Dielectric Applications Research Articles

Synthesis and Characterization of PVC/(Co3O4/CNT)@Au Semiconductor Nanocomposite for Enhanced Medium-Voltage Cable Insulation

Abstract This study presents the synthesis, characterization, and application of a novel PVC/(Co3O4/CNT)@Au nanocomposite for enhanced medium-voltage cable insulation. The nanocomposite was developed by incorporating Co3O4 octahedron nanoparticles, carbon nanotubes (CNTs), and gold nanoparticles (Au) into a polyvinyl chloride matrix. Compared to standard PVC insulation, the nanocomposite exhibited a 3% improvement in relative permittivity (increased from 2.34 to 2.41) and significantly enhanced field uniformity, as evidenced by simulation studies. Fourier-transform infrared spectroscopy, X-ray diffraction, and electron microscopy confirmed the successful integration of nanofillers and highlighted their contributions to the composite’s properties. Optical characterization revealed a direct bandgap of 4.60 eV and an Urbach energy of 0.3674 eV, indicating a wide-bandgap semiconductor with moderate structural disorder. AC conductivity measurements demonstrated frequency-dependent behavior, while dielectric constant and loss analyses suggested the material’s potential for energy storage and insulation applications. The choice of Co3O4 and CNTs was guided by their synergistic impact on charge trapping, field grading, and thermal management, while Au nanoparticles enhanced charge transfer and local electric field distribution. These findings demonstrate the nanocomposite’s promise in addressing the limitations of traditional PVC insulation, offering improved dielectric performance, reliability, and durability for power transmission and distribution systems.

Exploitation of Perennial Plant Biomass for Particleboards Designed for Insulation Applications

With rising demand for wood products and reduced wood harvesting due to the European Green Deal, alternative lignocellulosic materials for insulation are necessary. In this work, we manufactured reference particleboard from industrial particles and fifteen different board variants from alternative lignocellulosic plants material, i.e., five types of perennial plant biomass in three substitutions: 30, 50 and 75% of their share in the board with a nominal density of 250 kg/m3. Within the analysis of manufactured boards, the mechanical, chemical and thermal properties were investigated—internal bond, formaldehyde emissions, thermal insulation, heat transfer coefficient and thermal conductivity. In the case of thermal conductivity, the most promising results from a practical point of view (W/mK < 0.07) were obtained with Sida hermaphrodita and Miscanthus, achieving the best results at 50% substitution. The lowest formaldehyde emissions were recorded for boards with Panicum virgatum and Miscanthus, highlighting their positive environmental performance. In terms of mechanical properties, the highest internal bond was noticed in particleboards with a 30% substitution of Spartina pectinata and Miscanthus. Research findings confirm the potential of perennial plants as a sustainable source of raw materials for insulation panel manufacturing. Despite needing improvements in mechanical properties, most notably internal bond strength, these plants offer an ecologically responsible solution aligned with global construction trends, thus lessening reliance on traditional wood products. Thus, long-term benefits may be realized through the strategic combination of diverse raw materials within a single particleboard.

Poly(p-Phenylene Benzobisoxazole) Nanofiber: A Promising Nanoscale Building Block Toward Extremely Harsh Conditions.

Since the invention and commercialization of poly(p-phenylene benzobisoxazole) (PBO) fibers, numerous breakthroughs in applications have been realized both in the military and aerospace industries, attributed to its superb properties. Particularly, PBO nanofibers (PNFs) not only retain the high performance of PBO fiber but also exhibit impressive nanofeatures and desirable processability, which have been extensively applied in extreme scenarios. However, no review has yet comprehensively summarized the preparation, applications, and prospective challenges of PNFs to the best of our knowledge. Herein, the two fabrication pathways to acquire PNFs from bottom-up to top-down approaches are critically overviewed; the significant advantages and the problem caused simultaneously of the protonation approach compared with other methods are revealed. Besides, the construction strategies of multidimensional PNF-based advanced composites, including 1D fiber, 2D film/nanopaper, and 3D gel, are discussed. Moreover, the outstanding mechanical, insulating, and thermal stability properties of PNFs facilitate their extensive applications in thermal protection, electrical insulation, batteries, and flexible wearable devices, which are further comprehensively introduced. Finally, the perspective and challenges of the fabrication and application of PNFs are highlighted. It demonstrates that the PNFs as one of the promising high-performance nanoscale building blocks can be fully competent using extremely harsh conditions.

