Electron Microscopy Methods Research Articles

Metal-Organic Framework on Fullerene (MOFOF) as a Hierarchical Composite by the Integration of Coordination Chemistry and Supramolecular Chemistry.

There is a synergy between coordination chemistry and supramolecular chemistry that has led to the development of innovative hierarchical composites with diverse functionalities. Here, we present a novel approach for the synthesis and characterization of a metal-organic framework on fullerene (MOFOF) composites, achieved through the integration of coordination chemistry and supramolecular chemistry principles. The hierarchical nature of the MOFOF harnesses the inherent properties of metal-organic frameworks and fullerenes. The two-step synthesis procedure involves controlled assembly of fullerenes as tube-like nanostructures (fullerene nanotube: FNT), their surface functionalization, and the on-surface growth of the MOF (in this case, ZIF-67). The method permits the precise tuning of morphology, effective distribution of MOF-on-FNT, and tight compositional control. The materials were comprehensively structurally characterized using electron microscopy, spectroscopic techniques, and other methods to elucidate the unique features and interactions within the MOFOF composites. The main findings reveal that the novel synthesis and characterization of MOFOF composites demonstrate the successful integration of coordination chemistry and supramolecular chemistry for the designing and fabricating of advanced hierarchical composites with tailored properties, including micro- and mesopore channels, interfacial facets, and defect sites. These properties are expected to lead to numerous potential applications such as gas storage and separation, catalysis, sensing, energy storage, and environmental remediation. However, only the capability of acid vapor sensing was tested and is described here.

A Study on the Surface Oxidation Pretreatment and Nickel Plating Mechanism of Carbon Fiber.

This study explores the effects of various temperatures on the surface modification of carbon fibers, as well as the effect of differing voltages and currents on the morphology, deposition rate, and thickness of the Ni plating layers. Post-treatment characterization of the samples was conducted utilizing scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods, thus facilitating a discussion on the mechanism of Ni plating. The findings demonstrate that at a temperature of 500 °C, the carbon fiber surface exhibits the highest concentration of functional groups, including hydroxyl (-OH), carboxyl (-COOH), and carbonyl (-C=O), resulting in the most efficacious modification. Specifically, exceeding 500 °C leads to significant carbon fiber mass loss, compromising the reinforcement effect. Under a stable voltage of 7.5 V, the Ni-plated layer on the carbon fibers appear smooth, fine, uniform, and complete. Conversely, at a voltage of 15 V, the instantaneous high voltage induces the continuous growth of Ni2+ ions along a singular deposition point, forming a spherical Ni-plated layer. In addition, a current of 0.6 A yields a comparatively uniform and dense carbon fiber coating. Nickel-plated layers on a carbon fiber surface with different morphologies have certain innovative significance for the structural design of composite reinforcements.

Three-dimensional nanoporous gold/gold nanoparticles substrate for surface-enhanced Raman scattering detection of illegal additives in food

Owing to their nanoscale size and porous structure, both colloidal gold nanoparticles (AuNPs) and nanoporous gold (NPG) have demonstrated good and stable surface-enhanced Raman scattering (SERS) activity, and are therefore widely used as SERS substrates for the rapid detection of various components in food, environmental, biological, and other samples. In this study, we fabricated a novel, sensitive, and reproducible composite three-dimensional (3D) substrate for rapid SERS-based detection of illegal additives in food products. AuNPs and NPGs were prepared by chemical reduction and chemical dealloying methods, with the particle size of AuNPs about 60 nm and the pore size of NPG in the range of 5–36 nm. The AuNPs were then assembled on the surface of NPG to form the composite substrate 3D-NPG/AuNPs, which was characterized by transmission electron microscopy, scanning electron microscopy, X-ray diffraction, and other methods. Finally, the new SERS substrate combined with a portable Raman spectrometer was used to detect the illegal food additives 6-benzylaminopurine and melamine, with detection limits of 1 × 10−9 M and 5 × 10−7 M respectively. We further analyzed the relationship between the dealloying time-controlled morphology and the SERS properties of NPG, demonstrating that 3D-NPG/AuNPs as a novel SERS substrate have strong practical application potential in the rapid detection of food additives and other substances.

