Search Results (933)

Taconis oscillations represent spontaneous excitation of acoustic modes in tubes with large temperature gradients in cryogenic systems. In this study, Taconis oscillations in hydrogen and helium systems are enhanced with a porous material resulting in a standing-wave thermoacoustic engine. A theoretical model is developed using the thermoacoustic software DeltaEC, version v6.4b2.7, to predict system performance, and an experimental apparatus is constructed for engine characterization. The low-amplitude thermoacoustic model predicts the pressure amplitude, frequency, and temperature gradient required for excitation of the standing-wave system. Experimental measurements, including the onset temperature ratio, acoustic pressure amplitudes, and frequencies, are recorded for different stack materials and geometries. The findings indicate that, independent of stack, hydrogen systems excite at smaller temperature differentials than helium (because of different properties such as lower viscosity for hydrogen), and the stack geometry and material affect the onset temperature ratio. However, pressure amplitude in the excited states varies minimally. Initial measurements are also conducted in a cooling setup with an added regenerator. The configuration with stainless-steel mesh screens produces a small cryogenic refrigeration effect with a decrease in temperature of about 1 K. The reported characterization of a Taconis-based thermoacoustic engine can be useful for the development of novel thermal management systems for cryogenic storage vessels, including refrigeration and pressurization. Full article

This study demonstrates the successful fabrication of high-performance reaction-bonded silicon carbide (RBSC) ceramics through an optimized liquid silicon infiltration (LSI) process employing multi-modal SiC particle gradation and nano-carbon black (0.6 µm) additives. By engineering porous preforms with hierarchical SiC distributions and tailored carbon sources, the resulting ceramics achieved a compressive strength of 2393 MPa and a flexural strength of 380 MPa, surpassing conventional RBSC systems. Microstructural analyses revealed homogeneous β-SiC formation and crack deflection mechanisms as key contributors to mechanical enhancement. Ultrafine SiC particles (0.5–2 µm) refined pore architectures and mediated capillary dynamics during infiltration, enabling nanoscale dispersion of residual silicon phases and minimizing interfacial defects. Compared to coarse-grained counterparts, the ultrafine SiC system exhibited a 23% increase in compressive strength, attributed to reduced sintering defects and enhanced load transfer efficiency. This work establishes a scalable strategy for designing RBSC ceramics for extreme mechanical environments, bridging material innovation with applications in high-stress structural components. Full article

As the most unstable crystalline form of calcium carbonate, vaterite is rarely found in nature due to being highly prone to phase transitions. However, its high specific surface area, excellent biocompatibility, and high solubility properties have led to a research boom and the following breakthroughs in the last two decades: (1) From primitive calculations and spectroscopic analyses to modern multidimensional research methods combining calculations and experiments, the crystal structure of vaterite has turned from early identifications in orthorhombic and hexagonal crystal systems to a complex polymorphic structure within the monoclinic crystal system. (2) The formation process of vaterite not only conforms to the classical crystal growth theory but also encompasses the nanoparticle aggregation theory, which incorporates the concepts of oriented nanoparticle assembly and mesoscale transformation. (3) Regardless of the conditions, the formation of vaterite depends on an excess of CO₃²⁻ relative to Ca²⁺, and its stability duration relates to preservation conditions. (4) Vaterite demonstrates significant value in biomedical applications—including bone repair scaffolds, targeted drug carriers, and antibacterial coating materials—leveraging its porous structure, high specific surface area, and exceptional biocompatibility. While it also shows utility in environmental pollutant adsorption and general coating technologies, the current research remains predominantly concentrated on its medical applications. Currently, the rapid transformation of vaterite presents the primary limitation for its industrial application. Future research should prioritize investigating its formation kinetics and stability. Full article

Polyimide, a class of high-performance polymers, is renowned for its exceptional thermal stability, mechanical strength, and chemical resistance. However, in the context of high-integration and high-frequency electronic packaging, polyimides face critical challenges including relatively high dielectric constants, inadequate thermal conductivity, and mechanical brittleness. Recent advances have focused on molecular design and composite engineering strategies to address these limitations. This review first summarizes the intrinsic properties of polyimides, followed by a systematic discussion of chemical synthesis, surface modification approaches, molecular design principles, and composite fabrication methods. We comprehensively examine both conventional polymerization synthetic routes and emerging techniques such as microwave-assisted thermal imidization and chemical vapor deposition. Special emphasis is placed on porous structure engineering via solid-template and liquid-template methods. Three key modification strategies are highlighted: (1) surface modifications for enhanced hydrophobicity, chemical stability, and tribological properties; (2) molecular design for optimized dielectric performance and thermal stability; and (3) composite engineering for developing high-thermal-conductivity materials with improved mechanical strength and electromagnetic interference (EMI) shielding capabilities. The dielectric constant of polyimide is reduced while chemical stability and wear resistance can be enhanced through the introduction of fluorine groups. Ultra-low dielectric constant and high-temperature resistance can be achieved by employing rigid monomers and porous structures. Furthermore, the incorporation of fillers such as graphene and boron nitride can endow the composite materials with high thermal conductivity, excellent EMI shielding efficiency, and improved mechanical properties. Finally, we discuss representative applications of polyimide and composites in electronic device packaging, EMI shielding, and thermal management systems, providing insights into future development directions. Full article

