Search Results (35)

Corrosion fatigue damage significantly affects the long-term service of marine platforms such as propellers. Fatigue testing of pre-corrosion specimens is essential for understanding damage mechanisms and accurately predicting fatigue life. However, traditional seawater-based tests are time-consuming and yield inconsistent results, making them unsuitable for rapid evaluation of newly developed equipment. This study proposes an accelerated corrosion testing method for ZCuAl₈Mn₁₃Fe₃Ni₂ nickel–aluminum bronze, simulating the marine full immersion zone by increasing temperature, adding H₂O₂, reducing the solution pH, and preparing the special solution. Coupled with the fatigue test of pre-corrosion specimens, the corrosion damage characteristics and their influence on fatigue performance were analyzed. A numerical simulation method was developed to predict the fatigue life of pre-corrosion specimens, showing an average error of 13.82%. The S–N curves under different pre-corrosion cycles were also established. The research results show that using the test solution of 0.6 mol/L NaCl + 0.1 mol/L H₃PO₄-NaH₂PO₄ buffer solution + 1.0 mol/L H₂O₂ + 0.1 mL/500 mL concentrated hydrochloric acid for corrosion acceleration testing shows good corrosion acceleration. Moreover, the test methods ensure accuracy and reliability of the fatigue behavior evaluation of pre-corrosion specimens of the structure under actual service environments, offering a robust foundation for the material selection, corrosion resistance evaluation, and fatigue life prediction of marine structural components. Full article

We use Co doping to alter the magnetic relaxation dynamics in superparamagnetic nanofluids made of 18 nm average diameter Fe₃O₄ nanoparticles immersed in Isopar M. Ac-susceptibility data recorded at different frequencies and temperatures, χ″vs. T|_f, reveals a major (~100 K) increase in the superspin blocking temperature of the Co_0.2Fe_2.8O₄-based fluid (CFO) compared to its Fe₃O₄ counterpart (FO). We ascribe this behavior to the strengthening of the interparticle magnetic dipole interactions upon Co doping, as demonstrated by the relative χ″-peak temperature variation per frequency decade $\mathsf{\Phi }={\displaystyle \frac{∆\mathrm{T}}{\mathrm{T}·∆\mathrm{l}\mathrm{o}\mathrm{g}\left(\mathrm{f}\right)}}$, which decreases from Φ~0.15 in FO to Φ~0.025 in CFO. In addition, χ″vs. T|_f datasets from the CFO fluid reveal two magnetic events at temperatures T_p1 = 240 K and T_p2 = 275 K, both above the fluid’s freezing point (T_F = 197 K). We demonstrate that the physical rotation of the nanoparticles within the fluid, the Brown mechanism, is entirely responsible for the collective superspin relaxation observed at T_p1, whereas the Néel mechanism, the superspin flip across an energy barrier within the particle, is dominant at T_p2. We confirm this finding through fits of models that describe the temperature dependence of the relaxation time via the two mechanisms: ${\mathsf{\tau }}_{\mathrm{B}}(\mathrm{T})={\displaystyle \frac{3{\mathsf{\eta }}_0{\mathrm{V}}_{\mathrm{H}}}{{\mathrm{k}}_{\mathrm{B}}\mathrm{T}}}\exp \left[{\displaystyle \frac{{\mathrm{E}}^{\prime }}{{\mathrm{k}}_{\mathrm{B}}\left(\mathrm{T}-{{\mathrm{T}}_0}^{\prime }\right)}}\right]$ and ${\mathsf{\tau }}_{\mathrm{N}}\left(\mathrm{T}\right)={\mathsf{\tau }}_0\exp \left[{\displaystyle \frac{{\mathrm{E}}_{\mathrm{B}}}{{\mathrm{k}}_{\mathrm{B}}\left(\mathrm{T}-{\mathrm{T}}_0\right)}}\right]$. The best fits yield ${\mathsf{\gamma }}_0={\displaystyle \frac{3{\mathsf{\eta }}_0{\mathrm{V}}_{\mathrm{H}}}{{\mathrm{k}}_{\mathrm{B}}}}$= 1.5 × 10⁻⁸ s·K, E′/k_B = 7 03 K, and T₀′ = 201 K for the Brown relaxation, and E_B/k_B = 2818 K and T₀ = 143 K for the Néel relaxation. Full article