STUDY OF THE COMBINED EFFECT OF POST-SYNTHETIC ALKALINE TREATMENT AND NICKEL MODIFICATION OF MFI ZEOLITE ON THE DYNAMICS OF ITS DEACTIVATION IN THE PROCESS OF REFINING STRAIGHT-RUN GASOLINE

To determine the combined effect of post-synthetic treatments on the catalytic properties of MFI type zeolite (other names ZSM-5 or pentasil) during the upgrading of straight-run gasoline fraction of oil, MFI zeolite was synthesized and on its basis a sample was obtained, treated with an alkaline solution, as well as a nickel-containing sample after alkaline treatment of the zeolite. Modification of zeolite powder treated with an alkaline solution with nanosized nickel powder was carried out by dry mechanical mixing of the original powders in a vibrating mill. The activity and dynamics of deactivation of the obtained zeolite catalysts during the upgrading of straight-run gasoline fraction of oil were studied. Along with determining the characteristics of the target reaction products - high-octane gasoline, an analysis of the resulting gaseous hydrocarbons was carried out and the amount of carbon compaction products was determined. It has been shown that post-synthetic treatments of zeolite have a positive effect on the qualitative composition and yield of catalysates and reduce the rate of deactivation of zeolite catalysts. Post-synthetic alkaline treatment of MFI zeolite significantly reduces its aromatizing and cracking activity, resulting in an increased yield of high-octane gasoline with improved environmental characteristics. The introduction of nickel nanopowder into alkali-treated zeolite further enhances this tendency. Carrying out post-synthetic treatments of zeolite increases the time of stable operation of the resulting zeolite systems in the process of upgrading straight-run gasoline and reduces the amount of carbon compaction products formed. The state, location and dimensions of the zeolite carrier, nickel particles and carbon compaction products were determined using the transmission electron microscopy method. It has been shown that oxidative regeneration of a carbonized catalyst makes it possible to almost completely remove the resulting carbon deposits from the surface of both the active component and the zeolite support. For citation: Velichkina L.M., Gerasimov E.Yu., Vosmerikov A.V. Study of the combined effect of post-synthetic alkaline treatment and nickel modification of MFI zeolite on the dynamics of its deactivation in the process of refining straight-run gasoline. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 8. P. 103-112. DOI: 10.6060/ivkkt.20246708.10t.

Screen-printed glassy carbon electrodes for electrogenerated chemiluminescence.

Glassy carbon (GC) electrodes are crucial in electrochemistry due to their chemical stability and excellent electrochemical behaviour. This study presents the development of screen-printed glassy electrodes and demonstrates their suitability for electrogenerated electrochemiluminescence (ECL) applications. Model ECL system tris (2,2′-bipyridyl) ruthenium (II)/tripropylamine (Ru(bpy)32+/TPA) is used to benchmark the new electrodes. Different ink formulations are presented, and the electrochemical performance of the corresponding printed electrodes is discussed. In contrast to graphite screen printed electrodes, laser activation did not result in significant benefits at these new GC electrodes. A range of characterization techniques such as scanning electron microscopy, Raman spectroscopy, and spectroelectrochemical methods are used in the study. ECL studies of the GC electrodes was studied using both UV–Vis spectroscopy and image analysis. An ink formulation consisting of a GC to binder ratio of 5:1 by weight yielded the best results, surpassing the response of commercial graphite screen-printed electrodes, and in line with conventional (bulk) glassy carbon electrodes.

Ultrastructure of the mesonephros of whitefishes from the Lake Baikal basin.

The article presents a study of the mesonephros ultrastructure of Baikal omul Coregonus migratorius, Baikal whitefish Coregonus baicalensis, and a cross between Baikal whitefish and humpback whitefish (C. baicalensis × Coregonus pidschian). The mesonephros ultrastructure was studied using electron microscopy methods. The results of the study show that the number of mature granulocytes is a systematic feature and does not depend on the ecology of fish. The quantitative characteristics of blood cells and the ultrastructural features of leukocytes in the mesonephros are associated with the functioning of the nonspecific defence system in fish. Morphological diversity of epithelial cells in nephron tubules is the ancestral characteristic of the modern omul population, associated with geological and climatic events in the history of Lake Baikal. The development of haematopoietic tissue in the mesonephros, the ultrafine structure of ion-transporting interstitial cells, as well as some ultrastructural features found in the nephron, reflect the adaptive capabilities of the species to live in the ultra-deep Lake Baikal.

