When estimating mercury content by inductively coupled plasma mass spectrometry (ICP-MS), this element adsorbs on the surface of the sample introduction system of the instrument, which creates problems in the determination of trace amounts of mercury. Various methods of cleaning the instrument have been proposed in the literature. Objective: to experimentally compare the effectiveness of trace mercury removal methods proposed in the literature for elemental analysis by ICP-MS and to select the optimal cleaning agent. Methods: Mercury content in solution was determined by the Agilent Technologies 7900 inductively coupled plasma mass spectrometer using ²⁰²Hg isotope. Diluted solutions of nitric and hydrochloric acids, solutions of gold chloride, potassium dichromate, thiourea, L-cysteine, potassium bromide, potassium bromate of different concentrations in water and 1% nitric and hydrochloric acids, aqueous solution of ammonium pyrrolidinedithiocarbomate were used as washing agents. Results: The background level of mercury content is achieved by using solutions of copper chloride (5%), thiourea (0.01, 0.1, and 0.5%), L-cysteine (2%), potassium bromide and bromate (0.0005 M) in 1.0% hydrochloric acid solution. The background is lowered by using 3 and 5% HCl, potassium dichromate (60 mg/liter), potassium bromide and bromate (0.01 and 0.05 M) solutions in 1% hydrochloric acid. Application of aqueous solution of ammonium pyrrolidinedithiocarbamate causes sharp degradation of plastic tubes of the sample introduction system. Conclusion: The efficiency of washing agents based on hydrochloric acid is higher than that based on nitric acid and water. The most promising washing agents are bromide-containing solutions and potassium bichromate solution in hydrochloric acid. The optimal way to clean the device is its washing with 0.5 mM potassium bromide solution in 1.0% hydrochloric acid. Its use allows to reduce the background content of mercury and does not complicate the analysis of the content of other elements.

Ceramic, cement and composite biomaterials have been developed based on hydroxyapatites (HA) and tricalcium phosphates (TCP), which are analogous in phase and chemical composition to the mineral component of bone tissue. The crystal structures of HA and TCP are arranged in isomorphic substitutions. Recently, research has focused on the modification of HA and TCP structures with ions of various metals, including rare earth ions (REEs), with the aim of creating materials with a range of beneficial properties for medical applications. REEs are known to have a number of useful properties, including antibacterial, antitumour, catalytic, magnetic and luminescent properties. The replacement of some of the Ca ions in the structures of HA and TCP with REE ions therefore makes it possible to obtain a material with biocompatibility and biological activity, giving it the required properties depending on the REE used and its concentration. In order to achieve the specified properties, it is necessary to control not only the structure (phase composition, lattice parameters of the powders) and the presence of characteristic functional groups, but also the chemical elemental composition. Modifications of hydroxyapatites and tricalcium phosphates containing from one to several different alloying elements are currently being developed. Various analytical methods are used for this purpose, including X-ray, atomic emission and a number of others. This article is devoted to the study of the analytical capabilities of the method of atomic absorption spectrometry with electrothermal atomization and a continuous spectrum source in relation to the determination of Eu and Yb in hydroxyapatites and tricalcium phosphates. The article considers the optimal conditions and modes of analysis, including temperature-time programs, the use of modifiers, the construction of calibration curves, and other factors that can be adjusted for more precise results. The results demonstrated the possibility of simultaneous determination of both Eu and Yb in the concentration range of 0.09 to 2 wt.%, with a relative standard deviation of less than 6 rel.%.

There are developed the techniques of determining the content of chlorides, bromides and fluorides at their joint presence in two types of solid electrolytes differing in matrix content: the first type contains lithium, the second one — both lithium and aluminium, simultaneously. Determination of bromides mass fraction is fulfilled using a method of iodometric titration of iodic potassium excess after bromides are oxidized until free bromine. The fluorides mass fraction is measured by the gravimetric method in the form of fluoro-chloride of lead, in this case the aluminium interfering influence is eliminated by its precipitation in the form of hydroxide after it is fused with carbonates of potassium and natrium, as well as by the method of potentiometric titration with a fluoride ion-selective electrode using the nitrate lanthanum solution. The absence of aluminium interfering influence on the result of fluorine determination is estimated by the «input – found» method. The mass fraction of chlorides is determined by calculation by difference between results of determining the sum of chlorides and bromides using the method of mercurometric titration and — separately — the bromides mass fraction. Optimal conditions of samples preparation and analysis for each of mentioned methods of analysis were selected. The limits of the relative total error of determining bromides in the range of mass fractions from 28.0 to 41.0% is ±2.1%, chlorides within the mass fraction range from 8.0 to 15.0% — ±3.6%, fluorides within the mass fraction range from 3.0 to 7.0% — ±3.4% using gravimetric method and within the mass fraction range from 5.0 to 8.0% — ±1.5% using a method of potentiometric titration. The developed techniques were certified by a metrological service of the enterprise and are used to control the chemical composition of the ion-conducting electrolyte. The techniques do not require expensive equipment, and can be used in factory laboratories.

