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Dielectrics and Electrical Insulation, IEEE Transactions on

Issue 1 • Date February 2008

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Displaying Results 1 - 25 of 39
  • Table of contents

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    Freely Available from IEEE
  • IEEE Dielectrics and Electrical Insulation Society

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    Freely Available from IEEE
  • Nanodielectrics [Editorial]

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    The 26 papers in this special issue present some of the significant advances in nanodielectrics in the last five years. View full abstract»

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  • Permittivity and tan delta characteristics of epoxy nanocomposites in the frequency range of 1 MHz-1 GHz

    Page(s): 2 - 11
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    To achieve a compact and reliable design of electrical equipment for the present day requirements, there is an urgent need for better and smart insulating materials and in this respect, the reported enhancements in dielectric properties obtained for polymer nanocomposites seems to be very encouraging. To further understand the dielectric behavior of polymer nanocomposites, this experimental work reports the trends of dielectric permittivities and tan delta (loss tangent) of epoxy nanocomposites with single nano-fillers of Al2O3 and TiO2at low filler concentrations (0.1%, 0.5%, 1% & 5%) over a frequency range of 1 MHz-1 GHz. Results show that the nanocomposites demonstrate some very different dielectric characteristics when compared to those for polymer microcomposites. Unlike the usual expectations of increasing permittivity with increasing filler concentration in polymer microcomposites, it has been seen that up to a certain nano-filler concentration and depending on the permittivity of the nano-filler, the permittivities of the epoxy nanocomposites are less than that of the unfilled epoxy at all the measured frequencies. This suggests that there is a very strong dependence of the filler concentration and nano-filler permittivity on the final permittivity of the nanocomposites at all these frequencies. But, in the case of tan delta behavior in nanocomposites, significant effects of filler concentrations were not observed with both Al2O3 and TiO2 fillers. Tan delta values in nanocomposites with Al2O3 fillers are found to be marginally lower at all filler concentrations when compared with the value for unfilled epoxy. But, in TiO2Oepoxy nanocomposites, although the variations in tan delta are not significant with respect to unfilled epoxy, some interesting trends are observed with respect to the frequencies of measurement. View full abstract»

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  • Dielectric properties of epoxy nanocomposites

    Page(s): 12 - 23
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    The dielectric properties of epoxy nanocomposites with insulating nano-fillers, viz., TiO2, ZnO and AI2O3 were investigated at low filler concentrations by weight. Epoxy nanocomposite samples with a good dispersion of nanoparticles in the epoxy matrix were prepared and experiments were performed to measure the dielectric permittivity and tan delta (400 Hz-1 MHz), dc volume resistivity and ac dielectric strength. At very low nanoparticle loadings, results demonstrate some interesting dielectric behaviors for nanocomposites and some of the electrical properties are found to be unique and advantageous for use in several existing and potential electrical systems. The nanocomposite dielectric properties are analyzed in detail with respect to different experimental parameters like frequency (for permittivity/tan delta), filler size, filler concentration and filler permittivity. In addition, epoxy microcomposites for the same systems were synthesized and their dielectric properties were compared to the results already obtained for nanocomposites. The interesting dielectric characteristics for epoxy based nanodielectric systems are attributed to the large volume fraction of interfaces in the bulk of the material and the ensuing interactions between the charged nanoparticle surface and the epoxy chains. View full abstract»

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  • Dielectric properties of epoxy/clay nanocomposites - effects of curing agent and clay dispersion method

    Page(s): 24 - 32
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    Effects of the differences in the curing agent and filler dispersion method on the dielectric properties were examined for epoxy/clay nanocomposites. Irrespective of the clay dispersion method, relative permittivity and electrical conductivity are higher in the samples cured with the amine. Moreover, negative heterocharge accumulates in the vicinity of the anode in the amine-cured samples, whereas positive homocharge accumulates in the acid anhydride-cured samples. From the results of UV photon absorption and PL measurement, the bandgap or the energy at which the photon absorption increases drastically is smaller in the amine-cured samples than in the acid anhydride-cured samples. Ion migration can occur easily in the amine-cured samples whose electrical conductivity and relative permittivity are higher than the acid anhydride-cured samples. The curing agent gives the strongest effect, while the existence of clay affects secondly and the filler dispersion method has the weakest effect. View full abstract»

