The evident influence of the reduction in particle size to nanometric dimensions on many properties of polymeric dielectric composites emphasises the role of the filler particle-matrix interface. The interfacial environment itself, which is also of nanometric dimensions, can be dominant in determining the properties of the composite. Employing a cubic close-packed array of particles with appropriate interfaces to the polymer as a simple representation of a composite many of the features can be effectively demonstrated and used to model dielectric permittivity, electrical conduction and breakdown in polymeric composites.

抄録全体を表示

The field of nanotechnology has emerged as one of the most active technological areas worldwide, and interest in nanodielectrics has grown rapidly as a potential new generation of HV insulating materials with unique properties. Experimental progress in this field and the challenges facing practical implementation will be commented. A wide range of materials (largely nanofillers in a polymer matrix or intercalated or exfoliated layered natural or synthetic inorganics within a polymer matrix) are being evaluated by universities and industry, and several significant improvements in important electrical, mechanical, physical, and thermal properties were confirmed. This suggests that a number of HV insulation applications could benefit from such materials. However, some limitations have been identified which need to be understood and corrected or accommodated. The role of the nano-inorganic-polymer interface (dielectric and electronic properties, space charge mitigation, band-gap and charge injection effects, and morphology effects) will be considered. Based on this analysis, the ultimate potential that might be realized via nanodielectrics will be envisaged.

抄録全体を表示

The interface between the polymer and the filler particles influences the properties of dielectric materials. To understand how interfaces act, they should be considered as layers rather than interfaces. Therefore the term interphase is more appropriate for the polymer layer around a filler particle where the polymer chains are chemically and/or physically bound to the particle surface.
The interphase is characterized by an ordered polymer structure around the particles. This paper discusses the influence of the ordered polymer structure around the particles on the polymer properties with regard to explain the effect of nano particles on material properties.
In this paper also a model is given how to estimate the maximum interphase fraction depending on particle diameter and interphase thickness. It is postulated that the most significant results can be achieved at this maximum.

抄録全体を表示

Aluminum nitride (AlN) composite particles consisting of nano-particles dispersed on the surface of spherical micro-particles are one of the materials necessary for developing solid insulating materials with high thermal conductivity. This paper describes a novel method of synthesizing AlN composite particles using transferred type DC nitrogen arc plasma. The shape of the synthesized particles, the diameter of micro-particles and the volume fraction of micro-particles in the synthesized composite particles were controlled simply by varying the travelling time of the raw AlN angular particles in the arc plasma. The travelling time was controlled by varying the plasma length and the plasma gas flow rate. The diameter of the nano-particles in the synthesized composite particles was controlled simply by varying the travelling time of the raw AlN particles in the arc plasma, and varying the temperature and the vapor density in the nano-particle synthesis space. The temperature and the vapor density were controlled by varying the flow rate of reacting/quenching ammonia gas. The AlN content in the synthesized composite particles was higher than 99%.

抄録全体を表示

A range of nanocomposites containing polyethylene and montmorillonite (MMT) clay was prepared using different procedures, such that the extent of MMT dispersion varied. The interactions that occur were then studied, together with the effect of MMT dispersion on structure and short-term dielectric breakdown. When the MMT is poorly dispersed, the AC ramp breakdown strength is reduced. When the MMT is well dispersed, quenched samples with and without MMT appear to behave in an equivalent manner. However, while isothermal crystallization at 117 °C results in a significant increase in performance in the absence of MMT, no equivalent change was seen when the MMT was present. The crystallization behaviour of the polyethylene indicates that while well-dispersed MMT serves to enhance nucleation, it can also serve to inhibit crystallization. These results suggest that short-range thermodynamic interactions occur between the clay platelets and the polymer during the initial crystallization phase. The interaction zone can, however, be thought to extent throughout the material.

