The required onset flash sintering temperature of a ZnO ceramic was decreased to as low as room temperature under an applied Alternating Current (AC) field of 3530 V/cm, and the ZnO ceramic achieved ...99% of its theoretical density in 40 s without sintering aids. Due to electrical breakdown, flash sintering occurred once the AC field increased to 5 kV even with no increase in sample temperature and conductivity. Electrical breakdown happened at both edges of the sample, a phenomenon observed in thermal infrared images and confirmed by the simulation results. Electrical breakdown can be very useful in flash sintering even at room temperature.
Display omitted Experiment and simulation of initial breakdown from the both edge of electrodes, which induced the flash sintering.
‘Thermal runaway’ was the most popular mechanism in flash sintering, but this theory was inappropriate under high electric field. In this paper, we described electric discharge and breakdown ...phenomena in experiment to verify this point. And water moisture was found an important role in conducting electric discharge, that increasing moisture content of samples decreased the onset electric field of flash sintering and as low as 1628 V/cm of onset electric field was realized in this paper. With high electric field that can induce electric discharge in the sample, the flash sintering can be induced at room temperature and atmosphere.
With increasing electric field, discharge, sparks and arcs appeared continuously until the electric breakdown happened with flash sintering; moisture inside the sample intensified this process and reduce the onset electric field of flash sintering under high electric field. Display omitted
The remarkable characteristics of nanofibers mats electrospun are large surface area to volume ratio and high porosity, which are crucial to increase the ionic conductivity of membrane full of liquid ...electrolyte, in this aspect, electrospinning is prior to the other methods, such as dry method, wet method, etc. Therefore, fabricating the separator of Li-ion batteries by electrospinning is potential and promising. The PVDF membranes were fabricated by electrospinning. The experiment demonstrated that the main deficiency in the fabricating separators process by electrospinning was low mechanical property, which induced partial short circuits inside the cells. Several methods were presented to enhance the mechanical strength. The experiments demonstrated that the higher the solution concentration was, the stronger the mechanical strength was, and the higher the voltage was, the stronger the mechanical strength was. Additionally, the spherical hat collection target instead of conditional plane target was applied in the electrospinning system, as a result, the thickness of the membrane was more uniform and the fiber diameter was also more uniform. Therefore, the charge and discharge capacity of the coin type cell composed of the separator collected by spherical hat target exceeded the plane target, and the electrospinning separators exceeded the commercial polypropylene separator.
Typhoons are a serious threat to transmission towers and lines in coastal areas. The anti-wind performance of a transmission tower needs to be reinforced and optimized to avoid tower collapse. Here, ...an improved real-time wind-field mathematical model and a tower-line coupled simulation model were established to reproduce the wind field distribution, mechanical vibration, and interaction between the wind field and tower. The damage prediction of the transmission tower was analyzed. Furthermore, an actual scaled tower-line model was built, which was used to measure the acceleration and displacement responses in the anti-wind experiments. The research results show that the improved model is feasible and correct based on the verification of Typhoon Mujigae. The tower’s vibration response is mainly characterized by low frequencies, whereas the lines indicate a high frequency response. The transmission line has a remarkable impact on tower vibrations in high turbulence. A flow direction angle of 50° and a long span are dangerous conditions for transmission systems in coastal regions. The acceleration and displacement responses of the main bars show opposite trends to that of the auxiliary cross-bars. The contribution of this article is the possibility of tower collapse prediction and prevention.
In China high temperature vulcanized (HTV) silicone rubber has been applied to manufacture the sheds and sheath of composite insulators for decades. Being exposed to environmental stressors including ...sunlight, UV radiation, oxidization, electrical stress and moisture throughout the whole operation period, various aging phenomena could be observed, among which color fading and hardening are two important indexes which may be directly related to the performance of composite insulators. According to polymer aging theory, thermo-oxidative could be the main aging reaction leading to the hardening of HTV silicone rubber and in this paper, Thermogravimetric Analysis (TGA) combined with Differential Scanning Calorimetry (DSC), Infrared Spectroscopy (IR) and Mass Spectroscopy (MS) are applied to study the degradation and decomposition process of HTV silicone rubber in air (oxidizing atmosphere) and nitrogen (inert atmosphere) respectively. 18 composite insulator specimens have been collected and their color fading degree, hardness, crosslink density as well as thermal performance have been measured and calculated. A correlation analysis showed that physical crosslink density had a strong positive relation with hardness of specimens whereas chemical crosslink density showed negative relations with hardness. It is concluded that TGA is an effective method to simulate and study the thermo-oxidative aging process of HTV silicone rubber and the measurement results of crosslink density shows that decomposition and over crosslinking reactions have taken place simultaneously in HTV silicone rubber and led to the aging of composite insulators together.
