Inorganic Materials最新文献

Gaining current information about the chemical composition of samples from different areas of the deposit during geological exploration necessitates the use of methods of rapid analysis, most often X-ray fluorescence analysis in combination with a method of external standard and its modifications. The existing certified methods assume the construction of calibration characteristics using reference standards. We propose to use a rapid method of X-ray fluorescence analysis (XRF) in a version of the method of fundamental parameters to determine nonferrous metals in the samples of titanium–zirconium sands of the Beshpagirskoe deposit and specified conditions of analysis. It is shown that, when using the method of fundamental parameters, the accuracy indicators are highly competitive with the indicators obtained by the certified method.

The methods of fastening structural elements made of fiber-reinforced composites to other structural elements are almost the same as those used for metals. With the most common bolting, a hole is drilled in the element, i.e., a part of the material is removed, thus resulting in a stress concentration near the hole. Certain difficulties can thus arise in designing and calculating the bolted joints of metal elements in critical structures. The use of composites is associated with more serious problems. In this case, both the structural element and the material for this element are manufactured simultaneously. Subsequent machining is quite undesirable, since it violates the integrity of the element and, consequently, the bearing capacity of the entire structure. The efficiency of using composites depends on the technology of manufacturing the material of the element by 90%. We present the results of experimental and theoretical study of the effect of holes made by different technologies on the strength and bearing capacity of fiberglass specimens with different fiber laying patterns. The stress concentration factor is compared with the strength reduction factors for the holes made by drilling and by expanding the fibers without their damage. The results of tensile tests of specially made composite specimens with different reinforcement structures ([0], [0/90], [0/±45/90]) and with central holes are presented. The strength reduction factors calculated from the results of the experiment turned out to be significantly lower than the stress concentration factors. The reasons for this effect are considered and an estimation of the characteristic radius of curvature after “blunting” of a hole in a composite specimen is given. The obtained results of the study made it possible to draw conclusions about the effectiveness of the technology for production of holes in composite specimens without breaking fibers, as well as about the effect of the number of fiber families on the strength reduction factor near the holes.

The goal of the study is to elucidate the reasons for early fracture of the gear wheel teeth of a Cameron TA9000 turbocharger (1820 kW) after an operational load up to 1.3 × 10⁹ cycles. The chemical composition and the microstructure of the tooth metal were studied using the methods of metallography, microhardness and optical microscopy. The microrelief of fracture surfaces of operational fractures was studied using electron scanning microscopy. Analysis of the chemical composition proved the steel grade of the tooth metal (DIN 31CrMoV9) declared by the manufacturer. Visual analysis of the fragments under study revealed numerous cracks present on the tooth contact surfaces. The origins of fatigue fracture detected on the fracture surfaces are typical of high cycle and gigacycle fatigue fracture. In the latter case, the detected fracture looks like a “fisheye” exhibiting an area of structural heterogeneity with inclusions and pores in the center. The fracture probably developed from the first tooth fragment to the fifth one, being accompanied by an increase in the number of origins of fatigue fracture known to be attributed to an increase in the stress amplitude. Metallographic study showed the presence of a subsurface hardened layer with a thickness of 120–200 μm with a defect-containing structure associated with grain-boundary precipitates (presumably, carbides (Fe, Cr)₃C), which could have resulted from violation of the modes of heat treatment of the gear wheel. Formation of brittle intergranular cracks on the contact surface and their subsequent development in the entire depth of the subsurface hardened layer appeared to be the reason for a decrease in the strength and bearing capacity of the gear teeth. The interaction of the resulting cracks with longitudinal microcracks that originated from defects due to poor-quality mechanical processing of the gear led to the formation of centers of fatigue cracks, the development of which caused the final destruction of several teeth.

This article describes a comparative evaluation of effectiveness of certain commercial dispersants (Finasol OSR 52 (France) and Slickgone NS and Slickgone EW (Great Britain)) for spill response of three crude oils produced in Russia and characterized by different physicochemical properties (extra light, heavy, and bituminous) in waters of various salinity. The evaluation has been based on an adapted version of ASTM F2059-17 “Standard Test Method for Laboratory Oil Spill Dispersant Effectiveness Using the Swirling Flask” (the so called SFT test). The conventional lower limits of dispersant effectiveness have been determined using a low energy procedure. Comparative tests of dispersant effectiveness have been performed at the highest dispersant-to-oil ratio of 1 : 10 allowed in the Russian Federation (according to STO 318.4.02-2005 “Rules of Dispersant Application for Oil Spill Response”), water temperature 20°C, and water salinity of 0, 5, 10, 20, and 35‰. It has been revealed that the considered dispersants have low effectiveness for dispersion of the tested oil samples at water salinity of 35‰. A general trend of increase in dispersant effectiveness with decrease in water salinity is demonstrated. It has been established that all considered dispersants are not suitable for application throughout the analyzed salinity range in the case of spill of bituminous oil with high content of asphaltenes and polar compounds. The limits of dispersant application have been determined for all dispersants as a function of water salinity. The effectiveness of 45%, legally validated in the United States and Mexico, has been selected as the threshold value. It has been proved that, as a consequence of nonuniversality of dispersant action, it is recommended to carry out preliminary experimental examination of their effectiveness using a sample of spilled oil under climatic and hydrochemical conditions corresponding to the potential region of application.

