The expanding use of sulfur in medicine, science and technology has tightened the requirements for the impurity composition, including the content of selenium in sulfur. Combined extraction-atomic absorption methods have been developed to determine selenium in purified sulfur. The possibility of using thiourea derivatives such as sodium diethyldithiocarbamate and diphenylthiocarbazone for the extraction of microgram amounts of selenium from sulfuric acid solutions was studied. Optimal conditions for the extraction of selenium from sulfate solutions are determined. Two procedures for selenium separation are proposed: extraction of selenium diethyldithiocarbamate with ethyl acetate from a solution of sulfuric acid with pH 3 or extraction of selenium dithizonate with chloroform from a 5.25 – 6.0 M sulfuric acid solution. The results of the extraction-atomic absorption determination of selenium in sulfur are compared for both procedures of selenium separation. The accuracy of the selenium determination in purified sulfur is confirmed by the method of varying sample weight. The optimal temperature-time parameters for the electrothermal atomic absorption determination of selenium are determined. The limit of selenium determination is 1 × 10^–5 % wt. The values of sr in the range of selenium content 2 × 10^–5 — 1 × 10^–4 % wt. change from 0.10 to 0.12.

The purpose of the work was to develop Express methods for determining cationic and anionic surfactants in disinfectants and process solutions. The surfactant concentration was determined visually and colorimetrically by the intensity of color of the indicator zones of paper test strips or by the length of the colored (discolored) zones of test strips laminated in a polymer film. Semi-quantitative determination of surfactants in solutions was carried out by the intensity of color of the zones of indicator test strips pasted on the substrate (test titration on paper). Bromphenol blue was used as an indicator. The titrant was sodium dodecyl sulfate for cationic surfactants and cetylpyridinium chloride for anionic surfactants. Test strips were used for the determination of surfactants in the disinfectant solutions. The concentration in the range of 0.1 – 1.2% was determined by comparing the color with the standard color scale. The duration of the analysis was 3 – 5 min. Quantitative determination of surfactants was carried out by the length of the colored (discolored) zones of test strips glued in a polymer film. As an indicator for cationic surfactants, bromphenol blue (blue zone on the test strip) was used, and for anionic surfactants, an associate of bromphenol blue with cetylpyridinium chloride (discolored zone on the test strip). The determination range of the surfactant made up 16 – 1000 mg/liter. The concentration was determined according to a calibration graph representing the dependence of the length of the blue/discolored zone of the test strips on the concentration of surfactants in the solution. The relative standard deviation of the analysis results does not exceed 0.3; the analysis duration was 20 – 30 min.

A rapid method for the determination of Dibazol (bendazol hydrochloride) in liquid and solid dosage forms (DF) has been developed. The method is based on converting the drug into an analytical form and titrating the physiologically active compound (PAC) with a solution of photogenerated iodine obtained by irradiation of an auxiliary solution containing potassium iodide, a mixture of sensitizers (sodium eosinate: fluorescein: auramine, taken in a molar ratio of 1:1:1) and an acetate buffer solution (pH 5.6). A decrease in the titrant content in the cell due to interaction with Dibazol was recorded by a decrease in the current in the amperometric circuit. Stabilization of the current in the circuit indicated the completeness of the reaction, thus providing for estimation of the PAC content in a DF. Further irradiation of the solution and measurement of the generation time required to replenish the titrant loss in the cell also ensure the quantitative estimation of the PAC content in the preparation. The method has been tested on solid dosage form and sterile solutions of Dibazol intended for intramuscular and intravenous administration. A slight effect of stabilizers (hydrochloric acid, ethanol) and auxiliary substances (potato starch) present in the DF on the photogeneration of the titrant was observed. The determined Dibazol content in solid and liquid DF falls within the range recommended by the order of the Ministry of Health of the Russian Federation (26.10.2015 No. 751n) and OFS.1.4.2.0009.15, which indicates that the quality of the drug meets the GMP standards. The linear dependence of the analytical signal on the Dibazol concentration is observed in the range of 13.5 – 134.7 mg for the drug «Dibazol-UBF, tablets, 20 mg». The calculated limits of Dibazol detection and quantitative determination by changes in the current strength and generation time are (4.71; 3.56) and (14.26; 10.77) mg, respectively. The use of developed technique in the analysis of drugs containing Dibazol reduces both the time of single determination due to the absence of the need for standardization of solutions, and the cost of a single analysis, since it does not require the use of expensive equipment and reagents.

