Search Results (151)

This study centred on the parametric optimisation and performance prediction of NiCr/WC-Co coatings produced by high-velocity oxygen fuel (HVOF) spraying. An L18 orthogonal experimental design based on the Taguchi method and the response surface method (RSM) was adopted to examine how key process parameters affect the microstructure, phase composition and hardness of the coatings. The results revealed that analysis of variance (ANOVA) indicated that travel speed, methane flow rate, powder feed rate, and stand-off distance were the primary parameters affecting coating hardness, collectively accounting for 76.25% of the total variance. Also, the RSM model established in this study demonstrates remarkably high predictive accuracy, with a coefficient of determination (R²) of 0.985 and an average prediction error of just 1.16%. Verification experiments were also conducted under optimal conditions. The measured hardness was 1352.7 ± 75 HV, in close agreement with the predicted value of 1365 HV. The coating, which was applied using HVOF spraying, had a dense layered structure and low porosity, and the decarburisation of the tungsten carbide was extremely minimal. In addition, interfacial bonding is improved and structural defects are reduced by the addition of a NiCr intermediate layer. It is demonstrated by the results that the Taguchi-RSM method is reliable for the optimization of HVOF spraying parameters and the prediction of coating hardness. Full article

The growing demand for sustainable energy technologies has intensified interest in direct urea fuel cells as an environmentally friendly energy conversion system. In this work, a ternary NiCuZn electrocatalyst is synthesized via a single-step electrodeposition process, offering a rapid and scalable alternative to commonly used hydrothermal or multistep fabrication routes. Structural and compositional analyses (SEM, EDX) confirm the formation of coral-shaped particles of NiCuZn powders. Electrochemical evaluation in alkaline media demonstrates that powders of both tested variants exhibit clear anodic activity, with peak potentials in the range of 0.4–0.6 V_{vs Ag|AgCl (sat. KCl)}. Zinc presence was confirmed also after the process. Upon urea addition, a pronounced enhancement in anodic current density is observed. Notably, variant NiCuZn powder, which was produced using higher current density during electrodeposition, shows superior catalytic activity from approximately 0.4 V_{vs Ag|AgCl (sat. KCl)}, reaching a maximum of 10 mA/cm² near 0.75 V_{vs Ag|AgCl (sat. KCl)}, and stability, which are attributed to its highly homogeneous microstructure and dynamic surface activation mechanism uniquely by partial zinc leaching during operation. These findings demonstrate that electrodeposited NiCuZn systems can deliver competitive performance despite their structural simplicity, highlighting their potential as cost-effective and scalable anode materials for direct urea fuel cell applications. We address a critical bottleneck in fuel cell manufacturing by replacing time-intensive hydrothermal syntheses with a rapid, highly scalable electrodeposition method. Furthermore, the identification of zinc-leaching mechanisms provides crucial new insights into dynamic catalyst activation, moving beyond traditional, static anode designs. Full article

The use of resource-saving technology in road construction material production is a current problem, the solution of which will allow us to increase the environmental and economic efficiency of the road construction industry. Nowadays, secondary raw materials are widely used in highway construction, obtained both from the waste of old road construction materials and collected from other industries. During asphalt production, up to 90% of raw materials can be replaced by reclaimed asphalt pavement (RAP). This technology requires residual binder modification to reduce the negative impact on the technological and operational asphalt concrete properties. On the other hand, the use of rubber crumbs or granules obtained from the disposal of old car tires in asphalt–concrete mixtures is widespread. However, some types of car tires cannot be used as raw materials to produce an effective modifier. Truck tires and tires from special vehicles are suitable for use as a modifier for asphalt–concrete mixtures. Tires designed for passenger cars do not contain enough polymer. As an experiment on asphalt–concrete mixture production using secondary resources only, a testing facility was developed. The testing facility uses hot gas obtained by burning automobile tires in a special oven as a heat source. Rubber residues from the recycling of automobile tires are used as fuel, which cannot be used to produce rubber powder or granules. RAP obtained by cold milling of the pavements of city and public roads was used as the object of the research. When studying the characteristics of the asphalt–concrete-mixture-based binder, it was found that the sulfur compounds present in the composition of hot gases change the properties of the binder, leading to a serious deterioration in the technological characteristics of asphalt–concrete mixtures. The asphalt–concrete mixture obtained during RAP processing is characterized by a narrow temperature range in which it can be laid and compacted to the required density values. After laying the pavement, quality control revealed a significant variation (the number of air voids ranged from 0.8 to 5.5%) in the average density of samples taken from the compacted layer. In addition, there were significant violations of the longitudinal evenness of the finished coating. Experiments were carried out to extract the binder from asphalt–concrete mixtures before and after regeneration. The physico-mechanical and rheological characteristics were studied and qualitative analysis of the binder was realized by IR spectroscopy. The data obtained allow us to establish the mechanism of how sulfur-containing gases influence the bitumen binder’s properties in asphalt mixtures. Additionally, the features of thermo-oxidative degradation occurring during the hot recycling of asphalt–concrete mixtures were established. A justification is also given for the need to use anti-aging modifiers to restore the properties of the residual binder. Full article