The development of chemical sensors is relevant for solving environmental problems of monitoring the atmosphere of cities and industrial zones. Semiconductor sensors based on metal oxides are promising chemical gas sensors owing to their high sensitivity, low cost, small size, and low energy consumption. The first attempts at pilot operation of atmospheric air monitoring systems based on such sensors revealed insufficient response stability. Doping of the basic material with silicon can solve the problem. At the same time, data on the amount and distribution of the dopant in the material are necessary to determine the relationship “synthesis conditions–composition–properties.” We propose an approach to the determination of the composition of novel semiconductor materials based on β-Ga₂O₃ with a silicon dopant content from 0.5 to 2 at %. The approach included grinding of samples using a planetary mill and preparation of suspensions in ethylene glycol, followed by TXRF determination of the analytes on sapphire substrates using the method of absolute contents (Si) with S_r of 0.08 and the method of external standard (Ga) with S_r of 0.04. X-ray fluorescence analysis of the samples was performed using an S2 PICOFOX spectrometer (Bruker Nano GmbH, Germany). MoK_α radiation was used to excite X-ray fluorescence. The spectrum acquisition time was 250 s. It is shown that the homogeneity of the dopant distribution in the material can be estimated using the analysis of the suspensions. The studied materials demonstrate an irreproducible sensory response which we associate with the revealed inhomogeneity of the silicon distribution over the surface of β-Ga₂O₃.

Amperometric biosensors based on an immobilized tyrosinase enzyme and planar graphite electrodes modified with multiwalled carbon nanotubes (MWCNTs) in chitosan, reduced graphene oxide (RGO), and gold nanoparticles (Au NPs) in chitosan and nanocomposites based on them are developed for rapid and accurate determination of tetracycline. It is found that tetracycline is a tyrosinase inhibitor, which makes it possible to determine it using a tyrosinase biosensor in a range of concentrations of 1 nmol/L to 1 μmol/L. It is found on the basis of the results of kinetic studies of the reaction of enzymatic conversion of phenol that uncompetitive inhibition is observed on the tyrosinase biosensor in the presence of tetracycline. A combination of carbon nanomaterials with metal nanoparticles can form a nanocomposite with a synergistic effect. The use of carbon nanomaterials and metal nanoparticles as modifiers of the electrode surface makes it possible to improve the analytical characteristics of the developed sensors: to expand the range of determined concentrations and to decrease the limit of quantification (50 pmol/L for a biosensor with MWCNTs/Au NPs, 0.7 nmol/L for a biosensor with RGO/Au NPs). The relative standard deviation of the obtained using biosensors results does not exceed 0.08. Procedures for the determination of tetracycline using the proposed biosensors in milk and a cosmetic product are tested. The compounds present in these samples which are structurally unrelated to tetracycline do not interfere with its determination.

Radiation treatment of food makes it possible to solve some issues of the food industry, including suppression of pathogenic microbial contamination, retention of the nutritional value of the product, and increase in its shelf life. This treatment method in combination with highly sensitive methods of gas chromatography–mass spectrometry makes it possible to reveal biochemical markers of irradiation treatment in meat products with moderate fat content, such as chicken and turkey. This work describes the experimental results of the dependences of the content of volatile organic compounds in chilled chicken meat treated with 1 MeV accelerated electrons with the doses from 250 Gy to 20 kGy in two weeks of storage. The content of volatile organic compounds in irradiated and reference food samples has been determined on days 0, 1, 4, 6, 8, 11, and 13 after irradiation treatment. Similar behavior pattern of aldehydes identified in treated poultry meat, namely, hexanal, heptanal, and pentanal, has been determined in two weeks of product storage. An increase in the aldehyde concentration has been detected in samples treated with doses from 500 Gy to 10 kGy on days 1–4 after irradiation. It has been revealed that, with an increase in the irradiation dose the period of aldehyde accumulation in irradiated meat is displaced toward a shorter period of product storage. Thus, aldehydes can be considered as potential markers of irradiation treatment of chicken meat in the first four days after irradiation.