Magnesium alloys are widely used in all kinds of fields because of their excellent mechanical properties, but their application has been prevented by poor corrosion resistance. In this paper, Mg(OH)₂-Ca(OH)₂/Al(OH)₃/Al₂O₃ composite coatings with long-term corrosion resistance were fabricated on the surface of Mg alloys using the hydrothermal method. Among them, the calcium hydroxide/calcium nitrate–alumina coating successfully filled the cracks in the magnesium hydroxide coating. Meanwhile, we explored the influences of different heating times and temperatures on the coating and analyzed its composition. After immersing the coating in a 3.5% NaCl solution for 168 h, only a small portion of the surface dissolved. Electrochemical test results indicated that the corrosion potential and corrosion current density of the coating increased by three orders of magnitude, significantly improving corrosion resistance in comparison to bare samples. Adhesion tests showed that the coating exhibited good bonding performance to the substrate. This method features a simple, pollution-free preparation process and does not require complex instrumentation, thereby enhancing the longevity of the magnesium alloy. Full article

This paper presents a ZnO-Pt/Ru sensor prepared by a two-step hydrothermal method with in situ-grown ZnO nanorods and doped with Pt and Ru elements by immersion sintering. Characterization results showed that Pt and Ru were successfully modified on the surface of ZnO nanorods. ZnO-Pt/Ru achieved a response of 25–50 ppm H₂S at the optimum operating temperature of 198 °C. In addition, the lower limit of H₂S detection of ZnO-Pt/Ru reached 50 ppb with a response of about 10%, indicating a wide concentration detection range. Due to the good catalytic properties of Pt, the recovery characteristics of ZnO at high concentrations of H₂S were significantly improved. The response time of ZnO-Pt/Ru (30 s) was also significantly shorter than pristine ZnO (56 s), with excellent selectivity. As far as the gas-sensitive enhancement mechanism is concerned, at the macroscopic level, the ZnO surface was modified by Pt and Ru, and this special structure of ZnO-Pt/Ru significantly increased the specific surface area. At the microscopic level, the PN junction formed between Pt/Ru and ZnO provided abundant holes for electron migration. Full article

In order to broaden the working voltage (1.23 V) of aqueous supercapacitors, a high-performance asymmetric supercapacitor with a working voltage window reaching up to 2.1 V is assembled using a nanorod-shaped molybdenum trioxide (MoO₃) negative electrode and an activated carbon (AC) positive electrode, as well as a sodium sulfate–ethylene glycol ((Na₂SO₄-EG) electrolyte. MoO₃ electrode materials are fabricated by adjusting the hydrothermal temperature, hydrothermal time and solution’s pH value. The specific capacity of the optimal MoO₃ electrode material can reach as high as 244.35 F g⁻¹ at a current density of 0.5 A g⁻¹. For the assembled MoO₃//AC asymmetric supercapacitor with a voltage window of 2.1 V, its specific capacity, the energy density, and the power density are 13.52 F g⁻¹, 8.28 Wh kg⁻¹, and 382.15 W kg⁻¹ at 0.5 A g⁻¹, respectively. Moreover, after 5000 charge–discharge cycles, the capacity retention rate of the device still reaches 109.2%. This is mainly attributed to the small particle size of MoO₃ nanorods, which can expose more electrochemically active sites, thus greatly facilitating the transport of electrolyte ions, immersion at the electrolyte/electrolyte interface and the occurrence of electrochemical reactions. Full article

The oxide layer development of X6CrNiNb18-10 (AISI 347) during exposure to high-temperature water has been investigated. Stainless steels are known to form a dual oxide layer in corrosive environments. The secondary Fe-rich oxide layer has no significant protective effect. In contrast, the primary Cr-rich oxide layer is known to reach a stabilized state, protecting the base metal from further oxidation. This study’s purpose was to determine the development of oxide layer dimensions over exposure time using SEM, TEM and EDX line scans. While a parabolic development of Cr in the protective primary layer and Fe in the secondary layer was observed, the dimensions of the Ni layer remained constant. Ni required the presence of a pronounced Fe-rich secondary layer before being able to reside on the outer secondary layer. With increasing immersion time, the Ni element fraction surpassed the Cr element fraction in the secondary layer. Oxide growth on the secondary layer could be observed. After 480 h, nearly the entire surface was covered by the outer oxide layer. In the metal matrix, no depletion of Cr or Ni could be observed over time; however, an increased presence of Cr and Ni in the primary layer was found at the expense of Fe content. The Nb-stabilized stainless steel was subject to the formation of Niobium pentoxide (Nb₂O₅), with the quantity and magnitude of element fraction increasing over exposure time. Full article