Preceramic polymer-hybridized phenolic aerogels and the derived ZrC/SiC/C ceramic aerogels with ultrafine nanocrystallines.

Phenolic and carbon aerogels have important applications for thermal insulation and ablative resistance materials in aerospace field. However, their antioxidant ability in long-term high-temperature aerobic environments faces serious challenges. To solve this problem, Zr/Si preceramic polymer hybridized phenolic resin (PR-ZS) aerogels were prepared via a facile sol-gel method. Compared with pure phenolic aerogel, the hybrid aerogels possess similar porous microstructure but larger specific surface area, better thermo-oxidative stability, and higher compressive strength. After carbonization at 1700 °C, the hybrid aerogels can be transformed to carbide ceramic aerogels with ultrafine nanocrystalline ZrC and SiC particles embedded in the carbon matrix. Ceramic aerogels exhibit good thermal insulative and anti-ablative properties in a butane torch simulated high-temperature and aerobic environment. The linear ablation rate is as low as 0.017 mm min-1, and the backside temperature is below 330 °C at a 20 mm in-depth position after 300 s of burning test, when the front temperature is approximately 960 °C. This work provides a facile approach to fabricate hybrid phenolic aerogels and derived ZrC/SiC/C ceramic aerogels, which target on applications for extreme environments in aerospace field.

A self-clearing electrode concept for dielectric elastomer applications using single-wall carbon nanotubes line

A self-clearing electrode concept for dielectric elastomer applications using single-wall carbon nanotubes line

Facile controlled growth of multilayer h-BN thin films using spaced-confined APCVD and its gate dielectric application

Facile controlled growth of multilayer h-BN thin films using spaced-confined APCVD and its gate dielectric application

Non-linear thermohaline instability of a Jeffrey fluid in a porous layer with chemical reaction

Porous materials have various applications in solar energy systems, including adsorption, insulation, and evaporation. This study examines the use of porous materials in solar energy systems and focuses on the thermohaline convection of a Jeffrey fluid in a horizontal porous layer. The analysis includes both linear and non-linear approaches and employs the method of normal modes to solve the governing equations. It demonstrates that there is a coincidence between the linear and non-linear stability thresholds and shows that linear stability alone captures all the physics of the system. The linear instability is solved using the one-term Galerkin approach, while the non-linear instability is solved numerically using the bvp4c routine in MATLAB. The study highlights the destabilising effect of the Jeffrey parameter on the fluid layer, while the solute Rayleigh number is found to stabilise the flow. The Damkholer number shows no impact on the stationary convection when the thermal and solutal diffusivities are equal; however, it exhibits a stabilising influence on the oscillatory convection. Additionally, the Vadasz number does not affect the stationary instability but contributes to the destabilisation of the oscillatory instability.

Sintering‐resistant porous BaZrO3 ceramics using a particle‐stabilized foam method for thermal insulation applications

AbstractSintering and phase transitions of materials in current large‐area thermal insulation systems are critical problems for hypersonic vehicles. Searching for thermal insulation materials with good structure stability, thermal stability, and superior insulation performance is urgent for the development of these vehicles. Herein, we reported a novel porous BaZrO3 ceramic fabricated by a particle‐stabilized foam method. By controlling the sintering temperature, the porosity (92.96%–94.62%), thermal conductivity (0.088–0.193 W/(m·K)), and strength (0.30–1.31 MPa) of the porous ceramics are tunable. Most importantly, these porous BaZrO3 ceramics exhibit excellent sintering resistance. After being heat treated at 1300°C for 6 h, the shrinkage of porous BaZrO3 ceramics is nearly 0. The shrinkage of the samples heat‐treated even at 1600°C is still lower than 3%, demonstrating outstanding high‐temperature structure stability. Our results demonstrate that porous BaZrO3 ceramics are promising candidates for high‐temperature thermal insulation applications.

