Search Results (29)

Superhydrophilic micro/nano-porous media have extensive applications in electronic thermal management and energy storage systems. Predicting two-phase pressure drop in complex porous structures is of great importance for system design and optimization while remaining highly challenging. This study systematically investigates the two-phase flow resistance characteristics of bi-porous microstructures with multiple particle sizes and porosities under varying boiling regimes. Experimentally, porous samples were fabricated via vacuum sintering using nickel powders and pore-forming agents (CaCl₂), which exhibit superhydrophilicity and enhanced wicking characteristics. A visualized experimental platform was constructed to investigate the impact of pore size combinations, flow velocities, and boiling states on pressure drop. The dataset obtained through multi-factor saturated boiling experiments was further used to derive a semi-empirical model for the two-phase flow pressure drop based on the classic Kozeny-Carman (K-C) and Akagi-Chisholm (A-C) correlations. Results show that the pore size combinations and boiling states have a significant impact on the resistance performance. The proposed model achieves an average prediction deviation below 15.7%, confirming its reliability and its effectiveness as a design framework for optimizing high-capillary-force porous wicks in advanced thermal management systems. Full article

To address the issue of sound absorption valleys in open-cell aluminum foam and enhance mid-to-high frequency (800–6300 Hz) performance, we developed a novel pore-penetrating 316L stainless steel fiber–aluminum foam (PPFCAF) composite using an infiltration method. The formation mechanism of the pore-penetrating fibers, the resultant pore-structure, and the accompanying sound absorption properties were investigated systematically. The PPFCAF was fabricated using 316L stainless steel fiber–NaCl composites created by an evaporation crystallization process, which ensured the full embedding of fibers within the pore-forming agent, resulting in a three-dimensional fiber-pore interpenetrating network after infiltration and desalination. Experimental results demonstrate that the PPFCAF with a porosity of 82.8% and a main pore size of 0.5 mm achieves a sound absorption valley value of 0.861. An average sound absorption coefficient is 0.880 in the target frequency range, representing significant improvements of 9.8% and 9.9%, respectively, higher than that of the conventional infiltration aluminum foam (CIAF). Acoustic impedance reveal that the incorporated fibers improve the impedance matching between the composite material and air, thereby reducing sound reflection. Finite element simulations further elucidate the underlying mechanisms: the pore-penetrating fibers influence the paths followed by air particles and the internal surface area, thereby increasing the interaction between sound waves and the solid framework. A reduction in the main pore size intensifies the interaction between sound waves and pore walls, resulting in a lower overall reflection coefficient and a decreased reflected sound pressure amplitude (0.502 Pa). In terms of energy dissipation, the combined effects of the fibers and refinement increase the specific surface area, thereby strengthening viscous effects (instantaneous sound velocity up to 46.1 m/s) and thermal effects (temperature field increases to 0.735 K). This synergy leads to a notable rise in the total plane wave power dissipation density, reaching 0.0609 W/m³. Our work provides an effective strategy for designing high-performance composite metal foams for noise control applications. Full article

Mesoporous silica nanoparticles have been synthesized through sol–gel synthesis in basic conditions. Gemini surfactants having urea in the headgroups were used as pore-forming agents. The effect of the spacer length of the surfactant on the particle morphology was studied on the sub-micrometer and nanometer scales using nitrogen porosimetry, small-angle X-ray scattering (SAXS), ultra-small-angle neutron scattering, and scanning and transmission electron microscopy (SEM, TEM). Depending on the spacer, spherical and/or cylindrical nanoparticles formed in different proportions, as revealed by statistical analysis of SEM micrographs. All prepared materials showed the hexagonal pore structure characteristic of the MCM-41 molecular sieves, with the exception of the sample prepared using the gemini surfactant with the shortest spacer length. The influence of the spacer length on the lattice parameter of the pore network, as well as the average size of the ordered domains, has been assessed by SAXS and TEM. Detailed analysis of the TEM images revealed a spread of the lattice parameter in a range of 10–20%. The broadening of the diffraction peaks was shown to be due to the combination of the effects of the finite domain size and the variance of the lattice parameter across the crystalline domains. The structural differences between the silica gels synthesized with the different surfactants were related to the variation of the micelle morphologies, reported in previous light scattering and small-angle scattering experiments. No connection could be revealed between the micelle shape and size and the pore sizes, showing that surfactants with a broad range of spacer lengths can equally well be used for the preparation of MCM-41 materials. Full article