In order to explore the possibilities of increasing the hydrophilicity of carbon-based adsorbents, catalysts, or electrode materials in aqueous solutions, the oxidation of wood-based activated biochar using H₂O₂ was investigated. The properties of oxidized activated biochar obtained at different activation temperatures (600, 700, and 800 °C) and H₂O₂ oxidized for 15–180 min were investigated using the characteristics of surface functionality, elemental composition, porous structure, contact angle measurements, FTIR spectroscopy, and immersion calorimetry. It was observed that the optimal oxidation time was different for each sample depending on activation temperature, and the degree of oxidation can be tailored by changing the oxidation time. The course of oxidation depends on the degree of graphitization and functionalization, determined by the activation temperature. It was established that the highest degree of oxidation and increase in wettability is observed for samples with the lowest degree of activation obtained at a temperature of 600 °C. Full article

This article presents the results of research on the growth kinetics, microstructure (SEM/EDS/XRD), and corrosion behavior of Zn-5Al coatings obtained using a high-temperature hot dip process on B500B reinforcing steel. The corrosion resistance of the coatings was determined using the neutral salt spray (NSS) test (EN ISO 9227). Based on chemical composition tests in micro-areas (EDS) and phase composition tests (XRD), corrosion products formed on the coating surface after exposure to a corrosive environment containing chlorides were identified. In the outer layer of the coating, areas rich in Zn and Al were found, which were solid solutions of Al in Zn (α), while the diffusion layer was formed by a layer of Fe(Al,Zn)₃ intermetallics. The growth kinetics of the coatings indicate the sequential growth of the diffusion layer, controlled by diffusion in the initial phase of growth, and the formation of a periodic layered structure with a longer immersion time. The NSS test showed an improved corrosion resistance of reinforcing bars with Zn-5Al coatings compared to a conventional hot-dip-galvanized zinc coating. The increase in corrosion resistance was caused by the formation of beneficial corrosion products: layered double hydroxides (LDH) based on Zn²⁺ and Al³⁺ cations and Cl⁻ anions and simonkolleite—Zn₅(OH)₈Cl₂·H₂O. Full article

This study investigates the corrosion behavior of Ni-Cr binary alloys, including Ni-10Cr, Ni-15Cr, Ni-20Cr, Ni-25Cr, and Ni-30Cr, in a NaCl-KCl-MgCl₂ molten salt mixture through gravimetric analysis. Corrosion tests were conducted at 700 °C, with the maximum immersion time reaching up to 100 h. The corrosion rate was determined by measuring the mass loss of the specimens at various time intervals. Verifying corrosion rates by combining mass loss results with the determination of element dissolution in molten salts using Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES). Detailed examinations of the corrosion products and morphology were conducted using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Micro-area elemental analysis on the corroded surfaces was performed using an energy dispersive spectrometer (EDS), and the elemental distribution across the corrosion cross-sections was mapped. The results indicate that alloys with lower Cr content exhibit superior corrosion resistance in the NaCl-KCl-MgCl₂ molten salt under an argon atmosphere compared to those with higher Cr content; no corrosion products were retained on the surfaces of the lower Cr alloys (Ni-10Cr, Ni-15Cr). For the higher Cr alloys (Ni-20Cr, Ni-25Cr, Ni-30Cr), after 20 h of corrosion, a protective layer was observed in certain areas. The formation of a stable Cr₂O₃ layer in the initial stages of corrosion for high-Cr content alloys, which reacts with MgO in the molten salt to form a stable MgCr₂O₄ spinel structure, provides additional protection for the alloys. However, over time, even under argon protection, the MgCr₂O₄ protective layer gradually degrades due to chloride ion infiltration and chemical reactions at high temperatures. Further analysis revealed that chloride ions play a pivotal role in the corrosion process, not only facilitating the destruction of the Cr₂O₃ layer on the alloy surfaces but also possibly accelerating the corrosion of the metallic matrix through electrochemical reactions. In conclusion, the corrosion behavior of Ni-Cr alloys in the NaCl-KCl-MgCl₂ molten salt environment is influenced by a combination of factors, including Cr content, chloride ion activity, and the formation and degradation of protective layers. This study not only provides new insights into the corrosion resistance of Ni-Cr alloys in high-temperature molten salt environments but also offers significant theoretical support for the design and optimization of corrosion-resistant alloy materials. Full article

