Coatings

The most economical way to move liquids and gaseous hydrocarbons is by using pipelines. According to several international organizations and oil companies, the use of fossil fuels will continue in the following decades. For this reason, it is important to continue studying different corrosion mechanisms and their origins. One of the mechanisms that provoke small leaks, affecting pipeline hermeticity, is pitting corrosion. It is well-known that non-metallic inclusion dissolution can trigger pit nucleation. As pitting corrosion is recognized to be random in nature, it is also interesting to study the random nature of the inclusions present in API 5L X60 steel. Probability distributions commonly used to describe pitting corrosion characteristics are appropriate for studying inclusion characteristics. The size of inclusions plays a key role in pit nucleation because small inclusions tend to generate more defects, especially when these inclusions are compounds of MnS, and the steel is immersed in a corrosive solution. The results of this research work show that there is a close relationship between the random nature of pitting corrosion and inclusions. Full article

In this study, an Inconel625-Ni60-Ni60/25%WC (Inconel625-Ni/WC) composite coating was fabricated on Cr12MoV steel by first-stage laser cladding, followed by second-stage laser remelting with various laser powers, and the better laser energy density of 25.0 J/mm² for laser remelting test was obtained by macroscopic morphology and microhardness analysis. The effects of laser remelting on the microstructure, microhardness, wear resistance, and impact resistance of the composite coating was systematically investigated by combining various characterization methods. The results showed that laser remelting did not cause the composite coating to produce new phases. The microstructure of the Ni/WC layer in the remelted composite coating was denser and finer, and the average grain size of the surface layer was reduced by 11.69%. The impact depth of laser remelting was about 2.0 mm. The average microhardness of the Ni/WC layer in the remelted composite coating increased by 5.9%, and the average wear rate of the surface was reduced by 50.12% compared with that before laser remelting. The wear surface of remelted composite coating exhibited abrasive wear, and the wear resistance was significantly improved. In addition, the impact toughness value of the remelted composite coating reached 5.15 J/cm², which increased by 87.96% compared with that before laser remelting. The impact resistance of the composite coating was further improved. Full article

LiFePO₄ is a type of cathode material with good safety and long service life. However, the problems of the low Li ion diffusion rate and low electron conductivity limit the application of LiFePO₄ in the field of electric vehicles. In this paper, FePO₄ with different grain sizes was prepared via the air oxidation precipitation method and then sintered to prepare LiFePO₄. The refined grain can shorten the diffusion distance of Li⁺, accelerate the diffusion of Li⁺, and improve the diffusion coefficient of Li⁺. The results show that LiFePO₄ with a smaller grain size has better electrochemical performance. The discharge capacity of the first cycle is 151.3 mAh g⁻¹ at 1 C, and the capacity retention rate is 95.04% after 230 cycles. Its rate performance is more outstanding, not only at 0.2 C, where the discharge capacity is as high as 155 mAh g⁻¹, but also at 10 C, the capacity fade is less, and it can still reach 131 mAh g⁻¹. The air oxidation precipitation method reduces the production cost, shortens the production process, and prepares FePO₄ with small grains, which provides a reference for further improving the properties of precursors and LiFePO₄. Full article

Recently, the near-infrared-II (NIR-II, 1000–1350 nm) region has been extensively applied in deep-tissue photothermal therapy (PTT) on account of it having stronger tissue penetration and a higher maximum permissible exposure (MPE) than the near-infrared-I (NIR-I, 650–950 nm) region. In this study, we developed a rapid and convenient in situ polymerization strategy to fabricate polypyrrole nanosheets (PPy NSs) within a few minutes using manganese dioxide nanosheets (MnO₂ NSs) as both the oxidant and the self-sacrificed template. The fabricated PPy NSs exhibited excellent NIR-II absorption, which conferred its high photothermal conversion efficiency (66.01%) at 1064 nm and its photoacoustic (PA) imaging capability. Both in vivo and in vitro studies have shown that that PPy NSs possess good biological safety and excellent PTT efficacy and PA imaging performances. Thus, the as-synthesized PPy NSs could effectively achieve PA imaging-guided photothermal tumor ablation under 1064 nm excitation. Our work provides a novel and promising method for the rapid preparation of PPy NSs without the addition of exogenous oxidants and subsequent template removal, which could be regarded as potential photothermal agents (PTAs) to integrate the diagnosis and treatment of cancer. Full article