Reaction bonding (RB) using Al powder is an effective method for preparing porous ceramics with low shrinkage, high porosity, and high strength. However, it remains challenging to optimize mechanical strength and oil conductivity simultaneously for atomizer applications. Herein, aiming at addressing this issue, porous Al₂O₃ ceramics with ultra-high mechanical strength and oil conductivity were fabricated via the RB process using polymethyl methacrylate (PMMA) microspheres as the pore-forming agent. The pore structure was gradually optimized by regulating the additive amount, particle size, and particle gradation of PMMA microspheres. The bimodal pores, formed by Al oxidation-induced hollow structures (enhancing bonding force) and burnout of large-sized PMMA microspheres, significantly improved mechanical strength; meanwhile, three-dimensional interconnected pores derived from particle gradation increased the diversity and quantity of oil-conduction channels, boosting oil conductivity. Consequently, under an open porosity of 58.2 ± 0.1%, a high compressive strength of 7.9 ± 0.3 MPa (a 54.7% improvement) and an excellent oil conductivity of 2.1 ± 0.0 mg·s⁻¹ (a 46.5% improvement) were achieved. This superior performance combination, overcoming the trade-off between strength and oil conductivity, demonstrates substantial application potential in atomizers. Full article

PVDF/TiO₂ composite membranes show some potential to be used for water treatment as they combine the advantages of polymers and ceramics. However, conventional PVDF-based composite membranes are always fabricated by using conventional toxic solvents. Herein, PolarClean was used as a green solvent to fabricate PVDF/TiO₂ composite membranes via the phase inversion method. In this process, Pluronic F127 was used as a dispersion agent to distribute TiO₂ particles in the PVDF matrix and to serve as a pore former on the membrane surface. TiO₂ particles were well distributed on the membrane surface and bulk. TiO₂ particles in the PVDF matrix enhanced the mechanical strength and hydrophilic characteristics of the resulting composite membrane, facilitating water transport through the composite membranes and enhancing their water permeability. Membrane microstructures and mechanical strength of the composite membranes were finely tuned by varying the PVDF concentration, TiO₂ concentration, and coagulation bath temperature. It was demonstrated that the resulting green PVDF/TiO₂ composite membrane showed a high water permeance compared with those using conventional toxic solvents in terms of its small pore size. In addition, the particle rejection of green PVDF/TiO₂ membrane showed a 99.9% rejection rate in all the filtration process, while those using NMP showed 91.1% after 30 min of filtration. The water flux was similar at 121 and 130 Lm⁻²h⁻¹ for green and conventional solvents, respectively. This work provides important information for the future application of sustainable membranes. Full article

Mesoporous silica sieves have been prepared through sol–gel synthesis using diester gemini surfactants as pore templates, aiming to obtain new materials with potential use for water remediation. A series of mesoporous spherical silica particles of submicron size have been prepared in an alkali-catalyzed reaction, using a tetraethyl orthosilicate precursor and bis-quaternary ammonium gemini surfactants with diester spacers of varied lengths as pore-forming agents. The effect of the spacer length on the particle morphology was studied using nitrogen porosimetry, small-angle X-ray scattering (SAXS), ultra-small-angle neutron scattering, scanning, and transmission electron microscopy (SEM, TEM). The results revealed that for all spacer lengths, a long-range hexagonal pore ordering developed in the materials. The silica particles were nearly spherical, with sizes below 1 micrometer, and a weak dependence of the mean particle size on the spacer length could be observed. The template removal procedure had a strong influence on the porosity: calcination caused a moderate shrinkage of the pores while retaining the hexagonal structure, whereas treatment with acidified ethanol resulted in only partial removal of the surfactants; however, the hexagonal structure was severely destroyed. The applicability of the obtained calcined materials as adsorbents for heavy metal ions from water was studied with the example of Pb(II). A high sorption capacity of 110 mg/g was obtained in batch experiments, at pH 5 and 4 h contact time. Full article

Porous 430L stainless steel disks made by tape casting with various pore-former sizes and volume fractions were evaluated as substrates for solid oxide cell (SOC) fabrication by plasma spraying. This work reports the substrate properties relevant to the SOC operation of disks made by using extra fine metal powder with dense sintering to minimize the fine porosity between particles. In contrast, the coarse porosity is introduced by the pore former. We found that the 60 μm pore former at a 45 vol% fraction has the best application fit; it gives an adequate gas permeability of 3.11 × 10⁻¹³ m² and an average open pore size of 45.90 μm. Compared to a commercial substrate with a similar porosity perimeter/steel area ratio, the porosity and gas permeability are 1.6 and 3 times higher, respectively. The detected maximum surface pore is 49 μm, allowing gas-tight electrolytes fabricated by plasma spray deposition. Full article

