Papers by Author: Wei Ping Shen

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Authors: Chang Chun Ge, Jun Yu, Wei Ping Shen, Cheng Cheng, Guo Hua Ni, Lu Lu Meng, Ming Li, Cheng Xu Zhang, Yue Dong Meng
Abstract: Superfine and nano-sized Fe powders were prepared by a spark plasma discharge process in deionized water. The powders were characterized by Field Emission Scanning Electron Microscope (FESEM) with Oxford Inca EDX, and X-ray diffraction (XRD). The experimental results indicate that the powders prepared by the process have a bimodal size distribution, high purity, single phase, good spherical shape and high yield.
Authors: Wei Ping Shen, Chang Chun Ge, Li Feng Zhang, Tian Yong Pan
Abstract: The paper outlined here uses self-propagating high-temperature synthesis (SHS) or combustion synthesis that employs more efficient and effective high reaction and cooling rates to produce high quality, reproducible nitride fuels. The fundamental SHS processing parameters was determined to produce Mn-Si-C-N ceramic compounds in which Mn is a surrogate for Am. Because manganese nitride has a relatively low heat of formation the reaction can not be self-sustaining when Si was blended with Mn in the Si:Mn=0.25:1 ratio. The purity of MnSiN2 increases with an increase of the Mn content in Mn-Si-N system. Pure MnSiN2 can be synthesized when Si was blended with Mn in the Si:Mn = 0.5:1 ratio. Volume expansion and porosity decreases, so density, strength and hardness increase as increasing the Mn content in Mn-Si-N system. The powders and sintered cake of MnSiN2-Si3N4 or MnSiN2-Si3N4-SiC was produced by combustion synthesis. The sintered cake of MnSiN2-Si3N4-SiC is attacked by atmospheric moisture to fall to a powder.
Authors: Fei Wang, Wei Ping Shen, Ling Bai, Chang Chun Ge
Abstract: A combustion synthesis process was developed for the synthesis of magnesium silicon nitride powders in the Mg-Si-N system. The effects of ammonium halide addition and the nitrogen presssure on the phase composition and microstructure of the final product were discussed in detail. It was found that ammonium halides were helpful to enhance the nitrogen infiltration, decrease the agglomeration degree and improve the nitridation reaction. Furthermore, the nitrogen presssure greatly influenced the reaction process and the properties of the final MgSiN2 products, especially the phase composition. MgSiN2 powders with low level of impurities (MgO and free Si) could be synthesized through combustion synthesis process in the Mg-Si-N system.
Authors: Ling Bai, Chang Chun Ge, Wei Ping Shen, Ke Zhang, X.D. Mao
Abstract: The densification and phase transformation of high α-phase silicon nitride powder synthesized by SHS with a combination of Y2O3 and Al2O3 sintering additives were investigated. The densification process occurred rapidly from 1400 to 1500 °C and was nearly finished at 1500 °C. However, the α-β transformation of silicon nitride progressed rapidly from 1500 to 1600 °C, and completed at 1600 °C. The phase transformation of silicon nitride lagged behind the densification of Si3N4 ceramics. It showed that the solution and precipitation process did not play the main role in the densification of silicon nitride. The sufficient amount of liquid phase was crucial to complete the densification.
Authors: Chang Chun Ge, Wei Ping Shen, Fei Wang
Abstract: Since 1990, Ge and his earlier and present groups in LSCPM have made great efforts to investigate the Self-propagating High-temperature Synthesis (SHS) of Si-N2 gas-solid system including the SHS process control and its thermodynamics, structural macrokinetics and formation mechanism of SHS-Si3N4. In this presentation, some results that were firstly reported in the world are reviewed and new progress in recent years is reported.
Authors: Qiang Zhou, Peng Wan Chen, Xiang Gao, Wei Ping Shen
Abstract: Experiments have been conducted to consolidate tungsten powder using hot-shock consolidation technique combining with underwater shock wave. An exothermic mixture (TiO2-C-Al-Fe2O3) was ignited by an electric wire coil to release a large mount of heat via a self-propagating high-temperature synthesis reaction which was used to pre-heat the sample powder. As getting the needed isothermal temperature, the powder was subsequently consolidated by shock wave generated by explosion of nitro methane, with a detonation velocity of 6.3 km/s and a detonation pressure of 11.9 GPa. The density and Vickers micro-hardness of the consolidated sample were determined and its microstructure was analyzed by scanning electron microscope (SEM). High-density tungsten samples were obtained by optimizing the experimental conditions. In this paper, the relative density and hardness of the recovered sample are 96.5% and 670 HV, respectively.
Authors: Shu Ming Wang, Qing Zhi Yan, Wei Ping Shen, Chang Chun Ge
Abstract: Nuclear fusion is a promising source of environmental friendly energy for the future, and the ultra-fine grained Tungsten (W) is a hopeful candidate material to be used as plasma-facing materials (PFMs), which are the key materials in the International Thermonuclear Experimental Reactor (ITER), for its many useful advantages. While, due to its high melting point and high sintering temperature needed, the ultra-fine grain sized tungsten is not easy to be fabricated. In this paper, the method of explosive consolidation of powders as well as its mechanism and improvements are discussed, and finally the possibility of using this method to preparing of ultra-fine grained W plasma facing material are also introduced.
Authors: Wei Ping Shen, Wen Ma, Shu-Yuan Gu, Ye Zhang
Abstract: TiC-Ti porous materials have been successfully prepared using combustion synthesis in this paper. Adiabatic temperature of Ti-C and Ti-C-TiC systems was calculated. As to the Ti-C system, the studies show that when the ratio of C/Ti is the range of 0.5-0.6, the pressure of protecting atmosphere is 2-4 MPa, and the density of green compact is about 60%, the synthesized sample exhibits excellent properties such as porosity of 40%, volume density of 2.6 g/cm3, compressive strength over 4 MPa. Pore size is as large as 5-25 µm and the majority pores belong to interconnected pore.
Authors: Jun Yu, Chang Chun Ge, Guo Hua Ni, Lu Lu Meng, Wei Ping Shen, Yue Dong Meng
Abstract: Superalloy powders, which have a small particle size and spherical shape, were prepared by a spark plasma discharge process. The electrical parameter, spark voltage, current and pulse duration have very important effects on the size distribution of produced superalloy powders. When current or pulse duration changed the mean size significantly changed.
Authors: Ke Zhang, Ling Bai, Wei Ping Shen, Chang Chun Ge
Abstract: Silicon nitride was prepared by means of low-pressure preheating combustion synthesis in this paper. When N2 pressure is less than or equal to 2MPa, the lowest preheating temperature is about 653K, reactant could make silicon nitride by combustion synthesis. The additive of ammonium fluoride and ammonium chloride, as the reactive diluent, and Si react and make some useful intermediate products to α -Si3N4 after thermal decomposition. The reactive diluent content must be appropriate. At the same time, with the improvement of Si3N4, as the inert diluent, content in reactant, the adiabatic flame temperature of system would reduce, and combustion reaction rate of Si also drops, so it is propitious to make high level of α -Si3N4.
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