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  • DC conduction and electrical breakdown of MgO/LDPE nanocomposite

    Page(s): 33 - 39
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    To understand basic electric properties of nano-sized magnesium oxide (MgO) / low-density polyethylene (LDPE) nanocomposite under DC voltage application, the volume resistivity, the space charge distribution and the breakdown strength were investigated. By the addition of nano-sized MgO filler, both the DC breakdown strength and the volume resistivity of LDPE increased. At the average DC electric field of about 85 kV/mm and more, a positive packet space charge was observed in LDPE without MgO nano-filler, whereas a little homogeneous space charge was observed in MgO/LDPE nanocomposite material at the front of electrode. From these results, it is confirmed that the addition of MgO nano-filler leads to the improvement of DC electrical insulating properties of LDPE. View full abstract»

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  • Dielectric properties of nanostructured polypropylene-polyhedral oligomeric silsesquioxane compounds

    Page(s): 40 - 51
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    This paper presents the results of the dielectric measurements conducted on polymer nanocompounds consisting of polypropylene (PP) and polyhedral oligomeric silsesquioxane (POSS). The material compounds were analyzed with a scanning electron microscope (SEM) and Raman-atomic force microscope (Raman-AFM). Ac and lightning impulse (LI) breakdown strength of the material compounds were measured. Relative permittivity, loss factor and volume resistivity measurements were also conducted on the material samples. Two types of POSS, octamethyl and isooctyl, were used in different quantities. The thickness of the samples was approximately 600 mum. Statistical analysis was applied to the results to determine the effects of the additive type and amount on the breakdown strength of polypropylene. The paper discusses the possibilities and restrictions in order to achieve advantages in high voltage applications using polyhedral oligomeric silsesquioxanes. View full abstract»

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  • Degradation of polymer dielectrics with nanometric metal-oxide fillers due to surface discharges

    Page(s): 52 - 62
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    Recent research has indicated that dielectric properties of polymer insulating materials might be improved by the inclusion of nanosized particles dispersed in the polymer matrix. Insulating materials in power apparatus are often exposed to surface discharges in the course of normal operation. Surface degradation due to continued exposure to such discharges may cause deterioration of the surface, and could ultimately lead to catastrophic failure. The current work investigates the effect of inclusion of nanometric particles on the ability of a polymeric dielectric to resist degradation when exposed to surface discharges. The dielectric material used was epoxy resin, while nanosized alumina (Al2O3) and titania (TiO2) were used as fillers. Surface discharge tests were carried out on the specimens. The degraded surfaces were studied using a scanning electron microscope (SEM). Surface roughness measurements were made using a laser surface profilometer (LSP). It was observed that the degradation was greater for unfilled epoxy specimens than that for filled ones. Atomic force microscopy (AFM) and energy dispersive X-ray analysis (EDX) were used to identify surface changes in the dielectric material due to degradation. It has been conclusively shown that addition of even very small volume fractions of nanoparticles increases the resistance of the material to degradation due to surface discharges. A possible mechanism for surface degradation in nanocomposites has been proposed. View full abstract»

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  • Improvement in surface degradation properties of polymer composites due to pre-processed nanometric alumina fillers

    Page(s): 63 - 72
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    Insulating materials in power apparatus are often exposed to surface discharges in the course of normal operation, resulting in deterioration of the material surface. In an earlier work, the authors have shown that the inclusion of nanometric particles (Al2O3) improves the ability of a polymeric dielectric (epoxy) to resist degradation when exposed to surface discharges. In the current work, the effect of pre-processing the alumina nanoparticles before preparation of the composite, is investigated. Laser Surface Profilometry (LSP) was used to measure the degradation of the composite specimens after exposure to surface discharges. The use of a surfactant, viz. Sodium Dodecyl Sulfate (SDS) was found to be ineffective. However, the simple action of heating the nanoparticles before use, improved the resistance of the bulk composite to surface discharges. Further, the particles were functionalized using 3-glycidoxy-propyltrimethoxysilane (GPS). This process greatly enhanced the ability of the nanocomposite to resist surface degradation. In fact, best results were obtained when the particles were first heated and then coated with GPS. Fourier Transform Infra-Red (FTIR) spectroscopy and other techniques were used to investigate chemical changes at the particle-epoxy interfaces. A direct correlation was observed between the improvement of the resistance of the composite to surface degradation and the ability of the pre-processed nanoparticles to form strong bonds with the neighboring epoxy. Effect of pre-processing particles of larger dimensions (platelets) was negligible compared to nanoparticles, indicating the possible importance of the interfacial surface to volume ratio of the fillers. View full abstract»

