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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. Index Terms--Epoxy nanocomposite, curing agent, filler dispersion method, space charge distribution, permittivity, conductivity

In order to respond to soaring public concern about environmental protection, various biodegradable polymers have been developed. The present paper reports the electrical conduction and breakdown properties of various biodegradable polymers such as poly-L-lactic acid (PLLA), polyethylene terephthalate succinate (PETS), polycaprolactone butylene succinate (PCL-BS), polybutylene succinate (PBS), polybutylene succinate adipate (PBSA), and polyhydroxybutyrate/valerate (PHB/V) in comparison to those of low-density polyethylene (LDPE). While the permittivity and conductivity of PLLA and PETS are comparable to LDPE, those of PCL-BS and PBS are much higher. The conductivity is also higher in PBSA. This is because PLLA and PETS are in the glass state at room temperature, while PCL-BS, PBS, and PBSA are in the rubber state. Furthermore, PLLA and PETS show a strong temperature dependence of the conductivity, which is divided into two or three regions, and they also show thermally stimulated polarization or depolarization current around their respective glass transition temperatures. In contrast to the large difference in conductivity among different kinds of samples, all the polymers tested have almost similar impulse breakdown strength at room temperature. As for dc or ac breakdown strength, PLLA and PETS show a relatively higher strength than PCL-BS and PBS. Index Terms--Biodegradable polymers, breakdown properties, electrical conduction, glass transition.

Research describing nucleation and crystallization in oxide glasses is presented. In particular the size distribution and structure of nanoparticles in the glass matrix is investigated.

Through investigations made on crosslinked polyethylene (XLPE) insulated power cables that had experienced failures, blue-colored water trees were observed in addition to ordinary white water trees. The blue water tree was found to be much more harmful than the white water tree, since more electrical trees started at the blue trees. Elemental analysis revealed that iron and sulfur exist in the blue tree. In the case of this blue water tree, space charge exists abundantly but only at the tree tip, while no charge signal is observed on the electrode from which the tree starts. This indicates that the conductivity of the blue tree is very high. This is considered to be the main reason of the harmfulness of this tree.

We investigated the dielectric properties of a new type of polyethylene (PE) polymerized with a single-site catalyst. The new PE has much higher dielectric strength and volume resistivity than both conventional low-density PE and linear low-density PE. The increase in the density is considered to be responsible for the increase in dielectric strength. The type of the comonomer and melt flow rate (MFR) scarcely affect the dielectric properties.

Observations of the space charge distribution around water trees are reviewed, and the nature of water trees analyzed from those results is discussed. It was concluded that at least two mechanisms are responsible for the formation of space charges. One is interfacial polarization due to the high conductivity of a tree channel, and the other is carrier injection from the tree tip at high electric fields.

Water tree characteristics have been investigated for low-density polyethylene by applying power-frequency ac voltages with high-frequency components, which are simulated output voltages of a pulse-width-modulation inverter. If we compare the water-tree length among single-frequency voltages, the water tree grows faster if the frequency is higher However, if we superpose a power-frequency voltage on the high-frequency voltage, tree growth is suppressed. The tree length becomes shorter if the superposed power-frequency voltage is higher This surprising result is explainable by considering that the zero-crossing of the applied voltage plays an important role in tree propagation.

When polyethersulfone was irradiated by [Gamma] rays and then poled at 37 [degrees] C, a new TSC (thermally stimulated current) peak appeared at [approximately]1OO [degrees] C. This new peak and other peaks near 40 and 150 [degrees] C increase with an increase in dose of [approximately]0.6 kGy, and this is considered to be due to trapped charges and other ionic carriers becoming mobile when rearrangement of scissioned chains occurs. However, if the dose exceeds 0.6 kGy, the peak magnitude decreases. Furthermore, if the TSC was poled at 120 [degrees] C, only the peak near 150 [degrees] C appeared and this peak monotonically decreased with an increase in the irradiation dose. A similar decreasing tendency was also observed in the conduction current and in the residual voltage. These decreasing features are considered to be caused by the radiation-induced change that rearrangement of scissioned chains decreases free volume for ionic transport.

