Synthesis and application of a composite material «cross-linked polyvinyl alcohol (PVA) – magnetite» as a sensitive element for the determination of carbohydrates by optical micrometry has been studied. The chemical structure was confirmed by IR-spectroscopy. The content of Fe₃O₄ in PVA granules was calculated using magnetization curves. It is shown that the introduction of Fe₃O₄ particles into PVA granules at pH value of buffer solution 6.8 significantly narrows the range of carbohydrate concentrations to be determined and reduces the sensitivity of PVA to them. However, at pH 8.6 the presence of Fe₃O₄ particles in granules does not affect the metrological characteristics of the glucose and fructose determination (their detection limit equals 7.9 mmol/dm³) but reduces the relative standard deviation of their determination to 3 wt.%. Sensory granules with optimal magnetite content (1.54%) were tested in the determination of total content of glucose and fructose in natural syrups with a high level of fructose by optical micrometry. The results obtained match the accepted reference values specified by the syrup manufacturers.

Features of the iron determination in dust emissions of gas purification at electrometallurgical facilities are considered. The elemental and phase compositions of dust emissions were determined using energy dispersive x-ray fluorescence analysis (EDXRF) and inductively coupled plasma atomic emission spectrometry (ICP-AES). Sample preparation conditions were optimized with allowance for the analytical methods used. The phase composition of dust emissions represented mainly by zincite, zinc ferrite, halite and sylvite was preliminary determined by X-ray phase analysis. Model mixtures were prepared and used to construct calibration dependences taking into account the results of diffractometric studies. A technique for rapid x-ray fluorescence determination of iron in dust emissions of gas purification has been developed. The methods for iron determination tested on real samples of dust emissions of electrometallurgical production demonstrated a satisfactory convergence of the results obtained by EDXRF (S_r = 1.3%) and ICP-AES (S_r = 2.6%).

A method for quantification of lithium additives and calcium as a sample base component during synthesis of new materials based on hydroxyapatites (HA) using flame atomic emission spectroscopy is proposed to reveal a connection in the chain «synthesis conditions — composition — functional properties». Ceramic samples were obtained by co-deposition using Li carbonate and calcination at 1300°C. The materials were synthesized with a lithium content of 0.25 to 1 at.%, some of the samples were synthesized with the co-addition of cerium Ce(NO₃)₃ from 0.25 to 1 at.%. The method of additives and reference solutions were used to determine Li in HA samples. The determination of calcium was carried out in separate aliquots after 50-fold dilution. It is shown that the determination of lithium at concentrations of 0.1 mg/liter by flame photometry in hydroxyapatite solutions is possible with S_r of 0.1. It is shown that it is difficult to dope the material with lithium by co-precipitation from solutions, while heat treatment during synthesis does not affect the result. It is proposed to use joint doping of the material with lithium and cerium, while at least 0.25 at.% Li is included in the HA structure. The developed technique can be used to determine lithium and calcium using a flame photometer PFA 378 at all stages of the synthesis of new materials based on HA.

Dextrins are widely used in the food, textile, paper, mining, chemical and pharmaceutical industries. Pyrodextrin is one of the most known representatives of these materials. Its production is based on the heat treatment of starch in the absence of a catalyst. A significant demand for pyrodextrin, as well as an increase in the scope of its application, necessitates the improvement of existing methods of quality control of this material. The main parameter characterizing the solubility, viscosity and intensity of color is the degree of starch pyrodextrinization. The evaluation of this parameter in conditions of industrial production is carried out by visual observation. The use of such organoleptic methods leads to significant measurement errors. In this study, we have summarized information about the mechanism of starch pyrodextrinization, and considered the effect of the temperature and heating time on the color intensity of the resulting dextrins. A method of binary digital image colorimetry is proposed to be used for assessing the degree of starch pyrodextrinization, i.e., to measure the level of binarization of dextrins with subsequent determination of this parameter, taking into account the initial assumptions. The possibility of using a specialized software for quantitative analysis of images for the purpose of their transformation and subsequent determination of the binarization level of the studied dextrins is shown. The significance of the effect of temperature and heating time on the degree of starch pyrodextrinization was shown by analysis of variance (ANOVA). The mathematical description of the dependence of these parameters was obtained by multiple regression. The results presented in the study confirm the applicability of binary digital image colorimetry to assessing the degree of starch pyrodextrinization and process control.