Array tomography: trails to discovery.

Tissue slicing is at the core of many approaches to studying biological structures. Among the modern volume electron microscopy (vEM) methods, array tomography (AT) is based on serial ultramicrotomy, section collection onto solid support, imaging via light and/or scanning electron microscopy, and re-assembly of the serial images into a volume for analysis. While AT largely uses standard EM equipment, it provides several advantages, including long-term preservation of the sample and compatibility with multi-scale and multi-modal imaging. Furthermore, the collection of serial ultrathin sections improves axial resolution and provides access for molecular labeling, which is beneficial for light microscopy and immunolabeling, and facilitates correlation with EM. Despite these benefits, AT techniques are underrepresented in imaging facilities and labs, due to their perceived difficulty and lack of training opportunities. Here we point towards novel developments in serial sectioning and image analysis that facilitate the AT pipeline, and solutions to overcome constraints. Because no single vEM technique can serve all needs regarding field of view and resolution, we sketch a decision tree to aid researchers in navigating the plethora of options available. Lastly, we elaborate on the unexplored potential of AT approaches to add valuable insight in diverse biological fields.

Understanding of the correlation of structural and microwave dielectric performance of (1-x)MgTiO3 - xCaTiO3 ceramics for dielectric resonator antenna applications

In this article, the effect of CaTiO3 on the structural and microwave dielectric characteristics of MgTiO3 has been discussed. The (1-x)MgTiO3 - xCaTiO3 (abbreviated as (1-x)MT- xCT) for x = 0.025, 0.05, 0.075, 0.1 ceramics have been developed using a solid-state reaction route. The structural as well as morphological characteristics of specimens have been observed by employing X-ray diffraction and scanning electron microscope methods. The Rietveld refinement technique of X-ray diffraction data have been conducted for the refinement of structural phases. It suggests that two crystallographic phases have been present in all materials. The SEM images display dense well-identified grains of (1-x)MT - xCT (for x = 0.025–0.1) ceramics. The Raman spectroscopy method has been employed to detect the symmetry of ceramics and modes of vibration of the materials. The microwave dielectric characteristics like dielectric permittivity (εr), loss (tanδ), quality factor (Q×f), and temperature coefficient at resonant frequency (τf) of (1-x)MT - xCT (for x = 0.025–0.1) ceramics have been thoroughly investigated. The bond strength, bond valency, bond energy, and tolerance factor of (1-x)MT - xCT (for x = 0.025–0.1) materials have been evaluated and their relation with microwave dielectric characteristics has been discussed. The (1-x)MT - xCT (for x = 0.025–0.1) ceramics show excellent dielectric properties with near to zero τf. In addition, DRAs have been designed with (1-x)MT - xCT (for x = 0.025–0.1) materials as dielectric resonators and various antenna properties have been studied with the help of HFSS software. This work suggests that (1-x)MT - xCT for (x=0.05) material can be a promising candidate for DRA applications working in the C band.

Application of Weak-Beam Dark-Field STEM for Dislocation Loop Analysis†.

Nanoscale dislocation loops formed by irradiation can significantly contribute to both irradiation hardening and embrittlement of materials when subjected to extreme nuclear reactor environments. This study explores the application of weak-beam dark-field (WBDF) scanning transmission electron microscopy (STEM) methods for quantitative irradiation-induced defect analysis in crystalline materials, with a specific focus on dislocation loop imaging and analysis. A high-purity Fe-5 wt% Cr model alloy was irradiated with 8 MeV Fe2+ ions at 450°C to a fluence of 8.8 × 1019 m-2, inducing dislocation loops for analysis. While transmission electron microscopy (TEM) has traditionally been the primary tool for dislocation imaging, recent advancements in STEM technology have reignited interest in using STEM for defect imaging. This study introduces and compares three WBDF STEM methods, demonstrating their effectiveness in suppressing background contrasts, isolating defect information for dislocation loop type classification, providing finer dislocation line images for small loop analysis, and presenting inside-outside contrast for identifying loop nature. Experimental findings indicate that WBDF STEM methods surpass traditional TEM approaches, yielding clearer and more detailed images of dislocation loops. The study concludes by discussing the potential applications of WBDF STEM techniques in defect analysis, emphasizing their adaptability across various material systems beyond nuclear materials.

