Cefuroxime, cefuroxime axetil and cefalexin are broad-spectrum pluripotential cephalosporin antibiotics. Their determination in various objects suggests using expensive spectroscopic, chromatographic, electrochemical equipment and organic solvents. Potentiometric sensors can provide rapid detection of cephalosporin antibiotics in a small sample volume without a preliminary sample preparation. The study is aimed at the developing of modified solid-contact potentiometric sensors for determination of cefuroxime and cefalexin in aqueous, biological media, and pharmaceuticals. The electroanalytical characteristics of unmodified and modified polyaniline and copper oxide nanoparticle sensors are evaluated. Tetradecylammonium(TDA) with a silver (I) – cefuroxime complex are used as the active membrane components, whereas polyaniline and copper oxide nanoparticles are used as modifiers. The main electroanalytic and operational characteristics of the studied sensors in aqueous solutions of antibiotics and against the background of oral fluid (LRP) are determined. The results of comparative evaluation of the electroanalytical properties of unmodified and modified solid-contact sensors in aqueous media of some â-lactam antibiotics and against the background of oral fluid are presented. The sensors based on Ag (Cefur)2TDA are characterized by a short response time: for modified polyaniline (PAN) and copper oxide nanoparticles within 5 – 10 sec, for unmodified — 10 – 20 sec. The linear range of the electrode functions for unmodified and modified sensors is 1 × 10–4 – 1 × 10–1 M, the detection limit is 7.4 × 10–5 M for unmodified and 6.3 × 10–5 M for modified sensors, respectively. The potential drift is 6 – 12 and 4 – 6 mV/day, service life is 1.5 and 2 months for unmodified and modified sensors, respectively. The modifiers stabilize the electrode potential, perform the function of the electron transfer mediator thus enhancing the electroanalytical characteristics of the sensors. The effect of the redox agents on the sensor properties is revealed: 1 × 10–3 – 1 × 10–4 MK 2Cr2O7 and FeCl3 solutions reduce the linearity intervals of the electrode functions, KI and Mohr’s salt do not affect the characteristics of the sensors in cefuroxime and cephalexin solutions. The coefficients of potentiometric selectivity of cefuroxime-selective sensors (modified with CuO nanoparticles) with respect to cefazolin, cefotaxime, and cefalexin are close to unity; Kijpot with respect to inorganic anions being part of the oral fluid (, Cl Br,I,HCO3 ,H PO 24 ,HPO4 2) are n × 10–2 – n × 10–3. This indicates the possibility of using sensors for detecting individual cephalosporin antibiotics or their total content in the presence of 100 – 1000 fold excesses of inorganic ions in medicinal and biological environments, small sample volumes, which is important when studying the pharmacokinetics of antibiotics and in determination of the maximum therapeutic dose when adjusting the treatment process.

The possibility of using water soluble pyrogallol red (PRWS) as a photometric reagent for the quantitative determination of antimony (III) in real objects has been studied. Formation of a colored product is observed in acidic solutions (pH 3.8 - 4.5) with a weak oxidizing agent (iodine) present for preliminary oxidation of SbHg to salts of Sb (III). The excess iodine is eliminated through introduction of sodium thiosulfate solution after obtaining the photometric form. The maximum analytical signal of the colored form is observed at 378 nm (e = 5.936 x 103). A decrease in the acidity of the solution (pH > 7) is accompanied by the formation of sodium salts of the reagent which prevents further complexation, whereas the only one maximum in the absorbance within the recommended pH range directly indicates to the formation of the the only one ionic associate (AI). The ionic associate thus formed appeared low stability in time. Unfortunately, change in the dielectric constant of the solution failed to give a positive effect and measurements of the absorbance of the colored compound were limited to 3 minutes. Determination of the composition and possible mechanism of the ionic associate formation was carried out on using the methods of molar ratios and isomolar series. After stripping of stibine into the absorption system, an ionic associate of the composition M:R = 1:1 is formed with a calculated stability constant of 4.01 x 105. The obtained results are used to develop a spectrophotometric (SP) method for antimony determination with the limits of detection and quantitative determination of the element 1.30 and 4.32 pg/ml, respectively. The developed method is valid in terms of the specificity, linearity, precision and accuracy, and, therefore, can be recommended for determination of the antimony content in any control and analytical laboratory.

