Search Results (155)

This paper proposes a mathematical description of nitriding atmospheres obtained from a one-component ammonia ingoing atmosphere and a two-component ammonia inlet nitrogen-diluted atmosphere. The Fe-N phase equilibrium diagrams of the nitriding atmosphere in the hydrogen content-temperature (Q-T) system for selected NH₃/N₂ atmosphere compositions are presented. The nitriding atmosphere obtained with different degrees of nitrogen dilution of the ingoing atmosphere was characterized. It has been shown that in processes carried out in nitriding atmospheres obtained from a two-component atmosphere with nitrogen, there is no direct relationship between the value of the nitrogen potential and the degree of dilution of the ingoing atmosphere with nitrogen. It has been shown analytically and confirmed experimentally that with changes in the degree of dilution of ammonia with nitrogen, the hydrogen content of the nitriding atmosphere and, consequently, the nitrogen availability of the nitriding atmosphere change. Using the example of nitriding AISI 52100 steel, it has been experimentally demonstrated that the change in nitrogen availability, caused by a change in the degree of dilution of the ingoing atmosphere with nitrogen, is not accompanied by a change in the value of the nitrogen potential. It has also been shown that the change in the nitrogen availability of the nitriding atmosphere, induced by the change in the composition of the aNH₃/bN₂ ingoing atmosphere, affects the kinetics of nitrogen mass gain in the nitrided layer and the distribution of nitrogen mass between the iron nitride layer and the solution zone. It has also been shown that with the change in nitrogen availability, what changes in addition to the thickness of the iron nitride layer is also the phase composition of the layer. Using gravimetric tests, the mass of nitrogen in the iron nitride layer and the solution zone has been determined. To describe the equilibrium between the NH₃/H₂ atmosphere and nitrogen in the different iron phases, a modified Lehrer diagram in the coordinate system of temperature and hydrogen content in the nitriding atmospheres (T-Q) has been proposed. Full article

In this paper, magnetically responsive graphene/boron nitride/iron oxide fillers were prepared by growing iron oxide on the surface of graphene/boron nitride fillers via liquid-phase reaction. By adding the composite filler into the epoxy resin and utilising magnetic field-assisted curing, the composites were prepared to effectively improve the thermal conductivity of the composites while maintaining the insulating properties. The thermal conductivity of the composite filler is 2.1 Wm⁻¹K⁻¹, and the volume resistance is 4.63 × 10¹² Ω·cm when the mass ratio of the composite filler is 25%, and the thermal stability and ablation resistance of the composites are improved compared with that of the pure epoxy resin. Full article

Little research has focused on using iron nitride as thermoseed particles in magnetic hyperthermia, although magnetite (Fe₃O₄) is commonly used for this purpose. In the present study, we focus on iron nitride, especially ε-Fe_2–3N. ε-Fe_2–3N particles were synthesized from hematite (α-Fe₂O₃) and sodium amide (NaNH₂) under various synthesis conditions, and the heat-generation properties of the particles were investigated to reveal the synthesis conditions that lead to particles with notable heat-generation performance. The particles synthesized at 250 °C for 12 h increased the temperature of an agar phantom by approximately 20 °C under an alternating magnetic field (100 kHz, 125 Oe, 600 s), suggesting that ε-Fe_2–3N particles can be used for magnetic hyperthermia. The analysis results for the particles synthesized under different conditions suggest that the heat-generation properties of ε-Fe_2–3N were affected by several factors, including the nitrogen content, particle size, crystallite size, saturation magnetization, and coercive force. Full article

