Search Results (539)

This paper investigated the tunnel slags generated from a specific tunnel project to systematically assess their environmental risk through phase composition, chemical composition, acidification potential, and heavy metal speciation. Leaching experiments were conducted under various influencing factors, including particle size, time, liquid-to-solid ratio, pH, temperature. The release concentration of heavy metals from the tunnel slag particles follows the following order: Zn > Cu > Cr. This is primarily attributed to the preferential release of Zn under acidic conditions due to its high acid-soluble state, while Cr, which is predominantly present in the residual state, exhibits very low mobility. Furthermore, decreased particle sizes, increased liquid-to-solid ratios, elevated leaching temperatures, extended leaching times, and lower pH values can effectively promote the dissolution of heavy metals from the tunnel slag. The cumulative leaching curves of Cr, Cu, and Zn from the three types of tunnel slags conform to the Elovich equation (R² > 0.88), indicating that the release process of heavy metals is primarily controlled by diffusion mechanisms. The S- and Fe/Mg-rich characteristics of D3 confers a high acidification risk, accompanied by a rapid and persistent heavy metal release rate. In contrast, D2, which is influenced by the neutralizing effect of carbonate dissolution, releases heavy metals at a steady rate, while D1, which is dominated by inert minerals like quartz and muscovite, exhibits the slowest release rate. It is recommended that waste management engineering prioritize controlling S- and Fe/Mg-rich tunnel slags (D3) and mitigating risks of elements like Zn and Cu under acidic conditions. This study provides a scientific basis and technical support for the environmentally safe disposal and resource utilization of tunnel slag. Full article

Aqueous zinc-ion batteries (ZIBs) have emerged as a promising candidate for large-scale energy storage due to their inherent safety, low cost, and environmental friendliness. However, manganese dioxide (MnO₂)-based cathodes, which are widely studied for ZIBs owing to their high theoretical capacity and low cost, face severe capacity fading issues that hinder the commercialization of ZIBs. This performance degradation mainly stems from the weak van der Waals forces between MnO₂ layers leading to structural collapse during repeated Zn²⁺ insertion and extraction; it is also exacerbated by irreversible Mn dissolution via Mn³⁺ disproportionation that depletes active materials, and further aggravated by dynamic electrolyte pH fluctuations promoting insulating zinc hydroxide sulfate (ZHS) formation to block ion diffusion channels. To address these interconnected challenges, in this study, a synergistic strategy was developed combining crystal engineering and pH buffer regulation. We synthesized three MnO₂ polymorphs (α-, δ-, γ-MnO₂), identified δ-MnO₂ with flower-like microspheres as optimal, and introduced sodium dihydrogen phosphate (NaH₂PO₄) as a pH buffer (stabilizing pH at 2.8 ± 0.2). The modified electrolyte improved δ-MnO₂ wettability (contact angle of 17.8° in NaH₂PO₄-modified electrolyte vs. 26.1° in base electrolyte) and reduced charge transfer resistance (Rct = 78.17 Ω), enabling the optimized cathode to retain 117.25 mAh g⁻¹ (82.16% retention) after 2500 cycles at 1 A g⁻¹. This work provides an effective strategy for stable MnO₂-based ZIBs, promoting their application in renewable energy storage. Full article

Thermal barrier coatings (TBCs) extend gas-turbine blade lifetime by improving high-temperature oxidation resistance and mechanical performance. We investigated the microstructural evolution, TGO growth, and Al depletion in air-plasma-sprayed (APS) single-layer YSZ top coat over a NiCrCoAlY bond coat on Ni-based superalloy circular plates, heat treated isothermally at 850 °C and 1000 °C for 50–5000 h. Cross-sectional SEM/EDS analysis showed TGO quadratic thickening kinetics at both temperatures, reaching ~10 µm at 1000 °C/5000 h, the growth rate of which was ~5.8 times higher than at 850 °C. On top of the single-layer TGO of Al₂O₃ observed from the onset, a NiCrCo oxide layer appeared and grew from ≥500 h at 850 °C, with increasing growth rate and cracking. The layer configuration of the YSZ top coat, the TGO of Al₂O₃, and the bond coat (comprising β-NiAl and γ-NiCr) on top of GTD111, showed an Al concentration gradient in the bond coat starting at 850 °C for 250 h, which intensified with increased duration and temperature. The decrease in Al concentration in the bond coat and the growth of TGO are due to the dissolution of β-NiAl and subsequent Al diffusion to the Al₂O₃ TGO. Full article

