Search Results (113)

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

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 the first successful integration of Fe₃O₄ and Li_0.5Cr_0.5Fe₂O₄ into a well-defined core/shell nanostructure through a two-step synthesis that combines co-precipitation and sol–gel auto-combustion methods. Unlike conventional composites, the core/shell design effectively suppresses the magnetic dead layer and promotes exchange coupling at the interface, leading to enhanced saturation magnetization, superior magnetic heating (specific absorption rate; SAR), and improved dielectric properties. Our research introduces a novel interfacial engineering strategy that simultaneously optimizes both magnetic and dielectric performance, offering a multifunctional platform for applications in magnetic hyperthermia, electromagnetic interference (EMI) shielding, and microwave devices. Full article

Lithium hydride (LiH) is one promising material for nuclear reactor shielding due to its high hydrogen content, but its poor mechanical strength and thermal conductivity pose challenges for fabricating large, crack-free ceramic components via conventional sintering. This study explores microwave sintering as a potential solution to enhance heating uniformity and reduce thermal stress during densification of bulk LiH ceramics. Using implicit function and level set methods, we numerically simulated the microwave field distribution and thermal response in both stationary and rotating samples. The results show that rotational heating improves temperature uniformity by up to 12.9% for specific samples, although uniform temperature control remains difficult through rotation alone. To mitigate stress accumulation from thermal gradients, we propose a cyclic sintering–resting strategy, which leverages LiH’s tensile strength–temperature envelope to guide safe and efficient processing. This strategy successfully reduced total sintering time from several days to 1.63 h without inducing cracks. Our findings offer practical insights into optimizing microwave sintering parameters for large-scale LiH ceramic production and contribute to enabling its application in advanced nuclear shielding systems. Full article

Tungsten heavy alloys (WHAs) are two-phase composites known for their exceptional density, strength, hardness, and ductility, making them ideal for radiation shielding, kinetic energy penetrators, and aerospace components. Due to their high melting point, WHAs are primarily processed via powder metallurgy, with liquid-phase sintering (LPS). Spark plasma sintering (SPS) and microwave sintering are emerging as advanced consolidation techniques. Recent research has focused on improving WHA performance through microstructural manipulation, alloying with elements like Fe, Co, Mo, and Re; rare earth oxides like Y₂O₃, La₂O₃, and Ce₂O₃; and employing high-entropy alloys (HEAs) as matrix phase. Additionally, additive manufacturing (AM) techniques are increasingly being used to fabricate complex WHA components. Despite their advantages, WHAs still exhibit limitations in penetration performance, primarily due to their tendency to form mushroom-like heads upon impact rather than self-sharpening. Ongoing research seeks to enhance shear localization, refine grain structure, and optimize processing methods to improve the mechanical properties and impact resistance of WHAs. Furthermore, modeling and simulation approaches are being explored to understand the mechanical behavior of WHAs. This review comprehensively overviews the above aspects and presents recent advances in WHA processing. Full article

In both fundamental and applied scientific exploration, nanostructured protective materials have garnered substantial interest owing to their multifaceted utilization in the fields of medicine, pharmaceuticals, and electronics, among others. This study investigated the evolution of cutting-edge materials for electromagnetic radiation attenuation, with a specific emphasis on the incorporation of superparamagnetic magnetite nanoparticles, Fe₃O₄, into composite systems. The nanoparticles were generated through chemical condensation, meticulously adjusting the proportions of iron salts, specifically FeSO₄·7H₂O and FeCl₃·6H₂O, in conjunction with a 25% aqueous solution of ammonia, NH₄OH·H₂O. This study examined the intricate details of the crystalline structure, the precise composition of phases, and the intricate physicochemical attributes of these synthesized Fe₃O₄ nanoparticles. The analysis was conducted employing a suite of advanced techniques, including scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and energy-dispersive analysis (EDAX). The key findings of this research suggest that the magnetic nanoparticles generated through chemical condensation have an average size between 10 and 11 nm. This size was determined using BET surface area measurements, which were precise to within 0.1 nm. Moreover, this study demonstrated that incorporating superparamagnetic nanoparticles into composite materials significantly reduces microwave radiation. In particular, an optimal concentration of 0.25% by weight leads to a maximum decrease of 21.7 dB in cement specimens measuring 10 mm in thickness. Moreover, a critical threshold concentration of 0.5 weight percent is established, beyond which the interactions of nanoparticles inhibit the process of remagnetization. These investigations demonstrate that it is feasible to pursue a route towards the development of highly effective electromagnetic shielding materials tailored to specific requirements for diverse applications. Full article

