Hiroyuki Miyata

Observation of charge behavior in multiply low‐density polyethylene

Effects of interfaces such as metal/polymer interfaces and polymer/polymer interfaces on the space‐charge distribution in multiply low‐density polyethylene have been investigated using a pulsed electroacoustic method. It has been found that the heterocharge was dominant in an artificial interface existing in a polyethylene sample. The time dependence of the heterocharge distribution in the interface on applied voltages and polarity was studied. From these charge distributions, the modified electrical field was calculated based on Poisson’s equation. The calculated result indicated that the actual field was stronger than the applied uniform field at the artificial interface. A new data display method for a three‐ or two‐dimensional plot is employed to display all measurement data on one plot in which the space charge becomes visible so that the results can be easily and conveniently understood.

Development of the new polymer insulating materials for HVDC cable

The properties of modified HDPE, selected from various polymer materials by evaluations of DC characteristics, were examined in both sheet and cable samples. It was found that the modification, which introduced a small amount of polar group into HDPE, considerably enhanced DC breakdown strength to as high as 1.5-2.0 times those of XLPE (cross-linked polyethylene). Under a poling voltage of up to 30 kV/mm, the modified HDPE exhibits particular behavior, with its space charge decreasing as stress is increasing. In addition, the additives in HDPE have a large influence on space-charge characteristics, thereby affecting the DC breakdown strength. The evaluation of cable insulated with optimum modified HDPE was conducted to determine the breakdown strength under various voltage applications. Compared with the XLPE cable, modified HDPE cable exhibited excellent characteristics under all kinds of voltage applications, particularly DC dielectric breakdown strength, which was almost twice that of XLPE. >

Particle Size and Superconducting Transition Temperature of Aluminum Fine Particles

Aluminum fine particles of free surfaces were made by the evaporation method in helium gas to investigate the relation between the superconducting transition temperature Tc of the fine particle and its size. The fine particles were collected without exposure to the air to obtain clean surfaces, however, this process introduced some undesirable weak contacts among the particles. The size distribution was determined by means of electron micrographs, and the average diameter ranged from 90 to 160 A. The superconducting transition temperature Tc was determined from the change of diamagnetic susceptibility with temperature. The present experiment shows that Tc rises with a decrease in , and becomes about 1.8 K for of 90 A, considerably higher than that of bulk aluminum 1.16 K.

Studies on the improvement of breakdown strength of polyolefins

Breakdown tests were conducted on a variety of polyethylenes and polypropylenes. High density polyethylene (HDPE) and polypropylene random copolymers (PPR) exhibited the highest breakdown strengths among the examined polyolefins. Model cables insulated with HDPE and PPR were manufactured, and the impulse breakdown strength of the HDPE cables made under some specific manufacturing conditions was 1.6*larger than that of conventional crosslinked polyethylene (XLPE). However, improvements were not observed in the impulse breakdown strength of PPR. The AC breakdown strength of HDPE and PPR cables also did not improve. The reason for the improvement in impulse breakdown strength of HDPE is the increased crystallinity of the insulating material, is brought about by the heat annealing applied to the cable in a manufacturing process. >

The effect on dielectric loss of polyethylene caused by acetophenone and cumylalcohol

The effects of acetophenone (AP) and cumylalcohol (CA) on the tan/spl delta/ of low density polyethylene (LDPE) were investigated in detail taking the temperature range of 25 to 100/spl deg/C and electrical stress range of 5 to 40 kV/mm. The tan/spl delta/ of LDPEs to which AP and CA (reagent special grade) and these additives purified by absorbent (activated clay) have been added, was compared with the tan/spl delta/ of LDPE without any additives. The analysis by dividing tan/spl delta/ into the dipole factor tan/spl delta//sub D/ and the conductive factor tan/spl delta//sub c/ (tan/spl delta/-tan/spl delta//sub D/+tan/spl delta//sub C/) showed that the additives (AP, CA) have only very small influence on tan/spl delta//sub D/ above room temperature. On the other hand, since the contribution of tan/spl delta//sub C/ markedly increases in the higher temperature and higher electrical stress region depending so much on whether additives are added or not and whether the additives are purified or not, ionic carriers were estimated as carriers of tan/spl delta//sub C/. Two kinds of carrier source, that is to say, the carriers with small activation energy (/spl sim/9 kcal/mol) and the carriers with large activation energy (/spl sim/18 kcal/mol) were estimated in the tan/spl delta//sub C/ of LDPE with additives. The former carriers (with small activation energy) could be removed by purification of additives, resulting in large reduction of tan/spl delta//sub C/ in the high electrical stress region. However, even after the purification, the latter carriers (with large activation energy) could not be removed sufficiently, showing 2 to 3 times of the carrier concentration as much as LDPE without additives.<<ETX>>

