Search Results (1,246)

Natural gas hydrates, with their vast reserves and high gas storage density, have emerged as a highly promising alternative energy source and technology for gas storage and transportation. Wettability, as a core surface property of porous media, directly influences hydrate nucleation, growth, occurrence morphology, and flow behavior. In this study, quartz sand with varying surface properties was prepared with the octyltrimethoxysilane (OTMS) silane coupling agent via surface chemical reactions. The methane hydrate (MH) equilibrium conditions as well as the formation kinetics in silica sand were measured, and the mechanism and potential of the surface modification for enhancing methane hydrate storage capacity were analyzed. The experimental results indicate that surface modification of quartz sand has no significant effect on the MH equilibrium condition. Hydrophobic modification of quartz sand provides more gas–liquid interfaces, increases the contact area, and thereby significantly enhances mass transfer under high-water-saturation conditions and accelerates the MH formation rate. However, excessively high surface hydrophobicity may reduce the effective gas–liquid interfacial area and limit the overall hydrate formation rate. Due to the influences of the hydrate distribution and aggregation, as well as gas diffusion on hydrate formation, the effect of the initial formation pressure on MH formation is only observed during the early stages of MH formation, while the temperature effect is less pronounced than that of formation pressure. It is suggested to further consider combining stirring with continuous gas injection to enhance gas–liquid flow and improve gas–liquid contact, thereby increasing the formation rate of hydrates. Full article

The presence of ferrite in 316 austenitic stainless steel affects its magnetic permeability, and the secondary precipitates formed by ferrite decomposition can further degrade the corrosion resistance, limiting its application in industries such as nuclear power and medical devices. In previous studies, the characteristics of ferrite and precipitates in several 316 stainless steel continuous-casting billet samples with different Ni contents were analyzed. In this work, remelting experiments were further conducted on several 316L stainless steels with different Ni contents using a tube furnace; according to the Ni content, they are designated as L-316, M-316, and H-316 stainless steels. Metallographic analysis and electron back-scattered diffraction (EBSD) characterization were employed. The effects of Ni content and cooling rate on the microstructure of 316 stainless steel were systematically investigated. The results show that for the L-316 stainless steel, the ferrite morphologies in water-cooled, oil-cooled, air-cooled, and furnace-cooled samples change successively as follows: skeletal and lath-like, clustered network, lath-like and clustered network, and short rod-like. For the M-316 stainless steel remelted samples, the ferrite morphologies are network and skeletal, network and short rod-like, semi-network and short rod-like, and semi-network, respectively. The solidification modes of the L-316, M-316, and H-316 stainless steel remelted samples are FA, FA, and AF modes, respectively. Increasing Ni content reduces the ferrite content under all cooling conditions. When the Ni content increases from 10% to 12.17%, the ferrite content decreases significantly, with a greater reduction at higher cooling rates; when the Ni content further increases to 14.25%, the decrease in ferrite content slows down, indicating that after Ni content reaches a certain level, its inhibiting effect on ferrite formation weakens. The effect of cooling rate on ferrite content depends on the solidification mode: in the FA mode, slow cooling promotes diffusional transformation of ferrite to austenite, so the ferrite content decreases with decreasing cooling rate—for L-316 stainless steel, the ferrite content drops from 22.44% in the water-cooled sample to 2.71% in the furnace-cooled sample. In the AF mode, slow cooling favors the enrichment of elements at grain boundaries and promotes ferrite nucleation and growth; the overall trend of ferrite content increases as the cooling rate decreases. For the H-316 stainless steel specimens, the ferrite content is similar between water-cooled specimens (0.36%) and oil-cooled specimens (0.26%); for air-cooled specimens, the ferrite content increases significantly to 1.49%; and finally, it reaches 1.94% for the furnace-cooled specimen. Regarding secondary precipitates, the phase constituents of the L-316 stainless steel specimens after water cooling, oil cooling, and air cooling consist of an austenite matrix and ferrite, with a secondary precipitated Chi phase forming only under furnace cooling conditions. For the M-316 stainless steel, the Sigma phase and Chi phase begin to form under oil cooling conditions, and the Sigma phase also precipitates in the oil-cooled specimens of the H-316 stainless steel. In the air-cooled and furnace-cooled specimens of both M-316 and H-316 stainless steels, the secondary precipitated phase is the Sigma phase. All three types of water-cooled stainless steel specimens exhibited no secondary precipitate phase; increasing the cooling rate suppresses atomic diffusion, thereby reducing the precipitation of Chi phase and Sigma phase; however, a higher Ni content shifts the solidification mode toward the AF mode, making secondary precipitates more prone to form. Full article