High-entropy coatings based on CoCrFeNiMn obtained by thermal spraying have demonstrated the potential to improve the wear resistance of traditional materials used in extreme conditions. The aim of the work was to study the effect of the oxygen/fuel ratio when using kerosene as fuel in the HVOF process on the microstructural characteristics of CoCrFeNiMn coatings, including phase composition, microhardness, elastic modulus, and wear resistance. Phase and microstructural transformations in gas-atomized powder during HVOF spraying were analyzed using XRD, SEM, and EDS methods. The tribological and mechanical properties of the coatings obtained were also evaluated. The results obtained are consistent with thermodynamic predictions based on the Scheil model for non-equilibrium conditions. The data obtained indicate the high potential of high-entropy CoCrFeNiMn alloys for use as protective coatings for industrial purposes. In addition, the results of the study emphasize the promise of using thermodynamic prediction of high-entropy alloys using Thermo-Calc software. The best mechanical and tribological properties were obtained in the HVOF 1 regime, which provided a maximum microhardness of 783.8 HV and a minimum wear rate of 7.45 × 10⁻⁵ mm³ × N⁻¹ × m⁻¹. Full article

To investigate the explosive characteristics of solid–liquid mixed fuels containing different types of metal powders—including hydrogen-storage metal powders—and volatile liquid fuels, explosion experiments and corresponding numerical simulations were conducted under unconstrained space conditions. The studied system consisted of Et₂O/Al/B/MgH₂ mixed fuels with varying composition ratios. Research has shown that the dispersion effect of solid–liquid mixed fuel containing metal dust under strong shock waves is higher than that of pure liquid fuel. And the explosion overpressure and temperature of solid–liquid mixed fuel are higher than that of pure liquid fuel. Under the same solid–liquid ratio, the explosive overpressure of Et₂O/Al/B/MgH₂ mixed fuel was the highest, which was 110.8% higher than that of pure liquid fuel at the 5 m position. For solid–liquid mixed fuels containing different metal powders, due to the high reaction threshold of boron powder, a high-activity MgH₂ reaction is required to drive the reaction. Therefore, the explosive strength of the mixed fuel systems follows the order Et₂O/Al/B/MgH₂ > Et₂O/Al/MgH₂ > Et₂O/Al > Et₂O/Al/B. Meanwhile, simulation models for pure liquid and solid–liquid fuel explosions were established. The discrepancy between the simulated results and the experimental data was within 10%, demonstrating that the proposed model provides an effective and reliable approach for predicting the explosive power and hazardous range of fuel–air explosions. Full article

In this present study, sodium- and strontium-modified bismuth titanate—Bi_0.5Na_0.5TiO₃ (BNT) and Bi_0.5Sr_0.5TiO₃ (BST)—were synthesized using the auto-combustion technique with citric acid (C₆H₈O₇) and glycine (C₂H₅NO₂) as fuels in an optimized ratio of 1.5:1. The resulting powders were characterized using X-ray diffraction (XRD), energy-dispersive X-ray (EDX) spectroscopy, UV–Visible diffuse reflectance spectroscopy (DRS), and Fourier-transform infrared (FT-IR) spectroscopy. The electrical behavior of the samples was studied using an LCR meter. XRD analysis confirmed the formation of a single-phase perovskite structure with average crystallite sizes of 18.60 nm for BNT and 22.03 nm for BST, attributed to the difference in ionic radii between Na⁺ and Sr²⁺. An increase in crystallite size was accompanied by a corresponding increase in lattice parameters and unit-cell volume. The Williamson–Hall analysis further validated the strain-size contributions. EDX (Energy-Dispersive X-ray analysis) results confirmed successful incorporation of Na⁺ and Sr²⁺ without detectable impurity phases. Optical studies revealed distinct absorption peaks at 341 nm for BNT and 374 nm for BST, and the optical bandgap (E_g), calculated using Tauc’s relation, was found to be 2.6 eV and 2.0 eV, respectively. FT-IR spectra exhibited characteristic Ti-O vibrational bands in the range of 420–720 cm⁻¹, consistent with the perovskite structure. For electrical characterization, the powders were pelletized under 3-ton pressure and sintered at 1000 °C for 3 h. The dielectric constant (ε_r), dielectric loss (tan δ), and ac conductivity (σ) of both samples increased with frequency. The combined structural, optical, and electrical results indicate that the optimized compositions of BNT and BST possess properties suitable for use in capacitors and other energy-storage applications. Full article