Cesium tungsten bronzes (Cs_xWO₃), as functional materials with excellent near-infrared shielding properties, demonstrate significant potential for applications in smart windows. However, traditional synthesis methods, such as solid-state reactions and solvothermal/hydrothermal approaches, typically require harsh conditions, including high temperatures (above 200 °C), high pressure, inert atmospheres, or prolonged reaction times. In this study, we propose an optimized microwave-assisted solvothermal synthesis strategy that significantly reduces the severity of reaction conditions through precise parameter control. When benzyl alcohol was employed as the solvent, Cs_xWO₃ nanoparticles could be rapidly synthesized within a relatively short duration of 15 min at 180 °C, or alternatively obtained through 2 h at a low temperature of 140 °C. However, when anhydrous ethanol, which is cost-effective and environmentally friendly, was substituted for benzyl alcohol, successful synthesis was also achieved at 140 °C in 2 h. This method overcomes the limitations of traditional high-pressure reaction systems, achieving efficient crystallization under low-temperature and ambient-pressure conditions while eliminating safety hazards and significantly improving energy efficiency. The resulting materials retain excellent near-infrared shielding performance and visible-light transparency, providing an innovative solution for the safe, rapid, and controllable synthesis of functional nanomaterials. Full article

Laser-induced graphene (LIG) has become a promising stealth material due to its excellent electromagnetic loss characteristics in the terahertz and microwave bands (2–18 Ghz) and the advantages of low-cost large-scale manufacturing. With the rapid advancement of electromagnetic detection technologies toward multispectral and high-dynamic-range capabilities, there is an increasing demand for LIG-based stealth materials with superior absorption performance. The synergistic design of functional material doping and structural configurations has been identified as a critical approach to achieve high electromagnetic shielding performance in LIG-based composites. This article briefly reviews the developmental progress of LIG-based electromagnetic stealth materials, with a particular emphasis on doping technologies and shielding mechanisms tailored for stealth applications. Furthermore, we propose potential future development pathways for LIG-based stealth materials to facilitate their transition toward broader practical applications. Full article

MXene is widely used in the fields of microwave absorption and electromagnetic shielding to balance electromagnetic pollution with the development of communication technologies and human health, due to its excellent surface functional groups and tunable electronic properties. Although pure multilayered MXene has an excellent accordion-like structure, the weak dielectric loss and lack of magnetic loss result in poor microwave absorption performance. Here, we propose a strategy for the catalytic growth of CNTs by the electrophoretic deposition of adsorbed metal ions, leading to the successful preparation of Ni-MWCNTs/Ti₃C₂T_x composites with a “layer-by-layer” structure, achieved through in situ regulated growth of CNTs. By introducing dielectric–magnetic synergy to improve the impedance matching conditions, and by regulating the diameter of the CNTs to alter the electromagnetic parameters of Ni-MWCNTs/Ti₃C₂T_x, the 2-Ni-MWCNTs/Ti₃C₂T_x composite achieves the best reflection loss (RL) value of −44.08 dB and an effective absorption bandwidth of 1.52 GHz at only 2.49 mm thickness. This unique layered structure and the regulation strategy provide new opportunities for the development of few-layered MXene composites. Full article

