Abstract: Ti-doped SrLaAlO4 green-emitting phosphor was synthesized via solid-state reactions in air and N2 atmosphere. Sample heated in air showed no emission, however, sample heated in N2 showed broad green emission around 492 nm and broad near-infrared emission around 950 nm by 321 nm near-ultraviolet excitation. XPS measurement and UV-Vis diffuse reflectance spectra suggest that Ti in the sample was reduced to Ti3+ state when the sample was heated in N2. Possible emission mechanism of the sample can be explained as O2-–Ti3+ charge-transfer transition.
Abstract: As one of the most important parts of the generator, Epoxy/mica insulation system has the direct effect on the reliability of generator operation. The accelerated aging of insulation system was taking place under the complex operation condition, and resulting in the insulation system breakdown. It had always been the target for the researchers to find an efficient way to evaluate the state of generator insulation system. According to the real operation situation, the multi-factor aging test sequence with electric field, temperature field, mechanical vibration and thermal cycling was developed, and the test platform with multi-factor aging was built in this research. The partial discharge test was conducted at the end of each cycle. The result showed that, with the insulation aging time prolonged, the maximum partial discharge quantity decreased first then increased while skewness and kurtosis varied the opposite way. And the phase range of partial discharge began to expand. This research provided a new way to evaluate the state of generator insulation system.
Abstract: Ni/Al2O3 nanocomposites have a crack healing function which results in recovery of mechanical strength. The function is caused by oxidations of Ni particles within matrix. Oxidation of Ni dispersion also results in the evolution of oxidized zone, which consists of NiAl2O4 grains in Al2O3 matrix. Degradations by high-temperature oxidation before introduction of surface crack is necessary to investigate for estimating the life time of the present material system. Samples of Ni/Al2O3 nanocomposites were prepared by using pulsed electric current sintering and pre-oxidized at 1200°C for 1-6 d in air. Surface cracks were given by the Vickers indentation at 49 N for 10 s. The samples were oxidized again at 1200°C for 6 h in air to heal the surface cracks. Longer pre-oxidation time of samples results in degradation of the performance of surface crack disappearance. Bending strength of healed samples with 2 d pre-oxidation was comparable with the samples before cracks introduction. After oxidation at 1200°C for 6 h in air, the partially disappearance of cracks was observed on 6 d pre-oxidized samples. Hence, the recovery of bending strength depends on thickness of oxidized zone and depth of surface cracks.
Abstract: Two types of CuFe matrix composites with different reinforcements: silica and alumina particulates were developed using powder metallurgy. The mechanical properties were determined from Brinell hardness and flexural strength. The dry sliding friction and wear performance of the composites were investigated by the friction test. The results indicated that mechanical properties of alumina were superior to those of silica. The friction tests of the composites showed that the alumina reinforcement particle provides better braking performance. A wear track examination of composites showed that same abrasive wear. Our results indicated that composites with alumina reinforcement particles of high compatibility are to be preferred for braking performance.
Abstract: In this research, the anti-corona lacquer with different SiC content was fabricated. The surface resistivity of the lacquer at different voltage levels was measured, and the effect of the SiC content on electrical properties of SiC anti-corona coating was investigated. The results showed that the initial surface resistivity ρs decreased with increasing mass ratio of SiC to resin, while the non-linear coefficient β varied the opposite way. The surface resistivity was improved by adding suitable amount of graphite, which suited the requirements of multiple sections anti-corona structure.
Abstract: In this study, we synthesized the TiO2-modified hydroxyapatite (HAp) with various morphologies by hydrothermal treatment using urea decomposition, at 160 oC for 6 h. After hydrothermal treatment, carbonate-substituted HAp and TiO2 (anatase) phases were formed in products using 1.0-0.1 M urea solution. The morphology of synthesized HAp changed from small plate-shaped to long needle-shaped crystals with decreasing the urea concentration. The photocatalytic property for samples was investigated by decoloration test using 25 ppm methylene blue solution. In comparison with HAp samples without TiO2, the TiO2-modified HAp clearly showed the photocatalytic decomposition of methylene blue by UV irradiation.
Abstract: Cross-linked polyethylene (XLPE) is a main kind of insulation materials, used in medium and high voltage power cable. High voltage XLPE cable production mainly adopts peroxide crosslinking method, and the performance of XLPE cable will be affected by decomposing by-products of crosslinking agent (DCP, dicumyl peroxide).In this paper, the XLPE cable was degassed with different times. The XLPE samples were analyzed by infrared spectrum analysis, DSC analysis and electron microscopy, and the influences of degassing on XLPE crystalline morphology were analyzed. The results showed that the crystal structure of XLPE in the cable was affected by degassing treatment. With the degassing treatment time went on, the by-products kept releasing. The content of by-products in 110kV XLPE cable decreased obviously in 2-7 days’ degassing treatment, and changed slowly after 7 days’. The growth and perfection of the original crystal in XLPE material were obtained, and the new small grains were formed in the material.
Abstract: The oxidation of pentatitanium trisilicide (Ti5Si3) powder at high temperature was investigated in order to determine the suitability of this ceramic material for advanced application in an oxidation atmosphere at high temperature. Titanium silicide has been attracted for years as an engineering ceramics due to its high hardness, high melting point, and good chemical stability. The samples were oxidized from 300 to 1000 °C for 1 to 5 h in air. The mass changes were measured to estimate the oxidation resistance of the sample. The mass gain of the sample oxidized at 1000 °C for 5 h was about 26 % of the theoretical oxidation mass change. The commercial powder, Ti5Si3 showed an excellent oxidation resistance at 1000 °C, because the surface film of both titanium dioxide and silicon dioxide formed by oxidation acted as an oxidation resistant layer.
Abstract: Capacitive deionization (CDI) is a water desalination technique in which salt ions are removed from brackish water by flowing through a spacer channel with porous electrodes on each side. Upon applying a small voltage difference between the two electrodes, cations move to and are accumulated in electrostatic double layers inside the negatively charged cathode and the anions are removed by the positively charged anode. Therefore, one of the advanced merits of CDI is the low driven energy by compared to other desalination technologies. Inspired this, we have performed the calculation on energy consumption of activated carbon based CDI in different operation conditions. The results show that the energy consumptions are significantly related to cell voltage as well as solution concentration. Furthermore, the round trip efficiency as a vital indication in terms of energy consumption have been introduced and discussed as well.