Boron is a promising fuel, but its oxide layer impedes combustion. Alloying boron with other high-energy metals can significantly enhance its combustion performance. In this study, we sintered highly reactive lithium-containing Mg-Al-Li-B alloys using magnesium, aluminum–lithium alloy, and boron powder as raw materials. The effects of sintering temperature and holding time on the microstructure were investigated, and the combustion heat value and oxidation resistance of the alloy were tested. Results indicate that sintering temperature significantly influences phase formation: increasing temperature boosts phase content while reducing metallic phases, with 1100 °C identified as the optimal sintering temperature. Holding time had no discernible impact on the phase composition or combustion heat value of the sintered alloy. Alloying enhances material density, thereby increasing volumetric heat value. Thermal oxidation performance tests demonstrate that Li addition significantly lowers the alloy’s oxidation reaction temperature and activation energy, enhancing its reactivity. This high-heat-value, highly reactive alloy holds significant potential for application in pyrotechnics and propellants. Full article

Metallic interconnects are key components in planar solid oxide fuel cell (SOFC) stacks. In the present study, we evaluated four Fe-Cr powder metallurgy (PM) alloy specimens, obtained from a domestic manufacturer, at nominal compositions (in wt%) of 5% Fe-95% Cr, 30% Fe-70% Cr, 50% Fe-50% Cr, and 78% Fe-22% Cr. These specimens were tested and evaluated for use in SOFC stack applications. The verification items included coefficient of thermal expansion measurements, high-temperature oxidation resistance and weight gain tests, mechanical strength tests, high-temperature sealant bonding and leakage rate measurements, and high-temperature electrical property (i.e., area-specific resistance) measurements. In addition, the specimens’ microstructures and elemental compositions were observed and analyzed. The test results indicate that the Fe content of the Fe-Cr powder metallurgy alloys influences various properties, while Cr also plays a significant role in high-temperature oxidation resistance. Among the four alloy specimens, the 78Fe-Cr alloy exhibited all of the aforementioned advantages, including a suitable coefficient of thermal expansion of 12.4 × 10⁻⁶/°C, excellent high-temperature oxidation resistance, a thermal weight-gain rate of 5.31 × 10⁻¹⁴ g²/cm⁴·s, a remarkably low high-temperature area-specific resistance of 7.04 mΩ·cm², and superior bonding and interfacial stability with the GC9 glass–ceramic sealant, achieving a very low leakage rate of 3.47 × 10⁻⁶ mbar·l/s/cm. These results indicate that the 78Fe-Cr powder metallurgy alloy performs excellently and is the most promising candidate for metallic interconnects in SOFC stack applications. Full article

Metal powders have both a high specific energy and a high energy density, which explains their widespread use in energetic materials (propellants, explosives and pyrotechnics). Pyrotechnic compositions are used extensively for both civilian and military applications. However, the combustion of pyrotechnics remains challenging to understand or predict due to the diversity of the components and the wide range of parameters that affect their results. Therefore, ongoing research efforts worldwide aim to investigate the combustion mechanisms of pyrotechnic compositions to improve their performance. In this review, studies on the ignition and combustion mechanisms of four metal powders (Al, Mg, Fe and B) are discussed. Moreover, their use as fuel in pyrotechnic systems is reported, as well as the combustion performance and energy release of the pyrotechnic mixtures. Additionally, some mixtures composed of fluorinated oxidizers and Al, Mg and B are also presented. Thermal analysis methods such as DSC and TG are used to obtain the thermal behavior of the pyrotechnic compositions. Furthermore, parameters such as particle size and the equivalence ratio that affect the performance of pyrotechnic mixtures and those that remain little studied are reported in this review. Full article