抄録全体を表示

Molecular structure and morphology of a nanocomposite of low-density polyethylene (LDPE) and nano-SiO_x were studied by dynamic mechanical analysis (DMA). The storage modulus (E^/) and the glass transition temperature (T_g) of the nanocomposite are higher than those of pure LDPE and vary with nano-SiO_x contents in U-shapes. High field electrical conduction in the nanocomposite was investigated in the range of 293K˜353K, which is consistent with a theory based on the conventional thermally activated ionic hopping conduction. The average hopping distance for the nanocomposite containing 1wt % nano-SiO_x shifts from 4.3 to 4.7 nm as the temperature increases from 293K to 353K. Space charge distribution was taken to confirm ionic hopping conduction being the dominant one in the nanocompostie. It is interesting that the relationship between nano-SiO_x content and DC conduction was similar to a percolation conduction existing in a composite of conductive particles (or semi conductive particles) and a polymer. At last, high field electrical conduction mechanism in the composite was discussed on the basis of microscopic structure of the nanocomposite.

抄録全体を表示

This paper reports measurement results of instrumental analyses, permittivity, conduction current, and space charge distribution profiles observed in low-density polyethylene/MgO nanocomposites with various filler contents, done with the intention to clarify the filler-content dependence of dielectric properties. The permittivity shows the lowest value in the sample with 1-phr fillers and then increases monotonically with an increase in filler content. The conductivity measured under dc electric field lowers by the filler addition up to 5 phr at temperatures from 5 to 90°C. In all the samples, positive homocharge is formed in the vicinity of the anode, and its amount is largest at 1 phr. The most adequate filler content for the electrical insulation purpose is around 1 to 5 phr.

抄録全体を表示

This paper deals with the effect of magnesium oxide (MgO) nano-filler to stabilize internal electric field under DC voltage application. A low-density polyethylene (LDPE) film containing the MgO nano-filler (nano-composite film) was subjected to space charge measurement by applying DC voltages. The pulsed electroacoustic method was employed for the measurement. In addition, conduction current under the corresponding conditions was measured and correlated with the space charge evolution.
When the average DC field was as low as 80 kV/mm, very little space charge was observed with the “non-filled" film, whereas a positive space charge was observed with “filled" film. The density of the positive space charge in the vicinity of the anode was higher compared to that in the bulk. The more distant the position from the anode, the lower the charge density. The conduction current under the same condition was found to be lower with higher content of the MgO nano-filler. The conduction current determined by the space charge in the vicinity of the anode was calculated for the specimen with each content of MgO nano-filler, and good agreement between the estimated current and the measured one was found. It is concluded that the MgO nano-filler seems to trap the positive space charge in the vicinity of the anode and suppresses conduction current by reducing the local field at the anode.

抄録全体を表示

Space charge characteristics under high DC electric field of more than 100 kV/mm in a nano-composite film of the low density polyethylene (LDPE) mixed with a nano-size filler of MgO were studied using a pulsed electro-acoustic (PEA) method. To measure the space charge distribution using the PEA system under the high electric field in a thin film, a spatial resolution of the PEA system was improved. Using the improved system, the time dependence of space charge formation in LDPE and LDPE/MgO nano-composite under the high electric field was observed. It is found that a huge amount of packet-like charge generation in LDPE makes a local electric field in the bulk higher. On the other hand, there is almost no such huge packet-like charge observed in LDPE/MgO with MgO content of more than 0.5 phr, while it was observed in that of 0.2 phr. It is found that the generation of the packet-like charge under the high electric field strongly depends on the content of MgO in the LDPE/MgO nano-composite.

抄録全体を表示

Recent works indicate that polypropylene (PP) and ethylene-vinylacetate (EVA) filled by nanosilicates may present low content of space charge and high electric strength. Investigations are being made to explain nanocomposite behaviour and characterize their electrical, thermal and mechanical properties. In this paper, the results of broad-band dielectric spectroscopy performed on EVA and PP filled by layered nanosized silicates are reported. Isochronal and isothermal curves of complex permittivity, as well as activation energies of the relaxation processes, are presented and discussed. Nanostructuration gives rise to substantial changes in the polarisation and dielectric loss behaviour. While the relaxation process of EVA, associated with glass transition of the material amorphous phase, results unchanged from base to nanostructured material, nanocomposites EVA and PP have shown the rise of a new process at higher temperatures respect to the typical host material processes, as well as a different distribution of relaxation processes. Changes in space charge accumulation in relation to the effectiveness of the purification process performed upon nanostructured materials are also reported: while the dispersion of the clean clays leads to a reduction of the space charge, especially at high fields, an unclean filler gives rise to significant homo-charge accumulation and interfacial polarisation phenomena.

