Search Results (9,402)

This study presents the synthesis of sintered composite foams based on the Invar alloy (64Fe-36Ni), using hollow spherical particles from a nickel superalloy (NiCrSiB) in order to generate porosity. The Invar powder was obtained by mechanical alloying (MA), and the NiCrSiB hollow spherical particles were incorporated into the composite at 20 vol %. The sintering was realized using the spark plasma sintering (SPS) process in an argon atmosphere at 600 °C and 5 MPa, with 10 s holding time. The porous structures were structurally characterized by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). The coefficient of linear thermal expansion (CTE) of the Invar/NiCrSiB syntactic foams was found to be 2.52 × 10⁻⁶ °C⁻¹ in the 25–150 °C temperature range and 19.68 × 10⁻⁶ °C⁻¹ in the 150–400 °C range. Full article

The materials used as filaments for additive techniques should exhibit various properties depending on the application and the requirements. The motivation for this study was the need to obtain a filament exhibiting appropriate aesthetic (metal-like) and mechanical properties. Glycol-modified poly(ethylene terephthalate) copolymer (PETG) and micrometric steel powder were used for composite preparation. Subsequently, the obtained material was used as a filament for 3D printing, i.e., by fused deposition modeling (FDM) technique. The physicochemical properties of the obtained filaments were determined, such as morphology (roughness), moisture sorption ability, thermal properties, and mechanical performance (tensile and compressive strength). Importantly, the metal filler did not modify the thermal properties of the polyester matrix, indicating that the filament containing steel microfiller could be processed using the same parameters as for neat PETG. The thermal stability was slightly enhanced after steel powder addition (for 13 wt.% content, the temperature of 75% weight loss was 466 °C; for comparison, that for the reference sample was 446 °C). The reinforcing effect of steel microfiller was noted based on mechanical performance measurements. The steel particles acted as a stiffening agent; the highest maximal tensile strength was observed for the composite with 3 wt.% steel powder content (ca. 68 MPa). Further increasing the microfiller load resulted in a slight decrease in the value of this parameter. A different trend was reported considering the compressive strength, i.e., the value of this parameter increased with steel content. Based on the obtained results, the new PETG composites could be applied as structural materials. Full article

Supercritical CO₂ (scCO₂) is a versatile solvent for polymer processing; however, many partially fluorinated polymers exhibit limited solubility in neat scCO₂. Organic cosolvents such as toluene can enhance polymer–solvent interactions, thereby improving solubility. The cloud point behavior of poly(2,2,2-trifluoroethyl methacrylate) (poly(TFEMA)) at 3 wt% concentration in scCO₂–toluene binary mixtures was investigated over a temperature range of 31.5–50 °C and toluene contents of 0–20 wt%. Solvent mixture densities were estimated using the Altuin–Gadetskii–Haar–Gallagher–Kell (AG–HGK) equation of state for CO₂ and the Tait equation for toluene. For all compositions, the cloud point pressure was observed to increase linearly with temperature. The cloud point pressure decreased monotonically with increasing toluene concentration and at the highest concentration of 20 wt% was reduced by approximately 40% in comparison to neat scCO₂. The addition of toluene lowered the solvent density, but the increase in solvent–solute molecular interactions resulted in the observed decrease in cloud point pressure. Toluene is shown to be an effective cosolvent for dissolving poly(TFEMA) in scCO₂, offering a promising approach to lowering operating pressures in fluoropolymer processing. Our results provide valuable phase behavior data for designing scCO₂-based extraction, impregnation, and particle formation processes involving poly(TFEMA). Full article

To fulfil the goals of the circular economy, the treatment of textile wastewater should be focused on the recovery of valuable components. Monovalent anion-selective electrodialysis (MASED) was applied for the separation of reactive dyes from mineral salts. Standard cation-exchange membranes (CM membranes) and monovalent selective anion-exchange membranes (MVA membranes) were used in the electrodialysis (ED) stack. The separation efficiency was evaluated for model solutions of various reactive dyes (varying in molecular weight and chemical reactivity) containing NaCl. In the course of MASED, the mineral salt was successfully removed from the dye solutions with an efficacy of 97.4–99.4%, irrespectively of the composition of the treated solution. The transport of dye molecules through the ion-exchange membranes (IEMs) from diluate to concentrate compartments was irrelevant. Nonetheless, a significant adsorption of dye particles on the membranes was observed. Around 11–40% of the initial dye mass was deposited in the ED stack. Dye adsorption intensity was significantly affected by dye reactivity. This study showed the potential of the MASED process for the separation of the reactive dye from the mineral salt on condition that antifouling membrane properties are improved. The obtained streams (the concentrate rich in mineral salt and the diluate containing the reactive dye) can be reused in the dye-house textile operations; however, some loss of dye mass should be included. Full article