The escalating demand for efficient thermal management in lithium-ion batteries necessitates precise characterization of their thermal behavior under diverse operating conditions. This study develops a three-dimensional (3D) electrochemical–thermal coupling model grounded in porous electrode theory and energy conservation principles. The model solves multi-physics equations such as Fick’s law, Ohm’s law, and the Butler–Volmer equation, to resolve coupled electrochemical and thermal dynamics, with temperature-dependent parameters calibrated via the Arrhenius equation. Simulations under varying discharge rates reveal that high-rate discharges exacerbate internal heat accumulation. Low ambient temperatures amplify polarization effects. Forced convection cooling reduces surface temperatures but exacerbates core-to-surface thermal gradients. Structural optimization strategies demonstrate that enhancing through-thickness thermal conductivity reduces temperature differences. These findings underscore the necessity of balancing energy density and thermal management in lithium-ion battery design, proposing actionable insights such as preheating protocols for low-temperature operation, optimized cooling systems for high-rate scenarios, and material-level enhancements for improved thermal uniformity. Full article

Glancing Angle Deposition (GLAD) has emerged as a versatile and powerful nanofabrication technique for developing next-generation gas sensors by enabling precise control over nanostructure geometry, porosity, and material composition. Through dynamic substrate tilting and rotation, GLAD facilitates the fabrication of highly porous, anisotropic nanostructures, such as aligned, tilted, zigzag, helical, and multilayered nanorods, with tunable surface area and diffusion pathways optimized for gas detection. This review provides a comprehensive synthesis of recent advances in GLAD-based gas sensor design, focusing on how structural engineering and material integration converge to enhance sensor performance. Key materials strategies include the construction of heterojunctions and core–shell architectures, controlled doping, and nanoparticle decoration using noble metals or metal oxides to amplify charge transfer, catalytic activity, and redox responsiveness. GLAD-fabricated nanostructures have been effectively deployed across multiple gas sensing modalities, including resistive, capacitive, piezoelectric, and optical platforms, where their high aspect ratios, tailored porosity, and defect-rich surfaces facilitate enhanced gas adsorption kinetics and efficient signal transduction. These devices exhibit high sensitivity and selectivity toward a range of analytes, including NO₂, CO, H₂S, and volatile organic compounds (VOCs), with detection limits often reaching the parts-per-billion level. Emerging innovations, such as photo-assisted sensing and integration with artificial intelligence for data analysis and pattern recognition, further extend the capabilities of GLAD-based systems for multifunctional, real-time, and adaptive sensing. Finally, current challenges and future research directions are discussed, emphasizing the promise of GLAD as a scalable platform for next-generation gas sensing technologies. Full article

Direct Air Capture (DAC) is emerging as a critical climate change mitigation strategy, offering a pathway to actively remove atmospheric CO₂. This comprehensive review synthesizes advancements in DAC technologies, with a particular emphasis on the pivotal role of nanostructured solid sorbent materials. The work critically evaluates the characteristics, performance, and limitations of key nanomaterial classes, including metal–organic frameworks (MOFs), covalent organic frameworks (COFs), zeolites, amine-functionalized polymers, porous carbons, and layered double hydroxides (LDHs), alongside solid-supported ionic liquids, highlighting their varied CO₂ uptake capacities, regeneration energy requirements, and crucial water sensitivities. Beyond traditional temperature/pressure swing adsorption, the review delves into innovative DAC methodologies such as Moisture Swing Adsorption (MSA), Electro Swing Adsorption (ESA), Passive DAC, and CO₂-Binding Organic Liquids (CO₂ BOLs), detailing their unique mechanisms and potential for reduced energy footprints. Despite significant progress, the widespread deployment of DAC faces formidable challenges, notably high capital and operational costs (currently USD 300–USD 1000/tCO₂), substantial energy demands (1500–2400 kWh/tCO₂), water interference, scalability hurdles, and sorbent degradation. Furthermore, this review comprehensively examines the burgeoning global DAC market, its diverse applications, and the critical socio-economic barriers to adoption, particularly in developing countries. A comparative analysis of DAC within the broader carbon removal landscape (e.g., CCS, BECCS, afforestation) is also provided, alongside an address to the essential, often overlooked, environmental considerations for the sustainable production, regeneration, and disposal of spent nanomaterials, including insights from Life Cycle Assessments. The nuanced techno-economic landscape has been thoroughly summarized, highlighting that commercial viability is a multi-faceted challenge involving material performance, synthesis cost, regeneration energy, scalability, and long-term stability. It has been reiterated that no single ‘best’ material exists, but rather a portfolio of technologies will be necessary, with the ultimate success dependent on system-level integration and the availability of low-carbon energy. The review paper contributes to a holistic understanding of cutting-edge DAC technologies, bridging material science innovations with real-world implementation challenges and opportunities, thereby identifying critical knowledge gaps and pathways toward a net-zero carbon future. Full article