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  • Degradation assessment of nanostructured superhydrophobic insulating surfaces using multi-stress methods

    Page(s): 73 - 80
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    This paper describes the electrical insulation property of modified superhydrophobic surfaces, which are prepared on epoxy based composites by using special nano-particles. After surface modification the samples exhibit an extreme unwettability with a static contact angle thetasges130deg. In order to investigate the long term stability under multiple stress, the specimens are subjected to electric fields and moisture in accelerated aging tests like modified-rotating-wheel-dipping-test (MRWDT), clean fog test and condensation test, according to the critical outdoor and indoor service conditions, respectively. It is shown that leakage current and effective power dissipation of contamination layers are significantly suppressed in the presence of superhydrophobic insulating surfaces. Thus, the pollution performance of the insulation systems can be enhanced to a great extent in clean fog test and MRWDT, whereas the insulating surfaces covered with nanoparticles seem to have no beneficial effect during the condensation experiments because of the different wetting mode. In addition, the impact of release agents and fillers on the surface superhydrophobicity is also examined in this study. Moreover, the surface analyses are employed to characterize the topographical change of the nanostructure in connection with the material degradation. View full abstract»

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  • Enhanced partial discharge resistance of epoxy/clay nanocomposite prepared by newly developed organic modification and solubilization methods

    Page(s): 81 - 89
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    Frequency accelerated partial discharge (PD) aging of epoxy nanocomposite with 5 wt % additions of clay was investigated in comparison with that of epoxy without clay in terms of PD erosion depth. It was found that the change in the erosion depth is far smaller in specimens with clay than those without clay. The newly developed organic modification and solubilization methods give comparable PD resistance characteristics. The latter would be more resistant to PD's than the former, if specimens were prepared properly. It was clarified that nano-micro mixed composites were superior to the single nanocomposite. Nano segmentation with some interaction zone effect is proposed as a mechanism of improvement in PD resistance. View full abstract»

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  • Nanostructured polymer microcomposites: A distinct class of insulating materials

    Page(s): 90 - 105
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    Experimental evidence was produced and gathered to demonstrate the distinct nature of nanostructured polymer microcomposites. The case of a polymer composite consisting of a high-content of micrometric quartz with a small adjunct of nanoclay is discussed. Emphasis is put on dielectric behavior studies while some results on thermal characteristics are presented. Overall results strongly support the potential of this class of insulating material for electrotechnical applications. View full abstract»

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  • The effect of water absorption on the dielectric properties of epoxy nanocomposites

    Page(s): 106 - 117
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    In this research, the influence of water absorption on the dielectric properties of epoxy resin and epoxy micro-composites and nano-composites filled with silica has been studied. Nanocomposites were found to absorb significantly more water than unfilled epoxy. However, the microcomposite absorbed less water than unfilled epoxy: corresponding to the reduced proportion of the epoxy in this composite. The glass transition temperatures (Tg) of all the samples were measured by both differential scanning calorimetry and dielectric spectroscopy. The Tg decreased as the water absorption increased and, in all cases, corresponded to a drop of approximately 20 K as the humidity was increased from 0% to 100%. This implied that for all the samples, the amount of water in the resin component of the composites was almost identical. It was concluded that the extra water found in the nanocomposites was located around the surface of the nanoparticles. This was confirmed by measuring the water uptake, and the swelling and density change, as a function of humidity as water was absorbed. The water shell model, originally proposed by Lewis and developed by Tanaka, has been further developed to explain low frequency dielectric spectroscopy results in which percolation of charge carriers through overlapping water shells was shown to occur. This has been discussed in terms of a percolation model. At 100% relative humidity, water is believed to surround the nanoparticles with a thickness of approximately 5 monolayers. A second layer of water is proposed that is dispersed but sufficiently concentrated to be conductive; this may extend for approximately 25 nm. If all the water had existed in a single layer surrounding a nanoparticle, this layer would have been approximately 3 to 4 nm thick at 100%. This "characteristic thickness" of water surrounding a given size of nanoparticle appeared to be independent of the concentration of nanoparticles but approximately proportion- al to water uptake. Filler particles that have surfaces that are functionalized to be hydrophobic considerably reduce the amount of water absorbed in nanocomposites under the same conditions of humidity. Comments are made on the possible effect on electrical aging. View full abstract»