Aiming at the sensitivity of the droplet nucleation rate in the wet steam non-equilibrium condensation flow model to the value of the surface tension correction coefficient (NBTF), and to avoid the subjectivity and uncertainty in its selection, this study calibrated the quantitative relationship between the optimal NBTF values and the inlet pressure and inlet superheat degree across 81 operating conditions. This was achieved by comparing numerical simulations with experimental data from multiple sets of wet steam condensation flow experiments documented in the literature. Subsequently, a bivariate regression equation capable of directly predicting NBTF was established using the mathematical method of statistical regression analysis. The reliability of the equation was verified using the results of an independent experiment (the Dykas cascade experiment). Furthermore, taking the last stage of a certain marine steam turbine as the research object, the established equation was applied to conduct a numerical study of wet steam non-equilibrium condensation flow. The influence of the NBTF value on the nucleation process, droplet distribution, and flow loss was quantitatively analyzed. The results indicate that within a specific range (inlet pressure 15~280 kPa, inlet superheat degree −12~50 K), NBTF shows a significant positive correlation with inlet pressure and a significant negative correlation with inlet superheat degree. The value of NBTF directly affects the prediction results of droplet nucleation rate, particle size distribution, and condensation zone location within the last stage of the steam turbine. This research provides a data-based, reproducible prediction tool for determining the NBTF value in the numerical simulation of wet steam condensation flow and also offers a quantitative reference for the anti-water erosion design and operational optimization of the last stage of steam turbines. Full article

Microbially induced calcium carbonate precipitation (MICP) is a promising biotechnology for environmental remediation; however, the high cost of conventional chemical-grade calcium sources limits its large-scale scalability. This study evaluated the feasibility of utilizing an aqueous extract of natural attapulgite clay as a sustainable, low-cost calcium source for MICP-mediated arsenic (As) immobilization in both aqueous and soil systems. Among the tested minerals, Baiyin attapulgite (group B) exhibited the highest calcium content (62,808.94 mg kg⁻¹) and minimal toxic metal impurities, providing a favorable chemical matrix for biomineralization. At an optimal solid-to-liquid ratio of 1:10, Lysinibacillus fusiformis LF and Enterococcus LZU-1 successfully induced calcite precipitation driven by the attapulgite extract. In batch aqueous remediation experiments (20 days), the attapulgite extract significantly enhanced As removal efficiency compared to the controls; As removal rates peaked at 66.4% for strain LZU-1 (with LZ1 extract) and 65.8% for strain LF (with group B extract), drastically outperforming the standard CaCl₂ groups (31.2–37.3%) and blank controls (21.8–24.5%). Concurrently, soil incubation experiments (30 days) demonstrated that the combined application of attapulgite and MICP bacteria reduced the highly bioavailable exchangeable As fraction from 0.115 to approximately 0.03 mg kg⁻¹, while effectively driving its transformation into more stable carbonate-bound and organic-bound fractions without causing secondary soil salinization. Morphological and mechanistic analyses revealed that, compared to the well-defined euhedral crystals in the CaCl₂ control, the precipitates mediated by the clay extract exhibited distinctly irregular, defect-rich rhombohedral structures. This structural disruption was governed by the natural matrix effect of attapulgite, which simultaneously supplied dissolved Ca²⁺ and provided an abundance of fine clay fragments, calcite micro-grains, and associated amorphous Fe/Al/Mn-bearing phases. These constituents acted as physical scaffolding and heterogeneous nucleation sites that became embedded in the growing CaCO₃ lattice, driving the formation of highly reactive, defect-rich clay-calcite-arsenic composite precipitates that efficiently encapsulated arsenate. Mantel analysis further revealed that the remediation efficiency was significantly correlated with key environmental variables including Ni, V, Ca. These findings highlight the dual-system potential of natural attapulgite as an inexpensive, eco-friendly calcium alternative for sustainable MICP-based remediation of As-contaminated water and agricultural soils. Full article