Chloride ion erosion is an important factor affecting the durability of marine engineering concrete. In particular, concrete structures in wave splash and tidal zones are subjected to dry and wet cycles and multidimensional diffusion of chloride ions. To investigate the intricate diffusion of chloride ions within concrete under these dynamic conditions, we devised a comprehensive experiment. This experiment encompasses multiple dimensions, involving dry and wet cycles, as well as static immersion. The experiment intends to reveal how chloride ions are distributed in the concrete and clarify the changes that occur in its microstructure. Based on Fick’s second law, the multidimensional diffusion model of chloride ions in concrete under the dry and wet cycles and static immersion was established by comprehensively considering the effects of chloride ion exposure time, environment temperature, relative humidity, and the action of dry and wet cycles. The results show that, under the same conditions, the chloride content in concrete decreases with the increase in penetration depth but increases with the increase in the chloride diffusion dimension and exposure time. Dry and wet cycles and multidimensional diffusion of chloride ions increase the development of cracks and pores in the concrete structure and generate large quantities of C₃A·CaCl₂·10H₂O, which will exacerbate the chloride ion transport rate and penetration depth of concrete. Under the same exposure time and penetration depth, the chloride ion content in concrete under two-dimensional (2D) and three-dimensional (3D) diffusion under dry and wet cycles was 1.09~4.08 times higher than that under one-dimensional (1D) diffusion. The correlation coefficients between the simulation results of the multidimensional transport model of chloride ions in concrete under multi-factor coupling and the experimental results were all greater than 0.95, and the model can be utilized to predict the distribution of chloride ion concentration in concrete. Full article

A steel slag porous asphalt (SSPA) mixture, as the surfacing layer of permeable asphalt pavements, not only ensures the pavement surface drainage and noise reduction functions, but also improves the comprehensive utilization of steel slag resources and the inherent protection of the ecological environment. However, compared with ordinary asphalt mixtures, SSPA is more susceptible to water damage, such as scouring and frost swelling caused by external rainwater intrusion, resulting in the deterioration of the pavement performance. Therefore, it is of good practical imperative to study the water stability and moisture damage mechanism of SSPAs. In this study, the water stability of SSPA, that was subjected to a series of time–temperature H₂O-immersion schemes, was investigated using the pull-out and H₂O-immersion Marshall tests, whilst the microscopic mechanism of moisture damage was studied using the scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD) tests. The corresponding results showed that: (a) with the increase in the H₂O immersion time, the water stability of SSPA first increased and then decreased; and (b) the water stability of SSPA was strong under medium-temperature H₂O-immersion or short-term high-temperature H₂O-immersion. SEM, on the other hand, showed that the transition zone spacing was closely related to the chemical adhesion mechanism between the asphalt and steel slag aggregate. Additionally, the FTIR analysis further showed that the steel slag asphalt mastic spectra had new absorption peaks at 3200~3750 cm⁻¹, inherently indicating the existence of chemical bonding between the asphalt and steel slag, with the XRD results showing that CaSO₄·2H₂O had a beneficial effect on the water stability of SSPA. Full article

To prepare a novel cassava starch-based phosphorus releasing super-absorbent polymer (CST-PRP-SAP), the single factor and orthogonal experiment were applied to analyze the effects of different reaction conditions on the absorption and phosphorus release capacities of CST-PRP-SAP samples. The structural and morphological characteristics of the cassava starch (CST), powdered rock phosphate (PRP), cassava starch-based super-absorbent polymer (CST-SAP) and CST-PRP-SAP samples were all compared with various technologies, such as the Fourier transform infrared spectroscopy and X-ray diffraction pattern, etc. The results showed that the CST-PRP-SAP samples had good performances of water retention and phosphorus release which were synthesized, such as the reaction temperature, starch content, P₂O₅ content, crosslinking agent, initiator, neutralization degree, and acrylamide content, which were 60 °C, 20% w/w, 10% w/w, 0.02% w/w, 0.6% w/w, 70% w/w, and 15% w/w, respectively. The water absorbency of CST-PRP-SAP was almost larger than that of the CST-SAP sample with a P₂O₅ content of 5.0% and 7.5%, and they all gradually decreased after three consecutive water absorption cycles. The CST-PRP-SAP sample could maintain about 50% of the initial water content after 24 h, even at the temperature of 40 °C. The swelling process of CST-PRP-SAP conformed to the non-Fickian diffusion, which was determined by the diffusion of water molecules and the relaxation process of polymer chain segments. The cumulative phosphorus release amount and release rate of the CST-PRP-SAP samples were increased with the increasing PRP content and the decreasing neutralization degree. After a 216 h immersion, the cumulative phosphorus release amount and release rate of the CST-PRP-SAP samples with different PRP contents were increased by 17.4 and 3.7 times, respectively. The rough surface of the CST-PRP-SAP sample after swelling was beneficial to the performance of water absorption and phosphorus release. The crystallization degree of PRP in the CST-PRP-SAP system was decreased and most of the PRP existed in the form of physical filling, and the available phosphorus content was increased to a certain extent. It was concluded that the CST-PRP-SAP synthesized in this study has excellent properties of continuous water absorption and retention with functions of promotion and the slow-release phosphorus. Full article