Enhanced Thermal Safety of Hydrophobic SiO2 Aerogels Through Introduction of Layered Double Oxides.

This research enhances the thermal safety of hydrophobic silica aerogel (HSA) by integrating layered double oxides (LDOs). XRD and FTIR confirm that the introduction of LDOs does not affect the formation of SA. The LDO/SA composites demonstrate a low density (0.14-0.16 g/cm3), low thermal conductivity (23.28-28.72 mW/(m·K)), high porosity (93.4-96.1%), and a high surface area (899.2-1006.4 m2/g). The TG-DSC results reveal that LDO/SA shows enhanced thermal stability, with increases of 49 °C in the decomposition onset temperature and 47.4 °C in the peak decomposition temperature. The gross calorific value of LDO/SA-15% (with 15 wt% LDO) exhibits a 23.9% reduction in comparison to that of pure SA. The decrease in gross calorific value, along with improved thermal stability, indicates a boost in the thermal safety characteristics of the LDO/SA composites. This study demonstrates that incorporating LDOs enhances the thermal safety of HSA, while preserving its superior performance, thus broadening its potential applications in thermal insulation.

Boosting High Electric Breakdown Strength for Excellent Energy Storage Performance in Bi0.5Na0.5TiO3-Based Lead-Free Ceramics via a High Entropy Strategy.

High-performance dielectric capacitors featuring large recoverable energy storage density (Wrec) and high discharge efficiency (η) are beneficial to realize the device miniaturization, lightweight property, and sustainability of advanced pulse power systems. The obtainment of a high electric breakdown strength (Eb) is crucial for improving the energy storage performance of dielectric materials. However, as for Bi0.5Na0.5TiO3 (BNT) lead-free relaxor ferroelectric ceramics, the relatively lower Eb directly limits their electrical performance improvement and practical applications. Herein, a popular high entropy strategy was employed to rationally design and prepare the (Bi0.5Na0.5)x(Sr0.25Ba0.25La0.25K0.25)(1-x)TiO3 (BNSLBKT-x) lead-free relaxor ferroelectric ceramics based on the BNT matrix. Encouragingly, the BNSLBKT-0.2 high-entropy ceramic exhibits a high Eb of 510 kV/cm, and this can be ascribed to the refined grains and enhanced activation energy. Moreover, it is confirmed that the polar nanoregions (PNRs) exist in the BNSLBKT-0.2 ceramic by the piezoresponse force microscopy (PFM) and transmission electron microscopy (TEM) characteristics, further strengthening relaxation behaviors and decreasing remanent polarization (Pr). It is anticipated that a high Wrec of 4.6 J/cm3 and a good η of 86% are obtained in this BNSLBKT-0.2 high-entropy ceramic. More importantly, the BNSLBKT-0.2 ceramic displays excellent frequency stability of capacitive energy storage at 10-1000 Hz and good temperature stability at 20-140 °C. The fast discharge rate (τ0.9 = 0.26 μs) and the high PD of 49.2 MW/cm are also achieved in this BNSLBKT-0.2 ceramic. The findings demonstrate that this high entropy design is an effective strategy for developing dielectrics with excellent energy storage capability to meet the requirements of modern dielectric capacitor applications.