The basic aspects of the J-A concept of elastoplastic two-parameter fracture mechanics based on a three-term asymptotic description of the stress field at the crack tip are presented. It is noted that the field of elastoplastic stresses at the crack tip is controlled by two parameters of fracture mechanics, namely, J-integral and parameter A. Parameter A is a measure of the deviation of the stress field from the HRR stress field and can be considered a parameter of elastoplastic constraint at the crack tip under conditions of both small- and large-scale yielding. The results of studying the influence of the exponent of the strain hardening of the material, crack aspect ratio, and the thickness of standard specimens with a crack on the elastoplastic stress intensity factor and parameter A are presented. A two-parameter elastoplastic J-A fracture criterion based on the relationship between J-integral and strain (stress) on the surface of the crack-notch and the principle of linear summation of damage is formulated. To reflect the crack-tip constraint, the parameter A is introduced into the criterion equation as a function of applied failure stresses. The elastoplastic fracture toughness as a function of the crack-tip constraint in the fracture criterion is interpreted as the corrected elastoplastic fracture toughness of a specimen with the corresponding constraint parameters A. The results of studying the normalized corrected fracture toughness as a function of failure stresses, crack aspect ratio, and strain hardening exponent of the material are presented.

An approach to TXRF determination of the composition of perovskite nanocomposites of the putative compositions CsPbBr₂Cl and CsPbBr₂I is proposed. Sample preparation consists in the treatment of hydrophobic samples with dimethylformamide (DMFA) and the subsequent dilution of the obtained solutions with water. When using a copper solution as an internal standard, the reproducibility of the results of TXRF determination of the elements is attained with S_r no more than 0.05. The validity of the determination of Cs, Pb, Br, and I is confirmed by the results of their determination by ICP-MS in solutions after processing samples in DMFA followed by dilution with 2% HNO₃ for Cs, Pb, and Br or tetramethylammonium hydroxide (TMAH) for Cs, Pb, Br, and I, whereas the determination of chlorides is confirmed by the method of direct potentiometry in diluted solutions. It is shown that lead does not form insoluble chlorides in the TMAH solution and does not interfere with the determination. The effect of bromides on the determination of chlorides is characterized by a potentiometric coefficient of 10^–3. The results obtained provide the determination of the stoichiometry of the synthesized compounds CsPbBr₂Cl and CsPbBr_2.7I_0.3.

A method for the determination of Fe_tot, SiO₂, P, V₂O₅, TiO₂, Cr₂O₃, Ni, Cu, and Zn in iron ore raw materials (i.e., pellets, iron ore agglomerate, aspiration dust and slag component of scrap) by the method of atomic emission spectrometry with inductively coupled plasma (ICP-AES) has been developed using microwave sample preparation in analytical autoclaves. The composition of the acid mixture for the complete dissolution of the sample component was proposed, and the parameters of microwave decomposition, excluding the depressurization of the autoclave and the loss of sample elements which form volatile compounds, were selected. The developed method of microwave sample preparation in closed autoclaves made it possible to decompose iron ore samples using the minimum amount of acid (17 cm³) in 45 min. Conditions for the determination of normalized elements in iron ore samples by the ICP-AES method after microwave sample preparation were determined: the operating parameters of the spectrometer were optimized, the analytical lines of each determined element free from spectral overlaps were selected, and the efficiency of using cadmium as an internal standard was experimentally proved. The equations for calibration dependences and the ranges of determinable contents are presented. When using cadmium as an internal standard in the analysis of iron ore, a decrease in the value of the standard deviation from 0.17 to 0.04 is observed when determining Cr₂O₃; from 0.02 to 0.004 when determining Fe; from 0.03 to 0.002 when determining SiO₂; from 0.015 to 0.008 when determining TiO₂; and from 0.17 to 0.02 when determining V₂O₅. The correctness of the determination of the standardized elements by the developed method is evaluated using certified reference samples (CRS) similar in composition to the analyzed material. The results of determining the standardized elements according to the developed methodology were compared with the data obtained using GOST-approved methods of analysis and then checked in accordance with the recommendations of RMG 76-2014. The developed ICP-AES technique is characterized by a wider linear range of the determined concentrations than that in GOST-approved techniques, thus providing determination of the components in iron ore raw materials that could not be controlled before.