A sintered wick was formed in a heat pipe through the process of sintering a mixture of copper powder with particle sizes of 100 µm and 200 µm, mixed with a pore-forming agent. The heat pipe’s thermal resistance, which affects its heat transfer efficiency, is determined during manufacturing according to the powder type, thickness of the sintered wick, and filling rate of the working fluid. Heat transfer efficiency was then tested at various inclination angles (0°, 45°, and 90°) to evaluate the performance of heat pipes. Regardless of the filling amount and test angle, the 200 μm copper powder type exhibited superior heat transfer efficiency compared to the 100 μm type. After analyzing heat transfer performance at various filling rates between 20% and 50%, it was determined that the heat pipe’s optimal heat transfer capability occurred at a working fluid filling rate of 30%. The width of the wick was directly related to the heat transfer performance. Full article

This study presents a methodology to fabricate Ti6Al4V cylindrical compacts with a highly porous core and dense shell with the aim to mimic the bone microstructure. Compacts with different core diameters were obtained via conventional pressing and sintering. Large pores were created with the aid of pore formers. Dilatometry was used to determine the sintering kinetics, while X-ray computed tomography was used for characterization. Also, the permeability was evaluated on the 3D microstructure, and the mechanical strength was evaluated via compression tests. The results indicated that sintering was constrained by the different densification rates of the porous and dense layers. However, defect-free compacts were obtained due to neck bonding between the Ti6Al4V particles. Large pores were located in the designed core with a similar pore size distribution. The permeability increased following a power law as a function of the pore volume fraction. The porous core drove the stiffness of the bilayer components, while the combination of both layers increased their strength. The bilayer materials showed permeability (1.36 × 10⁻¹⁰ m²), mechanical properties (E = 6.83 GPa and σ_y = 299 MPa), and admissible strain (σ_y/E = 43 × 10⁻³) similar to those of human bones. Full article

The micro pores in loess show regional variation in structure on the Loess Plateau and greatly influence the physical properties and macro behaviors of loess. In this study, the 3D microstructures of Malan loess from Lanzhou (LZ), Qingyang (QY), Hengshan (HS) and Jingyang (JY) were established based on μ-CT scanning, and the corresponding microstructural parameters were compared and analyzed quantitatively. The results indicate that the LZ and HS loess both show overall homogeneous structures with dominant inter-particle pores, while the QY and JY loess have more intra-aggregate and constricted pores. Overall, the LZ loess has the largest pore size, followed by the JY loess, QY loess and HS loess, which is consistent with the throat sizes of the four loess samples. The average coordination numbers (CNs) of the LZ and HS loess are lower than those of the QY and JY loess, while the throat lengths of the former two loess are larger than those of the latter two loess. Analysis of the correlation between the micropore parameters and macro behaviors of the loess suggests that the void ratio is the precondition for loess collapse, but it shows weak relevance to collapsibility; meanwhile, the size of pores contributing to the major pore space presents a strong positive correlation. The throat length representing the pore structure is more closely related to loess permeability compared with the void ratio, average CN and throat size. Full article

There is a growing interest in tissue engineering, in which biomaterials play a pivotal role in promoting bone regeneration. Furthermore, smart functionalization can provide biomaterials with the additional role of preventing orthopedic infections. Due to the growing microbial resistance to antimicrobials used to treat those infections, metal ions, such as silver, thanks to their known wide range of bactericidal properties, are believed to be promising additives in developing antibacterial biomaterials. In this work, novel poly(ε-caprolactone) (PCL)-based 3D scaffolds have been designed and developed, where the polymer matrix was modified with both silver (Ag), to supply antibacterial behavior, and calcium phosphates (biphasic calcium phosphate, BCP) particles to impart bioactive/bioresorbable properties. The microstructural analysis showed that constructs were characterized by square-shaped macropores, in line with the morphology and size of the templating salts used as pore formers. Degradation tests demonstrated the important role of calcium phosphates in improving PCL hydrophilicity, leading to a higher degradation degree for BCP/PCL composites compared to the neat polymer after 18 days of soaking. The appearance of an inhibition halo around the silver-functionalized PCL scaffolds for assayed microorganisms and a significant (p < 0.05) decrease in both adherent and planktonic bacteria demonstrate the Ag+ release from the 3D constructs. Furthermore, the PCL scaffolds enriched with the lowest silver percentages did not hamper the viability and proliferation of Saos-2 cells. A synergic combination of antimicrobial, osteoproliferative and biodegradable features provided to 3D scaffolds the required potential for bone tissue engineering, beside anti-microbial properties for reduction in prosthetic joints infections. Full article