A widespread use of complex pharmacotherapy entails the necessity of studying the processes occurred in pharmaceutical mixtures. IR spectroscopy is one of the methods used to assess the stability of substances. To increase the efficiency of interpretation of the IR spectra of mixtures, a method combining matrix methods and graphic ranking of the array of experimental data has been developed. This approach has been tested for the analysis of model mixtures of pharmaceutical substances naproxen and pheniramine maleate. Absorption spectra were obtained on an Avatar 360 FT-IR ESP Fourier transform spectrometer (Nicolet, USA) using an ATR (primary attenuation total reflection) attachment Smart Perfbmer (optical crystal ZnSe; spectral range 1.35 - 26.6 pm, 7400 - 375 cm4). The obtained IR spectra were processed using Thermo Scientific Specta embedded software. Graphs for graphical ranking were plotted in the coordinates of the mixture heating temperature —relative frequency intensity. The points on the graph represent the relative intensity of the bands for a mixture kept at a certain temperature, whereas the curves with which they are connected reflect the processes occurring in the structure of the substance. Common trends in the relative intensity for different frequencies (at the same temperature) and/or for a number of frequencies of a certain characteristic region, indicates the unidirectionality of the process. Graphic ranking is applied to the characteristic bands of pyridine and aliphatic nitrogen of pheniramine maleate and characteristic frequencies of the intermolecular hydrogen bond and carbonyl group of naproxen. We also used the method of mathematical ranking of the matrices of transmittance values. For the characteristic bands of the studied compounds, a combined use of graphical and mathematical ranking allowed us to infer a change in the structure of naproxen and pheniramine maleate under the impact of elevated temperatures: the salt of pheniramine and maleic acid in aliphatic nitrogen has one structural conformation, whereas the binding force depends on the temperature.

Hexagonal metals (e.g., Be, Zr, Ti) are widely used in the nuclear industry, space and aircraft engineering (in manufacturing of the structural elements operating under extreme conditions). A promising way to improve the quality of products made of them is to improve the physical properties of materials using the natural anisotropy of metal single crystals. The results of studying anisotropy and a comparative analysis of the technical characteristics of the elastic properties of single crystals of hexagonal metals are presented. The equations of the elastic compliance matrix components are derived in the explicit form for arbitrary crystallographic direction proceeding from transformations of the elastic compliance tensor in the principal axes to a new arbitrary coordinate system with a subsequent use of Euler angles. Analytical expressions are presented for the technical characteristics of the elastic properties (shear and Young's moduli, Poisson's ratio) of the single crystals of 10 hep metals for an arbitrary crystallographic direction. The axial symmetry of the characteristics about the hexagonal axis is revealed. The sums of the elastic compliance coefficients which determine the shear moduli and the Poisson's ratios in two mutually perpendicular directions are constant in any crystallographic plane of the single crystal. A comparative analysis of the anisotropy of the elastic properties of single crystals of the studied group of metals revealed auxetic properties of Zn and Be single crystals and the region of crystallographic directions of uniaxia tension, leading to an auxetic effect The auxetic effect in Zn was observed under tension in the directions of the plane perpendicular to the hexagonal axis of the single crystal. The planes of the auxetic effect manifestation in Be single crystals are perpendicular to the directions making an angle of 45° with the hexagonal axis.