Flax fibers have found widespread use in eco-composite materials because of their remarkable mechanical properties compared to glass fibers. However, their low stability limits their use on a larger scale when employed in hot or humid environments. Therefore, the surfaces should be modified before the composite process to provide the best interfacial interactions and increase the dispersion of natural fibers. To tackle this problem, two kinds of modifications can be considered: wet and dry modifications. This research explores different methods to improve the adhesion between flax fibers and the poly lactic acid (PLA) polymer. Morphological and chemical modifications in the presence of acetone, alkali (as a wet modification), and with air atmospheric pressure plasma (as a dry modification) are compared in this research. The results revealed that altering the chemical characteristics on the surface significantly changed the mechanical properties of the final composite. More specifically, the Fourier transform infrared spectroscopy (FTIR) data indicate that wax-related peaks (2850 and 2920 cm⁻¹) were eliminated by both wet and dry treatments. Dynamic mechanical analysis (DMA) results also highlighted that a better bond between the flax fibers and the PLA matrix is obtained with the plasma modification. Full article

In order to further enhance the reinforcing effectiveness of polypropylene (PP) fibers on pavement concrete, waterborne epoxy (WBE) was introduced in this research and its effect on the flexural properties and freeze–thaw resistance of PP-fiber-reinforced concrete was evaluated. Compressive-strength tests, flexural-strength tests, three-point bending tests, freeze–thaw cycling tests and a scanning electron microscopic observation were carried out to analyze mainly the influence of WBE on the flexural properties and freeze–thaw resistance of PP-fiber-reinforced concrete. WBE contents of 0, 5%, 10%, 15% and 20% by weight of the cement were employed. The experimental results indicated that WBE was beneficial to improving the flexural properties of PP-fiber-reinforced concrete. With increasing content of WBE, the flexural strength and the peak load showed significant increases. Although a slight degradation in the abovementioned flexural parameters was observed when the WBE content was above 15%, the deflection at the peak, the fracture energy and the fracture toughness still showed an upward trend. In addition, the freeze–thaw resistance of PP-fiber-reinforced concrete was improved remarkably with the increasing addition of WBE content, leading to smaller mass loss and higher residual flexural strength. Moreover, microstructural images revealed that with the addition of WBE, the PP fiber/concrete interfacial bonding was effectively improved, and the concrete matrix tended to be denser as well, which provided higher resistance for crack initiation and propagation. In consideration of maximally improving the flexural properties of PP-fiber-reinforced pavement concrete, and while ensuring the compressive strength and meeting the freeze–thaw requirements, it was recommended that the content of WBE in PP-fiber-reinforced concrete should be 15%. Full article

This study is aimed to compare, through laboratory experimentations, the efficiency of UV-C irradiation and an essential-oils-based product as tools to reduce the biofilm identified in a semi-hypogeum room located in the archaeological park of Baia, Italy. During this study, the autotrophic component of the original biofilm, mostly composed of Chlorophyceae and Cyanophycean, was isolated in the laboratory, while simultaneously, the composition of the pigments used for the fresco paintings was examined in situ through X-ray fluorescence. These examinations were necessary for the creation of test samples that were similar to the original surfaces and used for subsequent experiments. The plaster testers were contaminated with artificial biofilm, exposed to UV-C at a distance of 80 cm for a fixed time interval and treated with ESSENZIO©, a product based on oregano and thyme essential oils, to eradicate the biological species. The treatment’s effectiveness was then assessed by employing optical microscopy and spectrometric techniques applied to the areas previously occupied by the biofilm on the different test samples. To obtain an additional parameter to evaluate the treatments efficacy, the concentrations of the photosynthetic pigments were also measured by spectrophotometry. Results showed that biofilms were successfully removed by the irradiation of the surfaces and by the essential-oils-based product at a dilution of 50% in demineralized water with a time of application of 1 h and 30 min; in addition, no visible change of the pigments used on the testers were observed, demonstrating the high efficiency of the treatments against biodeteriogens. The two methods and their different mechanisms of action have provided interesting aspects that suggest a combined strategy to contrast and prevent biological growth in archaeological contexts. Full article