The porosity, permeability, and capillary force of porous sintered copper were examined in relation to the effects of copper powder size, pore-forming agent, and sintering conditions. Cu powder with particle sizes of 100 and 200 μm was mixed with pore-forming agents ranging from 15 to 45 weight percent, and the mixture was sintered in a vacuum tube furnace. Copper powder necks were formed at sintering temperatures higher than 900 °C. The porosity, as determined by the Archimedes measurement method, and the permeability performance of the sintered body displayed higher values when the Cu powder size was uniform or small. To investigate the capillary force of the sintered foam, a test was conducted using a raised meniscus test device. As more forming agent was added, the capillary force increased. It was also higher when the Cu powder size was larger and the size of the powders was not uniform. The result was discussed in relation to porosity and pore size distribution. Full article

This paper presents the preparation and characterization of a porous and antimicrobial composite material consisting of diatomaceous earth, an inorganic pore-forming agent, and nano-zinc oxide (ZnO). A modified direct precipitation device produced high-surface area ZnO powder. The effect of reaction temperature, volume flow rate, and titration rate on ZnO particle size was studied. Using sodium chloride, potassium nitrate, and sodium percarbonate as porosity to create porous structures through dissolution was also investigated. This study found that adding cement sand to diatomaceous earth improved mold strength while lowering the volume flow rate, and increasing the reaction temperature increased the specific surface area of ZnO. At 60 °C, the crystalline structure changed from an irregular spherical form to a regular nanorod structure. The specific surface area of the prepared ZnO nanorods reached over 15 m²/g, which is about five times higher. In an antibacterial experiment, adding 5% ZnO nanorods of 50 nm diameter to the porous diatomaceous earth composite material resulted in a nearly 100% antibacterial rate against E. coli in an aqueous environment. The results suggest that the porous diatomaceous earth/nano-ZnO composite has potential applications as an antimicrobial material, and the modified direct precipitation method could have broader implications in materials science. Full article

Aluminum and its alloy castings are used more and more widely, and it is particularly important to remove impurities in the alloy. According to the principle of bubble floatation for degassing aluminum melt, a new porous nozzle with controllable pores was developed, and a hydraulic simulation experimental device was studied with the nozzle. The effects of the particle size ratio of the coarse sand to fine sand and volume fraction of fine sand on the porosity of the porous nozzle were studied by orthogonal experiment, and permeability and compressive strength of the porous nozzle were used as test indicators to determine the optimal parameters of preparation for the porous nozzle. The optimal parameters are fine sand of 100 mesh, and fine sand of 50 wt.%, binder of 17.5 wt.%, pore-forming agent of 6 wt.%, and pressure of making sample of 5 MPa. The nozzle with optimal parameters was prepared and tested, and the permeability is 112.2 × 10⁻¹² m² and the compressive strength is 2.3 MPa. In addition, a physical model of gas transmission in the porous nozzle was proposed. With the increase in the proportion of fine sand, the permeability of the porous nozzle decreases, the compressive strength increases, and the calculated porosity increases. The hydraulic simulation of melt injection was carried out, and the mathematical model for calculating the bubble diameter of bubble floatation was formulated. The model shows that the bubble diameter increases with the increase in gas flow rate. The experiment shows that the prepared porous nozzle has the merits of a simple preparation process and low-cost, which is expected to degas aluminum melts. Full article

Traditional microchannel needs to face the flow-reversal difficulty in high heat fluxes due to limited space. It results in large pressure and temperature fluctuation. Porous microchannels arouse more interest to provide a new solution to this problem. Flow boiling experiments in porous microchannels with PFA were investigated. Porous microchannels were sintered by 10 μm (or 30 μm) spherical copper particles with pore-forming agent (Na₂CO₃, 60–90 μm). Porous microchannels were composed of 23 parallel porous microchannels with 600 μm in width and 1200 μm in depth.The addition of PFA (pore-forming agent) could increase the sample porosity. For Q10 series, sample porosities increase from 20.4% to 52.9% with the PFA percentage change from 0% to 40%, while for the Q30 series they increase from 26.6% to 47.5%. Experimental results showed the boiling heat transfer coefficient (HTC) reached the maximum at the moderate porosity for both Q10 and Q30 series. Too large or too small porosity would degrade boiling heat transfer performance. It demonstrated that there existed an optimal range of PFA content for sintered microchannels. PFA content has a minor effect on the average pressure drop and would not cause the rapid increase in flow resistance. Visual observation disclosed that the sample porosity would affect the pressure instability significantly. The sample with moderate porosity showed periodic pressure fluctuation and could establish rhythmical boiling. Particle size also exerted a certain influence on the boiling heat transfer performance. Q30 series could achieve higher HTC and CHF (Critical heat flux) than Q10 series. This is attributed to the larger ratio of layer-thickness-to-particle-size (δ/d) for Q10-series samples. Full article