Mechanical activation significantly enhances the leaching of chalcopyrite, a process that is fundamentally electrochemical in nature. Thus, a comprehensive understanding of its impact on the electrochemical behavior of chalcopyrite in leaching systems is crucial. This study examines the effect of mechanical activation on the electrochemical and semiconductor properties of chalcopyrite in H₂SO₄ solutions containing Fe²⁺ or/and Fe³⁺ at pH = 1.5. Mechanical activation was carried out using a planetary ball mill at 700 rpm for durations ranging from 0 to 2.5 h to reduce particle size and induce lattice distortion, thereby increasing its electrochemical activity. In iron-containing electrolytes, mechanically activated chalcopyrite is more readily reduced, releasing Fe²⁺ and leading to a higher surface concentration of Fe²⁺, which consequently increases the diffusion coefficient at the solid–liquid interface. Mott–Schottky analysis revealed a decrease in flat band potentials (from 261.7 mV to 131.2 mV in 0.1 mol/L Fe³⁺ after 1.0 h of activation) and an elevation in Fermi levels. As a result, mechanical activation markedly accelerates the corrosion rate of chalcopyrite in ferric solutions—the corrosion current increased from 40.27 µA to 70.71 µA in 0.1 mol/L Fe³⁺ after 1.0 h of activation. These findings provide valuable insights for developing strategies to enhance mineral dissolution, and advance the hydrometallurgical processing of chalcopyrite. Full article

This study examined the leaching behavior of copper and iron from a sphalerite concentrate in sulfuric acid utilizing an ensemble MnO₂–KI oxidizing system. The temperature was shown to significantly influence the leaching kinetics, with the efficiency notably improving between 40 °C and 80 °C. The introduction of KI affected the balance between sulfur passivation and oxidant availability, facilitating increased leaching efficiencies. At 3 wt% KI, maximum recoveries of 82.1% Cu and 85.3% Fe were achieved, which indicates a notable decrease in surface passivation. Kinetic study analysis revealed low activation energies of 28.90 kJ mol⁻¹ for copper and 18.94 kJ mol⁻¹ for iron, indicating that both processes proceed readily at moderate temperature regimes. Despite being diffusion-controlled, the mechanisms of dissolution are different: iron leaching is more complicated, involving pyrite oxidation, sulfur layer formation, transformation to marcasite, and ultimately iron (III) release, whereas copper leaching involves direct interaction of chalcopyrite with the oxidants, similar to the behavior of sphalerite. Full article

Coalbed methane (CBM), mainly composed of methane (CH₄) and carbon dioxide (CO₂), has attracted increasing attention due to its dual significance as a clean energy resource and its role in greenhouse gas management. This research systematically examines the adsorption, desorption, diffusion, and bubble evolution dynamics of methane (CH₄) and carbon dioxide (CO₂) in graphene nanopores with diameters of 4 nm, 6 nm, and 8 nm by molecular dynamics simulations. Radial distribution function (RDF) analyses reveal strong solvation of both gases by water, with CO₂ exhibiting slightly stronger interactions. Adsorption and desorption dynamics indicate that CO₂ molecules display shorter residence times on the graphene surface (0.044–0.057 ns) compared with CH₄ (0.055–0.062 ns), reflecting faster surface exchange. Gas-phase molecular number analysis demonstrates that CH₄ accumulates more significantly in the vapor phase, while CO₂ is more prone to adsorption and re-dissolution. Mean square displacement (MSD) results confirm enhanced molecular mobility in larger pores, with CH₄ showing greater overall diffusivity. Structural evolution of the 8 nm system highlights asymmetric bubble dynamics, where large bubbles merge with the upper adsorption layer to form a thicker layer, while smaller bubbles contribute to a thinner layer near the lower surface. CH₄ and CO₂ follow similar pathways, though CO₂ diffuses farther post-desorption due to its weaker surface retention. These results provide fundamental insights into confinement-dependent gas behavior in graphene systems, offering guidance for gas separation and storage applications. Full article