This study explored advancements in photovoltaic technologies by enhancing the electronic quality of multicrystalline silicon (mc-Si) through silicon nitride (SiN_x) and hydrogen (H₂) plasma deposition via plasma-enhanced chemical vapor deposition (PECVD). This innovative approach replaced toxic chemical wet processes with H₂ plasma and SiN_x. The key parameters of silicon solar cells, including the effective lifetime (τ_eff), diffusion length (L_diff), and iron concentration ([Fe]), were analyzed before and after this sustainable solution. The results show significant improvements, particularly in the edge region, which initially exhibited a low τ_eff and a high iron concentration. After the treatment, the τ_eff and L_diff increased to 7 μs and 210 μm, respectively, compared to 2 μs and 70 μm for the untreated mc-Si. Additionally, the [Fe] decreased significantly after the process, dropping from 60 ppt to 10 ppt in most regions. Furthermore, the treatment led to a significant decrease in reflectivity, from 25% to 8% at a wavelength of 500 nm. These findings highlight the effectiveness of the PECVD-SiN_x and H₂ plasma treatments for improving the optoelectronic performance of mc-Si, making them promising options for high-efficiency photovoltaic devices. Full article

This work studied the effect of self-protective paste nitriding (SPN) and ion plasma nitriding (IPN) on the surface chemistry, microstructure, and nanohardness of AISI 304 and 316L stainless steels, with both treated at 440 °C for 5 h. Surface modifications analyzed using SEM and nanoindentation revealed distinct outcomes. SPN induced an oxynitriding effect due to the oxidation properties of the pastes, forming Fe₃O₄ and Fe_xC phases, while IPN produced an expanded austenite layer. Both methods enhanced surface nanohardness, but SPN showed superior results. For 316L SS, SPN increased nanohardness by 367.81% (6.83 GPa) compared to a 133.5% increase (3.41 GPa) with IPN. For 304 SS, SPN improved nanohardness by 26% (2.23 GPa), whereas IPN reduced it by 48% (0.92 GPa). These findings highlight SPN’s potential as an effective anti-wear treatment, particularly for 316L SS. The SPN process utilized a eutectic mixture of sodium cyanate and sodium carbonate, while IPN employed a N₂:H₂ (1:1) gas mixture. SEM analyses confirmed the formation of γ-Fe(N) phases, indicating dispersed iron nitrides (FeN, Fe₃N, Fe₄N). SPN’s simultaneous oxidation and nitrocarburization led to an oxide layer above the nitride diffusion layer, enhancing mechanical properties through iron oxides (Fe₃O₄) and carbides (Fe_xC). Comparative analysis showed that AISI 316L exhibited better performance than AISI 304, underscoring SPN’s effectiveness for surface modification. Full article

A comprehensive roadmap for advancing Electric Micromobility (EMM) systems addressing the fragmented and scarce information available in the field is defined as a transformative solution for urban transportation, targeting short-distance trips with compact, lightweight vehicles under 350 kg and maximum speeds of 45 km/h, such as bicycles, e-scooters, and skateboards, which offer flexible, eco-friendly alternatives to traditional transportation, easing congestion and promoting sustainable urban mobility ecosystems. This review aims to guide researchers by consolidating key technical insights and offering a foundation for future exploration in this domain. It examines critical components of EMM systems, including electric motors, batteries, power converters, and control strategies. Likewise, a comparative analysis of electric motors, such as PMSM, BLDC, SRM, and IM, highlights their unique advantages for micromobility applications. Battery technologies, including Lithium Iron Phosphate, Nickel Manganese Cobalt, Nickel-Cadmium, Sodium-Sulfur, Lithium-Ion and Sodium-Ion, are evaluated with a focus on energy density, efficiency, and environmental impact. The study delves deeply into power converters, emphasizing their critical role in optimizing energy flow and improving system performance. Furthermore, control techniques like PID, fuzzy logic, sliding mode, and model predictive control (MPC) are analyzed to enhance safety, efficiency, and adaptability in diverse EMM scenarios by using cutting-edge semiconductor devices like Silicon Carbide (SiC) and Gallium Nitride (GaN) in well-known configurations, such as buck, boost, buck–boost, and bidirectional converters to ensure great efficiency, reduce energy losses, and ensure compact and reliable designs. Ultimately, this review not only addresses existing gaps in the literature but also provides a guide for researchers, outlining future research directions to foster innovation and contribute to the development of sustainable, efficient, and environmentally friendly urban transportation systems. Full article

