Search Results (2,752)

To investigate the flow-field characteristics of a submerged pre-mixed abrasive water jet impinging on a wall, a physical model of the conical–cylindrical nozzle and computation domain of a submerged pre-mixed abrasive-water-jet flow field were established. Based on the software of FLUENT 2022R2, numerical simulation of the solid–liquid two-phase flow characteristics of the submerged pre-mixed abrasive water jet impinging on a wall was conducted using the DPM particle trajectory model and the realizable $k–\epsilon$ turbulence model. The simulation results indicate that a “water cushion layer” forms when the submerged pre-mixed abrasive water jet impinges on a wall. Tilting the nozzle appropriately facilitates the rapid dispersion of water and abrasive particles, which is beneficial for cutting. The axial-jet velocity increases rapidly in the convergent section of the nozzle, continues to accelerate over a certain distance after entering the cylindrical section, reaches its maximum value inside the nozzle, and then decelerates to a steady value before exiting the nozzle. In addition, the standoff distance has minimal impact on the flow-field characteristic inside the nozzle. When impinging on a wall surface, rapid decay of axial-jet velocity generates significant stagnation pressure. The stagnation pressure decreases with increasing standoff distance for different standoff-distance models. Considering the effects of standoff distance on jet velocity and abrasive particle dynamics, a standoff distance of 5 mm is determined to be optimal for submerged pre-mixed abrasive-water-jet pipe-cutting operations. When the submergence depth is less than 100 m, its effect on the flow-field characteristics of a submerged pre-mixed abrasive water jet impinging on a wall surface remains minimal. For underwater oil pipelines operating at depths not exceeding 100 m, the influence of submergence depth can be disregarded during cutting operations. Full article

Interactions of ZnO nanoplates with water are crucial in determining its structure and performance of the catalyst, yet the details for these processes remain missing due to the lack of an effective detection method that provides resolution at the atomic level. Here, ¹⁷O solid-state NMR spectroscopy is applied to investigate the interactions and the associated stabilization mechanisms for the polar surface of ZnO nanoplates. It shows that the specific O sites (around Zn vacancy) on the polar surface also contribute to the ¹⁷O NMR signal at −18.8 ppm. The observed trends in both ¹⁷O and ¹H spectra after exposing to water vapor further support the assignment of this ¹⁷O high-frequency signal (−18.8 ppm). In addition, the dissociation of water at defective sites of polar surfaces is evidenced, which leads to the generation of OH groups on both (000$\overline{1}$)-O and (0001)-Zn surfaces. The generated OH species obviously improves the dispersity of ZnO nanocrystals, as well as the stability of polar facets by significant electrostatic repulsion interactions. This study will provide insight into the adsorption properties of water on polar facets and the related stabilization mechanisms of the polar surface in nanocrystals. Full article

Three-dimensional-printed concrete (3DPC) is an additive manufacturing technology that forms 3D solids via layer-by-layer printing based on 3D model data, but it consumes large amounts of river sand (RS) and has poor frost resistance. To address these issues, this study used industrial waste electric arc furnace slag (EAFS) as an aggregate at 0–100% replacement ratios to test the workability, mechanical properties, frost resistance, and microstructures of 3DPC specimens. The results show that EAFS improves mortar flowability and extends the printing window, but full replacement increases slump and reduces constructability. The stress dispersion and dense packing effects of EAFS ensure excellent mechanical properties of specimens before and after freeze–thaw cycles. At an 80% EAFS replacement ratio, compressive and flexural strengths increase by 2.52%/13.8% and 10.6%/18.2%, respectively; after freeze–thaw cycles, the specimens exhibit the best frost resistance. The interfacial transition zone between EAFS and cement matrix is only 2 μm, with 1.8% lower porosity and 20.14% fewer harmful pores than the 100% RS specimen after freeze–thaw cycles. In conclusion, 80% EAFS replacement balances 3DPC performance and solid waste utilization, providing important references for EAFS’s safe application in 3DPC and its performance improvement mechanism. Full article