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  • Conductivity and space charge in LDPE containing nano- and micro-sized ZnO particles

    Page(s): 118 - 126
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    DC conductivity and ac impedance measurements were made in air and in vacuum on samples of low density polyethylene to which nano-sized and micro-sized ZnO particles and a dispersant had been added. The samples were 150-200 mum thick. The temperature range was 30-70degC. The temperature dependence of the vacuum dc conductivity in samples containing the dispersant and 10% w/w nanosized ZnO followed an Arrhenius relationship closely, the conductivity being 1-2 orders of magnitude lower than that of a sample containing dispersant only. The addition of 10% w/w microsized ZnO had very little effect on the dc conductivity. The ac measurements were made in the frequency range 10 mHz-1 MHz. Addition of nanoparticles increased the ac conductivity at higher frequencies but decreased it at lower frequencies, the cross-over frequency increasing with increasing temperature. The real part of the relative permittivity of samples with nanoparticles was increased relative to that of samples containing dispersant only, at all temperatures, but the corresponding values in samples with microparticles were unchanged, within experimental error. Space charge profiles were obtained using the laser-intensity-modulation-method (LIMM). Space charge densities of order 300 Cm-3 were measured in the bulk near the electrodes, several hours after poling at field strengths around 30 kV/mm. View full abstract»

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  • The effects of chemical structure on the dielectric properties of polyetherimide and nanocomposites

    Page(s): 127 - 133
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    Low dielectric constant polyetherimides have been synthesized by incorporating a bisphenol A dianhydride, BPADA, and 2,7-bis(4-aminophenoxy) naphthalene (BAPN), a phenylene ether diamine. The flexible ether and larger planar naphthalene structure of BAPN led to more spacing between polymer molecules, resulting in less efficient chain packing and an increase in the free volume, thus decreasing the dielectric constant. New PEI/silica hybrid nanocomposites were prepared from this novel polyetherimide via sol-gel process. The dielectric constants were further decreased with the incorporation of silica. These synthesized PEI and nanocomposites have high thermal stability and good mechanical properties. View full abstract»

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  • Structure property relationships in polyethylene/montmorillonite nanodielectrics

    Page(s): 134 - 143
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    The influence of a montmorillonite (MMT) nanoclay, functionalized with dimethyl-di(hydrogenated tallow) quaternary amine, on structural evolution and electrical characteristics of a designed polyethylene system has been studied. Samples were prepared by mixing a polyethylene/MMT masterbatch into a matrix system containing 10% high density polyethylene and 90% low density polyethylene using an extruder; X-ray diffraction results suggest good dispersion and exfoliation, as no basal peak was observed. The introduction of this MMT system was found to result in little disruption of the polymer crystallization process and analysis of the crystallization kinetics of the matrix polymer suggests that it interacts only weakly with the incorporated MMT. This is in sharp contrast to our previous studies of a differently functionalized MMT system. Electrically, this combination of highly dispersed MMT within a weakly interacting polymer matrix results in a significant enhancement in short-term breakdown strength. However, this is accompanied by a massive increase in dielectric loss. View full abstract»

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  • Particle patterning using fluidics and electric fields

    Page(s): 144 - 151
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    Electric-field manipulation of micro-particles in suspension can create patterns via a number of particle forces and fluid flows. These effects are assessed for their suitability for down-scaling to form nano-patterns such as may be incorporated into structured nano-composites. Consideration is given not only to the assembly of field-aligned chains or wires, but also to methods that can give cross-field assembly and even 2-D patterns or crystals. Dielectrophoresis is often the dominant driving force behind particle assembly, but other dipole-dipole interactions and also electrically-driven fluid flows are increasingly recognized as significant or dominant. Orientation of non-spherical particles in frequency-selectable directions is also possible. Estimates for the threshold field strengths required for using these effects to handle nano-particles are considered. Finally the use of media with modified permittivity to increase the field-induced forces or to optimize the selectivity of particle incorporation is discussed. View full abstract»

