Search Results (102)

The primary challenge associated with stainless steel in fuel cell operation is its susceptibility to corrosion, which leads to increased contact resistance and subsequent degradation of electrochemical performance. In general, the protective layers have been loaded onto the metal surface by widely used traditional techniques such as physical vapor deposition (PVD), or cathode arc ion plating. However, the above sputtering and evaporation ways require a high-vacuum condition, complicated experimental setups, higher costs, and an elevated temperature. Therefore, herein the achievement for uniform coatings over a large surface area has been realized by using a cost-effective strategy through a complete wet chemical process. The synergistic regulation of two conductive components and a plastic additive has been employed together with the entrapment of a surfactant to optimize the microstructure of the coating surface. The assembly of layered graphite and a polystyrene sphere could maintain both the high corrosion resistance feature and excellent electrical conductivity. In particular, the intrinsic vacant space in the above physical barriers has been filled with fine powders of indium tin oxide (ITO) due to its small size, and the interconnected conductive network with vertical/horizontal directions would be formed. All the key technical targets based on the U.S. Department of Energy (DOE) have been achieved under the simulated operating environments of a proton exchange membrane fuel cell. The corrosion current density has been measured as low as 0.52 μA/cm² (for the sample of graphite/mixed layer) over the applied potentials from −0.6 V to 1.2 V and its protective efficiency is evaluated to be 99.8%. The interfacial contact resistance between the sample and the carbon paper is much less than 10 mΩ·cm² (3.4 mΩ·cm²) under a contact pressure of 165 N/cm². The wettability has been investigated and its contact angle has been evolved from 48° (uncoated sample) to even 110°, providing superior hydrophobicity to prevent water penetration. Such an innovative approach opens up new possibilities for improving the durability and reducing the costs of carbon-based coatings. Full article

The growing demands for highly functional biomedical implants necessitate introducing innovative and easy-to-apply surface functionalization techniques, especially when it comes to stainless steel substrates. This study investigated the co-deposition of chitosan and Cu-doped bioactive glass on AISI 316L steel surfaces, with the latter providing a matrix in which fine bioactive glass powders are distributed. Cu-doping into the matrix of bioactive glass was conducted to assess its influence on the bioactivity, antibacterial properties, and structural integrity of the coating. The microstructure, mechanical properties, phase composition, and surface roughness of coated specimens were investigated through a scanning electron microscope (SEM), X-ray diffraction analysis (XRD), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma (ICP), contact angles, adhesion tensile tests, and laser profilometry analyses. Results of adhesion tests indicated that Cu addition did not have a major implication for the mechanical properties of the coating layers. Results also revealed that the Cu-doped bioactive glass featured a hydrophilic and a rather uneven surface, both being upsides for biomedical properties. The cytotoxicity and antibacterial assessments showed promising cell viability and antibacterial properties of the deposited coatings. Full article

To mitigate the environmental effects of oil spills, a novel hydrophilic–oleophobic mixed-coated filter was developed for efficient oil–water separation and surface oil recovery. The coating consisted of titanium dioxide nanoparticles (TiO₂) and ultra-fine carbon black powder, deposited onto a 304 stainless-steel mesh substrate via spray deposition, followed by high-temperature sintering. This process induced a phase transition in TiO₂ from anatase to rutile, and formed a TiC khamrabaevite. The filter’s performance was evaluated using contact angle measurements and filtration tests with a motor oil–water mixture, while SEM, EDS, and XRD analyses characterized its morphology and coating structure. Contact angle testing confirmed that carbon modification significantly enhanced the oleophobicity of the TiO₂ filter, and SEM imaging demonstrated higher substrate coating adhesion, enabling multiple reuse cycles. These findings highlight the potential of TiO₂ carbon composite coatings in improving oil spill remediation technologies by offering a reusable and efficient filtration system. Full article

To fulfill the harsh surface demand for key industrial components, metal matrix composite coatings (MMC) with hard ceramic particles located in the metallic matrix have attracted considerable attention in recent years. In this paper, WC/Stellite-6 composite coatings were fabricated via supersonic laser deposition (SLD). The effects of laser heating temperature, WC particle size and addition content on the deposition characteristics were systematically studied. The microstructures and mechanical properties of the as-prepared composite coatings were examined. The results demonstrated that increasing laser heating temperature can improve powder deposition efficiency for both coarse and fine WC-reinforced coatings. The peak coating height of fine WC-reinforced composite coating is 1157 μm, which is higher than that of coarse WC-reinforced composite coating (505.5 μm) deposited under the same laser heating temperature. The increase in laser heating temperature and WC addition content in original composite powder resulted in the increase in WC fraction in the composite coating, which can achieve a highest value of 55.9 vol.%. The SLD composite coating had comparable bonding strength (145.5 MPa) to that of laser cladded (LC) coating. The SLD specimen showed plastic fracture behavior, which was different from brittle fracture behavior for the LC sample. Full article