The development of efficient, sustainable, and cost-effective catalysts is crucial for energy storage technologies, such as zinc–air batteries (ZABs). These batteries require bifunctional catalysts capable of efficiently and selectively catalyzing oxygen redox reactions. However, the high cost and low selectivity of conventional catalysts hinder the large-scale integration of ZABs into the electric grid. This study presents binder-free Fe-based bifunctional electrocatalysts synthesized via a sol–gel method, followed by thermal treatment under ammonia flow. Supported on nickel foam, the catalyst exhibits enhanced activity for both the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), essential for ZAB operation. This work addresses two critical challenges in the development of ZABs: first, the replacement of costly cobalt or platinum-group-metal (PGM)-based catalysts with an efficient alternative; second, the achievement of prolonged battery performance under real conditions without passivation. Structural analysis confirms the integration of iron nitrides, oxides, and carbon, resulting in high conductivity and catalytic stability without relying on precious or cobalt-based metals. Electrochemical tests reveal that the catalyst calcined at 800 °C delivers superior performance, achieving a four-electron ORR mechanism and prolonged operational life compared to its 900 °C counterpart. Both catalysts outperform conventional Pt/C-RuO₂ systems in stability and selective bifunctionality, offering a more sustainable and cost-effective alternative. The innovative combination of nitrogen, carbon, and iron compounds overcomes limitations associated with traditional materials, paving the way for scalable, high-performance applications in renewable energy storage. This work underscores the potential of transition metal-based catalysts in advancing the commercial viability of ZABs. Full article

This research presents an innovative method for revisiting heterogeneous nucleation in the formation of spheroidal graphite during the production of ductile cast iron. This study incorporates controlled melting at a temperature of 1200 °C, followed by a rapid cooling process, to increase the likelihood of revealing and subsequently observing the graphite nuclei. Given the slow dissolution rate of spheroidal graphite, this sequence produces finer graphite nodules associated with residual graphite that has partially dissolved. Furthermore, the investigation explores diverse configurations of treatment agents to reexamine their effects during the nucleation of nodular graphite. The findings revealed that the graphite nucleus comprised oxides, sulfides, carbides, nitrides, and carbo-nitrides, confirming the reliability of the approach considered in this study. Additionally, the research highlights the crucial role of magnesium in the nucleation of nodular graphite structures. Several mechanisms are expected to be used in conjunction with distinct treatment agents. It involves segregation and solubility dynamics, desulfurization and deoxidation, and inclusions as heterogeneous nucleation sites. Full article

This study aims to optimize the turning parameters for EN-GJL-250 grey cast iron using hybrid machine learning techniques integrated with multi-objective optimization algorithms. The experimental design focused on evaluating the impact of cutting tool type, testing three tools: uncoated and coated silicon nitride (Si₃N₄) ceramic inserts and coated cubic boron nitride (CBN). Key cutting parameters such as depth of cut (ap), feed rate (f), and cutting speed (Vc) were varied to examine their effects on surface roughness (Ra), cutting force (Fr), and power consumption (Pc). The results showed that the coated Si₃N₄ tool achieved the best surface finish, with minimal cutting force and power consumption, while the uncoated Si₃N₄ and CBN tools performed slightly worse. Advanced optimization models including improved grey wolf optimizer–deep neural networks (DNN-IGWOs), genetic algorithm–deep neural networks (DNN-GAs), and deep neural network–extended Kalman filters (DNN-EKF) were compared with traditional methods like Support Vector Machines (SVMs), Decision Trees (DTs), and Levenberg–Marquardt (LM). The DNN-EKF model demonstrated exceptional predictive accuracy with an R² value of 0.99. The desirability function (DF) method identified the optimal machining parameters for the coated Si₃N₄ tool: ap = 0.25 mm, f = 0.08 mm/rev, and Vc = 437.76 m/min. At these settings, Fr ranged between 46.424 and 47.405 N, Ra remained around 0.520 µm, and Pc varied between 386.518 W and 392.412 W. The multi-objective grey wolf optimization (MOGWO) further refined these parameters to minimize Fr, Ra, and Pc. This study demonstrates the potential of integrating machine learning and optimization techniques to significantly enhance manufacturing efficiency. Full article