Extrusion through a die, vibrating with an ultrasonic frequency is a promising method for hardening ceramic materials (bricks, tiles, pipes, etc.). We present the results of studying low-frequency acoustic spectra of cylindrical samples of face brick ceramics reinforced by extrusion and addition of fiberglass waste. Correlations between structure changes in the obtained ceramics, parameters of the acoustic spectrum of the samples, and the destructive forces upon their compression (bending) in a press were analyzed. It is shown that ultrasonic extrusion increases the destruction force of the cylinders by 1 – 7 kN (~30 %) and thus shifts the frequency of the fundamental tones of transverse and longitudinal oscillations (6 and 17 kHz) with a coefficient of ~0.1 kHz/kN. The fiberglass particles strengthen the ceramics due to the formation of a needle-like crystalline bond during firing. At the same time, an increased addition of the fiberglass particles reduces the plasticity of the batch thus resulting in formation of the microcracks, cavities and internal stresses in the samples. The occurrence of internal defects shifts the frequency of longitudinal and transverse vibrations to a different extend, which can be used as an indicator of the defects present in the samples and provide the possible of their objective sorting and rejection. The vibration relaxation time (about 0.1 sec) does not change significantly under the described strengthening effects and being characterized by a wide scatter in each series of the samples cannot be considered an informative parameter. Thus, the effectiveness of the presented combined method of ceramics hardening can be accurately tested by the shift in the frequencies of longitudinal and transverse free vibrations of cylindrical specimens. The presented approach facilitates the process of developing new ceramic compositions and extrusion technology in conditions of depletion of sources of high-quality clay raw materials.

An urgent problem of non-destructive testing is measuring (or calculating) of the magnetic fields both inside and outside the ferromagnetic products. Determination of the parameters of defects is significantly complicated by the fact that ferromagnetic products can be made from different steel grades. Moreover, when calculating the magnetic fields of defects, it is necessary to take into account the nonlinear character of the dependence of the magnetization M and magnetic permeability μ on the magnetic field strength. At the same time, computer modeling provides an opportunity to study magnetic fields near the defects of different shape, orientation and size. We present the results of studying the topography of the magnetic fields of defects belonging to three classes: surface defects (cracks), inclusions, and extended subsurface defects. The distinguishing features of the defects and the algorithm providing assignment of the defect to a certain class using data of analysis of magnetic flux leakage with a subsequent choice of the appropriate approach to calculating the parameters of the defect are presented. A technique, based on determining the extrema of the normal component of magnetic fields is proposed to estimate the direction of inclination of the surface defects and extended subsurface defects (longitudinal delamination) in a ferromagnetic plate. The obtained results can be used for structuring data on the fields of defects of different classes and developing a software on their base for nondestructive measuring devices.

The operating conditions of modern equipment are often rather severe and the materials used for production are exposed to extremely high temperatures and force effects resulting in formation of increased macro-stresses the level of which should be controlled. We present the results of x-ray determination of macro-stresses. Flat specimens made of steel 20 were tested using a diffractometer supplemented with a small two — circle goniometer. Using a set-top box mounted on the proper site of the unit attachment, the object under control was rotated to provide implementation of the applied x-ray method sin²ψ. To simulate the processes which affect the level and distribution of stresses in the product (e.g., drilling, local heating, etc.), the attachment is equipped with a small-sized loading device. In addition to forming macro-stresses of a given value in the sample, the device provided control of the stress distribution over the product. The proposed technical solution can be used in developing a «check specimen», since the use of standard macro-stress samples faces known difficulties. In this case, the macro-stresses of a required level are formed in the specimen made of the same material (or directly of the product) using the loading device of the attachment to compare the results of measurements with the data of product testing.