Changes of wood surfaces treated with natural-based products – Structural and properties investigation

Preservative systems based on vegetable seed oils and natural waxes from renewable sources may confer protection to wood under exposure to various environmental conditions. These, as non-toxic substances, can form an environmentally friendly and efficient protective layer on the wood surfaces, with beneficial effects on their water resistance and dimensional stability. Thus, these natural coatings may hinder biodegradation of wood products to a certain degree. In present paper, softwood samples (from Abies alba fir tree species), prepared as dried discs (25 to 30 mm diameter, 8 to 10 mm thickness), were surface impregnated by dipping using vegetable oils, namely Asclepias syriaca seed oil, and soybean oil, respectively. Beeswax treatment was also applied for comparison purposes. Surface chemistry and morphology, biodegradation process under controlled and simulated natural conditions, and water sorption behavior of wood samples were investigated. Fourier Transform Infrared spectroscopy, X-ray diffraction, and scanning electron microscopy methods were used for investigation of surface changes in wood samples before and after impregnation with natural based products, as well as under biodegradation conditions in soil burial tests.

The effect of temperature and ultrasonic power on the microstructure evolution of coal modified by clean fracturing fluid: An experimental study

Ultrasonic-assisted fracturing permeability enhancement technology offers several advantages, including a broad range of hydraulic fracturing permeability enhancement, microstructure modified by fracturing fluid, and ultrasonic promotion of gas desorption and extraction. This technology can significantly improve the efficiency of coalbed methane extraction and has broad application prospects. To investigate the effect of ultrasonic action power and temperature on the microstructure evolution of coal by using clean fracturing fluid, experiments were conducted using coal samples from a mine in Shenyang. The pore structure of these samples was analyzed by scanning electron microscopy (SEM) and mercury intrusion method (MIP), while the chemical microstructure was evaluated with energy dispersive spectroscopy (EDS), X-ray diffraction experiment (XRD) and Fourier transform infrared spectroscopy (FTIR). The results showed that ultrasonic treatment improved the pore structure characteristics and connectivity by facilitating chemical reactions between fracturing fluid and mineral impurities. Specifically, when the ultrasonic parameter was set at 600W-60 °C, the pore volume of coal samples increased by 26.09 %, tortuosity decreased by 31.81 %, pore fractal dimension increased by 3.93 %, permeability increased by 100.45 %, aromaticity increased by 16.69 %, and the degree of branching aliphatic side-chains increased by 108.70 %. Under the same ultrasonic power, the effective temperature for ultrasonic-assisted fracturing fluid treatment on coal rock was found to be 60 °C. Additionally, under the same temperature conditions, an increase in ultrasonic power resulted in significant enhancements in both pore structure parameters and chemical structure parameters in coal, showing a certain linear relationship. The research results enrich the theoretical system of coalbed methane mining and provide theoretical guidance for the field practice of this technology.

Comparative analysis of experimental techniques for microstructural characterization of novel nanostructured aluminium alloys

Precipitation holds a pivotal role in comprehending the intrinsic behavior of materials. In the design of nanostructured metallic alloys, precipitates have found to increase the alloys' stability and response under extreme environmental conditions. Studies on precipitation often rely on conventional and ex situ electron-microscopy methods, but a systematic investigation that compares different sample conditions during heat treatment and its microstructural implications are rarely available. In this context, we employed a novel ultrafine-grained AlMgZnCuAg crossover alloy to compare three distinct conditions for investigating the precipitation sequence: (i) ex situ transmission electron microscopy (TEM) from bulk heating, (ii) ex situ TEM from TEM foil heating, and (iii) in situ TEM with microelectromechanical-system (MEMS) heating. Although the heat treatment procedure was consistent across all cases studied, the application of these three different experimental conditions in the same alloy system resulted in significant and non-negligible differences in the final precipitation behavior. Ultimately, it resulted in observable microstructural variations and precipitates with distinctively different shape and sizes and, as a result, we outline herein the major similarities and differences among these techniques to achieve comparable results. This knowledge will help to compare and assess results of precipitation sequences obtained in different conditions.