Multilayer thin films composed of cobalt (Co), carbon (C), and chromium (Cr) possess promising electromagnetic properties, yet the combined Co–C–Cr system remains underexplored, particularly regarding its performance as a microwave absorber. Existing research has primarily focused on binary Co–C or Co–Cr compositions, leaving a critical knowledge gap in understanding how ternary multilayer architectures influence electromagnetic behavior. This study addresses this gap by investigating the structure, phase composition, and microwave absorption performance of Co–C–Cr multilayer coatings fabricated via magnetron sputtering onto porous silicon substrates. This study compares four-layer and eight-layer configurations to assess how multilayer architecture affects impedance matching, reflection coefficients, and absorption characteristics within the 8.2–12.4 GHz frequency range. Structural analyses using X-ray diffraction and transmission electron microscopy confirm the coexistence of amorphous and nanocrystalline phases, which enhance absorption through dielectric and magnetic loss mechanisms. Both experimental and simulated results show that increasing the number of layers improves impedance gradients and broadens the operational bandwidth. The eight-layer coatings demonstrate a more uniform absorption response, while four-layer structures exhibit sharper resonant minima. These findings advance the understanding of ternary multilayer systems and contribute to the development of frequency-selective surfaces and broadband microwave shielding materials. Full article

This study presents research on the production of activated biocarbons derived from herbal waste. Sage stems were chemically activated with two activating agents of different chemical natures—H₃PO₄ and K₂CO₃—and subjected to two thermal treatment methods: conventional and microwave heating. The effect of the activating agent type and heating method on the basic physicochemical properties of the resulting activated biocarbons was investigated. These properties included surface morphology, elemental composition, ash content, pH of aqueous extracts, the content and nature of surface functional groups, points of zero charge, and isoelectric points, as well as the type of porous structure formed. In addition, the potential of the prepared carbonaceous materials as adsorbents of model organic (represented by Triton X-100 and methylene blue) and inorganic (represented by iodine) pollutants was assessed. The influence of the initial adsorbate concentration (5–150 (dye) and 10–800 mg/dm³ (surfactant)), temperature (20–40 °C), and pH (2–10) of the system on the efficiency of contaminant removal from aqueous solutions was evaluated. The adsorption kinetics were also investigated to better understand the rate and mechanism of contaminant uptake by the prepared activated biocarbons. The results showed that materials activated with orthophosphoric acid exhibited a significantly higher sorption capacity for all tested adsorbates compared to their potassium carbonate-activated counterparts. Microwave heating was found to be more effective in promoting the formation of a well-developed specific surface area (471–1151 m²/g) and porous structure (mean pore size 2.17–3.84 nm), which directly enhanced the sorption capacity of both organic and inorganic contaminants. The maximum adsorption capacities for iodine, methylene blue, and Triton X-100 reached the levels of 927.0, 298.4, and 644.3 mg/g, respectively, on the surface of the H₃PO₄-activated sample obtained by microwave heating. It was confirmed that the heating method used during the activation step plays a key role in determining the physicochemical properties and sorption efficiency of activated biocarbons. Full article

