Two microwave systems MARS-5 and UltraWAVE are compared in the efficiency with regard to the digestion of silicate rocks with subsequent determination of 32 elements (Sc, V, Cr, Co, Ni, Cu, Zn, Rb, Sr, Y, Nb, Ta, Cs, Ba, 14 REE, Hf, Ta, Th, U) by inductively coupled plasma mass spectrometry (ICP-MS). The development of digestion methods and validation of the obtained results has been carried out using international reference materials — basalts BHVO-2 and BCR-2, serpentinite UB-N and peridotite JP-1. Microwave digestion included a two-stage treatment of samples with a mixture of concentrated acids HF, HNO₃, HCl in MARS-5 (T = 190°C, P = 20 bar) and UltraWAVE (T = 240°C, P = 80 bar) with distillation of excess fluorides in the form of SiF₄ between microwave digestion stages. The determination of concentrations in the obtained solutions was carried out on a high-resolution mass spectrometer ELEMENT in low and medium resolution according to external calibration with the internal standard (In), taking into account the acid composition of the analyzed solutions. The detection limits of the analytes after acid digestion in MARS-5 and UltraWAVE are comparable and provide the determination of all specified elements, except for Ta in JP-1. The use of the developed sample preparation procedure in MARS-5 ensures complete decomposition of BHVO-2, BCR-2, UB-N followed by ICP-MS determination of 32 specified elements in the obtained solutions without additional preconcentration steps. The relative standard deviations for the determined elements are 2 – 9% for the reference materials BHVO-2, BCR-2, 3 – 12% for UB-N with an increase to 16 – 25% (Nb, Ta) due to the approach to the detection limit. The more efficient microwave digestion in UltraWAVE compared to MARS-5 was proved by the complete decomposition of JP-1 with the transfer of all the elements, including Cr, to the solution.

When developing new organometallic compounds, the necessity for a rapid control of the elemental composition of the substances obtained arises at different stages of synthesis. This makes urgent the goal of speeding up the procedure of elemental analysis. The XFA method is traditionally used in the laboratory for microanalysis when determining the metal content in the substance composition according to the method of an external standard with a dilution of the substance sample with emulsion polystyrene. Precise weighing of the sample and diluent is required in the manufacture of analyzed reflector samples, since a dilution factor is needed to calculate the content of the elements. When synthetic chemists are interested in the atomic ratio of metals included in the organic matrix rather than in the exact elemental composition of the resulting compound, we propose to eliminate the lengthy weighing procedure and use measured amounts of substances in the manufacture of the analyzed samples. The developed technique is tested on a number of ferrocene derivatives containing platinum atoms, and a rapid weightless method for determining the atomic ratios of Fe and Pt in synthesis products is proposed. Analytical signals were measured on an X-ray fluorescence spectrometer SPECTROSCAN MAX-GVM (NPO Spectron LLC, St. Petersburg) at the wavelengths of FeKα and PtLα lines in the 40 kV/0.5 mA mode. The metal content in the emitter samples was determined by the calibration equations. Simplification of the spectrometry procedure and the absence of weighing significantly speeds up the procedure. The proposed method can be used as a preliminary criterion for success synthesis of the desired product before the complete elemental analysis of the latter.

A highly sensitive electrochemical sensor based on a Surface Active Modifier (SAM) consisting of Taunit-M carbon nanotubes and mesoporous carbon (NanoTechCenter LLC, Tambov, Russia) is developed for the voltammetric determination of betulin and p-nitrophenol. The effect of the modifier concentration on the electrode surface on the analytical signal of betulin was studied, and a method for modifying the surface of the SAM graphite electrode was developed. The developed method is easy to use, fast, stable, sensitive, and cost-effective procedure, which can be used to detect these analytes in real samples. Voltammograms of p-nitrophenol were obtained for the first time on the developed modified electrochemical sensor and the dependence of the height of its analytical signal on the pH of a phosphate buffer thus obtained was studied in a wide pH range from 4 to 12, a background electrolyte with optimal pH was also chosen. Proceeding from the calibration dependences of the height of the betulin analytical signal on the concentration obtained for various background electrolytes with different pH and cation-anion composition, a background electrolyte with the maximum sensitivity of the analytical signal was selected on a modified electrochemical sensor. Study of cyclic voltammograms was carried out to understand the electrode processes, exhibiting a pronounced peak of anodic oxidation observed in a potential range from 0.7 to 0.9 V. However, there was no peak in the cathodic direction which indicates the irreversible nature of the electrode process. When determining the nature of currents, the Semerano criterion equal to 1.6 was calculated, which indicates the absence of the contribution of the diffusion component of the current. Verification of the correctness of the voltammetric method for determining betulin on a new  