Laser synthesis of oxide nanoparticles with controlled gas condensation

In this work, the oxide nanopowders of Al2O3, ZrO2, Y2O3, Gd2O3, CeO2, and SiO2 were synthesized by CW CO2 laser vaporization technique with controlled gas condensation in an inert atmosphere. Methods for controlling the size of the resulting nanoparticles by adjusting the gas composition and pressure during the vaporization process have been demonstrated. The potential for producing ultrasmall oxide nanoparticles with dimensions less than 5 nm has been shown. The size distribution of nanoparticles taken from different parts of the evaporation-condensation tract was studied using scanning (SEM) and transmission (TEM) electron microscopy methods. The effect of synthesis conditions (pressure and composition of the inert gas) on characteristics of the nanoparticles is discussed. Using a wide class of simple oxides as the example, it is shown that the powders synthesized by the laser method consist of three types of particles: target spherical particles with a diameter of 3–20 nm (more than 98%), larger spherical particles with a diameter of 50–200 nm, and shapeless large particles with sizes more than 200 nm. The possibility of separating large particles from the main particles using the original labyrinth system for gas pumping is shown. The obtained particles with controlled sizes can be effectively used in various applications, in particular, for the preparation of catalysts and adsorbents.

Application of digital image correlation for in-situ deformation studies using transmission electron microscopy

Digital Image correlation (DIC) is routinely applied using optical and scanning electron microscopy methods to map local strains during deformation. In this letter, we report its use for in-situ TEM imaged deformation evolution for a nanocrystalline metal. Since transmitted electrons give rise to complex contrast conditions, with such contrast associated with the mechanisms of deformation, one can track these changes if particular care is done in image analysis and interpretation. We describe these methodologies to enable this correlation through frame averaging. Using these collective correlation conditions, we found that the average DIC strain matches well with the far field strain values yielding increased confidence in its application. Through the utilization of DIC in the TEM, nanoscale deformation mechanisms can be further elucidated because of the increased spatial resolution offered by TEM.

Composition features of the Upper Carboniferous-Lower Permian rocks of the Losinoostrov Fm. and the role of extrabasin sources in their formation (Subpolar Urals)

Research subject. The Upper Carboniferous-Lower Permian rocks of the Losinoostrov Formation of the Belsk-Eletsk structural-formational zone, exposed on the left bank of the Kozhim river, near the mouth of the stream Northnichael of the western slope of the Subpolar Urals. Methods. Optical and electron microscopic methods (including cathodoluminescence), chemical silicate, carbonate and X-ray diffraction analyses. Results and conclusions. The studied rocks are assigned to three main groups: mixtolites (rocks of mixed composition), carbonatoliths, and silicytolites with varieties. Mixtoliths consist of three and four main components: carbonate, silty, argillaceous and siliceous. The variable ratio of rock-forming components of mixtolites was clearly reflected in the discriminative modular diagram. Here, fields of predominantly siliceous and silty mixolites (cluster I), predominantly argillaceous (cluster III), as well as transitional mixolites (cluster II) are identified. Relatively pure and silty-argillaceous-siliceous limestones were distinguished among carbonatoliths. According to the formed elements, pure limestones are divided into bioclastic and peloid-micritic. Silicytolites are represented by (1) radiolarites and radiolarian spongoliths; (2) silty-argillaceous silicytolites and (3) cherts (secondary siliceous formations). The established quantitative ratios of rock-forming components showed that more than half of the studied mixtoliths are composed mainly of the material of extrabasinal origin. Relatively high contents of extrabasinal fine material in carbonatoliths indicate a periodic decrement of the hydrodynamic regime during the accumulation of the upper part of the formation. The studied deposits were probably formed in distal and proximal ramp settings.