抄録全体を表示

Silicate nanocomposites might be a great source of innovation for the development of advanced electrical devices since filler introduction improves mechanical properties, thermal stability and some electrical properties. In a first part of this paper we summarize results obtained by photoluminescence and UV-visible absorption spectroscopy. The optical balance (absorption vs. diffusion) is discussed and a detailed photoluminescence emission spectra analysis is provided. Grafting maleïc anhydride (MA) on PP chains induces the formation of a broad absorption band (250-450nm) and changes in the photoluminescence emission spectrum whereas clay introduction increases light diffusion. In a second part we discuss results obtained using different luminescence techniques (recombination-induced luminescence - RIL-, thermoluminescence and electroluminescence) in order to characterise charge recombination mechanisms and the nature of trapping centres in such materials.

抄録全体を表示

Two very different kinds of polymer nanocomposites have been prepared, characterized and investigated by dielectric spectroscopy to investigate the effects of polymer-nanofiller matrix difference on the dielectric response of nanodielectric composites. Linear low density polyethylene (LLDPE) is a non-polar thermoplastic which has a high viscosity even in the melt phase and bisphenol-A epoxy resin with an anhydride hardener is a polar low viscosity thermosetting resin. Nanometric sized aluminium oxide filler was chosen as the common inorganic phase for both nanodielectrics. Generally, nanoparticles aggregate easily and are difficult to separate due to strong surface interactions. In this study various mixing methods were employed from ultrasonic liquid processing to controlled shear flow mixing to investigate the dispersion of the nanofillers. The resultant epoxy and polyethylene nanocomposites were characterized with SEM, TEM, and DSC. The dielectric properties and frequency response of the nanocomposites were measured in the frequency domain from 10^-2 Hz to 10⁶ Hz at different temperatures. In polyethylene nanocomposites, significant interfacial polarization is clearly seen. However, in epoxy nanocomposites, no obvious interfacial polarization is found. The results are discussed in terms of the difference in the electrical characteristics of the interfacial region between the polymers and the nano-alumina.

抄録全体を表示

In the present work, the electrical and mechanical properties of epoxy nanocomposite materials were studied. The hydrophobicity of the insulating material was analyzed through contact angle measurement. The diffusion coefficients of the material with different percentage of clay in epoxy nanocomposites were calculated. The exfoliation characteristics in epoxy nanocomposites were analyzed through Wide Angle X-ray Diffraction (WAXD) studies. The thermal behaviour of the epoxy nanocomposites was analyzed by carrying out Thermo gravimetric Differential Thermal Analysis (TG-DTA) studies. The tensile test, flexural test, impact test were carried out to understand the mechanical characteristics of the material with different percentage of clay. Heat deflection temperature of the material was measured to understand the stability of the material for intermittent temperature variation. The Dynamic Mechanical Analysis (DMA) results indicated that storage modulus of the material increases with small amount of clay in epoxy resin. The activation energy of the material was calculated from the DMA results. The short time insulation breakdown studies of nanocomposite material indicate that the breakdown voltage increases with small percentage of nano clay in epoxy resin. Also, it was shown that the positive DC breakdown voltage is higher than the negative DC voltage, irrespective of the percentage of nano clay in epoxy resin.