To enhance the abrasive wear resistance of mechanical components operating in corrosive environments, this study fabricated WC-10Co-4Cr coatings using high-velocity oxygen-fuel (HVOF) thermal spraying technology. A L9 (3⁴) orthogonal array was designed to optimize four key process parameters (kerosene flow rate, oxygen flow rate, powder feed rate, and spraying distance) at three levels each, aiming for minimal porosity. The phase composition, microstructure, hardness, abrasive wear resistance, and corrosion resistance of the coatings were systematically characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS), microhardness tester, wet sand rubber wheel abrasion tester, and electrochemical workstation. The results indicated that the optimal parameters were a kerosene flow rate of 0.0073 L/s, oxygen flow rate of 15.33 L/s, powder feed rate of 1 g/s, and spraying distance of 326 mm. The coating prepared under these conditions exhibited high density with a porosity of only 0.32% and a high microhardness of 1281 HV1. Compared to the AISI 1020 steel substrate, the optimized WC-10Co-4Cr coating demonstrated a 122-fold improvement in abrasive wear resistance and a better corrosion resistance, showcasing its excellent overall performance and great potential for wear-resistant surface protection in corrosive environments. Full article

Boron (B) powder is a promising high-energy fuel but suffers from inefficient combustion due to its native boron oxide (B₂O₃) passivation layer. Surface coating is a crucial strategy to overcome this limitation. In this study, core–shell structured B@NiF₂/ammonium perchlorate (AP) composite micro-units with varying mass ratios were prepared using planetary ball milling to optimize energy release and combustion performance. The optimal formulation for the ternary composite was determined to be 0.5% NiF₂, 13.3% B, and 86.2% AP. Morphological characterization revealed that NiF₂ was uniformly coated on the B particles, forming a dense shell. Thermal analysis indicated that the NiF₂ interfacial layer, through its high-temperature decomposition (NiF₂ → Ni + 2F·), released highly reactive fluorine radicals (F·) that etched the B₂O₃ layer, generating volatile boron oxyfluoride and creating void structures. This led to a maximum heat release of 8912 J/g and a reaction mass gain of 74.58%, indicating more complete combustion. The material also exhibited a minimal ignition delay of 0.618 s and the lowest ignition energy (22.17 J). Overall, the B@NiF₂/AP composite provides a novel solution for applying boron fuel in solid propellants and pyrotechnic technologies. Full article

The low hardness of copper alloys, which are the substrate material used for continuous casting molds, makes them prone to plastic deformation, wear, and high-temperature oxidation, leading to premature failure and the formation of surface defects on billets. In this work, the microstructure, phase composition, mechanical, and tribological properties of Cr₃C₂–NiCr coatings deposited by high-velocity oxy-fuel (HVOF) spraying onto copper substrates used in molds were investigated. This research was driven by the need to extend the service life of copper molds in continuous steel casting processes. It was established that spraying parameters have a decisive influence on porosity, coating thickness, microhardness, and friction behavior under conditions simulating billet contact with the working surface of the mold. Among the investigated regimes, the coating deposited at a powder feed rate of 11.39 m/s exhibited a dense lamellar structure and the highest level of microhardness. Tribological tests confirmed that this coating exhibited the lowest coefficient of friction, whereas the other coatings were characterized by higher porosity and poorer wear resistance. Thus, the results emphasize the necessity of optimizing spraying parameters to develop highly effective HVOF protective coatings for copper molds operating under extreme thermomechanical loads during steel casting. Full article