Acrylic solid surface composites made of poly (methyl methacrylate) (PMMA) and aluminum trihydrate, Al(OH)₃ (ATH) are widely used in furniture and interior applications. However, independent brand comparative data, especially on density-normalized (“specific”) properties, remain limited. This study quantifies the flexural response of 11 commercial sheets (6, 8, and 12 mm, including one translucent) under ISO 178 three-point bending and evaluates the effects of heating and cooling relevant to thermoforming. The density is concentrated in the range 1680–1748 kg/m³ (weighted mean of 1712 kg/m³). The flexural strength ranged between 51 and 79 MPa, divided into three groups—high (76–79 MPa), medium (63–67 MPa), and low (51–56 MPa) levels, while the modulus ranged between 7700 and 9400 MPa with a narrow dispersion. The strength showed no significant correlation with density, while the modulus increased with density, indicating that stiffness is composition-dominated, while strength is influenced by factors related to microstructural defects/particle boundaries. Heating at 160 °C and subsequent cooling have a significant influence on flexural strength and strain. Flexural strength increased by an average of approximately 7%, and flexural strain increased by approximately 12%, while the modulus remained virtually unchanged (within ±0.5%); additionally, shock cooling did not bring any benefits. The density-normalized parameters (σ/ρ, E/ρ) reflected these trends, allowing for a more accurate comparison when limited by mass or deformation. Overall, the results are broadly consistent with manufacturers’ declarations and demonstrate that thermoforming-relevant heating at 160 °C, followed by cooling, can be used not only to improve formability but also to modestly increase flexural strength and strain without compromising stiffness. Full article

This study employed atmospheric plasma spraying (APS) technology to successfully fabricate CoCrFeNiMo high-entropy alloy (HEA) coatings under varying spraying currents and systematically investigated the effects of the spraying current on the microstructure, mechanical properties, and tribological behavior of the coatings. Results showed that the material composition remained consistent across different current levels, primarily consisting of face-centered cubic (FCC) solid solution phases, FeCr₂O₄ spinel phases, and Cr-rich FCC1 phases. The FCC matrix was dispersed with spherical Cr oxide particles smaller than 30 nm in diameter, which significantly enhanced the strength of the coatings. As spraying current increased, both porosity and microhardness exhibited a non-monotonic trend—initial optimization followed by deterioration. At 500 A spraying current, the coating achieved optimal performance, with the lowest porosity (0.42%) and highest microhardness (569.8 HV). Correspondingly, this condition also yielded the best wear resistance, with stable friction coefficients and wear rates reaching 0.49 and 6.91 × 10⁻⁵ mm³/N m, respectively. Abrasion surface analysis revealed that excessively low or high currents triggered distinct wear mechanisms leading to reduced wear resistance. Full article

Unsymmetrical dimethylhydrazine (UDMH), a highly toxic rocket propellant, remains a significant environmental concern in Kazakhstan due to repeated rocket stage falls near the Baikonur Cosmodrome. This study integrates chemical analysis with stochastic contamination transport modeling to evaluate the persistence and migration of UDMH transformation products (TPs) in soils collected 15 years after the rocket crash. Vacuum-assisted headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry (Vac-HS-SPME-GC-MS) was used to determine five major TPs. Among these, pyrazine (PAN) and 1-methyl-1H-pyrazole (MPA) were consistently detected at concentrations ranging from 0.04–2.35 ng g⁻¹ and 0.06–3.48 ng g⁻¹, respectively. Stochastic simulations performed with HYDRUS-1D indicated that the long-term persistence of these compounds is mainly controlled by physical nonequilibrium transport processes, including diffusion-limited exchange, weak sorption, and slow inter-domain mass transfer, rather than by degradation. Sensitivity analysis demonstrated that low dispersivity and diffusion coefficients enhance solute retention within immobile domains, maintaining residual levels over extended periods. The results demonstrate the efficacy of combined long-term monitoring and predictive modeling frameworks for assessing contamination dynamics in rocket impact zones. Full article