To realize the remanufacturing of cast iron components, a WC-reinforced Fe-based composite powder was designed, and the WC/Fe-based composite coating was deposited on the HT250 substrate by laser cladding. The melting and dissolution mechanism of WC ceramic particles were investigated, and their influences on the microstructure, phase, microhardness, and wear resistance of the composite coatings were systematically analyzed. The results show that the WC/Fe-based composite coating achieves good metallurgical bonding with the HT250 substrate and possesses excellent forming quality. The incorporated WC particles can effectively optimize the microstructural morphology, acting as heterogeneous nucleation sites and inhibiting grain growth. As WC content increases, the grain size within the composite coating gradually refines. Moreover, partially melted WC particles release tungsten (W) and carbon (C) elements into the molten pool, promoting the in-situ generation of new hard phases, including W₂C and Fe₆W₆C. These newly formed phases, together with the residual unmelted WC particles, contribute a dispersion strengthening effect and improve the properties of the composite coatings. This effect becomes more pronounced with higher WC content. Notably, the composite coating with 20% WC exhibits a microhardness over twice that of the HT250 substrate, while its wear rate is only one-sixth that of the substrate and its corrosion resistance is much higher than that of the HT250 substrate. Full article

Poly(ethylene succinate) (PES) is a promising biodegradable polyester with excellent thermal and mechanical properties; however, slow crystallization rate has seriously restricted its widespread application. PES/talc composites at low talc contents of 0.5 to 2.0 wt% were synthesized via an in situ polymerization method in this research. The chemical structure, thermal stability, crystallization behavior, crystalline morphology, crystal structure, and tensile mechanical properties of PES/talc composites were extensively investigated with various techniques and compared with those of neat PES. Talc remarkably enhanced the crystallization behavior of PES under different crystallization conditions as an effective nucleating agent. For instance, 2 wt% talc increased the melt crystallization temperature of PES from 46.1 to 58.9 °C at a cooling rate of 5 °C/min and shortened the crystallization half time to 1.95 min from 7.69 min at 66 °C. However, talc remained the crystallization mechanism and crystal structure of PES. The nucleation mechanism of talc on the crystallization of PES was further discussed. The exact nucleation mechanism was still uncertain, which needs further investigation. The mechanical properties of PES/talc composites were dependent on the talc content. For instance, 0.5 and 1 wt% talc decreased the tensile strength values to 34.1 ± 1.9 and 33.7 ± 2.1 MPa from 44.9 ± 1.3 MPa, while the elongation at break values increased to 675.3 ± 24.8% and 560.4 ± 11.9% from 508.0 ± 13.4%, respectively, indicating an increase in toughness. Although the mechanical properties of PES/talc2.0 (2 wt% talc) were inferior to those of neat PES and the other two composites, it still displayed relatively good mechanical properties. Full article