that may be accompanied by the processes of mutual diffusion and phase formation. Controlled technological process of forming coatings with the given properties entails the necessity of forecasting the evolution of the phase composition. This in turn requires the development of algorithms and quantitative models of the processes. Reactive mutual diffusion in polycrystalline metal (oxide film systems with limited component solubility) has not been simulated before. The simulation allows selecting the annealing conditions (time and temperature) necessary for the inclusion and uniform distribution of metal in the oxide lattice. A quantitative model of the interaction in a multi-layer system metal — polycrystalline oxide of the other metal under conditions of limited solubility is developed. The model is based on the concepts of mutual diffusion of the components and the bulk reactions of the formation of complex oxides. The developed model was applied to the analysis of the process of modifying thin films of titanium oxide with transition metals. The model allowed us to perform a numerical analysis of the experimental concentrations of the component distributions in polycrystalline Co - Ti02 and Fe - Ti02 thin-film systems. The individual diffusion coefficients of the studied metals and titanium under conditions of vacuum annealing were determined. The model provides a good description of the basic systematic features of the process: the appearance of titanium in the metal film and deep penetration of Fe and Co into the film of titanium oxide. It also explains the fact that complex oxides are formed not by layer-by-layer growth at the metal-oxide interface, but throughout the entire thickness of Ti02 film. The results of analysis of the processes of interracial interaction in layered systems accompanied by the reaction mutual diffusion can be used to predict the evolution of the phase composition, as well as to control the technological processes of obtaining materials with the desired properties.

By virtue of high degree of anisotropy and small transverse stiffness, carbon nanotubes are known to form ring-shaped annular structures (fractal objects) in the polymer matrix of nanocomposites. We used the fractal dimension for quantitative and physically strict characterization of the nanofiller structure (carbon nanotubes) in the polymer matrix of nanocomposites. Two methods of calculation based on the models of irreversible aggregation and fractal analysis are proposed. The results obtained using both approaches match each other within 6%. It has been shown that formation of the annular structures occurs according to the cluster-cluster mechanism (i.e., by combining small formations into larger ones, rather than individual nanotubes). Moreover, the method of fractal analysis takes into account the effect of the polymer matrix on the structure of ring-shaped formations and, hence, on the properties of polymer nanocomposites. The correctness of the methods thus used was proved using the percolation model, which showed good agreement between the theory and experiment when using fractal dimensions determined by both methods. This means that for a fixed nanofiller content, the properties of nanocomposites are determined only by the nanofiller structure. In other words, a significant change in the properties (for the degree of reinforcement more than by an order of magnitude) is possible even at a low content of a nanofiller, which is realized only through change in the nanofiller structure using various methods of nanofiller treatment (ultrasound, functionalization, construction of special types of nanofiller frame, etc.).

The results of studying correlation between the crystallographic texture of polycrystalline materials and anisotropy of their physical and mechanical properties are considered. The methods for calculating the anisotropic properties of polycrystals based on the data obtained by X-ray methods of direct and inverse pole figures are reviewed. Calculation methods based on the use of the distribution function of crystallite orientations require the use of a large amount of experimental data and, hence, they are not suitable for express estimation of the anisotropy level of the physical properties of samples upon their thermomechanical processing. A method for rapid estimation of the anisotropic properties of the sample based on the use of Д; ("orientation factors") in the calculations, is proposed. Experimental data of X-ray analysis (method of inverse pole figures) are used to calculate the absolute and relative deviations of the physical parameter of textured polycrystal from the same value in the isotropic sample. The contributions of individual crystallographic orientations to the formation of the anisotropy of the properties of the sample are estimated. The dynamics of quantitative changes in the anisotropic properties of a polycrystal in the process of texture formation is studied. To analyze the source of the most rapid changes in the anisotropy of properties, we used the coefficients of the "response" matrix, the calculation of which does not depend on the results of specific diffractometric measurements, but is common for all metals with a hexagonal close-packed (hep) lattice. The anisotropy of the coefficient of thermal conductivity, electrical conductivity, and thermal diffusivity was calculated for the samples of deformed yttrium which underwent cold rolling with a reduction ratio of e = 25%. It is shown that the final physical properties_of the hep polycrystal are largely determined by the pyramidal crystallographic orientations {1015}, {1124}. The results of the study form a basis for analysis of the anisotropy of the physical properties of hep-metal samples upon thermomechanical processing.