Powdered magnesium has been widely applied in various fields. Magnesium is a highly reactive metal, with fine particles that are easy to agglomerate and have the risk of explosion. Furthermore, the storage of Mg particles is a challenge. Therefore, powdered magnesium is usually passivated by surface modification methods. In our research, an environmentally friendly phosphate solution was used to prepare conversion coating on magnesium particles. The results demonstrated that the phosphate coating layer attached on Mg particles surface successfully. From SEM images, the average particle size reduces slightly after the coating process. The composition of the coating layer is confirmed to be OCP and HAp by XRD and EPMA. The immersion test showed that the phosphate coating improved the corrosion resistance, and the ideal processing time is 20 min. Moreover, Mg and phosphate have good biocompatibility; therefore, the coated Mg powder can be a potential candidate for biomedical applications. Full article

The paper presents a technological approach for obtaining sintered components with tailored electromagnetic features from electromagnetically active powders through the selective recycling of electronic waste, in particular scrap electronic components. Printed circuit board (PCB) scraps were submitted to a succession of grinding processes, followed by progressive magnetic and electrostatic separation, resulting two final fractions: metallic particles and non-metallic particles including different metallic oxides. Three types of powders were analyzed, i.e., powder after fine grinding, after magnetic separation and after electrostatic separation, which were further processed within a spark plasma sintering furnace in order to obtain solid disk samples. All samples contained several classes of oxides, and also residual metals, leading to specific thermal decomposition processes at different temperatures, depending on the nature of the oxides present in the studied materials. The chemical analysis of powders, via spectrometry with X-ray fluorescence—XRF, emphasized the presence of a mixture of metal oxides and traces of metals (mainly Ag), with concentrations diminishing along with the purification process. The most important analysis was related to dielectric parameters, and it was concluded that the powders obtained by the proposed technology could efficiently substitute scarce raw materials actually used as additives in composites, coatings and paints, mainly due to their high permittivity (above 6 in all frequency domains) and, respectively, dielectric loss factor (above 0.2 in all cases, in all frequency domains). We estimate that the technology described in this paper is a sustainable one according to the concept of circular economy, as it could reduce, by a minimum of 15%, the embodied GHG emissions generated from information and communications technology (ICT) devices by advanced recycling. Full article

Catalytic performance decline is a general issue when shaping fine powder into macroscale catalysts (e.g., beads, fiber, pellets). To address this challenge, a phenolic resin-assisted strategy was proposed to prepare porous Co/N carbon beads (ZACBs) at millimeter scale via the phase inversion method followed by confined pyrolysis. Specially, p-aminophenol–formaldehyde (AF) resin-coated zeolitic imidazolate framework (ZIF-67) nanoparticles were introduced to polyacrylonitrile (PAN) solution before pyrolysis. The thermosetting of the coated AF improved the interface compatibility between the ZIF-67 and PAN matrix, inhibiting the shrinkage of ZIF-67 particles, thus significantly improving the void structure of ZIF-67 and the dispersion of active species. The obtained ZACBs exhibited a 99.9% removal rate of tetracycline (TC) within 120 min, with a rate constant of 0.069 min⁻¹ (2.3 times of ZIF-67/PAN carbon beads). The quenching experiments and electron paramagnetic resonance (EPR) tests showed that radicals dominated the reaction. This work provides new insight into the fabrication of high-performance MOF catalysts with outstanding recycling properties, which may promote the use of MOF powder in more practical applications. Full article

