Materials Science Forum Vol. 922

Abstract: We have reported the effect of support pretreatment with ammonia on Pd/SiO2 catalyst in this study. SiO2 was pretreated with ammonia water to increase the Pd dispersion before the preparation of Pd/SiO2 catalysts. The effect of support pretreatment with ammonia on Pd/SiO2 catalyst was investigated by XRD, FT-IR, N2-adsorption and FE-TEM. The Pd supported on pretreated SiO2 were characterized by XRD, CO-chemisorption and FE-TEM. The pretreatment of SiO2 with ammonia water lead to decrease of silanol groups (Si-OH) up to temperature 200 °C. This decline of silanol groups on the SiO2 affects highly dispersed Pd/SiO2 as 6.52 %. The result showed that the decrease of silanol group on the SiO2 was favorable for the Pd dispersion. It is reason that absence of the silanol groups contribute to the high metal reducibility.

Abstract: The purpose of this study is to present the effect of attracting-repelling force on the dispersion and particle size of palladium (Pd) between Pd and γ-Al₂O₃. The Pd supported on γ-Al₂O₃ catalyst were prepared by deposition-precipitation method with two different ways. From the CO-Chemisorption results, Pd/γ-Al₂O₃ (R2-FM) catalyst has the highest Pd dispersion of 43.16%. The results showed that particle size and distribution of Pd influenced by the surface charge state of γ-Al₂O₃ support, indicating relation of attracting-repelling force between Pd precursor and γ-Al₂O₃ surface.

Abstract: Orderly TiO₂ nanotube arrays (TNTs) with high surface area became a prospective catalyst support. TNTs were obtained by anodizing Ti plate, and then the Ni-Cu-B/TNTs electrodes were prepared by cyclic voltammetry electrodeposition (CVE) method. SEM, EDS and electrochemical testing were used to investigate the microstructure and catalytic performance Ni-Cu-B/TNTs electrodes for methanol electro-oxidation. Effects of electrodeposition time, CVE scanning rate and times on the methanol electrooxidation were studied. The results show the shape of Ni-Cu-B particles on surface change from fusiform-like to spherical with an increasing of deposition temperature. The peak current density initially increased and then decreased with increasing electrodeposition time, rate and number of CVE scanning. The Ni-Cu-B/ TNTs electrode prepared by 30 cyclic times in 30°C at-0.8~0.2V and the scan rate of 20mV s^-1 appear the best electrocatalytic activity for methanol oxidation. After cycled 1300 times for methanol oxidation, the peak current density decreased by 12%, indicating excellent long term stability of Ni-Cu-B/TNTs electrode.

Abstract: In this paper, clay bonded silicon carbide was prepared through pressureless sintering process with silicon carbide dusting powder as raw materials and clay as sintering additive. The effects of the ball-milling method, sintering temperature and clay contents on the density, microstructure and mechanical properties of clay bonded silicon carbide refractory were studied. The planetary ball-milling was a good method to improve the density of the green body, and the density was increased simultaneously with an increase of the clay content. The liquid phase derived from low-melting eutectic mixtures of clay could prevent the superlative oxidation of silicon carbide. The mass increment of sintered samples decreased firstly and then increased at the sintering temperature range from 1250 to 1500 °C. The open porosity of samples decreased with the clay addition at a content range from 10 to 30 wt.%. The bending strength of the samples decreased firstly and then increased with the clay addition increasing. The optimum condition for preparing clay bonded silicon carbide with silicon carbide dusting powder was sintering at 1350 °C with 20 wt.% clay, and the obtained sample with a porosity of 24% achieved the bending strength of 78±7 MPa.

Abstract: Metal foundries use high quality sand in the casting process and produce vast amounts of used foundry sand (UFS). Thus, in order to make the best use of foundry sand in the casting process, it is essential to demonstrate an appropriate recycling method and verify the influence of regenerated foundry sand (RFS) on the mechanical properties of core. In this study, physical and chemical characterizations were conducted on the RFS and the physical properties of cores containing different proportions of RFS were investigated with respect to the flexural strength. The UFS produced in controlled conditions was recycled by a wet type method and the regular foundry sand was replaced with varying proportions of RFS by weight (0, 20, 40 and 60 wt. %). Although the gradation of RFS was analogous with the regular foundry sand, the flexural strength test indicated that the sand mixture with 20 wt. % replacement of regular foundry sand was appropriate for core making without a drastic decrease of flexural strength. The flexural strength decreased with the increase of RFS contents at replacement proportion more than 20 wt. %.

