Papers by Author: Ji Gui Cheng

Abstract: W–Cu (0, 0.25, 0.75, 1.5, and 3 wt.%)/Lu₂O₃ composite materials were prepared through electroless plating with simplified pretreatment method and powder metallurgy. The phases and morphologies of the W–Cu/Lu₂O₃ composites were characterized by X-ray diffraction, field emission scanning electron microscopy and energy dispersive spectroscopy. The relative density, microhardness, electrical conductivity, and bending strength of the sintered samples were examined. The experimental results show that W–Cu composites with uniform structures can be obtained with pretreated W using the simplified method, followed by electroless Cu plating. The microstructure and properties of the composites were significantly affected by the addition of Lu₂O₃ nanoparticles, resulting in high electrical conductivity and strength. The electrical conductivity of W–Cu/1.5 wt.% Lu₂O₃ composites reached 63.3%, which is higher than the national standard value of 50.71%. The bending strength of W–Cu/1.5 wt. % Lu₂O₃ reached 1306.7 MPa, which is 65.41% higher than the national standard. These results may be attributed to the uniform distribution of refined particles with Lu₂O₃ content increased to 1.5 wt. %.

Abstract: A novel glycine-nitrate process (GNP)-reduction method has been developed to fabricate ultrafine tungsten heavy alloy powders, with ammonium metatungstate (AMT), iron nitrate nonahydrate (Fe (NO₃)₃·9H₂O), nickel nitrate hexahydrate (Ni (NO₃)₂·6H₂O) as raw materials and gylcine as a complexant and incendiary agent. Precursor powders were obtained by self-propagation reaction in a suspension containing above materials. The precursor powders were then hydrogen-reduced to obtain composite powders with 90W-7Ni-3Fe composition (wt.%). Phase constitution and morphology of the precursor powders and the reduced powders were characterized by X-ray diffraction (XRD) and scanning electron microscope (SEM). Chemical composition of resultant powders was analyzed by energy dispersive spectrometer (EDS) analysis. It was shown that the GNP-reduction method produces ultrafine 90W-7Ni-3Fe powders with particle size of about 200 nm and highly dispersion of the composition.

Abstract: Pr_1.2Sr_0.8NiO₄ (PSNO) and Sm_0.2Ce_0.8O_1.9 (SCO) powders were synthesized by a glycine-nitrate process and a gel-casting process, respectively. Pr_1.2Sr_0.8NiO₄-x Sm_0.2Ce_0.8O_1.9 (x=0, 25, 50) composite cathode materials were prepared by mechanically mixing the two powders. The particle size of the synthesized PSNO and SCO powders is about 100nm and 50nm, respectively. PSNO and SCO have a good chemical compatibility. Area specific resistance value for the Pr_1.2Sr_0.8NiO₄-x Sm_0.2Ce_0.8O_1.9 (x=25, 50) composite cathode on SCO electrolyte is 0.087 and 0.076Ωcm² at 750°C, which indicates Pr_1.2Sr_0.8NiO₄-Sm_0.2Ce_0.8O_1.9 composite materials may be a promising cathode material for intermediate temperature solid oxide fuel cell (IT-SOFC).

Abstract: WC-Co tapes with different Co contents were prepared by rolling the mixtures of WC-Co powders and polymer binders, and layered WC-Co green compacts with discontinuous distribution of Co contents were obtained by laminating the green WC-Co tapes together. After burning off the binders and other organic composition in H2 atmosphere, the green compacts were sintered in vacuum. Microstructure of both the green and the sintered tapes were observed by scanning electron microscope. An electron probe microanalyser was used to measure the linear distribution of Co element in the layered WC-Co cemented carbides. Sintering densification and mechanical property of the multilayered WC-Co alloys were also investigated and compared with those of conventional WC-Co alloys with nominal Co contents of 8% and 12%, respectively. It was shown that by controlling sintering temperature and time, a continuous graded distribution of Co composition can be realized in the laminated WC-Co alloys, with more Co-rich phase in the original high Co content side (12%). Furthermore, the graded WC-Co cemented carbides can realize a combination of high hardness and high strength.