La_0.6Sr_0.4CoO₃ (LSC) coatings with a thickness of 50–100 µm were deposited on Fe-25Cr ferritic stainless steel (DIN 50049) via screen printing. The required suspension had been prepared using fine LSC powders synthesised using EDTA gel processes. In its bulk form, the LSC consisted entirely of the rhombohedral phase with space group R-3c, and it exhibited high electrical conductivity (~144 S·cm⁻¹). LSC-coated steel was oxidised in air at 1073 K, i.e., under conditions corresponding to SOFC cathode operation, for times of up to 144 h. The in situ electrical resistance of the steel/La_0.6Sr_0.4CoO₃ layered system during oxidation was measured. The products formed on the samples after the oxidation reaction resulting from exposure to the corrosive medium were investigated using XRD, SEM-EDS, and TEM-SAD. The microstructural, nanostructural, phase, and chemical analysis of films was performed with a focus on the film/substrate interface. It was determined that the LSC coating interacts with the oxidised steel in the applied conditions, and a multi-layer interfacial zone is formed. Detailed TEM-SAD observations indicated the formation of a main layer consisting of SrCrO₄, which was the reaction product of (La,Sr)CoO₃, and the Cr₂O₃ scale formed on the metal surface. The formation of the SrCrO₄ phase resulted in improved electrical conductivity of the investigated metal/ceramics layered composite material, as demonstrated by the low area-specific resistance values of 5 mΩ·cm², thus making it potentially useful as a SOFC interconnect material operating at the tested temperature. In addition, the evaporation rate of chromium measured for the uncoated steel and the steel/La_0.6Sr_0.4CoO₃ layered system likewise indicates that the coating is capable of acting as an effective barrier against the formation of volatile compounds of chromium. Full article

In this study, a spherical CrCoFeNiMn high-entropy alloy (HEA) powder with uniform size was prepared using gas atomization. High-quality CrCoFeNiMn HEA coatings were then applied to a 316L stainless steel substrate using prepowdered laser cladding. The main focus of the study is on the phase structure composition and stability, microstructure evolution mechanism, mechanical properties, and wear resistance of CrCoFeNiMn HEA coatings. The results show that the CrCoFeNiMn HEA coatings prepared using gas atomization and laser melting techniques have a single FCC phase structure with a stable phase composition. The coatings had significantly higher diffraction peak intensities than the prepared HEA powders. The coating showed an evolution of columnar and equiaxed crystals, as well as twinned dislocation structures. Simultaneously, the microstructure transitions from large-angle grain boundaries to small-angle grain boundaries, resulting in a significant refinement of the grain structure. The CrCoFeNiMn HEA coating exhibits excellent mechanical properties. The microhardness of the coating increased by 66.06% when compared to the substrate, the maximum wear depth was reduced by 65.59%, and the average coefficient of friction decreased by 9.71%. These improvements are mainly attributed to the synergistic effects of grain boundary strengthening, fine grain strengthening, and twinning and dislocation strengthening within the coating. Full article

The wall friction angle is an important parameter in powder flow. In a recent study for various powders, a reduction in the wall friction angle for steel was demonstrated by the application of an a-C:H:Si film on the steel surface. This work presents the results of a study of this effect in more detail regarding the influence of the powder material, the wall normal stress and the particle size of the powder for mass median diameters from 4 µm to approximately 150 µm. The wall friction angles were measured using a Schulze ring shear tester for three different powder materials: aluminum oxide, calcium carbonate and silicon carbide. The results showed little difference with respect to powder chemistry. For the coarser powders, the reduction in the wall friction angle due to the a-C:H:Si coating was highest (10° to 12°) and rather stress-independent, while for the fine and medium-size powders the reduction was lower and stress-dependent. With increasing wall normal stress, the reduction in the wall friction angle increased. These results can be explained by the friction reduction mechanism of a-C:H:Si, which requires a certain contact pressure for superficial graphitization. Full article

In this work, a novel approach involving coating fine PEEK powder on prepreg is introduced to improve wedge peel strength and reduce interlaminar voids. CF/PEEK laminates with resin interleaving are in situ consolidated by laser-assisted fiber placement. The morphology of the powdered surface is obtained using an optical profilometer, and the surface roughness and volume of added resin are calculated accordingly. Interface and surface temperature are measured during the layup process. Thermal history indicates that very short bonding time is the dominating factor for voids and limited interlayer strength. Laminate porosity and microscopic features are characterized with an optical microscope. The porosity of resin-interleaved laminates decreases to 3.7%, while the resin content only increases by 4.5% in the meantime. This is because interlayer resin particles rapidly melt under laser heating and quickly fill the voids between layers. The wedge peel strength of resin-interleaved laminates can increase by 30.1% without a repass treatment. This could be attributed to the increase in resin intimate contact and reduction in interlayer voids. Full article

Amorphous thin films can be applied to increase the anti-corrosion ability of critical components. Atomized FeCrNiMoCSiB powders were hot-pressed into a disc target for R. F. magnetron sputtering on a 316L substrate to upgrade its corrosion resistance. The XRD spectrum confirmed that the film deposited by R. F. magnetron sputtering was amorphous. The corrosion resistance of the amorphous film was evaluated in a 1 M HCl solution with potentiodynamic polarization tests, and the results were contrasted with those of a high-velocity oxy-fuel (HVOF) coating and 316L, IN 600, and C 276 alloys. The results indicated that the film hardness and elastic modulus, as measured using a nanoindenter, were 11.1 and 182 GPa, respectively. The principal stresses in two normal directions of the amorphous film were about 60 MPa and in tension. The corrosion resistance of the amorphous film was much greater than that of the other samples, which showed a broad passivation region, even in a 1 M HCl solution. Although the amorphous film showed high corrosion resistance, the original pinholes in the film were weak sites to initiate corrosion pits. After polarization tests, large, deep trenches were seen in the corroded 316L substrate; numerous fine patches in the IN 600 alloy and grain boundary corrosion in the C276 alloy were observed. Full article