Abstract: Many failures had occurred in operation of insulated tubular bus because of the poor product quality, and its primary reason was that some defects were led into the insulation system in the production, then the local electric field would increase and then result in partial discharge, which could accelerate the aging and even breakdown of the materials. In this research, a 1/4 three-dimensional model was established according to the actual structure of insulated tubular bus, and the simulation results obtained from static electric field and quasi-static electric field were compared. Besides, the electric field distribution of insulated tubular bus with typical defects was simulated based on ANSYS software. These three defects were air void, moisture and damage of semi-conducting layer. The simulation results showed that the electric field distribution of insulated tubular bus with typical defects was more suitable with quasi-static electric field simulating. The maximum electric field value was different with different defects, and dependent on the location and size of defects.

Abstract: Epoxy resin composites filled with alumina (Al₂O₃) particles of different morphology and content were fabricated by vacuum casting method. Electric and thermal properties of the composites were tested at room temperature to investigate the influence of Al₂O₃ morphology on epoxy resin composites. Electrical tests demonstrated that, volume resistivity of epoxy resin composites filled with spherical Al₂O₃ was bigger than with spherical-like Al₂O₃, relative permittivity and dielectric loss of epoxy resin composites increased with increasing of Al₂O₃ content, the effect on dielectric properties of spherical-like Al₂O₃, which had larger specific surface areas, was larger than spherical Al₂O₃ for the same content of filler. Thermal conductivity tests proved that, at the same content, thermal conductivity of epoxy resin composites filled with spherical-like Al₂O₃ was higher than with spherical Al₂O₃. According to the Agari model, spherical-like Al₂O₃ particles were easier to form conducting pathways in epoxy resin composites than spherical Al₂O₃ particles, considering their matte edges.

Abstract: Uniform standard in the structural design for insulated tubular bus is not available both at China and abroad, and there are few reports about insulated tubular bus, which causes a waste of resources and even leads to grid failure. In this paper, epoxy/paper composites insulated tubular bus was investigated and a two-dimensional model was preferred in the simulation due to the axial symmetry of insulated tubular bus. The distribution of electric field and temperature in composite insulated materials were studied with the changes of the diameter/thickness of copper pipe and the thickness of insulation materials. According to the results simulation results, the structure of insulated tubular bus was optimized, the thickness of copper pipe conductor and insulation had been greatly reduced. Compared to the non-optimized initial structure, the amount of copper pipe conductor used for the optimized insulated tubular bus was reduced by 48%, the amount of insulation materials were reduced by 52.5%, and the current density of copper pipe conductor increased by 92.2%.

Abstract: Cross-linked polyethylene (XLPE) as insulation material has been widely used in the manufacturing of medium and high voltage cables for its excellent physical, chemical, mechanical and electrical properties. However, as cable insulation, the XLPE will degradate under service conditions, such as thermal oxidative degradation, mechanical treatment, operating environment etc. In this paper, the closed cable loop had been heated for 7 days by induced current of 1000A, and several diagnostic measurements had been adopted to characterize the performance of XLPE. Firstly FTIR has been conducted on different bending degree cable samples in order to reveal the effect of mechanical treatment on the content changes which occur in XLPE insulation layers. DSC analysis showed the effect of cooling process on the shoulder melting peak temperatures. In the last part, microstructure of the insulation of high current bending XLPE cable was studied. The results showed that the properties of the bending cable after heating by the high current changed a lot and the degree of bending also has an effect on the performance of the cable.

Abstract: In this paper, the insulation near the fault point of a breakdown 220 kV cable joint for burned cable, which kept burning for about one hour, was investigated. The relationship between insulation performance and damage degree of burned cable was analyzed by comprehensive test of material performance. Differential scanning calorimetry (DSC) test results showed that the shoulder peak temperature could reflect the heat history of the materials. There was a correlation between damage degree and the characteristic absorption peak of spectrum (IR) graph. The result of mechanical performance was different obviously. The results of broadband dielectric spectrum showed that the relative permittivity and dielectric loss factor for samples close to the fault point were smaller. By the microstructure observation of sample crystal distribution form, the above conclusions were proved. As a conclusion, DSC, IR, SEM and dielectric performance analysis results matched the real situation, showed that these methods was feasible and effective to judge the damage degree of burned cable.