Xiaobing Dong

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.

Space Charge in Low-density Polyethylene /micro-SiO2 composite and Low-density Polyethylene/ nano-SiOx composite with different metal electrode pairs

Nano-SiOx and micro-SiO2 particles were homogeneously dispersed in low-density polyethylene with a method of double-solution mixture. Both kinds of the composites were sputtered with Au and Ag on both surfaces as electrodes, respectively. Space charge in the composites was investigated with pulsed electro-acoustic method (PEA). It is shown that space charge distribution in the sample with different metal electrode pairs relates with the electrode polarity. The amount of hetero-polarity space charge in pure LDPE after being electrically prestressed with Au (+)~Ag(-) electrode pair is greater than that with Au (-)~Ag(+) electrode pair. However, homo-polarity space charge appears in the microcomposite after being electrically prestressed with either Au (+)~Ag (-) or Au (-)~Ag (+) electrode pair, and the amount of space charge increases with micro-SiO2 content. It also could be seen that the amount of homo-polarity space charge in the microcomposite with Au(-)~Ag(+) electrode pair is greater than that with Au(+)~Ag(-) electrode pair. With electrically prestressing, hetero-polarity space charge appears in the nanocomposite with either Au (+)~Ag(-)or Au(-)~Ag(+) electrode pair and the amount of space charge increases with nano-SiOx content. In addition, the amount of space charge in the nanocomposite with Au (-)~Ag(+) electrode pair is lower than that with Au(+)~Ag(-) electrode pair. The space charge distribution difference in all samples with different electrode pairs has close relation to electron and (or) hole injection efficiency of different electrode material, as well as charge trapping and detrapping process in the interfaces of the samples.

The effect of electrical field on the slow polarization of nano-SiO/sub x/ and low-density polyethylene composite

The composite of nano-SiOx and low-density polyethylene is prepared with the double-solution method. Charging currents of the composite at different dc stress, as well as discharging currents, are recorded with Keithley 6517A. It is found that the curves of charging and discharging currents increase with electrical field. Transferring those charging and discharging currents from time domain into frequency domain with Fourier Transform method, it is found that the shapes of the dielectric loss spectrum vary with electrical field. At the same time, it is also found that the dielectric loss peaks increase with electrical field in frequency domain. It is believed that these phenomena have close relation with traps of the interfaces between nano-SiOx and polyethylene, as well as carriers trapping and de-trapping in those interfaces

Low Frequency Polarization Behavior of Nano-Ag/Low-density Polyethylene Composite

The dielectric behavior of a composite system of low-density polyethylene filled with nano-Ag is investigated with time-domain method at the room temperature (293 K). It is shown that the charging vs. time of the composite is lower than that of the pure low-density, however, the depolarization of the composite is faster than that of the pure low-density polyethylene. It seems that nano-Ag/LDPE composite could prevent charge injection in some degree The dielectric behavior of the composite is also investigated in frequency domain via Fourier transformation of the charging and discharging currents vs. time. It is shown that dielectric loss of the composite varies from that of pure polyethylene in the range of 10-3-0.4 Hz. Moreover, the peak of dielectric loss of the composite is lower than that of pure polyethylene and shifts slightly to low frequency comparing to that of the pure polyethylene. It is shown that the status of the interfaces has great contribution to the interface polarization of the composite

Effect of pH value on the structures and optical properties of chemical bath deposition cadmium sulfide thin films

Hexagonal CdS thin films with a strong (002) orientation were successfully prepared by chemical bath deposition (CBD) using the reaction between CdCl2 and CS(NH2)2. A commonly available CBD system was successfully modified using a wetting agent (polyglycol) without agitation. The influence of pH value on the chemical bath deposition process was studied. It was found that pH value of the solution plays a vital role on the quality of the CdS films. The results of XRD indicated that the increase of hydroxide concentration in the bath results in the second phase of Cd3(OH)5(NO3). The optical transmission of the films is in the 75-95% range for the wavelength region above the band gap absorption, which makes them appropriate as window material in solar cells.

Space Charge Distribution Behavior of Nano-SiOx and Low-density Polyethylene Composite

The composite of nano-SiOx and low-density polyethylene is prepared with the double-solution method. Space charge distribution in the composite with various nano-SiOx contents is carried out by pulsed electro-acoustic method. It is shown that the amount of space charge in the composite increases with the nano-SiOx content. The space charge in the composite under 50 kV/mm dc stress is mainly hetero, which is very different from that in the pure polyethylene. However, after electrically stressed at 50kV/mm for one hour, homo space charge is found while the composite being short-circuited. It is believed that the homo space charge injects and accumulates during the dc stressing process, which mainly contributes to the formation of the space charge

Transient analysis on the process of chemical bath deposition cadmium sulfide thin films

The hexagonal CdS thin films with a strong (002) orientation is successfully prepared by Chemical Bath Deposition (CBD) technique using the reaction between CdCl2, CS(NH2)2. A commonly available CBD system has been successfully modified with wetting agent (poly-glycol) without agitation. In this paper, Studies have been made to understand the effect of bath temperature on the transient process and the properties of the films such as optical transmission, surface morphology and the structural property. The results show that poly-glycol can flatten the films and diminish the pinhole. SRD and TEM tests verify the deposited CdS films exhibit a hexagonal structure and no secondary or mixed phases were observed. A preferential columnar growth parallel to the substrate edge is observed.

Permeability study of high polymer membranes for gas-oil separation

Gas chromatography has been used to detect gases associated with transformer partial discharge, overheating, arcing and other problems. Since the analysis using lab chromatography is usually time-consuming and always involves certain time delays, online detecting of the chromatography of dissolved gases in transformer oil is very desirable. The gases dissolved in the transformer oil can be separated automatically with some high polymer membranes based on the differences in permeability of membranes to different gases. This paper discusses the development of a new type of polytetrafluoroethylene membrane with microholes (diameter 5 /spl mu/m to 10 /spl mu/m) that provide good permeability sensitivity, physical and mechanical characteristics for online transformer dissolved gas-in-oil analysis. With this new technology, it may become possible to detect fault-related gases from transformer oil automatically and predict incipient failures in the future.