An Fe-based coating was thermally sprayed onto the surface of AZ91 magnesium alloy via the High-Velocity-Oxygen-Fuel (HVOF) method. The thermally sprayed coating with a thickness of 530 ± 25 µm and a porosity of 0.7 ± 0.1% did not show any macrostructural defects and did not cause any degradation of the AZ91 alloy. Laser remelting of the surface layer of the sprayed coating resulted in the recrystallization of the structure and the disappearance of presented pores, splat boundaries, and other defects. This led to an increase in the hardness of the remelted layer from the original 535 ± 20 HV0.3 up to 625 ± 5 HV0.3. However, during the laser remelting at a laser power of 1000 W, stress cracking in the coating occurred. The tribological properties were evaluated by the ball-on-plate method under dry conditions. Compared to the uncoated AZ91 magnesium alloy, a higher value of friction coefficient (COF) was measured for the as-sprayed coating. However, there was a decrease in wear rate and weight loss. The remelting of the surface layer of the as-sprayed coating led to a further decrease in the wear rate and weight loss. Based on the obtained data, it has been shown that the application of laser-remelted thermally sprayed Fe-based coatings on AZ91 Mg alloy improves hardness and tribological properties compared to bare Mg alloy and as-sprayed Fe-based coatings. Full article

In this work, we fabricated lap joints between embossed projection phosphorus bronze and flat brass through resistance projection welding (RPW). The experimental results indicated that the bronze projection moves into the softer brass without being deformed during the welding process. The tensile shear loads of the joint reached a maximum value of 273.6 N at a welding current of 5.5 kA. Under this circumstance, a reaction layer, including a columnar crystal solidification layer and a diffusion layer, is formed at the interface beside the boundary of bronze. The EDS line scan shows an elemental transition diffusion layer of about 1.5 μm between the H62 brass columnar crystal and XYK-6 phosphorus bronze. The fracture occurred on the XYK-6 side, passing through the bump instead of the welding interface, resulting in intactness of the welding interface. The results revealed that resistance projection welding is an effective method for welding copper alloys, suggesting the bright prospects of this technology in welding electrical parts. Full article

The hot corrosion behavior of Co-9Al-9.5W-xSi (where x = 0%, 0.1%, 0.5%, at.%) alloys in a salt mixture at 900 °C was investigated. The effect of Si on hot corrosion resistance was examined using corrosion kinetics. The surface morphology of the corrosion products was explored via SEM with EDS and the phase constituents were examined using XRD. The results revealed that hot corrosion occurred as a combination of both sulfidation and oxidation behavior. With the increase in Si content, the hot corrosion resistance of the alloy was capable of remarkable advancement. Corrosion scales on the three Co-based alloys were mostly comprised of Co₃O₄, CoO, CoAl₂O₄, CoWO₄, and Al₂O₃. The hot corrosion mechanism for the Co-based alloy in the presence of 75 wt.% Na₂SO₄ and 25 wt.% NaCl deposits were analyzed. Full article

Lead-based ternary-chalcogenide thin films of the (PbTe)_1−x(PbS)_x system were obtained using the plasma-enhanced chemical-vapor-deposition (PECVD) technique under conditions of a nonequilibrium low-temperature argon plasma of an RF discharge (40.68 MHz) at a reduced pressure (0.01 Torr). High-purity elements were directly used as starting materials, namely Pb, S and Te. Plasma–chemical synthesis was carried out on the surface of c-sapphire and silicon substrate. The physicochemical properties of the films were studied using various analytical methods. The dependence of the Seebeck coefficient, resistivity and power factor on the structural properties and composition has been studied. The thermoelectric characteristics were found to be dependent on film composition. Upon the selection of optimal sulfur concentration, one can increase the power factor compared to single-phase PbS or PbTe films. Full article

This paper aims to study the possibility of improving the chemical and surface characteristics of the Ti6Al4V alloy by depositing phosphate layers on its surface. Accordingly, an innovative phosphating solution was developed and used in a chemical conversion process to obtain Ca–Zn phosphate layers on the base material surface. Moreover, the chemical composition of the phosphate solution was chosen considering the biocompatibility of the chemical elements and their possibility of contributing to the formation of phosphate compounds. The obtained layer was characterized by optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and potentiodynamic polarization tests. The wetting of the Ca–Zn sample surface was also investigated using water and two liquids similar to body fluids, namely, Ringer and Dulbecco solutions. According to the surface energy study, the polar component is almost two times larger compared with the dispersive one. The SEM and EDS tests revealed a uniformly coated surface with intercalated crystals leading to a rough surface. Furthermore, the XRD results showed not only the presence of hopeite and scholzite but also of phosphophyllite. By the vibrations of the PO₄⁻³ groups, the FTIR test confirmed the presence of these phases. The potentiodynamic tests revealed that the samples coated with the Ca–Zn phosphate layer present better corrosion resistance and a lower corrosion rate compared with the uncoated ones. Full article