electrochemical sensor was carried out using the «spike-test» method. The data obtained show that the voltammetric determination of betulin can be carried out with a measurement error not exceeding 15%. The proposed modified electrodes were compared with previously known electrodes for the determination of pentacyclic triterpenoids and pesticides at concentrations of 0.5 × 10^–3 – 8.0 × 10^–3 mg/dm³.

The transversal sensitivity of tri-axial vibration transducers, which have found vast application in various vibration measuring and material testing systems, decreases the accuracy of measurements. We present a solution to the problem of eliminating the error attributed to the presence of the transverse sensitivity. The measurement error depends on many factors including the ratio of vibration components along the sensitivity axes, the width of the vibration spectrum, and the presence of intrinsic resonances of the vibration transducers in the main and transverse directions. The developed method provides almost complete compensation of the error. Analysis of the components of sensitivity vectors along the measuring directions showed that the transversal sensitivity vectors are in fact the parasitic penetrations from other directions, and can be decomposed along the measuring axes. To orthogonalize the sensitivity vectors during calibration, the sensitivity vectors should be rotated until they coincide with the orthogonal directions. A measuring basis with zero transverse sensitivities is thus obtained, and the sensitivity matrix is reduced to a diagonal form. With this approach the fundamentals and practical algorithm using successive approximations of triaxial transducer calibration with orthogonalization are outlined. Each orthogonalization step is illustrated by the current sensitivity matrix, showing the progress of transversal sensitivity reduction. The results of the developed tri-axial transducer coupled to a special preamplifier-converter with transversal sensitivities reduced to nearly zero values using the developed method are presented. Since calibration is carried out without dismantling of a vibration transducer, it can be carried out not only during its manufacture, but also during verification upon operation, which increases the service life. The use of the described technique not only improves the metrological parameters of vibration transducers, but also provides a significant reduction of the requirements for the accuracy of manufacturing their measuring system, thus reducing the production costs. The presented method is promising for the developing new precise multi-axis vibration transducers and measuring systems on their base.

Modern metallography being a complex of qualitative and quantitative methods is widely used to analyze the microstructure of metal alloys. We present the results of studying the microstructure of austenitic chromium-manganese steel 14Kh15G9ND by optical and electron microscopy. The method of etching and the reagent, the most suitable for this steel grade, which provide identification of the main structural and phase components (austenite, twins, slip strips) of the steel were selected using the existing techniques. The results of optical and scanning microscopy of the samples deformed with a different degree of cold plastic deformation were compared with each other. It is shown that electrochemical etching in an aqueous solution of chromium anhydride should be used for qualitative determination of the steel microstructure. Optimal parameters of the current density and voltage were also determined. The results obtained can be used for optical microscopy of chromium-manganese steels, as well as for a more complete study of the dislocation structures present in them using scanning microscopy.

To achieve high accuracy in determining the dielectric properties of materials using guide cavity, measurements are performed using resonant oscillation with high Q-factor. The error in determination of the resonant frequency is considered given a priori in calculations of the dielectric permittivity and the dielectric loss tangent, whereas the dependence of the error of dielectric measurements on the resonance oscillation Q-factor is out of scope. We present the results of studying the relationship between the resonance frequency, Q-factor and resonating cavity transmission factor. Proceeding from the analysis of the shape of the resonance curve as a frequency dependence of the transmission factor, we determined a relationship between the error of the resonant frequency and Q-factor of the oscillations used for measuring the dielectric properties of the material. This is especially important when measuring the temperature dependences of the dielectric permittivity of materials under their heating at super high frequencies (SHF), when the conductivity of resonator walls and the Q-factor of resonant oscillations decrease as the temperature goes up. It was demonstrated that enhancing of the accuracy of measuring the transition factor is a provision for achieving the required accuracy of measuring the dielectric properties of materials at a lower values of the resonator Q-factor. The results obtained can be used in studying high-temperature resonator devices intended for measuring the dielectric properties of materials in SHF range.

