IET Nanodielectrics最新文献

Researchers are devoted to developing dielectric elastomers (DEs) with excellent electromechanical properties as an artificial muscle material. The authors report a new class of semi-interpenetrating network (semi-IPN) composites that contains siloxane-modified linear polyurethane (PU) and silicone rubber through reasonable design of polymer structure. The organic-filler copper phthalocyanine (CuPc) is chemically grafted into the semi-interpenetrating network as a cross-linking point and exhibits excellent dispersibility in the matrix. The various properties of the obtained composite films are also evaluated. The dielectric constant (8.65 at 1 kHz) and maximum actuation strain at 30 MV m⁻¹ (5.32%) are significantly higher than those of semi-IPN composites.

Polymer nanocomposites have attracted increased attention for use in the field of high-voltage direct current (HVDC) cable insulation. To study the use of polymer nanocomposites for this purpose, 3D flower-like MgO (flower-MgO) particles with hierarchical surface morphology are first synthesised. Polypropylene (PP) was simultaneously mixed with styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEBS) and flower-MgO to obtain PP/SEBS/flower-MgO composites. The microstructural, thermal, electrical, and mechanical properties of the obtained nanocomposites were then studied in detail. The results showed that flower-MgO particles loaded at low concentration were well dispersed in the PP/SEBS matrix. The incorporation of flower-MgO particles has been found to significantly suppress the injection of homocharges and strengthen the ability to release the charge, thus containing accumulation of the space charge. The DC breakdown strength of PP/SEBS/flower-MgO composites was increased to 323 MV/m. Meanwhile, the tensile strength and elongation at break of the obtained composites was improved by loading 0.5 phr flower-MgO because of the synergistic toughening effects of SEBS and MgO. The investigation demonstrates the immense potential to replace nonrecyclable cross-linked polyethylene as an HVDC cable insulating material.

In this article, the dielectric response of epoxy resin and epoxy-based barium titanate (BaTiO₃) nanocomposites is characterised in the time-domain, based on polarisation and depolarisation current measurements. The aim of this article is to understand the dominant polarisation mechanisms in neat epoxy and its nanocomposites and validate the findings in frequency-domain spectroscopy (FDS). The effect of various parameters on the dielectric response of the material is investigated to this end, namely, polarisation–depolarisation time, electrode material, electric field and specimen thickness. The effect of pre-processing the nano-particles before use is also studied. In order to validate the findings of FDS, time-domain spectroscopy (TDS) of neat epoxy and its nanocomposites is performed.

Polymer-based nanocomposites with excellent flexibility and intrinsic high breakdown strength are promising candidates for high energy density capacitors compared to ceramics counterparts. However, their energy density is relatively low due to the trade-off between permittivity and breakdown strength. In this work, the authors proposed a ferroconcrete-like structure for all-organic nanocomposites via combinatorial electrospinning and hot-pressing method. In this structure, polymethyl methacrylate (PMMA) serves as matrix while poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-HFP)) serves as reinforcement phase. This novel structure is highly effective in breaking the paradox of improved discharged energy density with decreased efficiency, as evidenced by the concurrently improved discharged energy density (∼12.15 J/cm³ compared to 8.82 J/cm³ of the matrix) and efficiency (∼81.7% compared to 76.8% of the matrix). Compared to conventional blending composite films, samples with ferroconcrete-like structure exhibit higher permittivity, breakdown strength, discharged energy density and efficiency. The superior energy storage performance is attributed to large aspect ratio P(VDF-HFP) fibres distributed perpendicularly to the external field, which brings about the extra enhancement of permittivity. Besides, mechanical properties are improved and restriction on carrier motion is facilitated, leading to enhanced breakdown strength and suppressed conduction. This work provides a new way to design dielectric composite for high energy density and efficiency applications.

Researches on the transformer oil-based nanofluids to determine its suitability for replacing the conventional liquid insulation has been consistently happening for more than a decade. Yet, to prepare an optimum blend of transformer oil-based nanofluid with the stability compliance and superior breakdown (BD) characteristics is still a key issue to be addressed. So to achieve the higher BD voltages (BDVs) with good stability, the nanoparticle and surfactant weights dispersed in the oil should be optimised to at least possible critical levels. In this work, dielectric BD characteristic of mineral oil dispersed with TiO₂ nanoparticle and surfactant cetyl trimethyl ammonium bromide (CTAB) is been studied with the applied AC and DC high voltages, which is termed as titania-based transformer nanofluid (TTNF) for this study. Series of TTNF samples were synthesised with different weights of TiO₂ nanoparticle and CTAB, and the partial discharge inception voltage, AC and DC BDV were experimented to ascertain the optimum concentration level. Results show that the AC and DC BDV enhanced up to 36.23 and 43.07%, respectively, for the TTNF prepared with 0.00562 wt% of TiO₂ and its 1% weight of CTAB, which was stable for around eight weeks.