The increasing demand for high-frequency applications and the widespread use of electromagnetic (EM) waves in communication systems necessitate the development of effective electromagnetic interference (EMI) shielding materials. This study investigates the structural and shielding effectiveness properties of novel polyaniline (PANI)-based NiO/ZnNb₂O₆ composites for sub-8 GHz applications. NiO and ZnNb₂O₆ were synthesized via conventional solid-state reactions and combined with PANI to form composites with varying compositions. X-ray diffraction (XRD) confirmed the successful formation of single-phase NiO and ZnNb₂O₆, while scanning electron microscopy (SEM) revealed well-defined microstructures, contributing to enhanced shielding efficiency. Shielding effectiveness (SE) measurements were performed across the 0–8 GHz frequency range using a vector network analyzer. Among the compositions tested, the epoxy-based NiO-ZnNb₂O₆ (75–25% by weight) with a 1:1 PANI ratio exhibited the highest SE value of −41.16 dB (decibels) at 6.24 GHz, demonstrating superior attenuation of EM waves. The observed shielding efficiency is attributed to multiple reflection effects, dipole interactions, and the conductive network formed by PANI. These findings highlight the potential of NiO/PANI/ZnNb₂O₆ composites as cost-effective, high-performance EMI shielding materials for next-generation microwave communication and electronic applications. Further optimization and hybridization approaches are recommended to enhance performance for broader frequency bands. Full article

Radiation-shielding concrete, widely used in protective structures because of its effective shielding properties, employs magnetite aggregates to achieve higher compressive strength than conventional concrete. However, prolonged exposure to high temperatures leads to mechanical degradation. This study investigates the thermal evolution of magnetite concrete under microwave heating across varying temperatures (38–800 °C). A microwave oven was utilized for heating, and COMSOL Multiphysics was employed to establish an electromagnetic-thermal-mechanical coupled model, analyzing surface characteristics, temperature distribution, stress-strain behavior, and residual compressive strength. Results indicate that internal temperatures exceed surface temperatures during microwave heating, with a maximum temperature difference surpassing 150 °C at 800 °C. Compressive stresses predominantly arise in the mortar, while tensile stresses concentrate in aggregates and the interface transition zone, causing stress concentration. Mortar exhibits greater deformation than aggregates as temperatures increase. Simulated and experimental residual compressive strengths show strong agreement, with a maximum deviation of 7.58%. The most rapid mechanical deterioration occurs at 450–600 °C, marked by a residual compressive strength decline of 0.07 MPa/°C and the formation of penetrating cracks. Full article

This study investigates innovative pathways for sustainable carbonization by comparing the performance and environmental impacts of microwave and muffle furnace heating technologies in the production of activated carbon from textile waste. The muffle furnace process demonstrated superior material properties, achieving a higher surface area (538.42 m²/g) and exceptional electromagnetic interference (EMI) shielding effectiveness (47.56 dB at 2 GHz). It also exhibited better electrical conductivity, making it highly suitable for EMI shielding applications. Conversely, the microwave method, while yielding a lower surface area (383.92 m²/g) and EMI shielding (38.60 dB at 1 GHz), showed promising electrical conductivity and remarkable advantages in time and energy efficiency. A novel Green Performance Efficiency (GPE) metric was developed to evaluate the sustainability of these processes holistically, integrating performance parameters such as EMI shielding with energy consumption and process duration. The GPE analysis revealed that the microwave method outperformed the muffle furnace in terms of energy and time efficiency, achieving a significantly higher GPE score. However, the muffle furnace method excelled in material performance metrics, highlighting the trade-offs between sustainability and functionality. The findings not only provide a standardized framework for evaluating and optimizing carbonization technologies but also offer actionable insights into balancing efficiency and performance in sustainable activated carbon production. This research paves the way for advanced applications in EMI shielding, energy storage, and sustainable material development, demonstrating the potential of GPE as a benchmark for green technology innovation. Full article