Within the framework of the XHe hypothesis, the positive results of the DAMA/NaI and DAMA/LIBRA experiments on the direct search for dark matter particles can be explained by the annual modulation of the radiative capture of dark atoms into low-energy bound states with sodium nuclei. Since this effect is not observed in other underground WIMP (weakly interacting massive particle) search experiments, it is necessary to explain these results by investigating the possibility of the existence of low-energy bound states between dark atoms and the nuclei of matter. Numerical modeling is used to solve this problem, since the study of the XHe–nucleus system is a three-body problem and leaves no possibility of an analytical solution. To understand the key properties and patterns underlying the interaction of dark atoms with the nuclei of baryonic matter, we develop the quantum mechanical description of such an interaction. In the numerical quantum mechanical model presented, takes into account the effects of quantum physics, self-consistent electromagnetic interaction, and nuclear attraction. This approach allows us to obtain a numerical model of the interaction between the dark atom and the nucleus of matter and interpret the results of direct experiments on the underground search for dark matter, within the framework of the dark atom hypothesis. Thus, in this paper, for the first time, steps are taken towards a consistent quantum mechanical description of the interaction of dark atoms, with unshielded nuclear attraction, with the nuclei of atoms of matter. The total effective interaction potential of the OHe–Na system has therefore been restored, the shape of which allows for the preservation of the integrity and stability of the dark atom, which is an essential requirement for confirming the validity of the OHe hypothesis. Full article

Graphite-phase carbon nitride (CN) has the advantages of high stability, non-toxicity, and harmlessness in degrading antibiotic pollutants in water. How to achieve the reduction of its electron-hole complexation efficiency as well as the improvement of its recyclability, while at the same time ensuring these advantages, is the focus of this paper. In this study, modified magnetic particles selected from coal gasification slag were used as carriers, which were compounded with CN and then subjected to a simple roasting process to obtain composite magnetic photocatalysts (MCN) with different ratios. The introduction of porous magnetic carriers increased the specific surface area of MCN, provided more active sites, and effectively improved the migration ability and redox capacity of CN carriers. Among them, 50% MCN showed excellent photodegradation performance, and the removal rate of tetracycline reached 82% within 60 min, which was much higher than that of CN. 50% MCN has a saturated magnetisation intensity of 1.55 emu·g⁻¹, which can be regenerated after recycling using a magnetic field, and the degradation efficiency of tetracycline is still more than 70% after five cycles, indicating that 50% MCN has good stability. This work demonstrates that magnetic gasification slag as a modified carrier can effectively promote the separation of photogenerated electron-hole pairs of graphite-phase carbon nitride, which provides a reference for the resourceful utilisation of coal gasification slag, as well as for the construction of g-C₃N₄-based photocatalysts with highly efficient and stable photodegradation activity. This work exemplifies how waste-derived materials can advance photocatalyst design, addressing both efficiency and sustainability challenges in water treatment. Full article

An experimental study was carried out on the ignition and combustion processes of particles (100–200 µm in size) of coals of different degrees of metamorphism and biomass, as well as mixtures based on them, under conditions of conductive and convective heating, which correspond to the conditions of fuel ignition in boiler furnaces at grates and flaring combustion. The biomass contents in the composition of the coal-based fuel mixtures were 10, 20, and 30 wt.%. Under the conductive (at 700–1000 °C) and convective (at 500–800 °C) heating of fuel particles, ignition delay times were determined using a hardware–software complex for the high-speed video registration of fast processes. The ignition delay times were found to vary from 1 to 12.2 s for conductive heating and from 0.01 to 0.19 s for convective heating. The addition of 10–30 wt.% biomass to coals reduced the ignition delay times of fuel mixtures by up to 70%. An analysis of the flue gas composition during the combustion of solid fuels allowed us to establish the concentrations of the main anthropogenic emissions. The use of biomass as an additive (from 10 to 230 wt.%) to coal reduced NO_x and SO_x emissions by 19–42% and 24–39%, respectively. The propensity of fuels to cause slagging depending on their component composition was established. The use of up to 30 wt.% of biomass in the mixture composition did not affect the increase in the tendency to cause slagging on heating surfaces in the boiler furnace and did not pose a threat to the layer agglomeration during the layer combustion of the mixtures. Full article