X-rays are commonly employed in medical institutions for diagnostic examinations, which often results in radiation exposure for both patients and medical personnel during treatments and procedures. Hands are typically the most exposed body parts, with scattered rays causing secondary exposure. To address this issue, a lightweight functional radiation protection fabric that guarantees the activity of medical personnel is required. In this study, a shielding fabric was fabricated with nanofibers using a mixture of tungsten and polyurethane to resolve the weight reduction problem of such nanofibers. To improve the shielding performance, the change in the performance arising from the spinning pattern in the nanofiber electrospinning manufacturing process was compared and tracked. The patterns reproduced via electrospinning included honeycomb, matrix-orthogonal, double-circle, and spider web patterns. Through this, a nanofiber fabric was produced, and the shielding performance was evaluated. The honeycomb pattern fabric exhibited the best shielding rate of 89.21% at an effective X-ray energy of 60.3 keV, and the double-circle pattern exhibited the lowest shielding rate of 62.55% at the same energy. Therefore, it was observed that the pattern arising from the nanofiber spinning conditions affects the dispersion of the shielding material, which affects the shielding performance. When 0.3 mm tungsten nanofiber fabric is compared with its lead equivalent of 0.25 mm, a difference of 8.7% was observed, suggesting that the nanofiber can be used in medical institutions. Future research will explore the potential of protective fabrics that minimally impact medical personnel’s mobility but provide enhanced protection against radiation exposure. Full article

This paper proposes an optical sensor based on nanoscale metamaterial structures. The design of the sensor has been explored with respect to biosensing applications through numerical modeling and analysis. The sensor comprises silica substrate and diamond nanostructures, both of which represent dielectrics. The sensing principle is based on the detection of ambient refractive index change. As the analyte properties change, the refractive index changes, as well. The refractive index change has been detected by striking electromagnetic waves onto the structure and noting the spectral response. Ultraviolet waves have been utilized for recording spectral responses and evaluating sensor performance. The sensor displays multiple sharp resonance peaks in the reflected beam. By altering the refractive index of the analyte present around the sensor, the peaks can be seen choosing different wavelengths. The resonance peaks have been investigated to observe electric and magnetic field dipoles in the sensor structure. The spectrum peaks have also been studied to understand fabrication tolerances. The sensor displays a linear response, along with a large Quality (Q) factor. The maximum value of the achieved Quality (Q) factor for the proposed sensor is 1229 while operating across the refractive index range of 1.4–1.45. The claim has been supported by comparison with contemporary works on similar platforms. A range of other sensing parameters have also been calculated and benchmarked. Metamaterial-based optical sensors can provide smaller device sizes, faster response times and label-free detection. Full article

The Marangoni effect has been applied in the preparation of large-area ultrathin films. However, defects occur frequently during the transfer progress of ultrathin films to substrates, which limits its application in scalable and massive fabrication. Carbon nanotubes (CNTs), as typical one-dimensional carbon materials, are widely used in wearable and flexible sensors due to their outstanding electrical and mechanical properties. In this paper, Marangoni-driven self-assembled CNTs film was obtained by injecting 0.5 mL 1 mg·mL⁻¹ CNTs/ethanol dispersion on 100 cm² water dropwise; the thickness, sheet resistance, and optical transmittance (at 550 nm) of the as-prepared ultrathin film were 38 nm, 7.3 kΩ/□, and 66.9%, respectively. The CNTs film was transferred onto polydimethylsiloxane (PDMS) to prepare a conductive composite of CNTs/PDMS film and the sheet resistance of the composite film reached 21.0 kΩ/□. Furthermore, the packaged PDMS/CNTs/PDMS (PCP) strain sensors with a sandwich-like structure exhibited satisfactory sensitivity with a gauge factor of 3.4 at 50% strain, a large working range (89%), and excellent stability (>8000 cycles). The easy-making and low-cost sensors show great potential in wearable electronics, real-time motion detection, and electronic skin. Full article