This work presents the potential of various iron-based catalysts, with an iron content between 10 and 30 wt%, supported on alumina that were explored for pure hydrogen production from ammonia decomposition reaction. The X-ray diffraction (XRD) results indicated that major diffraction peaks associated with the alumina support and iron oxide were found along with fractions of iron aluminate. The reduction profiles from temperature-programmed reduction (TPR) showed that the extent of reduction, number of reducible species, and iron oxide interaction with alumina varied with an increase in iron oxide content, from 10 to 30 wt%, such that an increase in iron oxide loading promoted easier reduction, enhanced reducibility, and improved number of reducible species. Temperature-programmed desorption profiles using hydrogen and nitrogen showed that an increase in iron content increased the amount of hydrogen desorbed; however, nitrogen desorption exhibited a decreasing trend. These factors influenced catalytic activity results and an increase in iron content increased the ammonia conversion. Kinetic data also showed that a higher iron content (30 wt%) demonstrated the lowest apparent activation energy of 48.2 kJ/mol. Full article

Industrialization trial production of high permeability (Hi-B) steel was carried out by “one cold rolled + decarburization and nitridation technologies”. The finished product reached the level of 23Q100 with an average grain size of 5.47 cm, magnetic flux density B₈ of 1.902T, and the iron loss P_1.7/50 of 0.975 W/Kg. The evolution law of the microstructure and texture under different processes was analyzed with the help of OM, EBSD, and XRD. The results showed that the microstructure of the hot rolled plate was equiaxed crystals in the surface layer, a mixture of recrystallization grains and banded fiber in the quarter of the thickness layer, and banded fiber in the center layer. The texture gradient of the hot rolled plate from the surface layer to the center layer was {112}<111> + {110}<114> → {441}<014> → {001}~{111}<110>. The texture of the normalized plate was in major {110}<113> in the surface layer, diffuse α-fiber texture and {441}<014> in the quarter of the thickness layer, and sharp α texture {001}~{111}<110> in the center layer. The texture of the cold-rolled sheet was concentrated in {001}~{332}<110>. The average grain size of the decarburizing and nitriding sheet was 26.4 μm, and the texture of the first recrystallization is sharp α*-fiber and weak {111}<112>. The finished product has a sharp single Goss texture. For Hi-B steel, the Goss secondary nucleus originated from the surface layer to 1/4 layer of the hot rolled plate and reached the highest content of 11.5% in the quarter of the thickness. The content of the Goss texture decreased with the subsequent normalization and cold rolling, then the Goss grains nucleated again during the decarburization annealing and high temperature annealing processes. Full article

Silicon nitride (Si₃N₄) is used for high-speed rotating bearings in machine tools, aircraft, and turbo pumps due to its excellent material properties such as high-temperature strength, hardness, and fracture toughness. Grinding with fixed abrasives enables high shape accuracy and high efficiency in machining brittle materials. However, it is difficult to completely remove surface damage, which limits its use in products requiring a nano surface. These defects also result in reduced reliability and shortened lifespan. Magnetic-assisted polishing (MAP) is a technology that can achieve a fine surface by using a mixture of iron powder and abrasives, but it requires a lot of time due to the low material removal rate (MRR). Therefore, this study developed a hybrid processing technology using a metal-bonded grinding wheel and a slurry with hard abrasives for the high precision of silicon nitride ceramic ball bearings. Experiments were conducted in order to compare and analyze the surface roughness and material removal rate. Through MAP, using a grinding wheel with low grit (#325), high-efficiency machining performance was confirmed with a maximum material removal rate of 1.193 mg/min. In MAP, using a grinding wheel with high grit (#2000), a nano-level surface roughness of 6.5 nm Ra was achieved. Full article

