Epoxy‐based dielectrics are extensively used in grid‐connected energy systems and modern microelectronics as electrical insulation, adhesive, and packaging components. However, space charge accumulation in epoxy‐based dielectrics is a foremost factor threatening device stability and lifespan, especially under conditions of high voltage direct current and high temperatures during long‐term operation, and thus are investigated systematically. This article reviews the state‐of‐the‐art progress in understanding and regulating the space charge behavior of epoxy‐based dielectric materials. The development of space charge measurement techniques is first introduced. Then, experimental observations of macroscopic space charge characteristics in epoxy dielectrics under different conditions, along with the advancement of nanofiller‐doping strategies for improving space charge suppression capabilities, are discussed and emphasized. Afterward, simulation progress based on the bipolar charge transport models and quantum chemistry calculations are summarized to provide some insight from a microscopic perspective. It is concluded by providing a brief summary and highlighting future research opportunities in inhibiting space charge accumulation of epoxy‐based dielectrics for practical applications in power equipment and electronic devices.

Space Charge Behavior in Epoxy‐Based Dielectrics: Progress and Perspective

Effect of micro- and nanofiller hybrids on the dynamic mechanical properties of glass reinforced epoxy composites

The dielectric properties of epoxy nanocomposites with conducting nanofillers, such as graphene based and fluffy carbon black (FCB) were investigated in the frequency range of 40 to 30 MHz using an impedance analyzer to measure the dielectric permittivity, tan δ and AC conductivity. At very low filler loadings, epoxy nanocomposites showed remarkable dielectric characteristics. Dielectric constant of the composites decreased with increasing frequency and increased with filler loading. This is related to a decrease in interfacial polarization with increasing frequency and greater interfacial polarization with increase in filler loading. Dielectric loss peaks of epoxy nanocomposites with frequency suggested that both DC conductivity and dielectric polarization processes due to inhomogeneity within the nanocomposites contribute towards dielectric loss. Rising of AC conductivity of the composites with frequency was mainly due to hopping of charge carriers. An AC conductivity of 8.33 × 10−4 S/m and 2.455 × 10−5 S/m at 30 MHz was recorded for FCB/epoxy at 5 phr composite and neat epoxy. This composite also exhibited the maximum dielectric permittivity, 3.16 at 40 Hz and 0.82 at 30 MHz. The distinctive dielectric properties of epoxy-based nano dielectric systems are due to the significant volume fraction of interfaces in the bulk of the material and the consequent interactions between charged nanoparticle surface and epoxy chains. 

A comprehensive investigation of dielectric properties of epoxy composites containing conducting fillers: Fluffy carbon black and various types of reduced graphene oxide

In the present study, hybrid composites are prepared by reinforcing various concentrations of high permittivity zirconia nanofiller into epoxy/CNT compositions to test their usability in EMI shielding applications in the X and Ku bands. ZrO2 nanofiller is added in different proportions to improve absorbance shielding while maintaining the composite conductivity uniform by adding constant CNT concentration to restrict the reflectance shielding. The microscopic studies have revealed an efficient dispersion of ZrO2 nanoparticles in the CNT networks and provided a smoother surface. The presence of zirconia nanofillers increased the dielectric properties, viz. the dielectric constant (194 at 0.1 Hz) and loss tangent (1.57 at 0.1 Hz), respectively, whereas the conductivity was found to be invariantly constant. The increased permittivity of composites enhanced the shielding by absorption, while the shielding by reflection is least influenced by the addition of zirconia nanofiller. The addition of zirconia nanofillers increased the permittivity and tan delta, allowing charges to accumulate at the interfacial areas for incoming EM radiations, resulting in increased absorbance shielding. Limiting the CNT concentration in all composites to the same level resulted in the formation of conductive networks, thus resulting in uniform reflectance shielding for all the hybrid composites in the present study. The dynamic mechanical analysis showed the improvement in the storage modulus and activation energy due to the enhanced interfacial adhesion and cross-linked polymer density.

Understanding the dielectric properties and electromagnetic shielding efficiency of zirconia filled epoxy-MWCNT composites

https://iopscience.iop.org/article/10.1088/2053-1591/ab6e83/pdf

Laboratory evaluation on water-based and flexible epoxy/SiO 2 nanocomposites to enhance anti-sliding effectiveness of pavement

Investigation on dielectric and mechanical properties of epoxy reinforced with glass fiber and nano-silica composites

Recently, there is a rise in demand for low-cost natural source-derived photocatalysts for the degradation of harmful dyes. Here, we report new mesoporous g-C 3 N 4 /HAp nanocomposites prepared by a simple hydrothermal method for efficient photocatalytic degradation of rhodamine B (RhB) dye. Ultrafine g-C 3 N 4 nanosheets were synthesized from the polymerization of melamine and exfoliation of bulk g-C 3 N 4 . HAp nanoparticles were obtained by mixing mussel shell powder with Na 2 HPO 4 and microwave irradiation of the mixture. The g-C 3 N 4 (1-3 wt. %)/HAp was produced from hydrothermally reacting g-C 3 N 4 and HAp. XRD analysis of g-C 3 N 4 /HAp confirms the presence of g-C 3 N 4 and HAp phases. From FT-IR, Raman, NMR, and XPS spectra, the chemical bonds of g-C 3 N 4 /HAp were confirmed. The microscopic (SEM, TEM, and AFM) images illustrate the fine fusion of g-C 3 N 4 and HAp. BET and TG/DTA studies reveal that the g-C 3 N 4 /HAp is mesoporous in nature and is thermally stable. Optoelectronic properties indicate that g-C 3 N 4 /HAp’s luminescence changes with the g-C 3 N 4 concentration. In addition, g-C 3 N 4 /HAp showed high photocatalytic efficiency for RhB degradation (99%) in comparision to g-C 3 N 4 and HAp. The g-C 3 N 4 /HAp is recyclable and possesses good photochemical stability. Superoxide and hydroxyl radicals play a key role in the photodegradation of RhB. A reaction mechanism involving charge (electrons, holes) transfer at Z-scheme heterojunction of g-C 3 N 4 /HAp is proposed. This ‘green’ method, of g-C 3 N 4 /HAp synthesis from g-C 3 N 4 and biowaste-derived HAp, can potentially be applied for catalytic removal of pollutants from industrial effluents. 

A Jeshurun

Papers

Investigation on dielectric and mechanical properties of epoxy reinforced with glass fiber and nano-silica composites

Mesoporous graphitic carbon nitride/hydroxyapatite (g-C3N4/HAp) nanocomposites for highly efficient photocatalytic degradation of rhodamine B dye