The potential effect of hydrate formation inhibitors (glycols, alcohols) — components of the liquid phase of gas pipeline operating media — on carbon dioxide corrosion during the transport of aggressive gas has not been sufficiently studied. The paper presents the results of a study of the corrosive effect of glycol (alcohol) present in the liquid phase on the composition and properties of corrosion products on steel when modeling the main aggressive factors under conditions of transport of CO₂-containing gas. On a corrosion stand, the aggressive conditions of alternating wetting of gas pipeline walls with water were reproduced. The fluid circulation characteristic of a partially filled pipeline can have an effect on preventing the formation or destruction of films of corrosion products (iron carbonate, siderite) on the steel surface. In places of cracking and peeling of siderite formed in the presence of CO₂, conditions will be created for the formation of general and local corrosion damage. During simulation tests, monoethylene glycol and isopropanol, as well as their aqueous solutions of different concentrations, were used. For the first time, data on the formation and composition of non-stoichiometric siderite in water-glycol and water-alcohol media at CO₂ partial pressures and temperature were obtained. By processing diffraction patterns obtained by X-ray diffraction, the degree of substitution of iron ions in non-stoichiometric siderites by other cations was determined. The dependence of the degree of substitution on the concentration of alcohol (glycol) in their aqueous solutions was analyzed. It was revealed that with an increase in glycol concentration, a decrease in the rate of local corrosion is observed. With a high glycol content, internal corrosion is completely suppressed in the presence of CO₂. It has been established that in aqueous-alcoholic media at elevated temperatures, local carbon dioxide corrosion does not occur. This is apparently due to the uneven distribution of water and alcohol in the mixture. The results obtained can be used in assessing internal carbon dioxide corrosion in the presence of glycol (alcohol), used at gas facilities as an inhibitor of hydrate formation.

For aviation binders at the moment there is no necessary methodological base on the basis of which it is possible to control the conditions of their curing by viscosity, reaction rate and glass transition temperature in real time. The paper presents a method of control of thermosetting binder parameters directly during the molding process. The epoxy binder VSE-59 was studied. A mathematical model of the relationship between the frequency maximum parameter of the imaginary component of the electrical impedance and the degree of curing is given, the results of dielectric analysis are compared with laboratory methods (differential scanning calorimetry and rheometry). It is shown that the convergence of the values of the degree of conversion is high. Rheological and dielectric analyses revealed a direct correlation between electrical and rheological properties in the range of injection temperatures. Equations were determined and coefficients were experimentally selected to describe the correlation between viscosity and glass transition temperature and dielectric parameters, which provides the possibility of their control in real time. The obtained results can be used to create a hardware and software base, which makes it possible to control the state of the binder at each moment of the process of forming products from polymer composite materials, as well as to carry out optimization to eliminate the emergence of conditions of uneven polymerization. Realization of the detailed control of the binder state in different parts of the product will allow to carry out verification of calculations, to predict and avoid the occurrence of warping and, accordingly, to increase the quality of composite products.

The paper examines the differences in the properties of new pipes, pipes artificially saturated with hydrogen and boiler screen pipes after long-term operation. The embrittlement process was studied by observing changes in the microstructural structure, mechanical properties and identifying the mechanism of hydrogen attack on the objects under study. It was discovered that there was no decarbonization characteristic of natural saturation with hydrogen and a decrease in the ultimate tensile strength of artificially saturated pipes. The nature of cracking was also different — transcrystalline with artificial saturation and intercrystalline with natural saturation. At the same time, the nature of the fractures — with areas of hydrogen fragility — and the average concentrations of accumulated hydrogen in pipes artificially hydrogenated and hydrogenated during operation were identical. Significant differences in the physical and mechanical properties of all three types of pipes have been recorded, which makes it impossible to transfer the results obtained with model samples artificially saturated with hydrogen to actually operated objects.