Calculation and experimental estimates of the residual life of steels P2M and EI415 of two strength levels (H and B) are carried out using two methods, the new one and the traditional. The loading was carried out for 300 thousand hours under conditions similar to those in which the metal operates in the zone of blade attachment in the rim of the disk of the first stage of medium-pressure rotors of K-300-240 LMZ and KhTZ turbines. When evaluating the residual life, a gradual decrease in stresses due to creep was taken into account by distinguishing several stages with conditionally constant stresses. According to the new methodology, the residual life was estimated by a change in the metal super-continuity at each stage 47 = ц/п + 1, where u/ is the continuity, n is the crack formation index; whereas in the traditional method the relative damage Р is estimated according to the principle of linear summation of damage (LSP). It is shown that the time dependences P and 47 obey the logarithmic law, while the metal of the fbrgings В (high strength) in all cases had a greater resource compared to the fbrgings H (low strength). For the first time, the process of resource depletion was considered by analyzing the sum of two functions: 47 + P = 1. It is shown that for R2M steel this amount is less than unity; for steel EI415 it is equal to or greater than unity. Proceeding from the literature data on the differences that follows from using LSP rule for a relatively viscous and brittle metal, we suggested that deviations from unity are attributed to the error in estimating the resource according to the LSP principle. Therefore, the result obtained by the new method should be recognized as more accurate. Taking into account the use of samples with a particularly deep sharp notch in which the brittle crack development is guaranteed by the proposed methodology, the new principle of calculating the residual life can be used in determination of the resource for any type of the parts made of the metal subjected to brittle fracture during operation under creep conditions.

We consider and analyze general methodological issues regarding the strength and endurance (life-time) of the materials and structure elements under a combined effect of various force, deformation and temperature factors. The Journal "Zavodskaya laboratoriya. Diagnostika materialov" (Industrial laboratory. Diagnostics of materials) has launched systematic publications on this problematic since 2018. For many decades, domestic and foreign laboratory studies have gleaned to a traditional methodology for obtaining initial curves of the long-term and cyclic strength that related the breaking stresses with time or number of cycles. These curves, with the characteristic sections and break points, separating the areas of elastic and inelastic (plastic strain or creep strain) strain, are used in analysis of long-term and cyclic damage. Using the elementary linear law of damage summation, it is possible to calculate at a first approximation the strength and endurance under varying conditions of loading. Stepping up the requirements to the accuracy of calculations necessitates a transition from force fracture criteria (at stresses a) to deformation criteria (in elastic and inelastic deformations e). Thus, it becomes possible to construct and use a unified expression for the curve of the long-term cyclic fracture (taking into account the temporal x and cyclic N factors) and a long-term cyclic damage. With such approach it is possible to remain the linear law of damage summation though those damages are obviously nonlinear. The goal of the study is to continue and support the discussion of the most complex problems of a comprehensive assessment of the strength, resource, survivability and safety of high-risk engineering equipment within the journal pages.

A method and procedures for determining the boundaries of the second stage of the kinetic crack resistance diagram or fracture toughness kinetic diagram, sample formation within the aforementioned boundaries and determination of the parameters С and n of the Paris equation from the sample are presented. The necessity of developing the method is attributed to the lack of rules and procedures for accurate determination of the boundaries of the second stage in the current standards and regulatory document (RD). The proposed method provides a given accuracy of determination of the number of cycles corresponding to the length of the fatigue crack at the upper boundary of the second stage obtained by numerical integration of the Paris equation with the found values of the parameters С and re. The developed method is based on the application of two criteria R2 and %. Statistical criterion R2 characterizes a degree of deviation of the experimental data from the linear fragment of the kinetic fracture toughness diagram. Parametric criterion у specifies the level of accuracy of the parameters С and re of the Paris equation. This level is set through a comparative evaluation of the experimental and calculated crack length I and the number of cycles N, obtained by integration of the Paris equation within the specified lower and upper limits of the interval of the stable growth of fatigue crack. Application of the method is shown by the example of the experimental data obtained when testing samples of VT9 titanium alloy, deformable nickel alloy EI437BU and granular nickel alloy EP741NP (granules up to 140 pm) at room and elevated temperatures. Application of the method indicates that the experimental and calculated curves "I - N" obtained by numerical integration of the Paris equation differ by less than the specified value of the criterion X ^ 3%, in contrast to the results obtained in accordance to the recommendations of the regulatory documents.