抄録全体を表示

Epoxy/ alumina nanocomposites were newly prepared by dispersing 3, 5, 7, and 10 weight (wt) % boehmite alumina nanofillers in a bisphenol-A epoxy resin using a special two-stage direct mixing method. It was confirmed by scanning electron microscopy imaging that the nanofillers were homogeneously dispersed in the epoxy matrix. Dielectric, mechanical, and thermal properties were investigated. It was elucidated that nanofillers affects various characteristics of epoxy resins, when they are nanostructrued. Such nano-effects we obtained are summarized as follows. Partial discharge resistance increases as the filler content increases; e.g. 7 wt% nanofiller content creates a 60 % decrease in depth of PD-caused erosion. Weibull analysis shows that short-time electrical treeing breakdown time is prolonged to 265 % by 5 wt% addition of nanofillers. But there was more data scatter in nanocomposites than in pure epoxy. Permittivity tends to increase from 3.7 to 4.0 by 5 wt% nanofiller addition as opposed to what was newly found in the recent past. Glass transition temperature remains unchanged as 109 °C. Mechanical properties such as flexural strength and flexural modulus increase; e.g. flexural strength and flexural modulus are improved by 5 % and 8 % with 5 wt% content, respectively. Excess addition causes a reverse effect. It is concluded from permittivity and glass transition temperature characteristics that interfacial bonding seems to be more or less weak in the nanocomposite specimens prepared this time, even though mechanical strengths increase. There is a possibility that the nanocomposites specimens will be improved in interfacial quality.

抄録全体を表示

Epoxy/alumina nanocomposites were prepared in laboratory to be shaped into specimens suitable for treeing experiments. It was elucidated that treeing breakdown strength would increase, if epoxy resins were nanostructured with nano-fillers such as nano boehmite alumina fillers with their loading from 5 to 10 wt%. Tree initiation time is prolonged, as the filler content increases. Tree morphology is different between base resin and its nanocomposite specimens. A new crossover phenomenon is recognized, i.e. thin channels extend more quickly to reach the opposite electrode in nanocomposites than in pure epoxy above ac 20 kV (1000 kV/mm in the tip of the needle), while they show slower growth in nanocomposites than in pure epoxy below ac 15 kV (750 kV/mm). It should be noted that the reach of such thin channels to the grounds does not mean breakdown, but such formed trees grow in width at later stage to cause final breakdown. Treeing phenomena obtained are analyzed and interpreted by a multi-core model to cover various findings of treeing phenomena in nanocomposites.

抄録全体を表示

The main contribution of this paper is to show the realizability of epoxy-based nanocomposites as industrial insulating materials. The nano- and micro-filler mixture was invented to boost the nanocomposite in industrial insulating materials. Nano- and micro-filler mixture composites were newly made by dispersing a few weight-percentages of nano-filler and approximately 60 weight-percentages of micro-silica fillers in epoxy resin. Two kinds of nano-filler were used, such as layered silicate and silica. Experimental results demonstrated that the approach by nano- and micro-filler mixture enables the nanocomposite to have not only superior insulation properties but also the same low thermal expansion in comparison with the conventional filled epoxy (approximately 60 weight-percentages of micro-silica loading). Moreover, the nano-silica and micro-filler mixture composite has the desired properties of resin viscosity and curing reaction whereas the layered silicate and micro-filler composite has higher resin viscosity and faster curing reaction than those of the conventional filled epoxy due to modifier ions of layered silicates. Consequently, the nano-silica and micro-filler mixture composite is presently the closest to the epoxy-based nanocomposite as an industiral insulation material.

抄録全体を表示

this paper, Polyimide/nano-SiO₂ composite films were prepared by means of ultrasonic mechanism. The corona-resistance of composite films were measured by high-voltage instrument which was assembled according to the international standard. The structure of the composite films were described by Fourier transform infrared analysis. The dispersion of the inorganic particles in the films, the morphology of the composite films before and after corona aging were characterized by atomic force microscopy. The results showed that it was effective for the dispersion of nano-SiO₂ particles to use ultrasonic. Nanoparticles distributed uniformly in the polyimide matrix. Comparing with pure polyimide films, corona-resistance time of the composite films involved the particles less than 6wt%, was longer. The longest corona-resistance time of composite films reached four times than pure polyimide films.

