The results of the determination of trace amounts of chromium in aqueous standard solutions of chromium and in high purity gallium arsenide using atomic ionization spectroscopy are presented. Single — and two-step schemes of chromium atom excitation from the ground state 3d⁵4s ⁷S₃ to septet states 3d⁵4p ⁷P_2,3,4, 3d⁴4s4p ⁷P_2,3,4 were studied using a «rod – flame» atomizer. A mechanism of forming atomic-ionization signal for two-step excitation schemes is revealed. The most effective two step excitation schemes for chromium atoms were determined and experimentally studied at different wavelengths λ₁ = 425.4 nm, λ₂ = 451.4 nm; λ₁ = 425.4 nm, λ₂ = 426.1 nm. The low limit of chromium detection in aqueous water solutions was 50 pg/ml. The analytical potentiality of the «rod – flame» system for determining traces of chromium in gallium arsenide solutions has been demonstrated. The possibility of determining traces of chromium in gallium arsenide using a flame – rod atomizer at a level of 5 × 10^–7 % is demonstrated. Two methods are proposed to increase the selectivity and sensitivity of atomic-ionization determination of chromium: optimization of the temperature program of the flame – rod atomizer and the use of two-stage excitation of chromium atoms. It is shown that the main interfering factor is the background attributed to the matrix ionization. Methods are proposed to reduce or eliminate the matrix impact, which ensure direct determination of elements in samples.

A rapid and easy to use method for identification and differentiation of normalized and reconstituted milk using digital colorimetry and near-infrared spectroscopy is proposed. A box device with LEDs (λ = 365, 390, 850, 880 nm) built in through resistors with a light scattering angle of 20° was used. A smartphone with PhotoMetrix PRO^®, ColorGrab, RGBer applications and an IR-Fourier spectrometer for a near-IR region (4000 – 10,000 cm^–1) were taken to record the analytical signal. Applications TQ Analyst, The Unscrambler X, XLSTAT, were used for processing the obtained diffuse reflectance spectra and colorimetric parameters. The principal component analysis (PCA) and hierarchical cluster analysis (HCA) were used to identify and differentiate the analyzed milk samples. The determination of the mass fraction of fat and protein in dairy products was carried out using the partial least squares (PLS) regression algorithm. The points corresponding to normalized and reconstituted milk are located in different quadrants on PCA plots in methods of digital colorimetry and IR spectroscopy. Using PCA and HCA graphs, it appeared possible to distinguish the analyzed milk by the type and differentiate skim milk by the protein content. The possibility of determining the fat and protein content in the studied milk samples using chemometric methods of analysis has been demonstrated. The relative standard deviation of the analysis results did not exceed 0.03 for reconstituted and normalized milk, and for skim milk — 0.02.

An original method for the quantitative determination of retinol palmitate (RP) and tocopherol acetate (TA) in lipid microcapsules using reverse-phase high-performance liquid chromatography with ultraviolet detection (HPLC-UV) in isocratic elution mode is proposed. The method includes sample preparation of lipid microcapsules, HPLC separation of microcapsule components TA and RP, as well as metrological support for the quantitative determination of vitamins. Sample preparation of microcapsules included the following stages: dissolution of microcapsules by heating, cooling of the solution, centrifugation and filtration. The proposed sample preparation procedure provides the extraction degree no less than 98.5% for TA and 99.6% for RP, respectively. Optimal HPLC-UV chromatography conditions for isocratic elution were selected. The optimal wavelength of 288 ± 2 nm determined from spectrophotometric measurements provides the joint determination of RP and TA. The effect of mobile phase (MP) composition on chromatographic parameters (retention time, peak area, resolution, peak width, peak asymmetry coefficient) for standard TA and RP samples is considered. The best values for these parameters were determined from the peaks obtained when using the mobile phase acetonitrile: isopropyl alcohol: 1,2-dichloroethane (55:40:5). Calibration dependences of the peak areas on the concentration of TA from 0 to 5% and RP from 0 to 10% were constructed; the correlation coefficients were 0.9981 and 0.9976, respectively. The accuracy of the method for the quantitative determination of fat-soluble vitamins (TA and RP) in lipid microcapsules was assessed in spike recovery tests. The method can be recommended for quality control laboratories to determine the quantitative content of fat-soluble vitamins such as retinol palmitate and tocopherol acetate in the pharmaceutical, cosmetic and food industries.