Poly(styrene-co-methyl methacrylate)-silver/reduced graphene oxide-nano hydroxyapatite nanocomposites for bone cement applications

Herein, we report (polystyrene-co-polymethylmethacrylate/silver/reduced graphene oxide)-(nano-hydroxyapatite) ((PS-PMMA/Ag/RGO)-(nHA)) nanocomposites as potential bone cement. The polymer nanocomposites were characterized using Fourier Transform Infrared spectroscopy (FT-IR), X-ray diffraction (XRD), nano-indentation, thermal, and electron microscopic methods. The FT-IR and XRD results confirmed the successful formation of the nanocomposites. The elastic modulus (E) was found to be 6.85 GPa, and hardness (H) was 0.181 GPa for the nanocomposite bone cement samples, while the E and H values of commercial counterparts are 7.22 and 0.218 GPa, respectively. The thermogravimetric analysis (TGA) has revealed that the nanocomposite bone cement are stable up to 371 °C. The addition of nHA enhances the biocompatibility of bone cement. Cytotoxicity studies were conducted using human osteosarcoma MG63 cell lines. In-vitro studies showed that the material does not display any toxicity on the MG63 cell line, and increased concentration of nHA did not significantly impact the material’s toxicity, only impacting the curing kinetics of the cement.

The Effect of Volcanic Stone and Metakaolin on the Compressive Properties of Ultrahigh-Performance Concrete Cubes

Over the past few decades, ultrahigh-performance concrete (UHPC) has been widely studied and applied because of its outstanding mechanical properties, such as its high strength and notable durability. However, because of its high cost and easy shrinkage cracking during early pouring in mass concrete construction, to reduce the cost of UHPC and reduce the cracks caused by early pouring, volcanic stone was used as a new type of UHPC coarse aggregate, while metakaolin (MK) was added to the system at the same time, and then two parameters, namely the volcanic rock particle size group and the MK dispersion ratio, were set. Scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermogravimetric (TG) microanalysis methods were used to reveal the influence of changes in the material microstructure, phase composition, material composition and crystallinity of the mineral composition on the compressive properties of the UHPC cubes. The results show that the mechanical “lock-in effect” of the structure formed by the volcanic rock holes and mortar can effectively improve the shear resistance of the UHPC–volcanic rock interface, and the compressive strength of the UHPC cubes increases with the volcanic stone’s particle size. When the MK dispersion ratio is less than 4%, the cube compressive strength of the UHPC and the contents of CaCO3 crystals, C-S-H gel and travertine in the UHPC increase with an increasing MK dispersion ratio. At an age of 28 days, compared with the addition of 1% MK, the addition of 4% MK increases the production of C-S-H gel and travertine in the UHPC matrix by 24.82%. When the MK dispersion ratio is 4%, the crystallinity values of the C-S-H gel, travertine and limestone in the UHPC are greater. Adding MK at a 4% dispersion ratio can promote the crystallization of limestone into a large amount of calcite, which can increase the strength of UHPC. On the one hand, the addition of volcanic coarse aggregate results in the retention of more free water and bound water; on the other hand, it also makes it difficult to crystallize CaCO3. The combined action of MK at a 4% dispersion ratio and volcanic rock significantly inhibits CaCO3 crystallization.