This work analyzes the hydrodynamic behavior of a magnetorheological valve, considering the microscopic fluid characteristics to generate a damper force. The magnetorheological fluid is composed of ferromagnetic particles dispersed in a non-magnetic carrier fluid, whose mechanical resistance depends on the magnetic field intensity. In the absence of a magnetic field, the magnetorheological fluid behaves as a liquid whose viscosity depends on the particle volume fraction. Conversely, the presence of a magnetic field generates particle chain-like structures that inhibit fluid motion, thereby regulating flow in the control valve. The mathematical model employs the continuity and momentum equations, the Bingham model, and the boundary conditions at the solid–liquid interfaces to determine the flow field. The results show the fluid hydrodynamic response under different flow conditions depending on dimensionless parameters such as the pressure gradient, the field-independent viscosity, the yield stress, the particle volume fraction, the Bingham number, the Mason number, and the critical Mason number. For a pressure gradient of $\Gamma =-10$, the flow rate inside the valve (with particle volume fraction $\varphi =0.2$) results in ${\overline{Q}}_{T,x}=0.34$, $0.06$, and 0 when the magnetic field is 80, 120, and 160 kA m⁻¹, respectively. Likewise, when the magnetic field increases from 80 to 160 kA m⁻¹, the damping capacity increases by $88\%$ when $\varphi =0.2$ and $128\%$ when $\varphi =0.3$ compared to the Newtonian viscous damping. This work contributes to our understanding of semi-active damping devices for flow control. Full article

Heavy metal ions in herbal medicine sometimes exceed the standard limit, inducing severe and harmful problems in human health. Exploring new nanomaterials to chelate heavy metal ions and reduce their concentration in herbal decoctions could be a solution route. In this study, the nanoadsorbent poly(2-(hydroxymethyl)acrylic acid (PHMAA) was prepared via free radical polymerization and the hydrolysis method. PHMAA showed excellent dispersion in aqueous solution and self-assembled into spherical aggregates with a negative surface charge. After freeze-drying, PHMAA was a white solid powder with a loose porous structure. PHMAA presented no significant influence on the cell viability and weight of normal BALB/c mice. PHMAA showed good removal efficiency towards Cd²⁺ ions in aqueous solution; the removal rate exceeded 80%. In herbal decoctions, PHMAA presented moderate to good removal capacity towards Cd²⁺ ions; the removal rate was 60%, 83%, and 89% for the Morindae officinalis radix decoction, Ligusticum wallichii decoction, and Coptidis rhizome decoction, separately. When the concentration of Cd²⁺ ions in the decoction was decreased to 5 μg/mL, PHMAA also presented good removal efficiency. During the removal process, PHMAA played no influence on the active ingredients. To conclude, PHMAA showed good biosafety and removal capacity towards Cd²⁺ ions, which might be utilized as nanoadsorbents to reduce the concentration of Cd²⁺ ions in aqueous solution and herbal decoctions. Full article

The aim of this study was to rigorously quantify and analyse the concentrations of atmospheric pollutants (PM₁₀, PM_2.5, SO₂, NO₂, CO, H₂S, and O₃) emitted by artisanal brick kilns in Juliaca City, Peru. The AERMOD dispersion model and a network of low-cost sensors (LCSs) were employed to characterise air quality at specific receptor sites. A georeferenced inventory of kiln operations was created to determine their parameters and operational intensity, providing a foundation for estimating emission factors and rates. Data were obtained from the United States Environmental Protection Agency (EPA) and supplemented with locally gathered meteorological records, which were processed for integration into the AERMOD model. The findings revealed that brick kilns are a principal source of atmospheric pollution in the region, with carbon monoxide (CO) emissions being especially pronounced. The LCSs facilitated the identification of pollutant concentrations at various locations and enabled the quantification of the specific contribution of brick production to ambient aerosol levels. Comparative assessments determined that these sources account for approximately 85% of CO emissions within the study area, underscoring a significant adverse impact on air quality and public health. Background pollutant levels, emission rates, spatial distributions, and concentration patterns were analysed within the assessment zones, resulting in solid model performance. These results provide a sound scientific basis for the formulation and implementation of targeted environmental mitigation policies in urban areas and the outskirts of Juliaca. Full article