Aluminum powder is the most commonly used metal fuel in the industry of explosives and propellants. The research progress in preparation technology, reactivity and application of nano-aluminum in explosives and propellants is systematically reviewed in this paper. The preparation technology of nano-aluminum powder includes mechanical pulverization technology (such as the ball milling method and ultrasonic ablation method, etc.), evaporation condensation technology (such as the laser induction composite heating method, high-frequency induction method, arc method, pulsed laser ablation method, resistance heating condensation method, gas-phase pyrolysis method, wire explosion pulverization method, etc.), chemical reduction technology (such as the solid-phase reduction method, solution reduction method, etc.) and the ionic liquid electrodeposition method, each of which has its own advantages. Some new preparation methods have emerged, providing important reference value for the large-scale production of high-purity, high-quality nano-aluminum powder. The reactivity differences between nano-aluminum powder and micro-aluminum powder are compared in the thesis. It is clear that the reactivity of nano-aluminum powder is much higher than that of micro-aluminum powder in terms of ignition performance, combustion performance and reaction completeness, and it has a stronger influence on the detonation performance of mixed explosives and the combustion performance of propellants. Nano-aluminum powder is highly prone to oxidation, which seriously affects its application efficiency. In addition, when aluminum powder oxidizes or burns, a surface oxide layer will be formed, which hinders the continued reaction of internal aluminum powder. In addition, nano-aluminum powder may deteriorate the preparation process of explosives or propellants. To improve these shortcomings, appropriate coating or modification treatment is required. The application of nano-aluminum powder in mixed explosives can improve many properties of mixed explosives, such as detonation velocity, detonation heat, peak value of shock wave overpressure, etc. Applying nano-aluminum powder to propellants can significantly increase the burning rate and improve the properties of combustion products. It is pointed out that the high reactivity of nano-aluminum powder makes the preparation and storage of high-purity nano-aluminum powder extremely difficult. It is recommended to increase research on the preparation and storage technology of high-purity nano-aluminum powder. Full article

The development of effective catalysts for the oxygen reduction reaction (ORR) is crucial for improving the performance of fuel cells. Efficient carbon-supported Pt-Co nanocatalysts were successfully prepared by a generic two-step method: (i) electroless deposition of a Co-P coating on Vulcan XC72R carbon powder and (ii) subsequent spontaneous partial galvanic replacement of Co by Pt, upon immersion of the Co/C precursor in a chloroplatinate solution. The prepared Pt-Co particles (of a core-shell structure) are dispersed on a Vulcan XC-72 support, forming agglomerates made of nanoparticles smaller than 10 nm. The composition and surface morphology of the samples were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM/EDS) as well as transmission electron microscopy (TEM). The crystal structures of the Co-P/C precursor and Pt-Co/C catalyst were investigated by X-ray diffraction (XRD). XPS analysis was performed to study the chemical state of the surface layers of the precursor and catalyst. The electrochemical behavior of the Pt-Co/C composites was evaluated by cyclic voltammetry (CV). Linear sweep voltammetry (LSV) experiments were used to assess the catalytic activity towards the ORR and compared with that of a commercial Pt/C catalyst. The Pt-Co/C catalysts exhibit mass-specific and surface-specific activities (of j_m = 133 mA mg⁻¹ and j_esa = 0.661 mA cm⁻², respectively) at a typical overpotential value of 380 mV (+0.85 V vs. RHE); these are superior to those of similar electrodes made of a commercial Pt/C catalyst (j_m = 50.6 mA mg⁻¹; j_esa = 0.165 mA cm⁻²). The beneficial effect of even small (<1% wt.%) quantities of Co in the catalyst on Pt ORR activity may be attributed to an optimum catalyst composition and particle size resulting from the proposed preparation method. Full article

Aluminum powder has the advantages of high calorific value, high density and convenient source, and is a commonly used metal fuel in the explosives and propellants industry. Nanometer aluminum powder (nAl) has higher reactivity and higher reaction completeness than micron aluminum powder (μAl), which can improve the energy performance of mixed explosives and the burning rate of propellant. However, nAl has some disadvantages, such as easy oxidation and deterioration of the preparation process, which seriously affect its application efficiency. In order to improve these shortcomings, suitable surface coating treatment is needed. The effects of surface coating on the characteristics of nAl and on the energy and safety of explosives are summarized in this paper. The results show that surface coating of nAl can not only improve the compatibility between nAl and energetic materials, reduce the hygroscopicity of energetic composites, mitigate the easy oxidation of nAl, and protect the preparation process, but also improve the energy performance of explosives and the burning rate of propellant, increase the reaction characteristics of energetic mixtures, and reduce the mechanical sensitivity of those mixtures. In addition, the surface coating modification of nAl can obviously reduce the agglomeration of condensed-phase combustion products, thus reducing the loss of propulsion efficiency caused by agglomeration. This study is expected to provide reference for the surface coating of nAl and its application in explosives. Full article