Magnetorheological elastomers (MREs) are smart composite materials with tunable mechanical properties by ferromagnetic particle interactions. This study applied the microstructure-based dipole and Maxwell methods to evaluate the magneto-mechanical coupling and magnetostrictive responses of MREs, focusing on various particle distributions. The finite element modeling of representative volume elements with fixed volume fractions revealed that the straight chain microstructure exhibits the most significant magnetostrictive effect due to its low initial shear stiffness and significant magnetic force contributions. For particle separations exceeding three radii, the dipole and Maxwell methods yield consistent results for vertically or horizontally aligned particles. For particle separations greater than three radii, the dipole and Maxwell methods produce consistent results for vertically and horizontally aligned particles. However, discrepancies emerge for angled configurations and complex microstructures, with the largest deviation observed in the hexagonal particle distribution, where the two methods differ by approximately 27%. These findings highlight the importance of selecting appropriate modeling methods for optimizing MRE performance. Since anisotropic MREs with straight-chain alignments are the most widely used, our results confirm that the dipole method offers an efficient alternative to the Maxwell method for simulating these structures. Full article

The design of piezoelectric roads is one of the future directions of smart roads. In order to ensure the environmentally friendly and long-lasting use of piezoelectric road materials, lead-free piezoelectric ceramics (barium titanate), polymer piezoelectric materials (polyvinylidene fluoride), and conductive particles (conductive carbon black and graphene) were used to prepare composite piezoelectric materials. The electrical performance was studied by the conductivity, dielectric properties, and piezoelectric properties of the composite materials. Then, the mechanical properties of the composite material were investigated by load compression tests. Finally, the microstructure of the composite materials was studied. The results showed that as the amount of conductive particles increased, the electrical performance was improved. However, further addition of conductive particles led to a decline in the electrical performance. The addition of conductive particles had a minimal effect on the mechanical properties of composite materials. The composite material met road use requirements. The overall structure of the composite materials was compact, with a clear wrapping effect of the polymer, and good interface compatibility. The addition of conductive carbon black and graphene had no significant impact on the structure of the composite materials. Full article

For the busting of heat, generated in electronic packages, relevant materials need to be developed. Metal matrix composites may be considered as an option to tailor the properties of a material (Cu) by incorporating an additional phase (SiC) for fulfilling the requirements of thermal management systems. The composite (Cu/SiC) was manufactured by friction stir processing. For good interfacial strength, the biggest challenge in the fabrication of Cu/SiC composite was to abolish the reaction between Cu and SiC. Being solid in nature, the process (friction stir processing) does not allow temperature to reach the interfacial interaction. Scanning electron microscopy, electron backscattered diffraction, and optical microscopy were used to characterise the composite for microstructural features (particle dispersion, phases present). To confirm the presence of reinforcement, EDS analysis was also performed on the composite. Results indicated the presence of Cu and SiC phases in the stir zone (SZ) with uniform and homogeneous separation of reinforcements. The composite displayed higher hardness, tensile strength, and wear resistance in comparison to unprocessed copper. However, ductility decreased due to high hardness in the composite. Full article

To significantly improve the tribological performance of epoxy resin (EP), a novel h-BN/MoS₂ composite was successfully synthesized using spherical MoS₂ particles with lamellar self-assembly generated through the calcination method, followed by utilizing the “bridging effect” of a silane coupling agent to achieve a uniform and vertically oriented decoration of hexagonal boron nitride (h-BN) nanosheets on the MoS₂ surface. The chemical composition and microstructure of the h-BN/MoS₂ composite were systematically investigated. Furthermore, the enhancement effect of composites with various contents on the frictional properties of epoxy coatings was studied, and the mechanism was elucidated. The results demonstrate that the uniform decoration of h-BN enhances the chemical stability of MoS₂ in friction tests, and the MoS₂ prevents oxidation and maintains its self-lubricating properties. Consequently, due to the protective effect of h-BN and the synergistic interaction between h-BN and MoS₂, the 5 wt % h-BN/MoS₂ composite exhibited the best friction and wear resistance when incorporated into EP. Compared to pure EP coatings, its average friction coefficient and specific wear rate (0.026 and 1.5 × 10⁻⁶ mm³ N⁻¹ m⁻¹, respectively) were significantly reduced. Specifically, the average friction coefficient decreased by 88% and the specific wear rate decreased by 99%, highlighting the superior performance of the h-BN/MoS₂-enhanced epoxy composite coating. Full article

This study investigated the compressive behavior of 30 vol.% boron carbide (B₄C)/2024 aluminum (Al) composites under quasi-static and dynamic loading at different temperatures. Building on the experimental findings, the Johnson–Cook (JC) model was modified, and a complete failure criterion was proposed. These were validated in Abaqus employing the user subroutine for hardening (VUHARD), which incorporated both the modified JC (MJC) model and the complete failure criterion. Experimental results revealed that strain softening was an important feature of the stress–strain curve. The analysis of mechanisms contributing to yield strength revealed that Taylor and load transfer mechanisms dominated, accounting for 89.6% of the total enhancement. Microstructural analysis identified particle fracture and matrix damage were the primary mechanisms driving material failure. Microcracks mainly propagated through the matrix and interface or directly through the ceramic particles and the matrix. The MJC model demonstrated high accuracy in describing the plastic deformation behavior of the composite, with a mean absolute error (MAE) below 15% under dynamic loading. Further simulation confirmed that finite element analyses using the VUHARD subroutine accurately captured the plastic deformation and crack propagation behaviors of the composite under dynamic loading. This study offers a novel approach to describe the plastic deformation and failure behaviors of ceramic-reinforced aluminum matrix composites under dynamic loading conditions. Full article