CaO-Al₂O₃-Ce₂O₃ is a potential new-type basic metallurgical slag system for rare earth steel. To investigate the effects of CaF₂ on the melting point and equilibrium phase types of this slag system, the phase equilibrium relationships and extent of the liquid phase region of CaO-Al₂O₃-Ce₂O₃-CaF₂ slag system at 1300 °C, 1400 °C, and 1500 °C in C/CO were determined by the high-temperature phase equilibrium experiment, Scanning Electron Microscope-Energy Dispersive X-ray Spectrometer (SEM-EDX) and X-ray Diffraction (XRD), and the isothermal phase diagram was plotted. The experimental results show that within the composition range in this study, the slag system has five, seven, and six liquid–solid equilibrium coexistence regions at 1300 °C, 1400 °C, and 1500 °C. The involved multiphase equilibrium regions include five two-phase regions (i.e., Liquid + CaO, Liquid + CaO·2Al₂O₃, Liquid + 2CaO·Al₂O₃·Ce₂O₃, Liquid + 2CaO·3Al₂O₃·Ce₂O₃, Liquid + 11CaO·7Al₂O₃·CaF₂), 4 three-phase regions (i.e., Liquid + CaO + 2CaO·Al₂O₃·Ce₂O₃, Liquid + 11CaO·7Al₂O₃·CaF₂ + 2CaO·Al₂O₃·Ce₂O₃, Liquid + CaO·2Al₂O₃ + 2CaO·3Al₂O₃·Ce₂O₃, Liquid + 11CaO·7Al₂O₃·CaF₂ + 2CaO·3Al₂O₃·Ce₂O₃), and 1 four-phase region (i.e., Liquid + CaO + 11CaO·7Al₂O₃·CaF₂ + 2CaO·Al₂O₃·Ce₂O₃). Meanwhile, based on liquid phase compositions under liquid–solid multiphase equilibrium, the slag system’s liquid phase ranges at the experimental temperatures were determined as follows: at 1300 °C: w(CaO)/w(Al₂O₃) = 0.42~0.92, w(Ce₂O₃) = 1.63%~8.02%, w(CaF₂) = 9.17%~21.46%; 1400 °C: 0.28~1.18, 0.9%~12.62%, 1.04%~23.34%, respectively; 1500 °C: 0.23~1.21, 0~14.42%, 0~26.32%, respectively. Full article

Under long-term high-temperature and static conditions, high-density workover fluid settles, increasing the risks of workover operations. In order to achieve a quantitative assessment of the sedimentation stability of oil well workover fluids, this study adopted spectral analysis to conduct stability tests on water dispersions of barite with different concentrations. Meanwhile, a comprehensive assessment was conducted on the sedimentation rate of the well repair fluid, the size of solid particles and the changes in the thickness of the sedimentary layer in 1# Well, 2# Well and 3# Well. With the increase in barite concentration, its sedimentation behavior changes from free sedimentation at low concentrations to flocculation sedimentation at high concentrations, and the sedimentation rate shows a slowing trend. The increase in sedimentation rate is positively correlated with the increase in density, and the intensity of the initial backscattered light at the bottom of the well also increases accordingly. In addition, during the sedimentation process of sediment, the variation pattern of particle velocity shows the characteristics of being relatively fast in the early stage and gradually accelerating in the middle and later stages. The results show that the average particle size of barite solution is 4.93 μm, and the average particle size of the three workover fluids is 87.5 μm. The deposition thickness range of barite solution is 5–50 mm, and that of the three workover fluids is 25–51.58 mm. It provides data support for the rapid quantitative evaluation of the long-term stability of oil well workover fluids. Full article