Low cycle fatigue behavior of nickel-base alloys EP741NP and EI698VD under strain-control loading with zero strain ratio was studied for a wide range of strain amplitudes and temperatures. Dependences of the stress amplitude, mean stress and plastic strain range on the number of cycles were analyzed. Three stages of the cyclic behavior were marked out: the first stage of non-steady behavior with hardening, or softening, or transition from hardening to softening; the second stage of steady hardening, softening or stability; and the third stage associated with a crack development. Qualitative and quantitative parameters are proposed that make it possible to determine a share of the first stage of cyclic instability in the total cyclic durability and the nature of the material behavior in the first and second stages proceeding from the analysis of the dependence of the range of plastic deformations on the cycle number. The absence of cyclic stability was demonstrated for both alloys almost in the whole range of testing. It was shown, that the contribution of the first stage to the fatigue life (total durability) can be up to 30% and the greater the strain range, the greater the contribution. The temperature dependence of the character of cyclic behavior of materials is revealed. Alloy EP741NP is softened at the first and second stages at room temperature and is liable to hardening at elevated temperatures 300, 450, and 600°C, whereas alloy EI698VD is hardened at the first stage at 20 and 400°C, but inclines to softening at 650°C. At the second stage alloy EI698VD inclines to softening at 20 and 650°C and is liable to hardening at 400°C. With strain ranges 0.6 and 0.7%, both alloys can be considered cyclic stable at the second stage over the entire temperature range

Changes in the mechanical stress-strain curves and sound velocity of longitudinal waves for epoxy resin ED-20 with different content of polyethylene polyamine (PPA) hardener and diethylene glycol (DEG) plasticizer were studied for cure time from one to 30 days. The obtained dependences of the applied force on the absolute value of stretching for samples with different PPA content and different curing time make it possible to divide the sample state into three types: highly elastic; not fully cured; vitreous fully cured. The parameters characterizing each state are determined. The polymerization process continues with a curing time of 24 – 720 h for all samples. Acoustic measurements were carried out by the pulse method using an automated measuring system. The dependences of the longitudinal sound velocity on the curing time for samples with different contents of PPA and DEG plasticizer are presented. The sound velocity changed much less than the static Young’s modulus within the considered interval of the curing time. The presence of a «kink» in the interval from about 20 to 180 h is a feature of the dependences of the sound velocity on the curing time. The data obtained revealed that the section of rapid growth of the sound velocity corresponds to the transition from the highly elastic state to the glassy solid one. Experimental study of the physical properties of compositions based on ED20 resin with a concentration of the curing agent less than standard provides the possibility of detailed study of the dynamics of polymerization process after the transition from the gel state to the solid state at a long curing time. It is shown that the curing process continues for a rather long time in the solid state. The observed features on the dependences of the sound velocity on the curing time are attributed to the formation of the 3D structure during the transition from the highly elastic state to the solid glassy state. In this case, the value of the longitudinal sound velocity can be an indicator of the degree of completion of the polymerization process of finished products from composite materials based on epoxy resin, for which it may be difficult to measure the mechanical properties.

The purpose of the study is developing and testing of the new computational technique for approximation of deformation curves of steel and silumin specimens under uniaxial tension. A scheme of testing steel and silumin specimens for uniaxial tensile is presented. The experiment was carried out in the mechanical testing laboratory of the Department of Applied Mathematics and Mechanics of the Voronezh S_tate Technical University. The experimental deformation curve of a steel specimen was approximated by P. Ludwig’s equation. Prediction of the true stress from the logarithmic strain using a pretrained artificial neural network with a multilayer perceptron architecture is discussed. The neural network model was trained using the RProp (resilient backpropagation) method. The software implementation of the neural network approximation was carried out in a framework of the open source for data analysis — Knime Analytics Platform. A scheme for the implementation of a multilayer perceptron that solves the approximation problem is considered. The simulation results are compared by the values of the mean squared error (MSE) of the approximation. The neural network approximation is turned out to be an order of magnitude more accurate for the steel specimen than the approximation by the P. Ludwig equation. The neural network approximation provided even a smaller MSE value for a silumin specimen than that or a steel specimen. It is revealed that changing the architecture of an artificial neural network affects the quality of modeling. With an increase in the number of hidden layers, the accuracy of the approximation increases. Neural network approximation is an effective approach to solving the problem of the analytical description of experimental deformation curves and leaves the possibility of using a universal technique for a variety of materials and different types of tests.