Data on the hydrocarbon composition of straight-run oil fractions are required to choose methods for their use directly after primary oil refining (fractionation) and subsequent secondary processing. The paper presents the results of determining the group hydrocarbon composition of straight-run oil narrow-temperature fractions (paraffins, naphthenes, aromatic hydrocarbons) by the refracto-densimetric method. We used the additivity of the characteristics (in terms of mass fractions of group components), i.e., derivatives of the refractive index and fraction density (specific refraction and specific volume). The values of group narrow-temperature hydrocarbon reference points were estimated proceeding from data on the initial refracto-densimetric characteristics of fractions and their dearomatized parts and data of gas-liquid chromatography. It is shown that the paraffin reference points are quite close to the reference points determined by chromatographic data. The values of narrow-temperature group reference points can be adjusted using available chromatographic data on the individual hydrocarbon composition of wide straight-run oil fractions. A method for determining the reliability of measurements using Kurtz – Lorentz maps is proposed. The results obtained can be used in the group analysis of hydrocarbon composition in production conditions in real time in situ performed both on ELOU AVT industrial installations and ARN-2 laboratory fractional distillation installations when installing in-line refractometers and densimeters or combined in-line refracto-densimetric analyzers.

The coercimetry based on the Hall effect as a source of primary information is the main method of magnetic control (when classified according to the primary informative parameter) in technical inspection of potentially dangerous metal structures. Coercive force (considered as the intensity of an external magnetic field applied to a ferromagnet magnetized to saturation for complete demagnetization of the latter) is the most structure-sensitive characteristic which provides for rapid diagnostics of the material in production conditions. A linear character of change in coercive force upon application of cyclically varying stresses provides the possibility of reliable determination of the residual life of the structure. We propose a method for determining the residual life of structures made of non-ferromagnetic materials exposed to cycle mechanical loads proceeding from data on changes in the coercive force of steel witness samples (samples made of ferromagnetic material, working together with the structure under study made of non-ferromagnetic material). It is shown that the rate of change of the coercive force in the ferromagnetic witness sample correlate with the stresses in the nonferromagnetic structure. This makes it possible to determine directly the residual life of a non-ferromagnetic structure, which significantly increases the accuracy of estimating the residual life of potentially hazardous structures made of non-ferromagnetic materials. The results obtained can be used to determine the technical condition (based on the level of accumulated damage) of such structures as, for example, pedestrian bridges made of aluminum alloys.

Electrotechnical prepregs are used as gluing gasket in the manufacture of multilayer printed circuit boards. These materials are obtained by fiberglass impregnation with a mixture of modified epoxy resins. The glass transition temperature (T_g) of the cured prepreg is determined by differential scanning calorimetry. This universal approach provides a wide range of instrumental parameters and does not contain numerical values of metrological characteristics. We present a methodology of T_g determination taking into account the requirements of GOST and experimental conditions and assess the metrological characteristics of the technique. Cured samples of prepregs produced in Russia and aboard were studied. Thermograms were recorded for two samples of each prepreg. T_g was calculated from the transition on the curve of second heating at a rate of 20 °C/min. It has been shown that the relative total error of the method is ±4%. Since in some cases the visible glass transition was not recorded on the thermograms of cured prepregs, a linear approximation of the T_g dependence from a high heating rate at which the glass transition is more pronounced to the value of 20 °C/min was carried out. Control of the correctness of the determination was carried on samples for which T_g can be confidently determined by extrapolation and traditional experimental-calculation methods. It is shown that both extrapolation and calculation methods lead to the same results within the limits of the analytical error. The obtained results can be used for determining T_g of electrotechnical prepregs and incoming inspection of the corresponding product.

