Yi Yin

Nanoparticle surface modification induced space charge suppression in linear low density polyethylene

This letter reports the role of nanoparticle surface modification in affecting the space charge distribution of polyethylene/silica nanocomposite dielectrics. Space charge distribution in the nanocomposites was measured using a pulsed electroacoustic method. The results suggested that the nanoparticle surface modification has significant effects on the space charge behaviors in polyethylene and that the nanocomposites with surface-treated silica showed improved space charge distribution, which can be understood in terms of the morphological variation of the matrix and the better interfacial adhesion between the surface-treated nanoparticles and the matrix.

Influence of aluminum nanoparticle surface treatment on the electrical properties of polyethylene composites

In this study, we investigated the influence of the surface treatment of Al nanoparticles on the electrical properties of linear low density polyethylene composites. Octyl-trimethoxysilane was used as a nonpolar silane coupling agent for the surface treatment of Al nanoparticles. It was found that the incorporation of nonpolar octyl groups onto the surface of Al nanoparticles not only increased the percolation threshold and the resistivity but also improved the dielectric properties as compared to the composites filled with unsurface-treated nanoparticles. The surface treatment makes it possible to easily control the frequency and concentration dependences of dielectric constant and provided an excellent approach able to considerably reduce the dielectric loss of the nanocomposites, which is of great significance from the viewpoint of practical application of the polymer/metal nanocomposites in the electrical and electronic industries. It is concluded that the improved electrical properties could be direc...

Dielectric properties and effect of electrical aging on space charge accumulation in polyimide/TiO2 nanocomposite films

In situ polymerized polyimide/TiO2 ?PI/TiO2? nanocomposite films with good electrical aging resistance are studied. Space charge distribution in the PI/TiO2 nanocomposite films are measured using the pulsed electroacoustic method. Dielectric properties of the films are measured in the frequency range of 102 Hz–106 Hz by an impedance analyzer ?Agilent 4294A? at room temperature. These nanocomposite films are also characterized by Fourier transform infrared spectroscopy and scanning electron microscopy ?SEM?. It is demonstrated that the nano-TiO2 particles strongly affect dielectric breakdown, lifetime and space charge distribution, and increase the voltage endurance of the nanocomposite films significantly. SEM analyses show that the nanocomposite films are destroyed after corona aging. The relation of space charge distribution with the concentration of the nano-TiO2 particles and the aging time is explored. Results show that an increase in dielectric permittivity of the nanocomposite films is observed with increasing filler concentration. However, the accumulation of space charge decreases with increasing nano-TiO2 particles concentration for the same corona aging time, and depends on the dielectric permittivity of the nanocomposite films.

Influence of nanoparticle surface treatment on the electrical properties of cycloaliphatic epoxy nanocomposites

This experimental study reports the influence of the surface treatment of silica nanoparticles on the morphology and electrical properties of epoxy composites. (3-Glycidoxypropyl)methyldiethoxysilane was used as a silane coupling agent for the surface treatment of the silica nanoparticles. It was found that the incorporation of the silane onto the surface of silica nanoparticles not only improved the dispersion of the nanoparticles in epoxy, but also improved the electrical properties as compared with the composites filled with unsurface-treated nanoparticles. The surface treatment makes it possible to increase volume resistivity, dielectric strength, and provides an excellent approach able to reduce the dielectric loss of the nanocomposites. It is concluded that the improved properties could be directly ascribed to the good dispersion and special physicochemical characteristics of the surface-treated nanoparticles in the polymer matrix.

Rescaled temperature dependence of dielectric behavior of ferroelectric polymer composites

Rescaled temperature dependence of dielectric behavior of ferroelectric polyvinylidene fluoride (PVDF) filled with electroactive ceramic particles of rocksalt-type Li and Ti codoped NiO (LTNO) was studied at wide frequency ranges. Dielectric behavior of the flexible PVDF-LTNO composites with LTNO filler at the volumetric function of 0.3 exhibits a dielectric constant value, e≈50 at broad temperature range (290–360 K), and the value is frequency independent from 103 to 106Hz. The dielectric response of the composite is almost in accordance to that of pure PVDF matrix polymer. It was found that though the dielectric constant value of the composites is high due to an introduction of the rock salt-type LTNO ceramic particles with high dielectric constant, the glass transition of the polymer and dielectric relaxation related to the wide-angle oscillation of polar groups attached to the main polymer chain determine the dielectric behavior of the composite.