Abstract: NiO/Ce0.8Sm0.2O1.9 (NiO/SDC, 65wt.% NiO) composite powders were synthesized by a glycine-nitrate process (GNP) to fabricate Ni/SDC anode-supported solid oxide fuel cell (SOFC). The results show that the composite powders are composed of single cubic phases of NiO and SDC and have a particle size in nanometer range. NiO/SDC ceramics were prepared from the NiO/SDC powders and were converted into Ni/SDC cermets by reduction in H2, which were employed as anode materials for SOFC with SDC electrolyte. It is shown that Ni/SDC cermets from the NiO/SDC composite powders by the GNP have porous and homogeneous microstructures and show good electrical conductivity. A single SOFC based on Ni/SDC anode with about 50µm SDC electrolyte film and about 80µm La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) cathode was constructed. Open circuit voltage (OCV) of the cell is about 0.8V and maximum power density is 361.42 and 394.78 mWcm-2 at 750 and 800°C, respectively.

Abstract: La1-xCaxCrO3 (0.1≤ x ≤ 0.4) is usually used as interconnect material for solid oxide fuel cells (SOFCs). In this paper, composite material, the two-phase mixtures of face-centered cubic fluorite structure CayCe1-yO2-y (0 ≤ y≤ 0.2) and orthorhombic perovskite structure [Sm(Eu,Gd)]1-zCazCrO3 (0 < z < 0.3), was prepared by an auto-ignition process in which mixed rare earth oxides (Sm2O3, Gd2O3, Eu2O3 and CeO2) are substituted for La2O3 in La1-xCaxCrO3. The direct current (DC) four-probe technique measurement indicated that the electrical conductivities of specimens increased along with the increase of Ca2+ content (x), especially when x=0.3 and 0.4. The material (x=0.4, about 94% relative density) showed excellent electrical conductivities of 48 Scm-1 in air and 13 Scm-1 in H2 (purity 99.999%) at 700°C respectively, which is about 3 times as high as that of La0.7Ca0.3CrO3.

Abstract: Perovskite Sm1-xSrxCoO3 ceramics have been successfully prepared by gelcasting from oxides and carbonate powders, which were characterized by sintering the gels cast from a suspension of low-solubility metallic oxide precursors and organic monomers. The porosity, pore size, microstructure and electrical conductivity of the obtained Sm1-xSrxCoO3 ceramics were also investigated. It has been shown that single Sm1-xSrxCoO3 perovskite phase forms at a relatively low calcination temperature of 1000°C. Especially, porous Sm1-xSrxCoO3 ceramics with homogeneous microstructure can be obtained by controlling sintering process of the gelcasts. In addition, the Sm1-xSrxCoO3 ceramics show good electrical conductivity, which can meet the demand for solid oxide fuel cell cathode application.

Abstract: NiO-Samaria-Doped-Ceria (NiO-SDC) composite powders with nanometer particle size were synthesized by an improved co-precipitation method, called the buffer solution method. NiO/SDC ceramics were then prepared from the NiO-SDC composite powders and were converted into Ni/SDC cermets, which were tested as the anode materials for solid oxide fuel cell (SOFC) with SDC electrolytes. Microstructure observation showed that the NiO/SDC ceramics and Ni/SDC cermets fabricated from the NiO-SDC composite powders have more uniform and finer grain and pore size than those prepared from the mechanically mixed NiO-SDC powders, and the resulting Ni/SDC cermets also showed higher electrical conductivity than those of Ni/SDC cermets from the mechanically mixed NiO-SDC powders. Furthermore, SOFC based on the buffer solution Ni/SDC anodes exhibited higher open circuit voltage (OCV) and maximum power density.