Chemical mixing of different types of magma, such as basaltic magma and silica-rich, hydrous magma, often triggers volcanic eruptions. However, the kinetics, mechanisms, and rates of sulfide dissolution reactions in hydrous melts are currently unknown, despite the fact that these reactions can influence the sulfur budget in the crust and mantle. I experimentally model dissolution of pyrrhotite minerals in hydrous rhyolite melt at conditions corresponding to the sulfate–sulfide transition field at 1 GPa pressure. The reaction results in the production of FeO, SO₄²⁻, H₂, H₂S and di- and tri-sulfur radical ions, (S₂⁻ or S₃⁻) in fluid/melt. The calculated sulfur diffusion coefficient implies extremely fast sulfur diffusion in the hydrous hybrid melt. The production of S-rich magma is controlled by the fastest-ever-recorded chemical diffusion of sulfur in the form of S₂⁻ or S₃⁻ in hybrid magma under sulfate-sulfide transition conditions. I demonstrate that such dissolution reactions can be responsible for triggering explosive volcanic eruptions (e.g., the 1991 Mount Pinatubo eruption) in volcanic arc settings. The sulfide dissolution reaction can also promote the production of chalcophile metal (sulfur-loving Au, Cu and Pt) ore deposits associated with the formation of volcanic arcs. Full article

The suspension arm is a crucial connecting component in the automotive powertrain system, required to withstand various working condition loads, thus necessitating high mechanical performance. With the continuous development of forming processes, the forming method of suspension arms has gradually shifted from traditional gravity casting to squeeze casting. Along with the demand for automotive lightweighting, there is an urgent need for lightweight requirements in suspension arm components. This study employs a multi-condition topology optimization method, incorporating the forming requirements of the squeeze casting process, to conduct lightweight design of a certain mounting bracket. The filling and solidification processes were numerically simulated using Anycasting, followed by mechanical property testing and microstructure analysis of the product. The results revealed that the topology-optimized suspension arm met the strength and stiffness requirements under all working conditions, with a mass reduction of approximately 54.7% compared to the pre-optimized version. Based on the forming process analysis of the suspension arm, the design of its squeeze casting mold was completed. Using AnyCasting software (AnyCasting 6.7), numerical simulations of the filling and solidification processes of the suspension arm were conducted. Combined with theoretical calculations, the forming process parameters for the suspension arm were finally determined as follows: extrusion speed of 15 cm/s-10 cm/s-5 cm/s (multi-stage speed), pouring temperature of 690 °C, mold temperature of 250 °C, extrusion pressure of 81.4 MPa, and holding time of 45 s. Through T6 heat treatment, the tensile strength, yield strength, and elongation after fracture of the suspension arm reached 326.05 MPa, 276.87 MPa, and 9.68%, respectively. Metallographic analysis showed that the eutectic silicon in the T6 heat-treated specimens was primarily spherical in shape, uniformly distributed without significant clustering. The reason for this difference may be that heat treatment affects the boundary dissolution degree of alloying elements. For eutectic Al-Si alloys, the boundary dissolution and diffusion of alloying elements are accelerated, which is beneficial for improving the mechanical properties of the alloy. Finally, in order to quantitatively analyze the microstructural properties of the material after heat treatment, analyses of secondary dendrite arm spacing and porosity were conducted, leading to the conclusion that the microstructure after heat treatment is more uniform and dense. Full article

The stress corrosion cracking (SCC) susceptibility of 2195-T8 Al-Li alloy in N₂O₄ medium was evaluated using slow strain rate testing (SSRT). The electrochemical corrosion behavior and morphological evolution of the alloy under different conditions were further examined through potentiodynamic polarization measurements. The results indicate that with the increase in electrochemical corrosion rate, the corrosion morphology of the alloy extends from localized pitting and intergranular corrosion to severe exfoliation corrosion. In the N₂O₄ medium, the alloy exhibits significant susceptibility to SCC at tensile rates of ε ≥ 5 × 10⁻⁶ s⁻¹. However, when strained at ε = 10⁻⁶ s⁻¹, a sudden increase in I_SCC is observed accompanied by a transition to brittle intergranular fracture mediated by anodic dissolution. At the same stretch rate (ε = 10⁻⁶ s⁻¹), the susceptibility to SCC of the alloy in N₂O₄ medium increased with higher water content ω(H₂O). This trend is attributed to enhanced generation of HNO₃ and HNO₂, as well as increased diffusion of hydrogen—produced by the cathodic reaction—to the crack tip. The synergistic interaction between anodic dissolution and hydrogen embrittlement ultimately promotes the initiation and propagation of SCC in the alloy. Full article