Today, the machining of heat-resistant alloys based on triple, quad, or penta equilibria high-entropy alloy systems of elements (ternary, quaternary, quinary iron-, titanium-, or nickel-rich alloys), including dual-phase by Gibb’s phase rule, steels of the austenite class, and nickel- and titanium-based alloys, are highly relevant for the airspace and aviation industry, especially for the production of gas turbine engines. Cutting tools in contact with those alloys should withstand intensive mechanical and thermal loads (tense state of 1.38·10⁸–1.54·10⁸ N/m², temperature up to 900–1200 °C). The most spread material for those tools is cutting ceramics based on oxides, nitrides of the transition and post-transition metals, and metalloids. This work considers the wear resistance of the cutting insert of silicon nitride with two unique development coatings — titanium–zirconium nitride coating (Ti,Zr)N and complex quad nitride coating with TiN content up to 70% (Ti,Al,Cr,Si)N with a thickness of 3.8–4.0 µm on which microtextures were produced by the assisted electric discharge machining with the electrode-tool of ø0.25 mm. The microtextures were three parallel microgrooves of R0.13^+0.02 mm at a depth of 0.025₋₀.₀₅. The operational life was increased by ~1.33 when the failure criterion in turning nickel alloy was 0.4 mm. Full article

Nitriding is a well-known thermochemical treatment improving the surface hardness and the wear resistance of steel. The phase composition and growth kinetics of the nitrided layer can be controlled using a gas nitriding with changeable nitriding potential. In this work, such a gas nitriding was used to produce, on 42CrMo4 steel, the two nitrided layers differing in the thickness of compound zone and diffusion zone. The microstructure and nanohardness of these layers were studied. For the first time, the tribological behavior of gas nitrided layers at elevated temperatures (from 23 to 400 °C) was investigated. The compound zone consisted of ε + (ε + γ’) iron nitrides and, in the diffusion zone, the nitric sorbite with γ’ precipitates was observed. The highest nanohardness was measured in the ε + γ’ zone. The lowest values of friction coefficients were obtained if the contact surface of the friction pair entered the ε + γ’ zone. After the wear process, at a final temperature of 400 °C, worn surfaces showed only intensive abrasive wear, evidenced by shallow grooves. The increased oxygen content at the edges of wear tracks indicated possible oxidative wear. Full article

Diamond grinding wheels have been widely used to remove the residual features of cast parts, such as parting lines and pouring risers. However, diamond grains are prone to chemical wear as a result of their strong interaction with ferrous metals. To mitigate this wear, this study proposes the use of a novel water-based hexagonal boron nitride (hBN) as a minimum quantity lubrication (MQL) during the grinding of cast steel and conducted the grinding experiment and molecular dynamics simulation. The experiment demonstrated that compared to dry grinding, the water-based hBN nanofluid can effectively reduce the maximum temperature of a workpiece at contact zone from 408 K to 335 K and change the serious abrasion wear of diamond grain to slightly micro-broken. The molecular dynamics simulation indicates that the flake of hBN can weaken the catalytic effect of iron on the diamond, prevent the diffusion of carbon atom to cast steel, and suppress the graphitization of diamond grain. Additionally, the flake of hBN improves the contact state between the diamond grain and cast steel and reduces the cutting heat and friction coefficient from about 0.5 to 0.25. Thus, the water-based hBN nanofluid as a new MQL was proven to be suitable for the wear inhibition of diamond grain when grinding cast steel. Full article