The paper is devoted to the study of the creep characteristics of 15Kh2NMFA-A vessel steel in the temperature range of 500 – 1200 °C, which can be achieved during emergency operating conditions of VVER-type nuclear reactors. An analysis of the creep curves of the 15Kh2NMFA-A steel in the studied temperature range obtained during specimens tensile tests was carried out with the construction of the parametric Larson – Miller relationship. It is shown that in the temperature range of 600 – 850 °C the generalized Larson – Miller temperature dependence has a changed slope, resulting in a high error in estimating the time to fracture of 15Kh2NMFA-A steel under creep conditions in this temperature range. To reveal the reasons for the change in creep resistance in the specified temperature range, the studies of the metal microstructure using optical and scanning electron microscopy on specimens in the initial state and after creep testing were carried out. Studies of the microstructure of steel have shown that in the temperature range of 600 – 700 °C, coagulation of V(CN) type carbonitrides occurs, leading to a change in the slope of the Larson – Miller parametric relationship. It is shown that in the temperature range of A_c1 – A_c3 there is an abrupt change in creep characteristics associated with phase transformations. The feasibility of dividing the Larson – Miller parametric relationship into several sections depending on temperature, taking into account structural changes in the steel, is substantiated, which makes it possible to increase the accuracy of estimating the destruction time of 15Kh2NMFA-A steel by at least an order of magnitude. Based on the results of the study, a calculated dependence of the long-term strength of steel on temperature was obtained on a basis of 6,24 and 120 hours.

A mathematical definition of the concept of «hybrid function of the first kind» (GF1) is given, which provides a smooth controlled transition from one basic mathematical function to another and contains the characteristic features of these two functions. The transition is controlled both by the place of transition and by its speed. At the same time, the transition remains smooth and differentiable. The functions of GF1 are characterized by the coincidence of the arguments of both the basic functions and the argument of the control complex that is part of GF1. Vectors and tensors, as well as complex numbers and functions, can be used as basic functions. Based on GF1, it is possible to design chain GF1 or CGF1, which is essential for expanding the range of GF1 applications. GF1 itself can be used as basic functions. Hybrid functions have a surprisingly high potential for approximating experimental data. The article provides examples of using GF1 to approximate curves in relation to two-parameter crack resistance criteria. An algorithm for eliminating the singularity in calculations for crack resistance is described. Based on GF1, new probability distribution functions of statistical data are proposed. The possibility of qualitative analytical approximation by CGF1 of existing statistical data with subsequent differentiation of the obtained CGF1 to obtain the density of their distribution is shown. An attempt has been made to use GF1 to describe the phenomenon of bifurcation.

Kinetics of simple and complex kinetic reactions is usually described by exponential and rational models. The fractional rational models include the well-known Michaelis – Menten model of enzymatic kinetics. In the presented article A-optimal designs are proposed for the Michaelis – Menten model. The elimination method used to construct A-optimal designs, allowed us to determine the nodes and weights of A-optimal designs separately and thereby extend this approach to other criteria and models of the rational type. It is shown that the nodes of A-optimal designs determined by this method are the roots of the 4^th degree algebraic equation with coefficients depending on the model parameters. If the nodes of the A-optimal design are already known, then the weights of the corresponding nodes are determined analytically by the Pukelsheim formula. The properties of the roots as well as the properties of the nodes of A-optimal designs were studied using the Sturm system constructed in the general form for the resulting equation. It is shown that with a certain combination of parameters of the Michaelis – Menten model, the degree of the resulting algebraic equation is reduced to three. A partition of the set of values of the parameters of the Michaelis – Menten model into two subsets has been found. In one of them, the A-optimal design is determined uniquely, whereas for the other one it is necessary to select the optimal node from two possible options. It is revealed that the degree of the algebraic equation is equal to three for points belonging to the curve which is the common boundary of the indicated subsets. Corresponding numerical examples are given to illustrate the results obtained.