The steep radial temperature gradients developed in UO₂ fuels during reactor operation can drive pore migration, making pore–grain boundary (GB) coupled migration an important mechanism governing microstructural evolution. Although pores are generally regarded as pinning features that hinder GB migration, the conditions under which mobile pores retard, co-migrate with, or promote GB migration remain poorly understood. In this study, we develop a phase field model coupling vapor-transport-driven pore migration and curvature-driven grain growth to investigate the coupled migration behavior between intergranular mobile pores and GBs. The simulations first focus on an idealized source-term-free system to isolate the effect of pore–GB migration coupling from irradiation-induced pore generation and growth. The results show that the effect of pores on GB migration depends on the relative migration rate of pores and GBs, which is determined by both the pore-to-GB mobility ratio and the corresponding driving-force ratio. When pores migrate more slowly than GBs, they retard GB migration and exhibit an effective pinning effect. In contrast, sufficiently mobile pores can co-migrate with GBs and promote apparent GB migration when the pore migration rate exceeds that of the GBs. Furthermore, to illustrate the regulating effect of pores on GB migration in UO₂ under a temperature gradient, we perform additional simulations under continuous irradiation, in which pores nucleate spontaneously, migrate along the temperature gradient, and interact with GBs, in agreement with experimental observations. Based on the simulated GB migration behavior, we construct a regime map that distinguishes pinning/retardation, weak interaction, and pore-assisted migration regimes. This work provides a mechanistic phase field interpretation of pore–GB coupled migration and offers insight into microstructural evolution in porous oxide fuel materials. Full article

This study was conducted to determine the optimal mineralization enhancement period for recycled aggregates, and to elucidate the mechanisms underlying the mineralization enhancement of recycled aggregates and the self-healing of concrete cracks. Microbial-induced calcium carbonate precipitation enables the self-healing of concrete cracks: microbial carriers can effectively increase the survival rate of microorganisms within the concrete matrix, thereby enhancing the self-healing performance of the concrete. However, current carriers suffer from poor mechanical properties, poor compatibility with cement-based materials, and high costs. This study proposed a crack-self-healing concrete based on a mixed culture of microorganisms immobilized in recycled aggregate, and investigated the effects of the time of recycled aggregate incorporation on the concrete’s compressive strength and self-healing performance. The results showed that the optimal adsorption and incubation times for the recycled aggregates were 15 min and 9 days, respectively. Following mineralization and reinforcement, the water absorption and crushing index of the recycled aggregates was 11.4% and 20.4%, respectively. Moreover, the precipitates at the concrete cracks were in the form of regular cubes and clusters, and the crystals were calcite and aragonite. Small amounts of phosphorus were detected, originating from extracellular polymers produced by microbial metabolism, indicating that the organic matrix was involved in the crystal nucleation and growth processes. The compressive strength of the concrete increased by 35%. After repair and curing, the crack healing rate of the concrete reinforced with microorganisms immobilized on the recycled aggregates reached 70%. Full article

Diffusion solidification is an effective method to produce non-dendritic microstructures and reduce casting defects in magnesium alloys. However, the influence of precursor alloy superheat on the solidification behavior and the resulting microstructure remains insufficiently understood. In this study, pure magnesium was used as the high thermal mass (HTM) alloy and three Mg-Al-Zn alloys with different aluminum and zinc contents were used as the low thermal mass (LTM) alloys. The effects of superheat on grain morphology, solute diffusion, and constitutional supercooling were investigated through a combination of experimental casting and numerical simulation using Ansys Fluent and Matlab. The results show that the solidified interface consists of five distinct regions, including two base metals, two transition zones, and a central controlled diffusion solidification zone. A higher superheat of the HTM alloy relative to the LTM alloy promotes a wider transition zone and finer globular grains, whereas equal or lower superheat leads to columnar or rosette structures. The Mg-30 wt.%Al-3.5 wt.%Zn alloy with moderate aluminum content produces fine globular grains due to a thinner constitutional supercooling layer and a higher degree of supercooling, which suppresses grain growth and increases nucleation rate. In contrast, the Mg-55 wt.%Al-6.5 wt.%Zn alloy with high aluminum content forms coarse rosette and columnar grains. Among the conditions investigated, the combination of 10 °C HTM and 5 °C LTM superheats tends to promote the formation of fine equiaxed grains. Increasing superheat above this range reduces supercooling and coarsens grains, while decreasing superheat inhibits interface diffusion and promotes solute segregation. The findings provide a theoretical basis for designing precursor alloy compositions and superheat parameters in controlled diffusion solidification of magnesium alloys. Full article