Thermally stimulated currents in amorphous selenium: Relationship to trapping levels and the noncrystalline state

Deep traps in amorphous selenium are measured using a thermally stimulated current (TSC) technique. A peak is found in the TSC curve, which arises from the thermal liberation of trapped carriers in the bulk of amorphous selenium. It is found that the trapped carriers are mainly positive holes in the temperature range 170∼310 °K. Three methods (Grossweiner’s method, initial rise plot method, and varying temperature rising rate method) are applied to obtain the trap activation energy. It is concluded that the trap activation energies are distributed from 0.6 to 1.1 eV.

Effect of water on the space charge formation in XLPE

In this paper, we describe the effect of water on the space charge in crosslinked polyethylene (XLPE). In order to study the effects of water and by-products of crosslinking, we prepared two types of samples. The water in the first one (Type A) is controlled by immersing in water after removing the by-products, and the water in the other type (Type B) of samples is controlled by the water from the decomposition of cumyl-alcohol by heating. We measured the space charge formation by the pulsed electro-acoustic (PEA) method. A large difference was observed between Type A and Type B. In Type A samples (containing only water) the space charge distribution changes from homogeneous to heterogeneous as the water content increases, whereas in Type B (containing water and by-products) all samples exhibit heterogeneous space charge distribution. However, merely the effect of water for both types was almost the same, including peculiar space charge behavior near the water solubility limit.

DC and impulse treeing characteristics in insulating material for HVDC cable

We have developed new insulating material, modified high density polyethylene (modified HDPE), for high voltage DC cable, and tested several electrical properties of the material (in the forms of sheet and cable), such as DC dielectric breakdown, conductivity, and space charge property. In practical use, defects in material, especially metallic impurities are serious matter for cables. In present paper, the breakdown characteristics of modified HDPE have tested, using treeing sample with needle electrode, for four kinds of voltage (DC, DC polarity reversal, impulse (Imp), and impulse superposed on to DC voltage). As a result, it was clarified that the treeing breakdown voltage largely depended on kind of voltage. Namely, the order of breakdown strength were DC>Imp>Imp superposed on to DC/spl ges/DC polarity reversal, and the scattering of breakdown voltage become smaller in the above order. With respect to radius dependence of needle tip, breakdown voltage was almost same value from 1.5 /spl mu/m to several tens /spl mu/m, showing polarity effect for DC and Imp. These experimental results are thought to correspond to the space charge formation near the needle tip, dependent on the kind of voltage.

Kinetics of Compound Formation in Mn–Sb Thin Films

Formation processes of intermetallic compounds on annealing of Sb–Mn two-layer thin films were studied by means of the helium ion backscattering technique, X-ray diffractometry and magnetic measurement. In the initial stage interdiffusion begins to form a MnSb film at the Sb/Mn interface, independently of the film composition. If a film contains enough Mn to form Mn2Sb at the final equilibrium, the MnSb formation proceeds as the first step of the reaction until Sb is completely consumed, and then the remaining Mn diffuses into the MnSb film to form Mn2Sb. The second step of the reaction has been found to be quite different from the first one in the mode of diffusion.

Exposure Method Using Photoresist Mask for High-Density Optical Disk Mastering

A high-density digital versatile disk (HD-DVD) is being developed, aiming for high definition television. It is thought that the capacity of HD-DVD would be 15 GB, for example when its track pitch is 0.42 µm, its minimum mark length must be 0.22 µm. To fabricate such a high-density optical disk, we develop an exposure method using a photoresist mask. Super-resolution is also studied in order to make the exposure beam diameter smaller.