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  • Space charge trapping in electrical potential well caused by permanent and induced dipoles for LDPE/MgO nanocomposite

    Page(s): 152 - 160
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    Space charge accumulation in low-density polyethylene film containing a small amount of MgO nanoparticles (LDPE/MgO nanocomposite film) subjected to an electric field greater than 100 kV/mm has been studied using an improved pulsed electroacoustic (PEA) system. No marked space charge accumulation was observed in LDPE/MgO nanocomposite films. To determine the mechanism of no space charge accumulation in the LDPE/MgO nanocomposite film, we compared electric potential wells produced by a permanent dipole moment such as that of carbonyl groups (C=0) and an induced dipole consisting of MgO nanoparticles (spherical dielectrics) under a high electric field to create a trapping site for electric charge carriers. The trapping depth created by the permanent dipole moment such as that of the carbonyl groups (C=0) of chemical defects is approximately 0.45 eV. However, the potential well induced by high-permittivity dielectric nanoparticles (MgO) is about 1.5 to 5.0 eV, which is much deeper than that induced by chemical defects. The suppression of space charge formation is explained using the potential well model consisting of a dipole induced by a high-permittivity dielectric nanoparticle. We explained the suppression mechanism of charge accumulation in the LDPE/MgO film that contains deep traps. View full abstract»

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  • Possible mechanisms of superior resistance of polyamide nanocomposites to partial discharges and plasmas

    Page(s): 161 - 169
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    Degradation profiles induced by partial discharges and those induced by oxygen plasmas are compared for polyamide/mica nanocomposites. Both the resistances to partial discharges and to plasmas improve with an increase in nanofiller content. On the other hand, the partial discharge resistance is not improved if mum-sized glass fibers are added to polyamide. In order to investigate these phenomena, the superior resistance mechanism of nanocomposites is discussed, focusing on the effects of the nanofillers on the bulk and surface structures of the resin. It was revealed from X-ray diffraction and permittivity measurements that the nanofiller loading increases crystallinity of the resin and restricts the molecular motion. This should enhance the resistance to degradation. Furthermore, observation results by scanning electron microscopy, energy dispersive X-ray spectroscopy, and X-ray diffraction revealed that the nanofillers had piled up themselves to form a layered structure on the sample surface in an early stage of degradation. Such a structure acts as a barrier against impact of charged particles and diffusion of gases such as oxygen, which should contribute to the improvement of resistance to degradation as its direct effect and also as its indirect effect by suppressing the oxidation of resin. Moreover, it was also revealed from scanning electron microscopy that the nanofillers impede the growth of surface cavities by partial discharges drastically. View full abstract»

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  • Local properties at interfaces in nanodielectrics: An ab initio computational study

    Page(s): 170 - 177
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    First-principles computational methodologies are presented to study the impact of surfaces and interfaces on the dielectric and electronic properties of emerging technologically important systems over length scales of the order of inter-atomic distances. The variation of dielectric constant across Si-SiO2, Si-HfO2 and SiO2-polymer interfaces has been correlated to interfacial chemical bonding environments, using the theory of the local dielectric permittivity. The local electronic structure variation across Si-HfO2 and SiO2-polymer interfaces, including band bending, band offsets and the creation of interfacial trap states have been investigated using a layer-decomposed density of states analysis. These computational methods form the groundwork for a more thorough analysis of the impact of surfaces, interfaces, and atomic level defects on dielectric and electronic properties of a wide variety of nano-structured systems. View full abstract»

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  • Understanding the hydrophobic characteristics of epoxy nanocomposites using wavelets and fractal technique