This study employed the Gurson–Tvergaard–Needleman (GTN) damage model to evaluate the ductile damage behavior of silicon carbide (SiC) reinforced aluminum matrix composites (SiC/Al composites). Uniaxial tensile experiments were conducted at room temperature under controlled strain rates ranging from 0.001 to 0.009 s⁻¹. Fracture surface analysis using scanning electron microscopy (SEM) revealed predominantly brittle cleavage features at lower strain rates, with an increasing presence of dimples associated with microvoid coalescence at the highest strain rate, highlighting a strain-rate-dependent fracture mechanism. GTN parameters were determined using finite element simulations combined with response surface methodology (RSM). The results demonstrated that higher strain rates accelerate void nucleation and growth, leading to faster damage evolution. Numerical simulations validated the identified GTN parameters, showing strong agreement with experimental observations. This work provides critical insights into strain-rate effects on damage evolution in SiC/Al composites, supporting their application in high-strain-rate environments. Full article

The structure–activity relationship of three oxyphosphonate inhibitors differing in heteroatom type (C, N, S) was examined to clarify their influence on the pitting corrosion resistance of ferritic–martensitic steel EP-450 in chloride media. Gravimetric tests in 10% FeCl₃, supported by surface microscopy and adsorption analysis, showed that EP-450 is highly susceptible to localized attack, with pits nucleating preferentially at carbide-enriched, chromium-depleted regions. Addition of dimethyl(1-hydroxycyclohexyl)phosphonate reduced the corrosion rate from 49 to 33 mm/year at 2.0 g/L, corresponding to ≈33% protection, while the nitrogen-containing dimethyl[1-(2-ethoxyethyl)-4-hydroxypiperidin-4-yl]phosphonate produced the largest decrease in mass loss, exceeding a 55% reduction under identical conditions. The sulfur-bearing dimethyl(4-hydroxytetrahydro-2H-thiopyran-4-yl)phosphonate afforded an intermediate effect. Adsorption analysis for the cyclohexyl derivative suggested mixed physisorption–chemisorption with limited surface coverage, while heteroatom substitution (N or S) is consistent with a change in adsorption configuration and interfacial packing that can yield a more compact protective layer. The observed inhibition efficiency increased in the sequence C < S < N, which is interpreted empirically in terms of heteroatom-dependent adsorption geometry and film integrity rather than conjugation-driven activation of the P=O group. Full article

A Laval nozzle is a pivotal component of supersonic separation technology for dehydration, but its performance is constrained by low separation efficiency due to intractable conflicts between droplet nucleation and growth rates. To address this issue, this work for the first time applied the Foelsch-MOC method to design an expansion section with a first-order differentiable and second-order continuous profile. A numerical model for pure water vapor condensation based on the ideal gas equation of state (EOS) was then established to optimize nozzle structures for droplet growth. Major findings revealed that the droplet radius of the Foelsch-MOC nozzle was 30.5% higher than that of the conical nozzle, while its outlet liquid mass fraction was 5.8% lower. The liquefaction capacity was found to increase first and then decrease with the expansion coefficient, peaking at 0.5. Moreover, increasing the axis shift from 9.3 mm to 25 mm promoted the outlet liquid mass fraction by 1.2% and decreased the droplet radius by 9.3%, thereby improving liquefaction capacity. These results highlight the droplet growth superiority of the novel expansion profile, providing a valuable guideline for designing nozzles that simultaneously ensure liquefaction efficiency and facilitate droplet development. Full article