Magnetic ionic liquid (MIL) based on alkyl phosphonium cation was used as a curing agent for developing epoxy nanocomposites (ENCs) modified with a graphene nanoplatelet (GNP)/carbon nanotube (CNT) hybrid filler. The materials were prepared by a solvent-free procedure involving ball-milling technology. ENCs containing as low as 3 phr of filler (GNP/CNT = 2.5:0.5 phr) exhibited electrical conductivity with approximately six orders of magnitude greater than the system loaded with GNP = 2.5 phr. Moreover, the use of MIL (10 phr) resulted in ENCs with higher conductivity compared with the same system cured using conventional aliphatic amine. The filler dispersion within the epoxy matrix was confirmed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electromagnetic interference shielding effectiveness (EMI SE), evaluated in the X- and Ku-band frequency range, revealed a great contribution of the absorption mechanism for the ENC containing the hybrid filler and cured with MIL. Moreover, the best microwave-absorbing response was achieved with the ENC containing GNP/CNT = 2.5/0.5 phr, and cured with ML, which a minimum RL of −23.61 dB and an effective absorption bandwidth of 5.18 GHz were observed for thickness of 1.5 mm. In summary, this system is a promising material for both civilian and military applications due to its simple and scalable nanocomposite preparation method, the lightweight nature of the composites resulting from the low filler content, the commercial availability and cost-effectiveness of GNP, and its high electromagnetic wave attenuation across a broad frequency range. Full article

This research investigates the synthesis and characterization of GdMnO₃/chopped strands composites using the conventional oxide mixing technique. A single-phase GdMnO₃ compound was successfully formed through sintering at 1350 °C for 20 h. Structural analysis using X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) confirmed phase purity and uniform grain morphology. The microwave shielding effectiveness of GdMnO₃/chopped strands composites was evaluated within the 6.5–17.5 GHz frequency range using a network analyzer (NA). The GdMnO₃/chopped strands composite with a 60–40% weight ratio exhibited superior shielding performance, achieving a minimum shielding effectiveness of −35.61 dB at 6.9 GHz, while the 80–20% composite reached −32.54 dB at 16.74 GHz. Both compositions demonstrated shielding effect values below −10 dB across wide frequency bands, with significant attenuation below −20 dB at various GHz ranges. The study demonstrates that by adjusting the content of the components in the samples, the microwave shielding effect performance of the GdMnO₃/chopped strands composites can be easily controlled to meet the requirements of specific frequency bands. These findings highlight the potential of GdMnO₃-based composites for tailored microwave shielding applications, particularly in the military, aerospace, and telecommunication industries. Full article

In recent years, W-Cu composite systems have become very interesting subjects due to good electrical and thermal conductivity, high-temperature strength, certain plasticity, and excellent radiation resistance. W-Cu composites are a very important class of materials in applications like PFM (plasma facing materials), functional graded materials (FGM), electronic packaging materials, high-voltage electrical contacts, sweating materials, shaped charge liners, electromagnetic gun-rail materials, kinetic energy penetrators, and radiation shielding/protection. There is no possibility of forming a crystalline structure between these two materials. However, due to the unique properties these materials possess, they can be used by preparing them as a composite. Generally, W-Cu composites are prepared via the conventional powder metallurgy routes, i.e., sintering, hot pressing, hot isostatic pressing, isostatic cold pressing, sintering and infiltration, and microwave sintering. However, these processes have certain limitations, like the inability to produce bulk material, they are expensive, and their adoptability is limited. Here, in this review, we will discuss in detail the fabrication routes of additive manufacturing, and its current progress, challenges, trends, and associated properties obtained. We will also explain the challenges for the additive manufacturing of the composite. We will also compare W-Cu composites to other materials that can challenge them in terms of specific applications or service conditions. The solidification mechanism will be explained for W-Cu composites in additive manufacturing. Finally, we will conclude the progress of additive manufacturing of W-Cu composites to date and suggest future recommendations based on the current challenges in additive manufacturing. Full article