In the alkaline process for sodium stannate preparation, the oxidative dissolution of tin in the NaOH-H₂O₂ system originates from a spontaneous electrochemical reaction. This study elucidates the mechanism of ultrasound-enhanced tin dissolution in NaOH/H₂O₂ solutions from an electrochemical perspective, with particular emphasis on the tripartite regulatory effects of ultrasound on mass transfer, passivation suppression, and reaction pathway modulation. Electrochemical analysis indicates that ultrasound enhances mass transfer by disrupting the diffusion boundary layer, delays passivation, accelerates the exfoliation of the passive layer, and generates hydroxyl radicals that lower cathodic activation barriers. Under the action of 30 W ultrasound, the apparent diffusion coefficient of the solution increases and the passivation process of the tin sheet is delayed (the oxidation peak potential shift changes from −0.76 V to −0.70 V). After the passive layer is exfoliated by ultrasound, the charge transfer resistance decreases by 85.8% (from 8.09 ± 0.01 Ω to 1.15 ± 0.01 Ω). Ultrasound effectively overcomes the kinetic limitations imposed by the passivation layer through a triple synergistic mechanism involving mass transfer enhancement, passivation inhibition, and -OH path regulation. Full article

To address the challenge of low iron extraction efficiency from boiling furnace pyrite cinder (BPC), a significant secondary iron resource posing environmental risks due to massive stockpiling in China, this study investigated the kinetics and reactivity regulation of an oxalic acid-sulfuric acid hybrid leaching system to overcome the inertness and diffusion barriers of hematite. Single-factor experiments and Response Surface Methodology (RSM) optimization were employed to determine optimal leaching parameters (time, temperature, liquid–solid ratio, H₂SO₄ concentration) under constant stirring (400 r/min) and BPC–oxalic acid ratio (50:1). Shrinking core kinetic modeling, complemented by SEM-EDS/XRD residue characterization, elucidated the dissolution mechanism. Results showed a maximum iron leaching rate of 94.7% at 90 °C, 40 wt% H₂SO₄, an L/S ratio of 5 mL/g, and a time of 7 h. Kinetics transitioned from liquid-film diffusion control (Ea = 76.9 kJ/mol) below 70 °C to mixed interfacial reaction/internal diffusion control (Ea = 32.4 kJ/mol) above 80 °C. Highly concentrated acid conditions (50% H₂SO₄) reduced efficiency by >20% due to oxalate protonation, CaSO₄ pore occlusion, and increased viscosity. RSM confirmed temperature-dominated kinetics and acid concentration-governed thermodynamics, with no synergy under combined high-temperature/high-acidity conditions. This optimized process enables efficient iron recovery from refractory BPC using minimal reagent consumption. Full article

Based on molecular simulation methods, this paper constructs a molecular model of the CH₄-drilling fluid system to conduct an in-depth analysis of the microscopic dissolution behavior of CH₄ in drilling fluids. By utilizing key parameters such as molecular motion trajectories, interaction energies and solubility free energies, the mechanisms of CH₄ dissolution and diffusion are revealed. The factors influencing CH₄ solubility and their variation mechanisms are elucidated at the molecular level. Through gas solubility experiments, the variation patterns of CH₄ solubility in drilling fluids under different temperature and pressure conditions are investigated, and optimized solubility models for CH₄-drilling fluid systems are selected. The results indicate that the dissolution and diffusion behavior of CH₄ in drilling fluids can be described using free volume, interaction energy and solubility free energy, with the degree of influence ranked as follows: interaction energy > free volume > solubility free energy. The interaction and free volume of CH₄ in oil-based drilling fluids are both greater than those in water-based drilling fluids, suggesting a higher solubility of CH₄ in oil-based drilling fluids. Solubility models of CH₄ in drilling fluids under conditions of 30~120 °C and 10~60 MPa are obtained by regression. The research findings not only deepen the understanding of the dissolution and diffusion behavior of CH₄ in drilling fluids for shale gas horizontal wells, but also provide crucial parameters for establishing wellbore pressure models in managed pressure drilling. Full article

Background: Large porous particles (LPPs) offer significant potential in drug delivery due to their porous structure and suitable particle size and shape, which can improve powder dispersibility and control drug release. Methods: In this study, sustained-release large porous microparticles of mannitol, PVA, and diclofenac sodium (MPDs) were developed using a spray drying technique. The influence of PVA co-spray drying and its concentration (0–40%) on the characteristics of the spray-dried particles was investigated. Results: Co-spray drying with PVA enhanced particle morphology, producing MPDs with a spherical shape and smooth surface, which minimized particle adhesion. This improvement correlated with a low Carr’s Index value (17.56%), indicating favorable particle dispersibility and aerosol performance. The large geometric diameter (>5 μm) of the MPDs, coupled with their low bulk density (<0.1 g/cm³), suggested potential for inhalation use. FTIR, XRD, and DSC analyses revealed that PVA altered the polymorphic form of mannitol, with the MPDs exhibiting a mixture of the α and δ forms. In vitro dissolution tests demonstrated that PVA co-spray drying effectively prolonged drug release, with the formulation containing 40% PVA (MPD-4) showing an optimal release profile. The release kinetics followed first-order Higuchi models, suggesting drug release occurred through a matrix diffusion mechanism facilitated by the porous structure. Conclusions: These findings demonstrate the feasibility of engineering large porous microparticles with tailored release characteristics and physicochemical properties suitable for further development in inhalable or other controlled-release dosage forms. Full article