The macroscopic mechanical properties of near-β titanium alloys depend inherently on their complex microstructural morphologies and phase transformation kinetics. This study investigates the deformation behavior of a lamellar Ti-55531 alloy during isothermal compression and in situ tensile testing. Pronounced strain rate sensitivity dictates the deformation of the lamellar microstructure. Low strain rate deformation (0.001 s⁻¹) induces dynamic recovery and recrystallization, which in turn drive α-lamellae fragmentation and the nucleation of new α phase during compression. The α precipitation is governed by a strict Burgers orientation relationship (BOR), but extensive plastic deformation may lead to the breakdown of the BOR. During tension, continuous slip transfer between adjacent phases is critically restricted by α/β interfacial thickness. As plastic strain accumulates, lath-like, V-shaped, and acicular α phases precipitate concurrently within β grains, creating a complex α microstructure. Full article

Protein crystal nucleation remains difficult to predict and control and is still a critical issue in structural biology, protein crystal formulations, and crystal engineering. Heterogeneous nucleants can regulate protein crystallization by providing solid interfaces, enriching protein molecules, and stabilizing prenucleation aggregates; however, their dominant action stage, particle-size effect, and interfacial interaction mechanism remain unclear. In this study, hen egg white lysozyme (HEWL) was selected as a model protein, and silica nanoparticles (SNPs) with average diameters of 80, 120, and 200 nm were prepared using the modified Stöber method. Under a constant total particle surface area, the effects of SNPs on HEWL crystallization, prenucleation aggregation, interfacial adsorption, and subsequent crystal growth were systematically investigated. The results showed that, under 30 mg·mL⁻¹ HEWL and 0.6 M NaCl conditions, all SNPs shortened the apparent induction time, with 200 nm SNPs showing the strongest effect. In contrast, 80 nm SNPs produced the largest crystal size at the fixed observation time of 72 h, suggesting that crystal size within a fixed incubation period is jointly affected by nucleation rate, nucleus number, local solute consumption, and subsequent crystal growth. Under low protein concentration and low NaCl concentration conditions, SNPs promoted crystal formation in systems with weak spontaneous nucleation. Zeta potential, UV-Vis, fluorescence, FT-IR, CD, and DLS results suggested that SNPs interacted with HEWL at the interface and promoted apparent aggregation behavior, whereas polarized optical microscopy indicated no detectable influence on the later linear growth of visible crystals. These results suggest that SNPs mainly affect processes before visible crystal formation and provide insight into their application as heterogeneous nucleants for protein crystallization. Full article

In the process of offshore natural gas extraction, natural gas hydrates tend to form within the wellbore. This secondary hydrate formation can potentially cause severe blockages. Current prediction methods primarily rely on temperature–pressure curves, which often overlook the critical effects of high-velocity fluid flow, particularly the impact and drag forces acting on the hydrates. To address this limitation, this study proposes a novel risk prediction model that innovatively decomposes the hydrate-induced wellbore blockage into three distinct stages: implantation, scour, and fracture. Each stage is mathematically evaluated using a dedicated analytical model: the impulse equation for implantation, the negative pressure suction equation for scour, and the hydrate fracture toughness equation for fracture. A region is deemed at risk of hydrate blockage only when all three stage conditions are simultaneously satisfied. Sensitivity analysis focusing on four key parameters—hydrate particle size, temperature, gas flow rate, and impact angle—revealed that increasing either the hydrate particle size during nucleation or the extraction temperature significantly reduces the risk of secondary hydrate blockage. Moreover, a typical case study demonstrated that the application of this three-stage model considerably narrows and refines the predicted risk area compared to traditional thermodynamic models. These results provide a solid theoretical foundation for accurately predicting secondary hydrate blockage risks and offer targeted strategies for flow assurance and mitigation in critical wellbore sections. Full article