    Page(s): 178 - 186
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    In the present study, the influence of water ageing on the surface characteristics of epoxy nanocomposites was analyzed through atomic force microscopy (AFM) studies. The hydrophobic properties of the epoxy nanocomposite material were analyzed through contact angle and diffusion coefficient measurements. Fractal dimension were calculated by adopting a multi resolution signal decomposition (MRSD) to the 1D-AFM signal through power spectral density calculations at each level of decomposition. 2D-MRSD studies were applied to AFM pictures to understand the surface characteristics of the material. The result of the study shows the presence of high and low frequency signals indicating characteristic variation in surface roughness of the material. The surface roughness parameter measured through the MRSD technique indicates that the surface roughness is lower for epoxy nanocomposites (upto 5Wt%) compared to pure epoxy resin. It is observed that the fractal dimension and the root mean square roughness values vary proportionately. Also it is realized that diffusion coefficient and surface roughness of the material shows an inverse relationship. View full abstract»

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  • The mechanisms leading to the useful electrical properties of polymer nanodielectrics

    Page(s): 187 - 196
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    Polymer nanocomposites with metal oxide nanoparticle fillers exhibit enhanced electrical breakdown strength and voltage endurance compared to their unfilled or micron filled counterparts. This paper presents the following hypothesis for the mechanisms leading to improved properties. The inclusion of nanoparticles provides myriad scattering obstacles and trap sites in the charge carriers' paths, effectively reducing carrier mobility and thus carrier energy. The result is homocharge buildup at the electrodes, which increases the voltage required for further charge injection due to blocking by the homocharge. The hypothesis is supported by electroluminescence, pulsed electro acoustic analysis, thermally stimulated current measurements, a comparison of AC, DC, and impulse breakdown, as well as absorption current measurements, in silica/crosslinked polyethylene matrix composites with supporting evidence from titania/epoxy composites. View full abstract»

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  • The use of electron paramagnetic resonance in the probing of the nano-dielectric interface

    Page(s): 197 - 204
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    Electron paramagnetic resonance (EPR) has been used to study the properties of trapped electrons or holes in XLPE and in 12.5% vinylsilane-treated SiO2 nano-particles in XLPE specimens. Both electrically unstressed and electrically stressed (up to 25 kV/mm) specimens were used. The EPR spectra of both materials indicated that the acceptors/donors were oxygen radicals in the polymer, probably originating during the cross-linking. It was found that the anisotropic oxygen environments were not randomly oriented, but were textured, presumably during the fabrication of the sheet specimens. It was found that under the action of an applied electric field, the population of an additional number of oxygen radicals occurred. This result is discussed in relation to the implied polymer structure and conductivity mechanisms. View full abstract»

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  • Thermal, electrical characteristics and morphology of poly(Ethylene-Co-Ethyl Acrylate)/CNT nanocomposites

    Page(s): 205 - 213
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    In this study, nanocomposites with binary elements of poly (ethylene-co-ethyl acrylate)/carbon nanotube (EEA/CNT) were prepared so that their thermal and electrical characteristics and morphology, not reported in any literature, could be measured. For the thermal characteristics, their thermal degradation and activation energy were measured by using the thermogram (TG) curve, which was obtained by a heating from 100deg C to 600degC with a thermogravimetric analysis (TGA). In addition, after maintaining a thermal equilibrium at each temperature of 25degC, 50degC, 75degC, 100degC, 125degC and 150degC, their thermoluminescence was measured for 20 minutes. Then, the volume resistivity of EEA/CNT was measured by means of ASTM D991. Morphology of EEA/CNT was measured at 15 kV. First, with the TGA experiments, the thermal degradation temperatures of the specimens containing a CNT were found to shift to a higher temperature region, while activation energy values between 204 kJ/mol and 213 kJ/mol were obtained. Secondly, with the thermoluminescence experiment, the specimens containing a CNT were found to show a much smaller thermoluminescence than the specimens without a CNT. Thirdly, the volume resistivity was lowered as the CNT content increased, which is not enough to create a semiconductivity. This is thought to reveal that the melting blend method has a worse dispersibility than the solution method. Lastly, with the measurements of the fractured surfaces from the field emission scanning electron microscope (FESEM) experiment, it was observed that the CNT was dispersed in the form of many lumps as its content increased. View full abstract»

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Aims & Scope

IEEE Transactions on Dielectrics and Electrical Insulation contains topics concerned with dielectric phenomena and measurements with development and characterization of gaseous, vacuum, liquid and solid electrical insulating materials and systems.

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Reuben Hackam