抄録全体を表示

In order to modify material properties, nano Ag (diameter less than 20 nm) was successfully made from Ag colloidal sol and uniformly dispersed into silicone resin modified polyester (SP). The dielectric properties of the composite were studied. Resistivity- temperature characteristic of the composite is some different from that of pure SP. The maximal breakdown voltage of the composite is 112% of that of pure SP and dielectric loss can be 8 times of pure SP at power frequency. Dielectric constants of the composites all increased with various contents of nano Ag. Two types of shallow traps (0.52eV and 0.62eV) with trap densities (1.2 × 10¹⁰/cm³ and 2.0 × 10¹¹/cm³) are found in the composite, which differs from those of pure SP (0.58eV, 3.1 × 10¹⁰/cm³) significantly. Resistivity of the composite is much greater than that of pure SP under cryogenic temperature (77K), which might be treated as the result of Coulomb Blockade effect. From the view of dielectric physics, the different characteristic between the composite and pure SP was discussed and a new concept of nano metal/dielectric materials composite used for device surface protection was introduced.

抄録全体を表示

The demand for smaller and lighter capacitors with higher temperature capability is increasing in the power electronic industry and military arena. This article reviews existing capacitor technologies and the potential new capacitor technologies toward realizing these goals. Various dielectric materials beneficial to high dielectric constant and breakdown strength potentially meeting the high requirements are discussed. The importance of dielectric composites including selection of nanofillers and matrix is discussed. The successful implementation of these dielectric materials for high energy density purpose requires a detailed understanding of both materials engineering and processing.

抄録全体を表示

A rapid growth of mixed-signal integrated circuits is driving the needs of multifunction and miniaturization of the component in electronics applications. Polymer-ceramic composites have been of great interest as embedded capacitor materials because they enabled companies to combine the processability of polymers with the high dielectric constant of ceramics. Polymer-ceramic nanocomposites based on new concepts were developed for embedded capacitor applications. The dielectric constant was above 80 at 1 MHz and the specific capacitance was successfully achieved 8 nF/cm². By use of this nanocomposites, multilayer printed wiring boards with embedded passive components were fabricated for prototypes. The following technologies are reported in this paper. Firstly, based on the investigation of barium titanium oxide (BaTiO₃) crystallites, various particles with the sizes from 17 nm to 100 nm were prepared by the 2-step thermal decomposition method from barium titanyl oxalate (BaTiO(C₂O₄)₂·4H₂O). It was clarified that BaTiO₃ particles with a size of around 70 nm exhibited a maximum dielectric constant of over 15,000 by FEM analysis from the measured dielectric constants of BaTiO₃ suspensions. Secondary, the BaTiO₃ surface modification based on a new concept was applied to improve the affinity between BaTiO₃ particles and polymer matrix. Thirdly, the blend polymer of an aromatic polyamide (PA) and an aromatic bismaleimide (BMI) was employed as the matrix from a view-point of both the processabilty during fabricating the substrates with embedded passive components and the thermal stability during assembling LSI chips. Finally, these technologies were combined and optimized for embedded capacitor materials.

抄録全体を表示

We studied certain kinds of diepoxy monomers, with so-called `mesogens'- molecular groups that cause self-ordering - and cured them with appropriate curing agents. Their thermal conductivities were up to 5 times higher than those of conventional epoxy resins. We believe that the mesogens formed nanoscopic high-order structures and the structures formed mezoscopic structures, which were covalently bound together, suppressing phonon scattering. Such resin system is therefore considered to be a kind of polymer-polymer composite with controlled nanostructures. We confirmed the existence of crystal-like structures in the epoxy resins directly by transmission electron microscope (TEM) observation. We also observed mezoscopic structures in the resins with an atomic force microscope (AFM). The results suggest a novel method to improve the thermal conductivities of insulating resins themselves by controlling the nanoscopic high-order structures.
Subsequently, laminates were prepared with the developed resin composite consisting of a kind of epoxy resins with mesogens and ceramic fillers, and tested as a part of a feasibility study. The thermal conductivities of the test pieces were more than 10 times that of commercial FR-4 laminates. This result shows that controlling the nanoscopic high-order structure of the resins is effective in improving the thermal conductivity of resin composites, and the heat dissipation of electric devices as well.