Effects of Copper-Modified Activated Carbon on Natural Rubber Composite for Dielectric Materials

This study reports the development of an elastomeric dielectric material based on natural rubber (NR) composites reinforced with copper-modified activated carbon (Cu-Ac) derived from coconut shells. The Cu-Ac content was varied systematically (0, 5, 10, and 15 phr) at a fixed Cu concentration (2 wt%). The investigation focused on the influence of Cu-Ac content on various material properties, including curing time (tc⁹⁰), density, crosslink density, mechanical behavior, morphology, and dielectric response. The results revealed a significant impact of Cu-Ac content on the curing process, with an observed decrease in tc90 at higher Cu-Ac loadings (10 and 15 phr). However, crosslink density exhibited a decreasing trend with increasing Cu-Ac content. Encouragingly, the inclusion of Cu-Ac demonstrated a positive influence on the mechanical properties of the composite. Notably, the dielectric properties confirmed the effect of Cu-Ac on NR, with enhancements observed within the frequency range of 1.35 to 2.03 GHz. This study provides valuable insights into the influence of Cu-Ac content on NR composites, suggesting their potential for improved performance in dielectric applications.

Geopolymer Foam with Low Thermal Conductivity Based on Industrial Waste.

Geopolymer materials are increasingly being considered as an alternative to environmentally damaging concrete based on Portland cement. The presented work analyzed waste from mines and waste incineration plants as potential precursors for producing geopolymer materials that could be used to make lightweight foamed geopolymers for insulation applications. The chemical and phase composition, radioactivity properties, and leachability of selected precursors were analyzed. Then, geopolymer materials were produced, and their strength properties were examined through compression and flexural tests. The results of the strength tests guided the material selection for foamed geopolymer materials. Next, geopolymer foams were foamed with hydrogen peroxide and aluminum powder. The produced foamed materials were subjected to strength and thermal conductivity tests. The results demonstrated the great potential of mine waste in the synthesis of geopolymers and the production of lightweight geopolymer foams with good insulating properties.

Ultra-High Capacitive Energy Storage Density at 150°C Achieved in Polyetherimide Composite Films by Filler and Structure Design.

Polymer dielectrics are crucial for electronic communications and industrial applications due to their high breakdown field strength (Eb), fast charge/discharge speed, and temperature stability. The upcoming electronic-electrical systems pose a significant challenge, necessitating polymeric dielectrics to exhibit exceptional thermal stability and energy storage capabilities at high temperatures. Here, ultra-high dielectric constant (ɛr) and charge/discharge efficiency (η) of 0.55Bi0.5(Na0.84K0.16)0.5TiO3-0.45(Bi0.1Sr0.85)TiO3 (BNKT-BST) ceramics are prepared by the solid-phase reaction method and added to polyetherimide (PEI) to form BNKT-BST/PEI nanocomposites with various structures. The findings indicate that the sandwich-structured BNKT-BST/PEI nanocomposite achieves the highest discharged energy density (Ud) of 7.7 Jcm-3 with η of 80.2% when the Eb is 650 MVm-1 at 150°C. This is primarily due to the incorporation of BNKT-BST nanoparticles and the multilayer structure design, which significantly improves the composite's ɛr and Eb. Additionally, the sandwich-structured composites show excellent cycling stability at 500 MVm-1 and 150°C, with Ud of ≈ 4.7 Jcm-3 and η greater than 90%. The research presents nanocomposites with high energy storage density and excellent stability, crucial for the practical application of polymer dielectrics in high-temperature environments.

INFLUENCE OF BOUNDARY CONDINIONS ON THE PLASMA POTENTIAL IN A HELICON DISCHARGE WITH PLANAR ANTENNA

In a helicon discharge excited by a flat inductive antenna, situated at the discharge chamber end, distributions of plasma parameters have been measured by a thermo-emissive probe. The aim of the work was to define an influence producing by the bias potential of the surface being processed on plasma parameters in discharge chambers with either the dielectric or with conducting side walls. It was found that in the dielectric chamber application of a positive voltage and taking electron current to the surface under treatment causes increasing the plasma potential because the opposite sine current can not flow to the insulating wall. In the metal chamber increase of positive voltage on the surface leads to the discharge instability and break off for considerable taking electrons away from the discharge volume.