This study explores the synergistic development of natural gypsum-based composites (NGBCs) with enhanced multifunctional characteristics, employing hollow glass microspheres (HGMs) as density-reducing agents and sisal fibers (SFs) as mechanical reinforcement phases while maintaining superior whiteness properties. Five HGM variants with precisely graded particle sizes (20, 40, 60, 80, and 100 μm) were systematically incorporated into the composite matrix. Sisal fibers with controlled length parameters (10–15 mm) were uniformly dispersed within the gypsum matrix. The multifunctional effects of these additives were comprehensively assessed via integrated mechanical characterization, spectrophotometric whiteness evaluation, and microstructural interrogation. The findings revealed that the incorporation of HGMs resulted in a significant decrease in the NGBC density while concurrently enhancing whiteness; they also exerted an adverse impact on both processability and mechanical properties. Moreover, the fusion of HGMs and SFs within the NGBCs achieved an optimal balance between lightness and strength. The peak density of NGBCs was ascertained to be 1.41 g/cm³, complemented by flexural and compressive strengths of 6.12 and 9.78 MPa, respectively. Such optimizations were realized with HGMs at a particle size of 80 um and a composition of 20 vol.%, alongside sisal fibers present at a concentration of 0.3 vol.%. The current research affords significant revelations regarding the fabrication of architectural gypsum materials that are lightweight, possess high tensile strength, exhibit an aesthetically appealing finish, and demonstrate superior whiteness, presenting a prospective resolution for applications within the high-performance construction sector. Full article

To address the issue of insufficient accuracy in traditional settlement prediction methods for shield tunneling undercrossing in composite strata in Hangzhou, this paper proposes a particle swarm optimization (PSO)-based Bidirectional Long Short-Term Memory neural network (Bi-LSTM) prediction model for high-precision dynamic prediction of ground settlement under small-sample conditions. Shield tunneling is a key method for urban tunnel construction. This paper presents the measurement and prediction of ground settlement caused by shield tunneling undercrossing existing tunnels in composite strata in Hangzhou. The longitudinal ground settlement curve resulting from shield tunnel excavation was analyzed using measured data, and the measured lateral ground settlement was compared with the Peck empirical formula. Using PSO, the performance of three machine learning models in predicting the maximum ground settlement at monitoring points was compared: Long Short-Term Memory neural network (LSTM), Gated Recurrent Unit neural network (GRU), and Bi-LSTM. The linear relationships between different input parameters and between input parameters and the output parameter were analyzed using the Pearson correlation coefficient. Based on this analysis, the model was optimized, and its prediction performance before and after optimization was compared. The results show that the Bi-LSTM model optimized with the PSO algorithm demonstrates superior performance, achieving both accuracy and stability. Full article

The fabrication of AA5083/SiC composites by the friction stir processing (FSP) method is the main objective of this study. The study looks at how the mechanical properties of the composites are affected by three important process parameters: traversal speed, rotational speed, and tilt angle. The Taguchi L₉ design matrix was used to effectively investigate parameter effects, decreasing experimental trials and cutting expenses. Tensile testing measured tensile strength, whereas microhardness tests evaluated hardness. The findings showed that a maximum tensile strength of 243 MPa and a maximum microhardness of 94.80 HV were attained. The findings also showed that the optimal ultimate tensile strength (UTS) and percentage elongation (PE) were achieved at a tilt angle of 2°, a traverse speed of 30 mm per minute, and a rotating speed of 900 rev/min. On the other hand, a slightly greater traverse speed of 45 mm per minute was required to reach maximal microhardness (MH) with the same rotational speed and tilt angle. Analysis of variance (ANOVA) showed that rotational speed has a substantial impact on all mechanical properties, highlighting how important it is for particle dispersion and grain refining. This work is unique in that it systematically optimizes FSP parameters by using regression analysis and the Taguchi technique in addition to ANOVA. This allows for a better understanding of how these factors affect the mechanical properties of SiC-reinforced composites. The findings contribute to advancing the cost-effective fabrication of high-performance metal matrix composites for industrial applications requiring enhanced strength and durability. Full article