Titanium dioxide is attractive for energy storage due to its abundance, stability, non-toxicity, low cost, and favorable electronic/optical properties. Colossal permittivity (CP) in co-doped TiO₂ is mainly linked to defect structures rather than intrinsic bulk behavior. This work studies the dielectric properties of TiO₂ co-doped with niobium and magnesium, synthesized by solid-state reaction. Grain size effects were examined by varying ball milling parameters of (½Mg½Nb)_0.05Ti_0.95O₂ and then were correlated with structure, morphology, and dielectric response. X-ray diffraction (XRD), infrared spectroscopy (FTIR), scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray photoelectron spectroscopy (XPS), and impedance spectroscopy (IS) (40 Hz–10⁶ Hz, 150–370 K) were employed for structural, morphological, and electrical characterization. XRD confirmed the rutile phase. For co-doped samples, larger grains yielded higher dielectric constants, reaching high permittivity (ε′ = 429, T = 300 K, f = 10 kHz at 500 rpm for 2 h). Lower loss tangent (tan δ = 0.11, T = 300 K, f = 10 kHz at 200 rpm for 2 h) is linked to Mg segregation at grain boundaries. The most conductive sample showed the highest dielectric constant, suggesting an IBLC polarization mechanism driven by grain boundary effects. XPS confirmed Nb and Mg incorporation, with Ti⁴⁺ dominant and minor Ti³⁺ from oxygen vacancies and surface hydroxylation/defects. Full article

Coal spontaneous combustion causes both human casualties and environmental pollution. Owing to special flow behaviors, foam materials used in fire-fighting technology can effectively bring water and solid non-combustible substances into the fire-fighting area, greatly preventing spontaneous combustion. This paper systematically elucidates three foam materials, three-phase foam, gel foam and curing foam, and analyzes their physical and chemical inhibition mechanisms on coal spontaneous combustion. In particular, the preparation, performance and latest chemical modification methods of the foam materials are summarized in detail. It is found that foam materials with environmental friendliness, economy and excellent anti-fire performance need to be consistently explored. The primary application areas for cement-based foamed materials remain the building materials and civil engineering industries, and their modification should be studied accordingly based on the specific application context. Furthermore, a new component of foam materials, coal gasification slag (a solid waste), is proposed. In addition, the seepage properties of fire-fighting foam in porous media should be fully studied to accurately grasp the dispersion of foam materials in mine goafs. This review provides new insights and guidance for the development of fire-fighting foam materials. Full article

Background: Solid dispersions (SDs) of etodolac (ETD), a poorly water-soluble drug model, were developed to enhance its solubility and dissolution rate by employing various preparation methods and hydrophilic or amphiphilic polymers. Methods: Polyvinylpyrrolidone-poly(vinyl acetate) copolymers (PVP/VA), hydroxypropyl methylcellulose (HPMC) and poloxamer were used as carriers, while cryo-milling and lyophilization were utilized as routine methods to SDs preparation. Obtained SDs were characterized by drug content, solubility, dissolution rate and moisture content. The physical structure of SDs was estimated via scanning electron microscopy (SEM), whereas differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FTIR) were employed to assess the potential drug-carrier interactions. Results: SD formulations demonstrated enhanced solubility of ETD in aqueous media, including water and buffers (pH 5.5 and 7.4). DSC analysis confirmed that PVP/VA and poloxamer ensured better ETD dissolution and protection against recrystallization. Furthermore, FTIR indicated the formation of hydrogen bonds between ETD and polymer, particularly in lyophilized dispersions. Conclusions: The optimized SD formulation for ETD contained PVP/VA and/or poloxamer as carriers and was obtained via lyophilization. This SD formulation exhibited the most favorable properties, enhanced the solubility and dissolution of ETD in aqueous media and effectively reduced its crystallinity. Full article

Sea pollution caused by anthropological activities represents a risk both for the organisms that inhabit it and for humans themselves. Great attention is paid to plastic waste because it takes decades to decompose and fragments into microscopic pieces that can be easily dispersed and ingested by marine fauna. Polymeric materials, in general, are rich in plasticizers (phthalates, PAEs; and bisphenol A, BPA), substances recognized as toxic both for aquatic organisms and for humans who could ingest them once contaminated marine organisms were to enter their diet. In this work, effective analytical protocols based on the use of solid phase microextraction (SPME) coupled with chromatography techniques were employed to evaluate the presence of PAEs and BPA in the extracted pulp of shrimps of the commercial species Aristaemorpha foliacea from four different fishing stations in the Mediterranean Sea. In addition to chemical analysis, a comprehensive microbiological characterization was carried out to assess microbiological risk due to shrimps’ consumption. This dual approach provides a more complete evaluation of the impact of human pollution on these crustaceans, revealing both chemical contamination and potential biological disruptions that could pose a danger to food safety. Full article