The results of studying the low-cycle fatigue characteristics of steel 15NiCuMoNb5 (WB36) and its welded joints are presented. Brief information is given on the specific features of WB36 steel proceeding from the nalysis of literature data. An emphasis is made on the absence of available information on the studies of WB36 steel and its welded joints produced in Russia. The study was carried out on an experimental welded metal billet produced by standard technology and simulating a full-scale fragment of a high-pressure drum. The methodological aspects of the conducted research are described. Tests for low-cycle fatigue of WB36 steel and its welded joints were performed in the mode of hard loading in a symmetrical cycle at room (20 – 25°C) and operating (350°C) temperatures. Corset-type tensile and compression samples were used; the onset of a macro-fracture on the surface of the corset part was taken as the criterion for the destruction of the sample. It is shown that with an increase in the test temperature, the resistance to low-cycle fatigue of steel and weld metal decreases. At the same time, the base metal and the weld metal demonstrate identical characteristics of low-cycle fatigue at each of the test temperatures. A certain part of the study touched the effect of temperature ageing on the low-cycle fatigue of steel. It is shown that the values of the low-cycle strength of the material under study slightly exceeds the results of similar tests of WB36 steel presented in foreign technical literature. A comparative analysis of experimental low-cycle fatigue curves and corresponding standard calculation curves obtained using analytical expressions for the actual mechanical properties of steel has shown that experimental data on the low-cycle fatigue of steel demonstrate a higher fatigue resistance at room temperature and approximately a similar level at operating temperature compared with calculated fatigue curves obtained using the mechanical properties of the metal. An example of the low-cycle fatigue calculation for a high-pressure drum of a steam-gas recovery boiler is given. It is confirmed that for the given initial parameters and resource indicators, conditions of the drum strength met the criteria of low-cycle fatigue.

Tensile tests of steel specimens with plotting loaded and unloaded true stress curves were carried out. It is shown that «true stress – true strain» curves in the necked region of the tensile specimen have the form of a sloping ascending straight line up to failure. It is revealed that the straightness of the curve is also observed for austenitic steel in the structure of which martensite is formed under the effect of plastic deformation, whereas «true stress S – true relative area reduction ψ» curves exhibit a violation of the straightness with upward deviation at the final stage of necking. When using Davidenkov correction, the calculated values of the true ultimate tensile stress decrease and approach the straight line. Although the unloaded values of the true stresses and true strains exceed the loaded values at the same tensile force, they fit on the same curves at different stages of the material deformation. It is possible to apply Kerber’s rule to «true stress – true relative area reduction ψ» if a sufficiently long rectilinear section of the curve is clearly identified after the true ultimate tensile stress has been reached in order to extrapolate this section to a true relative reduction of area equal to unity. Kerber rule is not applicable for «true stress – true strain» curves despite their straightness in the necked region due to the uncertainty in calculating the true strain at the unit value of true relative area reduction. At the same time the presence of a linear section in these curves during the specimen necking greatly simplifies the derivation of the entire tensile curve up to fracture.

The purpose of this study is to develop a method for experimental modeling of contact interaction in a worm – worm wheel pair on an MT-8 friction machine with an assessment of a complex criterion of physical similarity between the processes of friction and wear in a worm pair and in laboratory samples. Modeling of the processes of contact interaction of the worm pair in operation based on the analysis of the contact conditions of the «worm – worm wheel» pair is performed in laboratory conditions on an MT-8 friction machine with the determination of a complex similarity criterion for the selected laboratory installation. Dependences of the wear intensity on the contact pressure in a worm gear and in laboratory samples were obtained, with recalculation of the contact pressures and taking into account the real contour contact area. The developed method for experimental modeling of contact interaction in a worm-worm wheel pair has shown that the processes of contact interaction in operation of a worm pair and in a model experiment on a reverse sliding friction machine are similar. The use of the developed method for experimental modeling of contact interaction in a worm-worm wheel pair is recommended when planning preliminary tribological tests, which will reduce the costs and time for carrying out full-scale tests of a worm gear with assessment of tribological parameters: wear rate, contact pressure, relative sliding speed, oil temperature with the goal of predicting the parametric boundaries of the tribotechnical performance of a worm gear.