PbHf_1−x Sn_x O₃ (PSH) ceramics were synthesised by a conventional solid-state reaction method. Dielectric properties were investigated in the temperature range of 20–650°C. As the Sn⁴⁺ content goes up, the phase transition temperatures of an antiferroelectric (AFE1) to another intermediate antiferroelectric (AFE2) phase and AFE2 to the paraelectric (PE) phase decrease gradually. When x ≥0.1 for PSH ceramics, the ferroelectric (FE) phase appears around 225°C, and phase transition temperature from FE phase to PE phase goes up with the increasing concentration of Sn⁴⁺. Moreover, high-temperature dielectric relaxation (HTDR) phenomenon can be seen from all samples. Mechanism of HTDR was discussed from impedance spectroscopy and conductivity for PSH ceramics. It was found that three dielectric responses were observed in complex impedance plots and HTDR was involved with the movement of oxygen vacancies. Activation energy calculated from dielectric data suggested that the HTDR was governed by the hopping conduction process.

Barium titanate (BaTiO₃, BT) is widely used in the manufacture of electronic components such as multilayer ceramic capacitors, supercapacitors, thermistors, ferroelectric devices and piezoelectric devices due to its excellent dielectric, ferroelectric, piezoelectric and insulating properties. The performance of BT-based components is highly dependent on the quality of the BT nanoparticles. Large particle size and uneven distribution are the disadvantages of the BT nanoparticles synthesised by the traditional solid-phase reaction, however, the liquid-phase method can overcome these shortcomings, which has the characteristics of high purity and uniform composition with small particle size, and therefore is the main method for the preparation of BT nanoparticles. This review described various liquid-phase preparation methods of BT nanoparticles and compared the advantages and disadvantages of these methods, thereafter the optimised process parameters that affected the BT crystalline quality were summarised so as to obtain BT nanoparticles with a high crystalline quality, small particle size and even distribution.

Trends in the studies of mineral oil (MO)-based nanofluids (NFs) show that most of the conducted works have focused only on the thermal and dielectric properties but few numbers on the ageing performance. In the present study, ZnO NF, in combination with cellulose insulation experienced accelerated thermal ageing at 120 °C for 20 days to study the ageing performance and it was compared with that of MO–cellulose insulation. The deterioration rate of cellulose was evaluated through tensile strength, breakdown voltage (BDV) and dielectric dissipation factor properties. Whereas oils deterioration was evaluated through BDV, interfacial tension, kinematic viscosity, acidity and colour. The results demonstrate that for cellulose aged in NF (NFIP), the tensile strength and BDV are 3 and 6.9% higher, respectively; than those aged in MO. For aged oils, NF exhibits higher values of the viscosity and acidity by 3 and 33.3%, respectively, than MO. The BDV of NF is superior to that of MO in the initial ageing period, after that; it shows a lesser reduction tendency with ageing. The most important observation from this study is that despite this increment of ageing indicators for NF, it could improve the anti-ageing properties of cellulose insulation.

In this study, the relationship between thermal ageing and charge trapping properties of epoxy-based nanocomposites has been investigated. With ageing, any dielectric material undergoes thorough degradation. This degradation significantly affects the space charge accumulation and charge trapping behaviour of the dielectric, which are very important parameters for insulation health under high-voltage direct current (HVDC) environment. In this work, an improved model based on the isothermal relaxation current (IRC) has been developed to study the charge trapping behaviour of pure epoxy and epoxy alumina (Al₂ O₃) nano-composites at different ageing conditions. A methodology based on polarisation–depolarisation current (PDC) measurements has been proposed to identify the current component due to a dipolar relaxation in measured total IRC. This will help to identify the trap distribution characteristics more accurately compared to conventional IRC measurements. It was experimentally observed that the addition of nanoparticles significantly reduces trapped charge formation and reduces thermal degradation. It is observed that aging leads to the generation of deeper traps, while the addition of Al₂ O₃ nanoparticles mainly enhances the density of shallow traps. Results presented in this work indicate that epoxy–alumina nanocomposites are very much suitable in HVDC applications from the perspective of trapped charge accumulation.