The fast detection of classical contaminants and their distribution on high-voltage transmission line insulators is essential for ensuring the safe operation of the power grid. The analysis of ...existing insulator contamination has traditionally relied on taking samples during a power cut, taking the samples back to the lab and then testing them with elemental analysis equipment, especially for sugars, bird droppings, and heavy metal particulates, which cannot be analysed by the equivalent salt deposit density (ESDD) or non-soluble deposit density (NSDD) methods. In this study, a novel method called laser-induced breakdown spectroscopy (LIBS) offering the advantages of no sample preparation, being nearly nondestructive and having a fast speed was applied for the analysis of metal contamination. Several LIBS parameters (laser energy and delay time) were optimized to obtain better resolution of the spectral data. The limit of detection (LOD) of the observed elements was obtained using a calibration curve. Compared to calibration curves, multivariate analysis methods including principal component analysis (PCA), k-means and partial least squares regression (PLSR) showed their superiority in analyzing metal contamination in insulators. Then, the elemental distribution of natural pollution was predicted using LIBS to fully capture information about the bulk elements (Na, Ni, Cu, Mn, Ca, etc.) of entire areas with PLSR. The results showed that LIBS could be a promising method for accurate direct online quantification of metal contamination in insulators.
With laser-induced breakdown spectroscopy (LIBS), the elemental compositions of the room temperature-vulcanized silicone rubber and the high-temperature-vulcanized silicone rubber newly prepared ...samples were analyzed in this paper. The LIBS spectra showed that carbon (C), oxygen (O), aluminum (Al), silicon (Si), iron (Fe), and zinc (Zn) were contained in the samples, consistent with the energy dispersive X-ray spectroscopy (EDS) results. With scanning electron microscopy (SEM), the micromorphology and the depth of the ablation craters were observed. The craters' sizes were only about 200~400 μm, and there was nearly no difference between the hydrophobicity of the nonablated area and the ablated area, and the static contact angle of the craters was even larger than that of the nonablated area, meaning that the LIBS analysis was almost nondestructive. The depth of the ablation craters showed linearity relationship with the laser pulse number that would help a lot in the in situ analysis. Increasing the laser energy of the shot, the intensity of spectra lines of definite element and the electron number density would increase at the same time. The study result showed that the LIBS would be a promising element analysis technique of silicone rubber especially on line, and the composition of the composites could be clearly observed.
Recently, composite materials with nonlinear dielectric or resistive properties performed well in electric field homogenization and space charge suppression in a high voltage transmission and ...distribution system. For the purpose of obtaining insulation materials with desirable dielectric and electrical resistance properties, we investigated several fillers with nonlinear electrical properties doped in silicon rubber composites, and their dependency on the temperature and field. The samples of silicone rubber composites with different components were prepared using barium strontium titanate (BST) and zinc oxide (ZnO) as the filler, and high temperature vulcanized silicone rubber (SiR) as the matrix. The investigations revealed that the BST-doped samples showed different dielectric properties compared to ZnO-doped composites, with an increase in the electric field, which was nonlinear. The resistivity of both doped samples was similar. Results demonstrated that it was possible to achieve higher values of permittivity, and lower values of tanδ and resistivity, with respect to unfilled silicone rubber composites over a wide electrical field and temperature range. Discussion of the results attributes these important functional behaviours to the spontaneous polarization of nonlinear nanoparticles and the interaction between the SiR chains and the nonlinear nanoparticles at the interfacial area.
In this paper, ZnO was used as a sintering aid as well as reactant in the reactive flash sintering (RFS) of zinc-containing ceramic materials at room temperature (25 °C). The RFS of ZnO-based ...ceramics, both ZnAl2O4 and Zn2TiO4, were achieved with the application of a high electric field. Contrary to previous reports, the RFS of ZnAl2O4 was divided into two stages according to temperature changes, and the effect of the reaction exotherm on the RFS was presented for the first time in this paper. In addition, the RFS produced a larger grain size of ZnAl2O4 than conventional sintering did.
Silicone rubber material is widely used in high-voltage external insulation systems due to its excellent hydrophobicity and hydrophobicity transfer performance. However, silicone rubber is a ...polymeric material with a poor ability to resist electrical tracking and erosion; therefore, some fillers must be added to the material for performance enhancement. The inclined plane test is a standard method used for evaluating the tracking and erosion resistance by subjecting the materials to a combination of voltage stress and contaminate droplets to produce failure. This test is time-consuming and difficult to apply in field inspection. In this paper, a new and faster way to evaluate the tracking and erosion resistance performance is proposed using laser-induced breakdown spectroscopy (LIBS). The influence of filler content on the tracking and erosion resistance performance was studied, and the filler content was characterized by thermogravimetric analysis and the LIBS technique. In this paper, the tracking and erosion resistance of silicone rubber samples was correctly classified using principal component analysis (PCA) and neural network algorithms based on LIBS spectra. The conclusions of this work are of great significance to the performance characterization of silicone rubber composite materials.
PDF