In order to research the displacement characteristics and stability of a soil slope reinforced with carbon-fiber-reinforced plastic (CFRP) and anti-slide piles, the displacement composition, aging deformation and failure mode of a soil mass were analyzed. According to the Mohr–Coulomb strength criterion, a new nonlinear, accelerated creep model of soil mass was founded with the addition of a self-building M-C plastic element. Furthermore, a viscoplastic strain analytical formula of an M-C plastic element was obtained, and the tensile deformation characteristics of a CFRP sheet were also discovered under a landslide thrust creep load. According to the environmental conditions of the anti-slide pile, the CFRP was arranged along the load-bearing side of the pile to control deformation. Combining the calculation example, it is shown that the horizontal displacement of the soil slope’s composite structure decreases by approximately 40% with CFRP reinforcement. Furthermore, for the first two calculation conditions, after one year, the maximum horizontal displacement decreased by 50% and increased by 10%, respectively. Simultaneously, the overall safety factor increased by 31.3% without soil creep properties. On the contrary, the overall safety factor was reduced, and the slope has a tendency toward unstable failure. Moreover, there is no through plastic zone in the slope. The stability of the reinforced slope and the bearing capacity of the pile are related to the CFRP method. Simultaneously, the structure can reduce the costs and construction difficulty of anti-slide piles in a complex environment surrounded by the soil creep effect. Full article

In this study, a high-hardness and wear-resistant ceramic coating was prepared on the surface of 319S aluminum alloy using the micro-arc oxidation (MAO) technique. The effects of pulse width, negative voltage, and KOH concentration on the MAO coating were investigated, and the microhardness and surface roughness of the coating were measured. The morphology, elemental distribution, and phase composition of the coating were analyzed using SEM, EDS, XRD, and digital microscopy. The influence of the MAO coating on the wear of the 319S aluminum alloy was evaluated using a friction-wear tester. The results showed that in the sodium silicate solution system, with an increase in pulse width, the thickness of the coating gradually increased and the surface hardness initially increased and then decreased. With an increase in negative voltage, the density of the coating first increased and then decreased, the thickness of the dense layer initially increased and then decreased, and the surface hardness initially increased and then decreased. With an increase in the KOH concentration, the coating thickness increased and the roughness initially decreased and then increased. When the pulse width was 3000 ms, the negative voltage was 130 V, and the KOH concentration was 1 g/L, the coating exhibited the best density, with the highest surface hardness of 1426.8 HV and the thickest dense layer of 55 μm. The reduction in surface cracks and improvement in density indicated an enhancement in the hardness and wear resistance of the coating. The decrease in width and depth of the wear scars demonstrated the excellent wear resistance of the coating. Full article

The contact surface corrosion of friction high-strength bolt (FHSB) joints was analyzed to examine the characteristics of corrosion products and influence factors in steel bridges. Samples were selected from the Dongying Shengli Yellow River Bridge, which has been in service for 33 years. Scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were utilized to analyze the microscopic morphology and chemical composition of the corroded surface of the samples. The study identifies that construction quality issues accelerate corrosion of the contact surface and that the contact surface of the aluminum spraying layer transforms from rugged and dense to smooth and porous as corrosion increases. The findings also suggest that the friction coefficient of the FHSB connection node initially decreases and then increases as the corroded surface changes. Corrosion products contained S, Cl, Mn, Si, FeS, and their oxides, indicating that atmospheric, industrial, and Yellow River soil environments contribute to joint corrosion. The study proposes sandblasting and coating the corroded contact surface and deck steel plate with inorganic zinc-rich paint to prevent media penetration and delay substrate corrosion. Adopting ultra-high-performance concrete (UHPC) as the deck structure is also recommended to reduce top plate tensile stress, deck cracking, and media invasion. This study provides insights into the characteristics and mechanisms of FHSB joint corrosion to aid the maintenance, repair, and protection of steel bridges. Full article

In the present study, the ablation of a pintle injector on a 500N GOX/GCH₄ rocket engine under different working conditions is studied experimentally and numerically. The temperature of the pintle tip and the combustion gas in the head zone was measured in a series of experiments by the thermocouples. Moreover, a three-dimensional model was established to simulate combustion and heat transfer concurrently and analyze the ablation state of the pintle injectors. The obtained results indicate that under a low chamber pressure ($p_c=0.25 \mathrm{MPa}$) and an increasing O/F ratio from 0.8 to 2, the tip temperature declines first, and then rises. At the designed working condition ($p_c=1.05 \mathrm{MPa}$and O/F = 3.2), the pintle tip suffered serious ablation, and the microstructure analysis indicates that the ablation failure of the stainless steel pintle tip originates from chromium precipitation. This phenomenon is especially more pronounced when the temperature exceeds 1273 K, which makes the structure fragile and vulnerable. This article helps to provide an understanding of the ablation failure of the pintle injectors, and the established model is capable of giving a prediction on the ablation status of the pintle tips consistent with the experiment. Full article