We present a theoretical model for the electrophoresis of a weakly charged oil drop migrating through an uncharged polymer gel medium saturated with an aqueous electrolyte solution. The surface charge of the drop arises from the specific adsorption of ions onto its interface. Unlike solid particles, liquid drops exhibit internal fluidity and interfacial dynamics, leading to distinct electrokinetic behavior. In this study, the drop motion is driven by long-range hydrodynamic effects from the surrounding gel, which are treated using the Debye–Bueche–Brinkman continuum framework. A simplified version of the Baygents–Saville theory is adopted, assuming that no ions are present inside the drop and that the surface charge distribution results from linear ion adsorption. An approximate analytical expression is derived for the electrophoretic mobility of the drop under the condition of low zeta potential. Importantly, the derived expression explicitly includes the Marangoni effect, which arises from spatial variations in interfacial tension due to non-uniform ion adsorption. This model provides a physically consistent and mathematically tractable basis for understanding the electrophoretic transport of oil drops in soft porous media such as hydrogels, with potential applications in microfluidics, separation processes, and biomimetic systems. These results also show that the theory could be applied to more complicated or biologically important soft materials. Full article

Improving photovoltaic (PV) panel performance under extreme climatic conditions is critical for advancing sustainable energy systems. In hyper-arid regions, elevated operating temperatures significantly reduce panel efficiency. This study investigates and compares three cooling techniques—air cooling, water cooling, and porous media cooling—using thermal and electrical modeling based on CFD simulations in ANSYS. The numerical model replicates a PV system operating under peak solar irradiance (900 W/m²) and realistic ambient conditions in Adrar, Algeria. Simulation results show that air cooling leads to a modest temperature reduction of 6 °C and a marginal efficiency gain of 0.25%. Water cooling, employing a top-down laminar flow, reduces cell temperature by over 35 °C and improves net electrical output by 30.9%, despite pump energy consumption. Porous media cooling, leveraging passive evaporation through gravel, decreases panel temperature by around 30 °C and achieves a net output gain of 26.3%. Mesh sensitivity and validation against experimental data support the accuracy of the model. These findings highlight the significant potential of water and porous material cooling strategies to enhance PV performance in hyper-arid environments. The study also demonstrates that porous media can deliver high thermal effectiveness with minimal energy input, making it a suitable low-cost option for off-grid applications. Future work will integrate long-term climate data, real diffuser geometries, and experimental validation to further refine these models. Full article

This study investigated the degradation efficacy, kinetics, and mechanism of the ozone (O₃) process and two enhanced O₃ processes (O₃/peroxymonosulfate (O₃/PMS) and O₃/peroxymonosulfate/iron molybdates/biochar composite (O₃/PMS/FeMoBC)), especially the O₃/PMS/FeMoBC process, for the degradation of tetracycline (TC) in water. An FeMoBC sample was synthesized by the impregnation–pyrolysis method. The XRD results showed that the material loaded on BC was an iron molybdates composite, in which Fe₂Mo₃O₈ and FeMoO₄ accounted for 26.3% and 73.7% of the composite, respectively. The experiments showed that, for the O₃/PMS/FeMoBC process, the optimum conditions were obtained at pH 6.8 ± 0.1, an initial concentration of TC of 0.03 mM, an FeMoBC dosage set at 200 mg/L, a gaseous O₃ concentration set at 3.6 mg/L, and a PMS concentration set at 30 μM. Under these reaction conditions, the degradation rate of TC in 8 min and 14 min reached 94.3% and 98.6%, respectively, and the TC could be reduced below the detection limit (10 μg/L) after 20 min of reaction. After recycling for five times, the degradation rate of TC could still reach about 40%. The introduction of FeMoBC into the O₃/PMS system significantly improved the TC degradation efficacy and resistance to inorganic anion interference. Meanwhile, it enhanced the generation of hydroxyl radicals (^•OH) and sulfate radicals (SO₄^•−), thus improving the oxidizing efficiency of TC in water. Material characterization analysis showed that FeMoBC has a well-developed porous structure and abundant active sites, which is beneficial for the degradation of pollutants. The reaction mechanism of the O₃/PMS/FeMoBC system was speculated by the EPR technique and quenching experiments. The results showed that FeMoBC efficiently catalyzed the O₃/PMS process to generate a variety of reactive oxygen species, leading to the efficient degradation of TC. There are four active oxidants in O₃/PMS/FeMoBC system, namely ^•OH, SO₄^•−, ¹O₂, and •O₂⁻. The order of their contribution importance was ^•OH, ¹O₂, SO₄^•−, and •O₂⁻. This study provides an effective technological pathway for the removal of refractory organic matter in the aquatic environment. Full article