Effect of space charge in nanocomposite of LDPE/TiO/sub 2/

Nanocomposite of low density polyethylene (LDPE)/TiO/sub 2/ was prepared via solution blending method. The disperse performance of TiO/sub 2/ in LDPE was observed with Scanning Electron Microscope. It is shown that TiO/sub 2/ could be dispersed uniformly in LDPE through controlling temperature and content of the solution of LDPE, and the largest conglomeration diameter of TiO/sub 2/ in LDPE is less than 80 nm. At the same time, space charge distribution of samples with and without nano TiO/sub 2/ was measured with Pulsed Electroacoustic Method. Hetero-polar space charge near electrodes is much less in sample of nanocomposite of LDPE/TiO/sub 2/ than that in pure LDPE under lower direct current (DC) stress (no more than 40 kV/mm), and space charge in the central of sample of LDPE/TiO/sub 2/ is much more uniform than that in pure LDPE. Thus electrical stress concentration is improved under DC stress in LDPE/TiO/sub 2/. After being pre-stressed under stress of 50 kV/mm for 1h, samples with and without nano TiO/sub 2/ were short-circuited, and space charge in these samples was measured. It is shown that decaying rate of the remnant of space charge in LDPE sample containing TiO/sub 2/ increases with increasing of the TiO/sub 2/.

Effect of temperature on space charge trapping and conduction in cross-linked polyethylene

This paper presented the measurement results of space charge distribution and high field conduction in cross-linked polyethylene (XLPE) plate sample at various electric fields for a broad temperature range from 30 to 90 °C. The temperature effect on charge trapping and transport mechanism is discussed based on estimation of threshold characteristic and apparent mobility. It is shown that the threshold field for space charge accumulation apparently decreased with the temperature, probably associated with acceleration of charge injection and ionic dissociation. The apparent mobility of charges showed an exponential dependence on temperature, which indicates enhancement of charge detrapping and transfer rate at higher temperature. The field dependence of the space charge decreases with the temperature, results in more space charge accumulate at room temperature than at high temperature at certain high field. This behavior indicates that the space charge formation rate increases slower than the charge detrapping rate as the temperature increases. Besides, negative charge is always dominant in the sample at the measuring field and temperature range. This is probably due to stronger electron injection at XLPE-aluminum interface or more negative ion formed by dissociation of chemical species.

The Effect of Electrically Prestressing on DC Breakdown Strength in the Nanocomposite of Low-density Polyethylene / nano-SiOx

Nano-SiOx and micro-SiO2 particles were homogeneously dispersed in low-density polyethylene with double-solution method. The dc breakdown strength of the composite containing various contents of nano-SiOx was experimentally investigated, as well as the composite containing micro-SiO2. The breakdown strength of the nanocomposite is greater than that of pure LDPE. For example, the breakdown strength of the nanocomposite is 16% greater than that of pure LDPE. However, the breakdown strength increment of the nanocomposite decreases as the nano-SiOx content increases. The breakdown strength of the composite containing micro-SiO2 is lower than that of pure LDPE and the breakdown strength decrement increases as the micro-SiO2 content increases. It is very interesting that electrical prestressing enhances the breakdown strength of the nanocomposite and the more content, the more enhancements. As the nano-SiOx content reaches 3%wt, the breakdown strength of prestressed nanocomposite is 20% higher than that of non-prestressed nanocomposite. However, electrical prestressing decreases the breakdown strength of microcomposite, and it could hardly find any distinct content effect on the breakdown strength in the prestressed microcomposite. Finally, the different prestressing effects on breakdown strength in both kinds of composites are discussed with the different interface characteristic in both composites.

Electrical Prestressing of High-Electric-Field Conduction in Composite of Low-Density Polyethylene/Nano-SiOx

An electrical prestressing in a composite of low-density polyethylene (LDPE)/nano-SiOx was observed when measuring high-electric-field conduction in the composite. This means that the DC conduction of a composite after being electrically prestressed with a high DC electrical field (about 8×107 V/m) for 2 h was lower than that of a non-prestressed composite. It is interesting that the electrical prestressing becomes more distinct with increasing nano-SiOx content. The interfaces between nano-SiOx particles and LDPE molecules were investigated by transmission electron microscopy (TEM), so did the dispersal status of nano-SiOx in LDPE. The effects of nano-SiOx on the crystallinity and crystal morphology of LDPE were verified by X-ray diffraction (XRD) analysis. In addition, the interaction between nano-SiOx particles and LDPE molecules was studied by Fourier transform infrared (FTIR) spectroscopy. Finally, the relationship between the electrical prestressing of high-electric-field conduction and the microscopic structure of a LDPE/nano-SiOx composite was discussed.

Effect of Free Radical Scavenger on Space Charge Distribution in Polyethylene during Electrical Aging

Electrical aging of polyethylene was inhibited effectively by incorporation of a free radical scavenger (FRS). Samples of polyethylene with and without the FRS were electrically aged for various times and then the space charge distributions of these samples under dc stress and short-circuited were measured, respectively. It is shown that during electrical aging, the space charge distribution of all samples changed in a complex manner, and splitting or superposing of positive or negative charge peaks occurred at the same time. In addition, the total amount of space charge linearly increased with aging time, which corresponds to the remnant breakdown strength of the samples. Considering to the degradation of polyethylene under other types of stresses, the effects of the FRS of reducing the production of space charge and inhibiting electrical aging in polyethylene were discussed. Finally, the feasibility of space charge as a parameter in quantifying electrical aging of polyethylene was discussed.