抄録全体を表示

This paper analyzes propagation of wideband electromagnetic (EM) wave in the ionosphere. The influence of total electron contents (TEC) of the ionosphere on the propagation of EM wave is investigated numerically. Our attention is paid to very high frequency (VHF) band, which is dominant frequency band of EM waves emitted from lightning discharges. A one-dimensional model of the ionosphere is considered for simplicity. The ionosphere is treated as an anisotropic and dispersive medium. Particularly, the altitude distribution of electron density is taken into consideration. Variation of pulse width and difference in the arrival time between each frequency component due to the dispersion in the ionosphere are revealed. For our numerical investigation, group delay of the EM wave is found to be dependent on the altitude distribution of electron density, especially when the peak electron density is the order of 10¹²m^-3 or more.

抄録全体を表示

Radially Convergent Beam Fusion (RCBF) device is a compact fusion proton/neutron source with an extremely simple configuration, high controllability, and hence high safety. Therefore, it has been studied for practical use as a portable neutron/proton source for various applications such as landmine detection and medical positron emission tomography. However, some problems remain for the practical use, and the most critical one is the insufficiency of absolute neutron/proton yields. In this study, a new RCBF device was designed to obtain higher neutron/proton yields, and tested by using deuterium gas. The key features of the new device are the cylindrical electrode configuration in consideration of better electrostatic confinement of ions and extraction of protons, and an integrated ion source that consists of a cusp magnetic field and a negatively biased grid anode. To investigate the performance characteristics of the device and the effect of the ion source, three kinds of experimental setup were used for comparison. At first, the device was operated with the basic setup. Then a cusp magnetic field was applied by using ferrite magnets, and finally the grid anode was negatively biased. As a result, it was confirmed that the ion source works effectively. At the same voltage and current, the obtained neutron production rate was about one order of magnitude higher than that of the conventional spherical RCBF device. The maximum neutron production rate of 6.8 × 10⁹ n/s was obtained at a pulsed discharge of -70 kV and 10 A with an anode bias voltage of -1.0 kV.

抄録全体を表示

Remote calibration system for standard inductors of 10 mH has been developed. At the National Metrology Institute of Japan (NMIJ), the calibration of inductors which is traceable to the national standards is provided to clients, only if their devices under test (DUTs), i.e. their own inductors, are carried by themselves to the NMIJ. On the contrary, the remote calibration method enables the clients' inductors to be calibrated without being carried to the NMIJ. The calibration capability of the developed system for the remote calibration was evaluated to be the relative standard uncertainty of about 20 parts per million (ppm), in the case of the calibration of 10 mH standard inductors. From the verification test of this method for three clients in Japan, the results by the remote calibration agreed with those by the conventional method within the standard uncertainties.

抄録全体を表示

The structural response of tree growth in epoxy resin blended with silica filler has been investigated. The physical properties of the resin were varied by changing its filler content and exposing to humid air. The fractal dimension of the electrical tree and its relationship with filler content and humidity were determined. The damaged area of tree in various contents of filler was also estimated. It is considered that the filler would create such an obstruction to the tree growth both in humid and dry conditions. At the ambient condition, the more filler content, the more obstruction would be generated, leading to the significant suppression of tree growth. Likewise, the introduction of filler brought a rise in fractal dimension due to the increase of branches. It is concluded that the existence of filler makes the tree structure more complicated by introducing obstacles to tree propagation, leading to the high fractal dimension of the tree. In addition, it was found that the fractal dimension of the tree was very relational to the fractal dimension of the composite material including filler particles.

抄録全体を表示