Conditions for the development of cavitation are studied using the effect of light emission from a liquid during the collapse of cavitation bubbles. The results of studying cavitation in technical fluids by recording hydro- and sonoluminescence are presented. Conditions for the occurrence of hydro- and sonoluminescence were analyzed in relation to the geometry of a narrow channel; a high-speed video camera and a photomultiplier were used for recording. Universal threshold values for the strain rate of hydroluminescence in the range of 10⁵ – 10⁶ sec^–1 have been obtained, and a methodology has been developed for recording hydro- and sonoluminescence in narrow channels to study the stages of the cavitation development. The proposed experimental setup contained two high-pressure circuits, i.e., a pressure circuit and a measuring circuit. In the pressure circuit, hydraulic oil pressure was created using a gear pump. By means of a hydraulic cylinder and a movable piston, it was transmitted to the liquid in the measuring circuit, which was then passed under pressure through a narrow channel. The proposed geometry of a narrow channel provided separation of the phenomena of hydroluminescence in a narrow channel and sonoluminescence with subsequent cavitation when the liquid exits into the diffuser as a result of a pressure drop. The design of the setup and methodology made it possible to study cavitation effects in a wide range of technical fluids, including those that are aggressive to high-pressure pump materials. The results obtained can be used to improve the means of comprehensive diagnostics of lubricated friction units proceeding from the parameters of wear products in the oil, methods for suppressing the acoustic effects of cavitation, etc.

The quality and properties of the deposited wear-resistant layers depend on the technological modes of surfacing and the type of filler materials used. The results of studying the structure of filler composite wire for surfacing wear-resistant layers are presented. Wires based on aluminum alloy (hypereutectic silumin), silicon carbide (SiC) and titanium intermetallic (Ti₂NbAl) powders were produced by powder metallurgy. Powders of SiC or Ti₂NbAl (their content in the final material about 5 wt.%) and the silumin matrix alloy prepared in the form of chips were processed in a planetary mill. The wire was produced by hot extrusion after holding the prepared components at a temperature of 600°C. Tribological tests of the samples were carried out under conditions of dry sliding friction (the friction coefficient was recorded continuously during tests). It is shown that the selected modes of extrusion and a preliminary preparation of the material in a planetary mill make it possible to obtain a non-porous compact material. An analysis of the structure of the resulting material and the nature of the distribution of reinforcing discrete powders revealed that Ti₂NbAl particles are uniformly distributed over the cross section of the wire, while SiC particles are practically absent in the central part and are concentrated along the periphery of the section. The results obtained can be used when using composite wire as a filler material. Data on the nature of the distribution of reinforcing fillers should be taken into account when choosing schemes and modes of arc surfacing processes.

A method of sintering tungsten nanopowders with individual components (added or deposited), e.g., Ni, Fe, Co, is used in the production of new high-strength nano- and fine-grained heavy tungsten alloys. The presence of such components facilitates conditions for traditional liquid-phase sintering of tungsten-based powders or for solid-phase sintering using spark plasma sintering technology. We present the results of an X-ray diffraction study of binary systems of W + (Ni, Fe, Co) powders containing 95 – 99.5 wt.% of tungsten. The evaluation of the reproducibility of the results demonstrated that the intensity of the X-ray diffraction maxima of the studied phases is replicated with an accuracy of at least 3% for the main phase (tungsten) and at least 6% for the additive (specifically, nickel). It has been demonstrated that in analysis of powders using X-ray diffraction the sensitivity to nickel, iron and cobalt is 0.5, 1, and 3 wt.%, respectively. The obtained estimates are compared with the value calculated proceeding from structural and crystallographic phase data. The impracticality of using structural theoretical relations for quantitative phase analysis of W – Fe and W – Co systems is demonstrated due to the significant absorption of CuKα radiation by iron and cobalt. The results obtained can be used to improve the technique of X-ray diffraction control of the phase composition of high-strength nano- and fine-grained heavy tungsten alloys.

Fatigue tests of two geometrically identical and similar in design models of the lower wing panel of a commercial aircraft were performed. The models differ in the way of mounting bolts which join the skin and stringers. Cold expansion of holes drilled both in the skin and stringer has been performed for the first panel before joining. No additional treatment of holes was performed in the second panel after drilling pilot holes and final reaming. Bolts are mounted with the interference fit ranging from 1.3 to 2.1% and from 2.9 to 3.2% for the first and the second panel, respectively. The range of the interference fit values is attributed to the tolerance fields for the diameters of bolts and assemblage holes. A comparison of both technologies proceeded from the experimental study of residual stress fields. The second stage, which is the subject of present paper, includes the analysis of the values of residual stress components in the vicinity of skin holes filled by bolts mounted with the interference fit. The components of residual stressed were determined using the method of hole drilling and successive cracking (crack compliance) method. The deformation response was measured by electronic speckle-pattern interferometry. The first point-wise method, based on drilling a probe hole, provides the quantitative determination of residual stress components, starting from a distance of 1.1 mm from the assemblage hole edge. The second technique consists in successive extension of the notch length. A new version of the crack compliance technique providing the determination of fracture mechanics parameters for notches propagating in the contact zone has been developed. The essence of this approach consists in drilling the initial hole equidistant from two assemblage holes of interest. The edge of this through hole is a starting point of the sequence of artificial notches, the end point of this sequence is the outer contour of the bolt. This approach provides quantitative analysis of residual stress fields proceeding from the comparison of the values of stress intensity factors (SIF) related to different technologies of bolt mounting. Two experimental approaches reveal advantages of joining with bolts mounted into cold-expanded holes. The high efficiency and accuracy of the methods for residual stress determination which employ optical interferometric measurements of the deformation response to local removing of the material is substantiated and clearly demonstrated. The methods are based on recording high-quality interferograms, which provide the resolution of interference fringes of the ultimate density directly on the hole edge and along borders of the artificial notch.