The dynamic non-equilibrium effect (DNE) describes the non-unique character of saturation–capillary pressure relationships observed under static, steady-state, or monotonic hydrodynamic conditions. Macroscopically, the DNE manifests as variations in soil hydraulic characteristic curves arising from varying hydrodynamic testing conditions and is fundamentally governed by soil matrix particle size distribution. Changes in the DNE across porous media with discrete particle size fractions are investigated via stepwise drying experiments. Through quantification of saturation–capillary pressure hysteresis and DNE metrics, three critical signatures are identified: (1) the temporal lag between peak capillary pressure and minimum water saturation; (2) the pressure gap between transient and equilibrium states; and (3) residual water saturation. In the four experimental sets, with the finest material (Test 1), the peak capillary pressure consistently precedes the minimum water saturation by up to 60 s. Conversely, with the coarsest material (Test 4), peak capillary pressure does not consistently precede minimum saturation, with a maximum lag of only 30 s. The pressure gap between transient and equilibrium states reached 14.04 cm H₂O in the finest sand, compared to only 2.65 cm H₂O in the coarsest sand. Simultaneously, residual water saturation was significantly higher in the finest sand (0.364) than in the coarsest sand (0.086). The results further reveal that the intensity of the DNE scales inversely with particle size and linearly with wetting phase saturation (Sw), exhibiting systematic decay as Sw decreases. Coarse media exhibit negligible hysteresis due to suppressed capillary retention; this is in stark contrast with fine sands, in which the DNE is observed to persist in advanced drying stages. These results establish pore geometry and capillary dominance as fundamental factors controlling non-equilibrium fluid dynamics, providing a mechanistic framework for the refinement of multi-phase flow models in heterogeneous porous systems. Full article

With the rapid development of wearable electronics, traditional rigid thermal management materials face limitations in flexibility, conformability, and multi-physics adaptability. Low-dimensional carbon materials such as graphene and carbon nanotubes combine ultrahigh thermal conductivity with outstanding mechanical compliance, making them promising building blocks for flexible thermal regulation. This review summarizes recent advances in integrating these materials into textile architectures, mapping the evolution of this emerging field. Key topics include phonon-dominated heat transfer mechanisms, strategies for modulating interfacial thermal resistance, and dimensional effects across scales; beyond these intrinsic factors, hierarchical textile configurations further tailor macroscopic performance. We highlight how one-dimensional fiber bundles, two-dimensional woven fabrics, and three-dimensional porous networks construct multi-directional thermal pathways while enhancing porosity and stress tolerance. As for practical applications, the performance of carbon-based textiles in wearable systems, flexible electronic packaging, and thermal coatings is also critically assessed. Current obstacles—namely limited manufacturing scalability, interfacial mismatches, and thermal performance degradation under repeated deformation—are analyzed. To overcome these challenges, future studies should prioritize the co-design of structural and thermo-mechanical properties, the integration of multiple functionalities, and optimization guided by data-driven approaches. This review thus lays a solid foundation for advancing carbon-based smart textiles toward next-generation flexible thermal management technologies. Full article

Magnetorheological (MR) foams represent a class of smart materials with unique tunable viscoelastic properties when subjected to external magnetic fields. Combining porous structures with embedded magnetic particles, these materials address challenges such as leakage and sedimentation, typically encountered in conventional MR fluids while offering advantages like lightweight design, acoustic absorption, high energy harvesting capability, and tailored mechanical responses. Despite their potential, challenges such as non-uniform particle dispersion, limited durability under cyclic loads, and suboptimal magneto-mechanical coupling continue to hinder their broader adoption. This review systematically addresses these issues by evaluating the synthesis methods (ex situ vs. in situ), microstructural design strategies, and the role of magnetic particle alignment under varying curing conditions. Special attention is given to the influence of material composition—including matrix types, magnetic fillers, and additives—on the mechanical and magnetorheological behaviors. While the primary focus of this review is on MR foams, relevant studies on MR elastomers, which share fundamental principles, are also considered to provide a broader context. Recent advancements are also discussed, including the growing use of artificial intelligence (AI) to predict the rheological and magneto-mechanical behavior of MR materials, model complex device responses, and optimize material composition and processing conditions. AI applications in MR systems range from estimating shear stress, viscosity, and storage/loss moduli to analyzing nonlinear hysteresis, magnetostriction, and mixed-mode loading behavior. These data-driven approaches offer powerful new capabilities for material design and performance optimization, helping overcome long-standing limitations in conventional modeling techniques. Despite significant progress in MR foams, several challenges remain to be addressed, including achieving uniform particle dispersion, enhancing viscoelastic performance (storage modulus and MR effect), and improving durability under cyclic loading. Addressing these issues is essential for unlocking the full potential of MR foams in demanding applications where consistent performance, mechanical reliability, and long-term stability are crucial for safety, effectiveness, and operational longevity. By bridging experimental methods, theoretical modeling, and AI-driven design, this work identifies pathways toward enhancing the functionality and reliability of MR foams for applications in vibration damping, energy harvesting, biomedical devices, and soft robotics. Full article