Partial discharge characteristics of syntactic foam filled with hollow polymer microspheres

AbstractSyntactic foam materials, due to their advantages of low densities, low water absorption, and high dielectric strengths, have significant application potential in the cores of post insulators. However, because of a large number of microbubble structures within the syntactic foam, it might decrease the partial discharge inception voltage. It is necessary to investigate the partial discharge characteristics of the foam to assess the feasibility of its internal insulation application. In this study, the syntactic foam samples with four different microsphere contents (0%–2%) were prepared, and the physical structures of the materials were characterised by using Fourier transform infrared spectroscopy, scanning electron microscopy, and three‐dimensional computed tomography. Subsequently, finite element simulations of the electric field were performed to analyse the influence of the microsphere content and distribution on the internal electric field of the syntactic foam. The results suggested that both the microsphere content and distribution affected the partial discharge activity. When the microsphere content was low, the doping of microspheres essentially meant that more air gap defects were present, leading to a decrease in the partial discharge performance. However, when the microsphere content was high, the microspheres were distributed in a dense and orderly manner, improving the field concentration phenomenon and hence inhibiting the partial discharge to a certain extent. In conclusion, the findings of this study provide a data reference and theoretical support for the application of syntactic foam in the cores of composite post insulators.

Humidity Resistant Biodegradable Starch Foams Reinforced with Polyvinyl Butyral (PVB) and Chitosan.

In this study, water-insoluble, moisture-resistant starch foams were prepared using an optimized one-step extrusion-foaming process in a ZSK-30 twin screw extruder. The extrusion parameters, including temperature, screw configuration, die diameter, water content, and feeding rates, were optimized to achieve foams with the lowest density and controlled expansion. A screw configuration made up of three kneading sections was found to be the most effective for better mixing and foaming. Polyvinyl butyral (PVB) acted as a plasticizer, resulting in foams with a density of 21 kg/m3 and an expansion ratio of 38.7, while chitosan served as a nucleating agent, reducing cell size and promoting a uniform cell size distribution. The addition of PVB and chitosan reduced the moisture sensitivity of the foams, rendering them hydrophobic and water-insoluble. The contact angle increased from 0° for control foams to 101.5° for foams containing 10% chitosan and 10% PVB. Confocal laser scanning microscopy (CLSM) confirmed the migration of chitosan to the foam surface, enhancing hydrophobicity. Aqueous biodegradation tests, conducted at 30 °C in accordance with ISO 14852 standards, demonstrated that despite enhanced moisture resistance, the foams remained readily biodegradable, achieving approximately 80% biodegradation within 80 days. These modified starch foams present a sustainable solution for packaging and insulation applications that demand long-term humidity resistance.

Ultralight and robust polyimide aerogels with tunable porous structures based on cation-π interactions for superior thermal insulation

Polyimide (PI) aerogels, renowned for their ultra-low density and exceptional porosity, exhibit substantial potential for thermal insulation applications. However, conventional freeze-drying method often produces irregular and large pore structures, which compromise the mechanical properties of PI aerogels and limit their practical applications. In this work, the enhanced PI-Cu aerogels by cation-π interactions are fabricated through the introduction of Cu ions and benzimidazole. The findings reveal that cation-π interactions facilitate the transformation of PI aerogels from two-dimensional layered structure to three-dimensional honeycomb structure characterized by smaller and more uniform pores, significantly reducing shrinkage and leading to ultra-light properties. Remarkably, a significant improvement of mechanical performance is also achieved after introducing cation-π interactions, even at a decreased density (0.046 g/cm3). Specifically, for samples with 3.5 wt% solid content, the yield strength and modulus of PI-Cu aerogels increase to 0.71 MPa and 13.58 MPa, respectively, representing improvements of 344 % and 520 % over pristine PI aerogels, which are superior to those of many other previously reported PI aerogels/foams with similar or even higher densities. Additionally, the toughness is significantly elevated from 13.5 MPa to 48.8 MPa. More importantly, after introducing cation-π interactions, the thermal insulation of PI-Cu aerogels are also improved with thermal conductivity decreasing from 0.04214 to 0.03997 W/m·K in axial direction and from 0.0399 to 0.03688 W/m·K in radial direction at 25°C. Interestingly, the thermal conductivity show only a slight increase under 180°C less than 0.05741 W/m·K in axial direction and 0.04923 W/m·K in radial direction owning to their exceptional thermal stability (Tg = 404 °C, T5%=524 °C). These exceptional properties position PI-Cu aerogels as promising candidates for diverse functional applications in the field of energy conservation.