Unidirectional composites exhibit the highest strength when stretched along the fibers. However, the proper determination of the strength faces great methodological difficulties. The main problems of tensile testing of polymer composites consisted in developing of the specimen shape and the method of specimen fixation which ensure the minimum impact of the stress concentration near the grips on the strength measurements. A conventional shape of the specimen with fillets is unsuitable for unidirectional polymers due to the splitting occurred in the fillet zones upon loading. Therefore, the specimens are usually standardized in the form of rectangular strips fixed using pads or special grips which provide constant transverse forces. However, with such a specimen shape, a significant stress concentration inevitably occurs at the edge of grips and the lower the ratio of the interlayer shear modulus to the longitudinal Young’s modulus, the greater the stress concentration impact. For the purpose of the most correct determination of the strength we propose to use specimens with smoothly varying dimensions at the same cross-sectional area which ensures keeping the total number of unbroken fibers in each section. The specimen thickness decreases when moving from the working part of the specimen to the gripping part, whereas the width (while maintaining the section area) grows to prevent the specimen collapsing resulting from transverse forces in standard self-tightening grips. Analytical and FEM modeling is performed to select a rational contour shape. Technological equipment has been developed and a procedure of manufacturing testing specimens has been worked out. The tensile test of specially manufactured curvilinear reinforced specimens showed higher strength values compared to standard rectangular strips or specimens with semicircular fillets.

Different stress distributions for an elastic behavior are presented as analytical expressions for an ideal crack, a sharp notch and a blunt notch. The elastic plastic distribution at a blunt notch tip is analyzed. The concept of the notch stress intensity factor is deduced from the definition of the effective stress and the effective distance. The impacts of the notch radius and constraint on the critical notch stress intensity factor are presented. The paper ends with the presentation of the crack driving force J_ρ for a notch in the elastic case and the impact of the notch radius on the notch fracture toughness J_ρ,c. The notch fracture toughness J_ρ,c is a measure of the fracture resistance which increases linearly with the notch radius due to the plastic work in the notch plastic zone. If this notch plastic zone does not invade totally the ligament, the notch fracture toughness J_ρ,c is constant. This occurs when the notch radius is less than a critical one and there is no need to use the cracked specimen to measure a lower bound of the fracture resistance.

The effectiveness of experimental studies of the mechanical properties of materials and the reliability of the results obtained are determined by the technical level of testing machines. The stress-strain state of the object is monitored using recording sensors. The reading accuracy for the existing CL unit is 8%. However, this accuracy appeared insufficient when studying the developed plastic deformations. The problem of insufficient accuracy is partially related to the outdated recording system of the experimental setup, both when taking the results of the experiments and when managing the experiment. Getting of the reliable data upon complex loading is necessary to identify the reserves of the bearing capacity of structural elements in conditions of multi-parameter loading. All the experiments on a CL testing machine were carried out at room temperature. An additional amplifier of the electric signal of the strain gauge sensor was introduced to improve the accuracy of the readings of the recording system. The results of modernizing the recording system of the CL testing machine intended for static isothermal tests of tubular specimens are presented. The testing machine provides testing of the samples under axial tensile force and torque.

The goal of the study is to develop methods for determination of the active components in acidic and alkaline detergents of complex composition. The objects of analysis are acidic (KATELON 202 – 208) and alkaline (KATELON 111 – 115) detergents of complex composition, which, in addition to easily detectable components (KOH and/or NaOH, HNO₃, and H₃PO₄), contain weak organic acids (lactic, glycolic, acetic), including polybasic acids — aminotrimethylenephosphonic and diethylenetriaminepenta (methylenephosphonic) acids or salts — tetrasodium salt of glutamic acid N,N-diacetate, trisodium salt of methylglycine diacetic acid. An acid-base potentiometric titration was carried out for each of the listed objects and calculation formulas were derived to determine the concentration of the active substances (except for KATELON 115) in terms of nitric or phosphoric acid for acidic detergents or sodium or potassium hydroxide for alkaline detergents, respectively. A specific titration procedure (with indication of the sample weight, the pH value at the end of titration and corresponding calculation formula) is given in the application data sheet for each detergent along with the metrological characteristics of the methods.