Hydrate-based CO₂ sequestration is considered one of the most promising methods in the field of carbon capture, utilization, and storage. The abundant fractured environments in marine sediments provide an ideal setting for the sequestration of CO₂ hydrate. Investigating the kinetics and morphological characteristics of CO₂ hydrate formation within fractures is a critical prerequisite for achieving efficient and safe CO₂ sequestration using hydrate technology in subsea environments. Based on the aforementioned considerations, the kinetic experiments on the formation, dissociation, and reformation of CO₂ hydrates were conducted using a high-pressure visualization experimental system in this study. The kinetic behaviors and morphological characteristics of CO₂ hydrates within sandstone fractures were comprehensively investigated. Particular emphasis was placed on analyzing the effects of fracture width, type, and surface roughness on the processes of hydrate formation, dissociation, and reformation. The experimental results indicate the following: (1) At a formation pressure of 2.9 MPa, the 10 mm width fracture exhibited the shortest induction time, the longest formation duration, and the highest hydrate yield (approximately 0.52 mol) compared to the other two fracture widths. The formed CO₂ hydrates exhibited a smooth, thin-walled morphology. (2) In X-type fractures, the formation of CO₂ hydrates was characterized by concurrent induction and dissolution processes. Compared to I-type fractures, the hydrate formation process in X-type fractures exhibited shorter formation durations and generally lower hydrate yields. (3) An increase in fracture roughness enhances the number of nucleation sites for the formation of hydrates. In both fracture types (I-type and X-type), the induction time for CO₂ hydrate formation was nearly negligible. However, a significant difference in the trend of formation duration was observed under varying roughness conditions. (4) Hydrate dissociation follows a diffusion-controlled mechanism, progressing from the fracture walls towards the interior. The maximum gas production was achieved in the 10 mm-width fracture, reaching 0.24 mol, indicating optimal heat and mass transfer conditions under this configuration. (5) During the reformation process, the induction time was significantly shortened due to the “memory effect.” However, the hydrate yield after the reformation process remained consistently lower than that of the first formation, which is primarily attributed to the high solubility of CO₂ in the aqueous phase. Full article

Apigenin (AP) is a natural flavonoid with senomorphic potential and neuroprotective action; however, poor aqueous solubility (<1 μg/mL) limits its bioavailability and therapeutic use. Therefore, the aim of this study was to obtain an amorphous dispersion of AP and evaluate its biological properties. Screening of AP solubilization capabilities under supercritical carbon dioxide processing conditions showed that the system with Soluplus (SOL) achieved the greatest improvement in AP dissolution (6455.4 ± 27.2 μg/mL). Using optimized process parameters (50 °C, 6500 PSI), the AP solubility increased to 8050.2 ± 35.1 μg/mL. X-ray powder diffraction (XRPD) confirmed amorphization, aligning with improved dissolution of AP in both acidic and neutral pH media. As a result, using the PAMPA model, an improvement in AP penetration through membranes simulating gastrointestinal and blood–brain barriers was demonstrated. The significant stability of the obtained amorphous AP dispersion (12 months at room conditions) was associated with stabilizing AP–solubilizer intermolecular interactions, mainly expressed as the shifts in the bands of AP in the range of 1018–1269 cm⁻¹ observed in ATR-FT-IR spectra. Chromatographic analysis confirmed the lack of AP decomposition immediately after the preparation of the amorphous dispersion, as well as after 12 months. As expected, the improvement of AP solubility is correlated with better biological activity assessed in selected in vitro tests such as antioxidant properties (2,2-diphenyl-1-picrylhydrazyl (DPPH), 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS), and cupric ion reducing antioxidant capacity (CUPRAC) assays) and anticholinesterase inhibition capabilities (AChE and BChE assays). The effect of the studies on improving AP solubility under supercritical carbon dioxide processing conditions is obtaining a stable amorphous AP dispersion (up to 12 months). Regardless of the pH of the media, an improvement in AP dissolution and penetration, conditioned by the passive diffusion process, through biological membranes was noted. Moreover, a more efficient antioxidant and neuroprotective effect of AP in the developed amorphous dispersion can also be suggested. Full article