In order to understand the dominant carrier species in electrical conduction in polyethersulfone (PES), thermally stimulated current (TSC) measurements were carried out under various conditions. It was found that PES has two TSC peaks in the temperature range from 20 to 220 [degrees] C, consisting of an [Alpha] peak at [approximately] 210 [degrees] C and a [Beta] peak whose peak temperature moves towards a higher temperature with an increasing poling temperature. Even when the sample was not poled, PES shows a spontaneous current with its peak at [approximately] 210 [degrees] C. Both the spontaneous current peak and the [Alpha] peak were found to disappear when the sample had been heated to 230 [degrees] C, keeping the external circuit closed. From such similarity of appearance and disappearance between the two peaks, it is concluded that they have the same origin. From the change in the spatial distribution of space charges inside the sample measured simultaneously with the TSC measurements, positive charges, probably due to [K.sup.+] ions, existed nonuniformly in the sample from the beginning, and are thought to be responsible for the two peaks. From a similar study, the [Beta]peak is considered to be due to polarization of ionic space charges during the poling process.

Glasses doped with rare-earth ions were used to study photoluminescence. The silica and ZBLAN ions in the glasses were excited by different photon sources such as synchrotron radiation, an excimer laser, and a Xe flash lamp. Optical absorption was observed with the use of synchrotron radiation. Where there were two emission states with small energy differences, the luminescence was found to be dependent on temperature inversely. This reaction can be explained by the assuming the electrons were in thermal equilibrium between the two emission states.

The conduction process in polyetheretherketone (PEEK) is discussed mainly from the results of dc conduction, thermal pulse current (TPC), thermally stimulated current (TSC), and pulsed electroacoustic (PEA) measurements. It was found that dc conduction currents in PEEK are consistent with the values predicted by a theory based on the conventional thermally activated ionic hopping process. The ionic hopping distance was calculated to change from 2.5 to 3.9 nm when the temperature crosses the glass transition temperature. The results of TPC and PEA measurements show the existence of heterocharges in the vicinity of both electrodes. In TSC spectra, a peak appears at a temperature of [approximately] 5 to 20 [degrees] C above the biasing temperature. The peak position approaches to the constant temperature of 155 [degrees] C when the biasing temperature is > 150 [degrees] C. The peak height is maximum when the biasing temperature is 150 [degrees] C. It is considered that this peak is related to the glass transition and caused by the depolarization of ionic space charge. From these results, it is concluded that ionic carriers which may come from byproducts of synthesis play an important role in the dc conduction process in PEEK.

Variable-energy positron annihilation spectroscopy and infrared spectroscopy are used in the study of amorphous SiO2 films grown by thermal oxidation and plasma chemical vapor deposition, CVD. CVD is performed in tetraethylorthosilicate and oxygen atmospheres. The investigation shows that measured doppler broadening parameters are dependent on the substrate temperature of deposition which strongly influences Si-OH concentration in the SiO2 layer.

The partial discharge (PD) resistance of three kinds of biodegradable polymers, namely poly-L-lactic acid (PLLA), polybutylene succinate (PBS), and poly [epsilon]-caprolactone butylene succinate (PCL-BS), was studied in comparison to that of low-density polyethylene (LDPE). The polymers were exposed to PDs under the IEC (b) electrode system, and the PD resistance was judged by the surface erosion depth or the time to breakdown induced by PDs. As a result, the 'practical' PD resistance, which is the resistance to PDs under a constant voltage application, is ranked as LDPE > PLLA >> PBS [greater than or equal to] PCL-BS, while the 'true' PD resistance, which is the resistance to PDs with a constant charge quantity, is ranked as PLLA [congruent to] LDPE > PBS >> PCL-BS. Index Terms--Biodegradable polymers, partial Discharge.

Effects of endothermic reaction associated with glass transition on the impulse, dc, and ac breakdown strengths of poly-L-lactic acid (PLLA) and polyethylene terephthalate succinate (PETS) were studied experimentally. Impulse breakdown strength at first decreases monotonically with an increase in temperature for both PLLA and PETS. However, it increases and shows a hump when the temperature approaches a certain temperature that is slightly lower than the glass transition temperature. Then it decreases again. Moreover, it is shown that the degree of increment in impulse breakdown strength at this hump depends upon the crystallinity in PLLA. In the case of dc and ac breakdown, a similar local maximum as seen in impulse breakdown is not observed. Two possibilities, namely energy absorption and structural change both due to glass transition are discussed to explain the experimental results. Index Terms--Biodegradable Polymers, Breakdown Strength, Glass Transition.