High-velocity oxy-fuel (HVOF) thermally sprayed Cr₃C₂-NiCr coatings have been shown to be effective in shielding important machinery and equipment components from wear in harsh, high-temperature conditions. In this investigation, the HVOF thermal spray coating technique was used to deposit Cr₃C₂-NiCr powder with 10% Co particles onto ductile cast iron. The effect of the Co particles on the mechanical, tribological, and microstructure characteristics of a Cr₃C₂-NiCr/ductile cast iron system was investigated. The microstructure analysis employed various techniques, including light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray spectroscopy (EDS). Scratch tests were applied to analyze the coating quality and adhesion. The coatings created using the HVOF spray method with Cr₃C₂-NiCr powders mixed with Co particles exhibited a dense structure containing large Co particles, partially melted, and very fine Cr₃C₂ particles embedded into the NiCr alloy matrix. Additionally, they possessed high hardness and excellent adhesion to the substrate. The results of bending strength tests were also presented, together with information on the coating’s microhardness and fracture toughness. These included an analysis of the cracks and delamination in the Cr₃C₂-NiCr/ductile cast iron system. It was observed that the addition of Co particles significantly increased the resistance to cracking and wear behavior in the studied system. Full article

With the rapid development of wind energy, large-scale disposal of retired wind turbine blades (rWTBs) has become a hotspot issue worldwide, especially in China. Currently, some practices have reused them in producing artworks, bus stations, concrete structures, etc., but their consumption and value are considered to be very low. Therefore, the recycling of rWTBs into asphalt pavement may be a good way to achieve the goals of large consumption and added value. On this basis, this study first obtained rWTBs crushed and ground into fine powders and then mechanically mixed with styrene–butadiene rubber after silane treatment for the final preparation of the powder modifier (R-Si-rWTB). Afterward, these modifiers were used to prepare composite-modified asphalt mixtures in combination with SBS. Through a series of structure and performance characterizations, the following valuable findings were reached: after the silane and rubber treatments, the microstructure of rWTBs became tougher and almost all of the fibers were coated by the rubber; the R-Si-rWTB modifier had a significant effect on improving the resistances of the asphalt mixture to moisture-induced damage, reaching 95.6%; compared to that of the virgin asphalt mixture (83.67%), the immersed residual Marshall stability of the 30R-Si-rWTB/70SBS asphalt mixture was higher, being between 86% and 90%; the rut depth development of 30R-Si-rWTB/70SBS was very close to that of 0R-Si-rWTB/100SBS, and their dynamic stabilities were close to each other, namely, 5887 pass/mm and 5972 pass/mm; and after aging, the resistances of the 30R-Si-rWTB/70SBS asphalt mixture to moisture and freeze–thaw damage improved. Overall, the value-added recycling of rWTBs into a modifier can contribute to better and more durable asphalt pavement. Full article

Very recently, the synthesis of 2D MoS₂ and WS₂ through pulsed laser-directed thermolysis can achieve wafer-scale and large-area structures, in ambient conditions. In this paper, we report the synthesis of MoS₂ and MoS₂ oxides from (NH₄)₂MoS₄ film using a visible continuous-wave (CW) laser at 532 nm, instead of the infrared pulsed laser for the laser-directed thermolysis. The (NH₄)₂MoS₄ film is prepared by dissolving its crystal powder in DI water, sonicating the solution, and dip-coating onto a glass slide. We observed a laser intensity threshold for the laser synthesis of MoS₂, however, it occurred in a narrow laser intensity range. Above that range, a mixture of MoS₂ and MoO₂ is formed, which can be used for a memristor device, as demonstrated by other research groups. We did not observe a mixture of MoS₂ and MoO₃ in the laser thermolysis of (NH₄)₂MoS₄. The laser synthesis of MoS₂ in a line pattern is also achieved through laser scanning. Due to of the ease of CW beam steering and the fine control of laser intensities, this study can lead toward the CW laser-directed thermolysis of (NH₄)₂MoS₄ film for the fast, non-vacuum, patternable, and wafer-scale synthesis of 2D MoS₂. Full article