UTILIZATION OF WASTE MATERIALS FOR ULTRA-LIGHTWEIGHT AND THERMAL INSULATING CONCRETE BLOCKS

This study investigates the feasibility of utilizing waste materials—specifically fly ash, residual fuel catalytic cracking catalyst (RFCC), and honeycomb briquette ash—in the production of ultra-lightweight concrete blocks for thermal insulation applications. Physical properties such as dry density, water absorption, and compressive strength were evaluated alongside thermal conductivity and microstructural analysis. Additionally, the materials' compliance with hazardous substance regulations and fire resistance were examined. Economic analysis demonstrated substantial cost savings compared to conventional materials. Results indicate that while higher cement replacement ratios with waste materials generally reduce compressive strength, they enhance thermal insulation properties. The study concludes that these materials offer a viable solution for sustainable building construction, aligning environmental benefits with economic advantages.

Understanding the dielectric properties of silicone rubber‐BN nanocomposites under DC voltage

AbstractThe present study explores the dielectric and structural properties of silicone rubber composites with low‐weight percentages of boron nitride (BN) fillers aimed at insulation applications. The incorporation of BN fillers into the silicone rubber matrix significantly enhances the glass transition temperature (Tg), melting temperature (Tm), and crystallization temperature (Tc). Notably, the dielectric constant increases while the loss factor remains minimal with a low concentration of BN fillers with silicone rubber matrix. J–V characteristics from space charge limited current (SCLC) measurements were employed to evaluate trap density. The addition of 3 wt% BN filler notably improves the crossover voltage and trap density in the silicone rubber matrix. A strong correlation has been observed between trap density values derived from SCLC measurements and surface potential decay experiments. Furthermore, the SCLC measurements at different temperatures exhibit an Arrhenius behavior, providing insights into the charge transport and trapping mechanisms. Overall, the experiment results indicate that the inclusion of 3 wt % of BN filler has significant improvement in dielectric as well as charge trap characteristics.Highlights BN filler impacts permittivity and tan (δ) based on concentration levels. Differential scanning calorimetry shows crystallinity changes with increased BN filler in silicone rubber. Surface potential relates to J–V characteristics, following SCLC mechanism. Arrhenius relation to temperature‐based SCLC shows thermally activated conduction. Trap density trends align in SCLC and surface potential decay methods.

Closed-loop recylcing of thermoset poly(vinylogous urethane) foams

Foams are an intriguing class of porous and lightweight materials which have found widespread applications in thermal insulation, pollutant adsorption, catalyst support, and energy storage. However, their covalently cross-linked structure makes foam unable to be recycled resulting in serious environmental burden. To address this challenge, we report the first example of closed-loop chemically recyclable foam. A simple, catalyst-free cryo-polymerization process with multifunctional amines and acetoacetates was utilized to successfully prepare a series of poly(vinylogous urethane) foams, containing dynamic covalent bonds which can selectively be cleaved on demand. The resulting foams exhibit macroporous structure with diameters exceeding 14 μm, pronounced thermal stability (Td,5% > 262.5 °C), robust hydrophobicity (WCA > 93°) and unique reactivity. Applications have been demonstrated for efficient adsorption of organic solvents and anionic dyes. More importantly, the foams show excellent recyclability under acidic conditions with high monomer recovery yields of up to 97 % and high purity levels. Fresh foams could be regenerated from the retrieved building blocks, thus demonstrating efficient closed-loop recycling. This work provides a new “monomer-foam-monomer” ecological chain and may inspire the advancement of next-generation closed-looped recyclable foam materials.