The effect of various types of surface post-treatment on the fatigue characteristics of Ti – 6Al – 4V, titanium alloy samples produced by selective laser melting has been studied. The values of the low-cycle fatigue of Ti – 6Al – 4V, titanium alloy samples as built and after turning, waterjet and vibro-grinding treatment were compared. The surface roughness Ra nano-hardness after selective laser melting were 8 μm and 5.1 GPa, respectively. These samples have a low fatigue life. The surface roughness Ra after vibro-grinding treatment decreased to 3.5 μm, whereas the fatigue characteristics remained the same. After turning, the minimum roughness value 0.1 μm at the nanohardness of 5 GPa were obtained. This treatment allows a slight increase in the fatigue characteristics. However, the maximum fatigue properties were obtained on samples after waterjet treatment (Ra attained 1 μm and the nano-hardness of the subsurface zone increased to 6.1 GPa). One of the reasons for a significant increase in the fatigue characteristics after waterjet treatment is hardening of the surface layer of the material, which becomes an effective obstacle to the occurrence and spread of microcracks. Waterjet treatment of samples produced by selective laser melting makes it possible to solve the problem of increasing fatigue characteristics and improving the surface quality of Ti – 6Al – 4V, titanium alloy products to be used in biomedicine.

An epoxy resin is an important modifier in the production of polymer asphalt concretes; adding epoxy resins to bitumen increases the crack resistance, shear resistance, and the long-term strength of the final product. However, polymer asphalt concrete production is chargeable compared to that of traditional asphalt concrete due to high fraction of epoxy introduced. Hyperbranched polymers (HBP) with epoxy end groups form a highly branched spatial network at curing, their application as an active modifier in bitumen composition leads to the formation of additional spatial reinforcement architectures in asphalt concrete, which allows to strengthen the effects achieved by epoxy resins, as well as to increase impact toughness, moisture resistance, fuel resistance, and temperature stability of asphalt concrete at low fraction of the modifier. We present an experimental study of the mechanical properties of asphalt concrete with a bitumen modified by a hyperbranched polymer. The bitumen was modified with relatively low fractions (3, 5, and 8 wt.%) of the hyperbranched epoxy resin. The mechanical properties of asphalt concrete were characterized with the modulus of elasticity, compressive strength, tensile strength at break, shear strength, residual compressive strength after low-cycle loading, coefficient of residual compressive strength, and the ultimate percent compression. The results demonstrated that asphalt concrete with modified bitumen has improved characteristics compared to the original asphalt concrete, even at low fractions of the modifier. The elastic modulus and compressive strength are closely bound and, during the formation of the architecture of links in bitumen, increase almost linearly with an increase of hyperbranched modifier fraction, achieving an improvement of 9.0 and 17.7%, respectively, for samples with 8 wt.% of epoxy modifier. At the same time, asphalt concrete becomes more ductile; the ultimate percent compression increases from 2.75 to 3.5% and does not depend significantly on the amount of hyperbranched polymer. The tensile strength at break decreases as the fraction of an epoxy modifier increases, which is consistent with the literature data. However, the ductility of asphalt concrete is significantly improved, reaching the ultimate percent deformation of 1.8% at 5 wt.% of the modifier. At the same fraction of the modifier, the highest shear strength of 0.48 MPa is achieved. With an increase in the mass fraction of the epoxy modifier, the compaction under low-cycle loading decreases; the residual strength coefficient, as the ratio of the residual compressive strength after low-cycle fatigue to the static compressive strength, tends to unity for asphalt concrete, also modified with 5 wt.% of hyperbranched polymer. Thus, the best result, as a compromise of all factors under study, is achieved when 5 wt.% of epoxy hyperbranched modifier is introduced into the bitumen.