RESISTANCE OF FERRITE-PERLITE STEEL TUBING BRANCH PIPE METAL TO DESTRUCTION IN HYDROGEN SULFIDE MEDIUM

This paper discusses the problems of resistance of the metal of the tubing branch pipe (tubing) to the process of its destruction in a medium containing hydrogen sulfide and when exposed to external forces. A 73х73 tubing nozzle made of 38G2SFA steel was selected as the material for research. The tubing fragment was destroyed during production well operation. To establish the reasons for the failure of the tubing nozzle, a visual inspection was carried out, tests were performed to assess the hardness and mechanical properties, the microstructure and microtexture of the metal were analyzed using scanning electron microscopy (SEM) methods. To analyze the nature of the distribution of introduced defects, the mutual orientation of structural components and crystallographic texture, studies were carried out by the method electron backscatter diffraction (EBSD). Studies of the suspended branch pipe, which does not have chemical protection, showed that the cause of its destruction was hydrogen sulfide stress corrosion cracking (SSCC) as a result of hydrogen embrittlement and the action of external tensile forces exceeding the yield strength of the metal. It was established that as a result of the interaction of hydrogen sulfide of the distilled product with the metal of the branch pipe, hydrogen embrittlement of the material of the branch pipe occurred. The process of hydrogen embrittlement of the fragment was proved by detecting hydrogen blisters in the metal microstructure and establishing the process of coalescence of neighboring inclusions. In addition, the results of the test to measure the hardness of the metal along the wall thickness further supported the hypothesis of hydrogen embrittlement of the tubing. EBSD analysis showed that the threaded part of the branch pipe is characterized by a small size of structural elements and an increased density of introduced defects (geometrically necessary dislocations), which are a promising site for the deposition of molecular hydrogen. It is concluded that reaching the limit concentration of molecular hydrogen reduces the binding energy of metal atoms and this process initiates the formation of pores. It has been established that the development of cracks along large-angle grain boundaries is facilitated, and small-angle and coincidence site lattice (Σ3, Σ5, Σ11 and Σ13b) grain boundaries are active barriers to crack propagation. It has been shown that by optimizing the elemental composition of steel, controlling the microstructure, crystallographic texture, as well as the type and state of grain boundaries, new pipeline steels can be produced that are more resistant to SSCC.

Antibacterial behavior and mechanism of nitrogen, silicon-doped amphiphilic carbon dots

A new kind of amphiphilic carbon dots (CDs) was prepared with citric acid and silane coupling agent as raw materials. Due to the doping of nitrogen and silicon elements, the surface of CDs contains not only oxygen-containing functional groups, but also alkyl hydrophobic chains, showing amphiphilic characteristic. The micro molecular structure and elemental composition of CDs were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD), and other tests. The antibacterial behavior of CDs against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) was studied by the disk antibacterial method, plate colony, scanning electron microscopy (SEM) and other methods. The biocompatibility of CDs was evaluated by cytotoxicity and hemolysis in vitro. The results proved that CDs possessed the average particle size of 1.75 nm and the negative surface potential of −2.71 mV. For E. coli and S. aureus, the minimum bactericidal concentrations of CDs were 500 μg/mL and 400 μg/mL, respectively. These co-doped CDs also possessed the ability to inhibit biofilm formation. The antibacterial mechanism was mainly through the adsorption force to rupture the bacterial membrane and induce the generation of reactive oxygen species in bacterial cells. In addition, CDs exhibited excellent biocompatibility because of their low cytotoxicity and hemolysis, indicating that they can be used as a new material in the antibacterial field.

Endohelminth diversity in the invasive Clarias gariepinus (Burchell, 1822) from two freshwater lakes: Naivasha and Ol'Bolossat, Kenya.

Fish parasitology contributes to our understanding of the potential risks posed by diverse groups of parasitic organisms on fish stocks in either wild and culture systems. This study was conducted in May 2023 and aimed at assessing the diversity of endohelminths in the invasive North African catfish Clarias gariepinus (Burchell, 1822) obtained from two freshwater lakes, Naivasha and Ol'Bolossat, in Kenya. Parasitological examination of 66 and 35 fish samples collected from the two lakes respectively was achieved using light and scanning electron microscopy methods. Results revealed endohelminth diversity broadly classified as four digeneans, two nematodes, and one cestode. Seven taxa of endohelminths were found in C. gariepinus samples, but only four of these taxa could be identified up to the species level. Six of the taxa (Diplostomum sp., Tylodelphys mashonense, Plagiorchioidea sp., Paracamallanus cyathopharynx, Contracaecum sp., and Tetracampos ciliotheca) were common in samples from the two lakes. Glossidium pedatum only occurred in samples from Lake Ol'Bolossat. Parasite prevalence ranged from 8.6 (T. mashonense) to 100% (Diplostomum sp., T. ciliotheca, and Contracaecum sp.) and mean intensity from 1.4 (T. mashonense) to 16.9 (Diplostomum sp.). The diversity and richness indices were comparatively higher in fish samples from Lake Ol'Bolossat and attributed to the occurrence of G. pedatum in the Ol'Bolossat. However, parasitic infestation of fish samples from the two lakes depicted close similarity, both in diversity and prevalence. These findings form an important baseline data for further follow-up studies, and they suggest the need for further molecular analyses to fully describe three of the taxa only identified up to the genus level.