To decrease energy consumption and improve the performance of micro-arc oxidation (MAO) films on 6063 Al alloy, a policy of K₂TiF₆ additive and electrolyte temperature control was adapted. The specific energy consumption relied on the K₂TiF₆ additive and more particularly on the electrolyte temperatures. Scanning electron microscopy demonstrates that electrolytes with 5 g/L K₂TiF₆ can effectively seal the surface pores and increase the thickness of the compact inner layer. Spectral analysis shows that the surface oxide coating consists of γ-Al₂O₃ phase. Following 336 h of the total immersion process, the impedance modulus of the oxidation film, prepared at 25 °C (Ti5-25), remained 1.08 × 10⁶ Ω·cm². Moreover, Ti5-25 has the best performance/energy-consumption ratio with a compact inner layer (2.5 ± 0.3 μm). This research found that the time of the big arc stage increased with the temperature, resulting in producing more internal defects in the film. In this work, we employ a dual-track strategy of additive and temperature providing an avenue to reduce the energy consumption of MAO on alloys. Full article

Environmentally friendly plywood panels were produced by a hot-pressing process using magnesium oxychloride cement (MOC) as a no-added formaldehyde adhesive. Magnesium oxychloride cement binders were prepared with different molar ratios of MgO:MgCl₂ (M/C) and H₂O:MgCl₂ (W/C) ranging from 6 to 12 and 15 to 21, respectively, for plywood production. The binder properties measured were gel time, differential scanning calorimetry (DSC) and Fourier transom infrared spectroscopy (FTIR). The quality of the plywood panels was analyzed based on their mechanical (shear and bending) and physical (thickness swelling and water absorption) properties. A positive effect on the properties of the MOC binder as well as on the properties of the plywood was observed by increasing the molar ratio M/C up to a value of 9. The shear and flexural properties of the plywood specimens were negatively affected by further increasing the molar ratio M/C to 12 and the molar ratio W/C from 15 to 21. Differential scanning calorimetry analysis showed a peak temperature of less than 100 °C for MOC curing, which meets the requirements of hot press technology. No delamination of the plywood specimens was observed after 24 h immersion in tap water or 6 h immersion in boiling water and after a cyclic delamination test. In general, mineral-bonded plywood with magnesium oxychloride shows promising properties for indoor and outdoor use, although the binder quality should still be improved. Full article

This paper aims to explore a new-type Mo-based composite conversion coating on 6061 aluminum alloy, systematically evaluate its corrosion resistance, and further reveal the formation mechanism. The effects of pH, conversion time (CTI) and H₂ZrF₆ content on the corrosion resistance were determined by the dropping test and electrochemical tests, and the average corrosion rate (ACR) in neutral 3.5 wt.% NaCl solution under different temperatures was calculated by the immersion test. The micro-morphology and phase compositions were systematically investigated by SEM, EDS and XPS. The results showed that the optimal pH and CTI were 4.5 and 12 min respectively, and the most suitable addition amount of H₂ZrF₆ was 1.2 mL/L. The micro-morphology of the Mo/Ti/Zr conversion coating (MoTiZrCC) under the best conversion condition was relatively smooth and dense, and its phase compositions mainly consisted of MoO₃, Mo₂O₅, TiO₂, ZrO₂ and Al₂O₃. The MoTiZrCC could significantly improve corrosion resistance with the lower icorr and higher R_p, and the ACR of the MoTiZrCC could be reduced to 16.7% of the Al alloy matrix. Additionally, based on the above results, the formation mechanism for the MoTiZrCC was logically deduced. Full article