity coefficients were determined and graphs of the statistical distributions of the values of the characteristics of mechanical properties were constructed.

The widespread use of heavy tungsten alloys (HTAs) in power engineering and mechanical engineering stimulates the development of new methods of synthesis, powder processing and sintering, including additive technologies. At the same time, the mechanisms of HTAs microplastic deformation and their relationship with interphase boundaries remain poorly understood. The paper presents the results of a study of the features of microplastic deformation in coarse-grained HTAs with different strength levels. HTAs with different initial grain sizes were studied. The samples were tested in the initial state and after annealing in a vacuum at 1400°C, the melting point of the γ-phase. Microplastic tests were carried out using the standard technique of relaxation tests of flat microspecimens for compression. The microstructure of the samples was analyzed after loading (at stresses less than and greater than the yield strength). It is shown

that the deformation of pure tungsten at stresses close to the yield strength leads to the formation of dislocation «steps» in the volume of grains and the appearance of grain-boundary microcracks. In coarse-grained strain-hardened HTAs, the formation of dislocation «steps» begins in the region of microplastic deformation at stresses below the yield point. With increasing stress, the size and number of traces of dislocations emerging on the grain surface increase. Deformed HTAs have a high Hall-Petch coefficient due to the increased dislocation density in the interphase boundaries. Annealing of deformed HTAs leads to a decrease in the density of deformation-induced defects and an increase in the concentration of atoms in the interphase boundaries. During deformation of fine-grained HTAs, the formation of dislocation «steps» is not observed, which indicates a significant contribution of plastic interphase boundaries to the deformation process. The results obtained can be used in the manufacture of HTAs for use in the nuclear and aerospace industries.