High-Performance Ceramics IV

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Authors: Rui Zhang, Qiang Xu, Wei Pan, Chun Lei Wan, Long Hao Qi, He Zhuo Miao
Abstract: Three rare earth zirconates (Sm2Zr2O7, Gd2Zr2O7 and Er2Zr2O7) were prepared by solid state reaction. The crystal structure and ionic conductivity of these zirconates were characterized by X-ray diffraction (XRD) and complex impedance spectroscopy. The results show that Sm2Zr2O7 exhibits single-phase pyrochlore structure and Er2Zr2O7 exhibits single-phase fluorite structure, while Gd2Zr2O7 has pyrochlore and fluorite structure. Among three zirconates, the ionic conductivity of Sm2Zr2O7 is highest, while that of Er2Zr2O7 is lowest.
Authors: Xiang Yong Zhou, Zeng Fan, Zi Long Tang, Zhong Tai Zhang
Abstract: The Y2O3-ZrO2 binary system ceramic is considered to be most developed in application to the ZrO2-based materials. A cubic fluorite structure is generally achieved, as the metal ion of the additive (Y) takes place of the Zr4+ and oxygen ion vacancies are produced in the lattice to maintain the charge balance. This leads to almost totally ionic conductivity. The introduction of changeable valued CeO2 can further improve the total electronic conductivity through the defect equilibrium reaction between tetravalent Ce4+ and trivalent Ce3+ at high temperature and reducing atmosphere. In this study, solid phase synthesis method was employed for the preparation of (YO1.5)x-(CeO2)0.08-(ZrO2)0.9-x and (YO1.5)0.05-(CeO2)y- (ZrO2)0.95-y ceramics, while four probe DC conductivity measurement method was also applied under the temperature between 300 to 800°C. The results prove that the concentration of Y3+ is the main contribution of the electrical conductivity at low temperature.
Authors: Bin Zhu, Xiang Rong Liu, Ye Cheng, Mi Lin Zhang
Abstract: The all-ceria-composite ITSOFCs have demonstrated extraordinary fuel cell performances since the ceria-composite electrodes are very catalytic and conductive, and the ceria-composite electrolytes are highly conductive and also electrolytic, in addition to excellent compatibility between the electrolyte and electrodes based on the same ceria-based composite materials. The power density outputs from 200 to 800 mWcm-2, were obtained for temperatures between 400 and 700°C. The maximum power density 0.72 Wcm-2 (1500 mAcm-2) at 600°C and 0.82 Wcm-2 (1800 mAcm-2) at 700°C were achieved, respectively. These highly catalytic electrodes functioned extensively for many different fuels, such as hydrogen and hydrocarbon fuels, e.g., natural gas, coal gas, methanol and ethanol etc. In some special cases, the ITSOFCs with the ceria-composite electrodes could also work at as low as 200°C. All these good performances are based on the novel catalyst function of the ceria-composite electrodes and internal reforming mechanism.
Authors: Zhong Zhou Yi, Wei Liu, Jing Tao Ma
Authors: Tie Song Lin, De Chang Jia, Ke Ning Sun
Abstract: Ni-YSZ cermets were prepared by combustion synthesis of Y(NO3)3, Zr(NO3)4, Ni(NO3)2 and urea followed by hydrogen reduction at 800°C. The microstructure and electrical conductivity of Ni-YSZ cermets were investigated as contrasted to those of the cermets with the same Ni contents prepared by mechanically mixing method. The cermets prepared by combustion synthesis method had better homogeneity of Ni distributed in YSZ than those prepared by mechanically mixed method; thus, both Ni and YSZ phases formed, to a certain extent, a continuous network structure. The electrical conductivity of the cermets prepared by combustion synthesis method was always better than that obtained with the samples prepared by mechanically mixed method.
Authors: Ji Gui Cheng, Li Ping Deng, Er Tao Xiong, Ping Shi
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.
Authors: Ji Gui Cheng, Ping Shi, Hong Hai Zhong, Bu Mei Wang
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.
Authors: Hong Hai Zhong, Ji Gui Cheng, Xing Qin Liu, Guang Yao Meng
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.
Authors: Min Fang Han, Zhong Li Wang, Yu Qian Wang
Abstract: Processing of sealing materials is a key technology in planar SOFC. In this paper, compositions of sealing materials were determined and then mixed and milled for 7~8 h. Glass materials were obtained by melt at 1300 ~ 1600°C and quenched in cold water. The powder materials were made by milling and screening. Properties of thermal expansion of sealing materials were on the same level to both electrolyte and interconnect. Experiments using 7 kinds of materials were carried respectively at 900°C and 1300°C. The most suitable sealing temperatures related to sealing materials were then determined. Thermal cycle experiments were carried and hermetical properties were tested by red-absorption. Microstructure were observed with SEM and it revealed that the prepared sealing materials joins well with YSZ but not so good with metal.
Authors: Xiu Juan Shi, Yong Ping Zheng, Fei Yu Kang, Xin Lu Li, Wan Ci Shen
Abstract: Cathode material Li[Ni1/3Co1/3Mn1/3]O2 for lithium-ion batteries with layered hexagonal structure was successfully synthesized in sol-gel way. The influences of calcination temperature (from 700° to 1000°C) on the structure and electrochemical behaviors of Li[Ni1/3Co1/3Mn1/3]O2 were extensively investigated. The results of XRD show that all samples are isostructural with α-NaFeO2 with a space group R-3m. XPS analysis shows that the oxidation states of Co and Mn were Co3+ and Mn4+ respectively, while Ni exists as Ni2+ and Ni3+. The charge-discharge experiments show that the sample calcined at 850°C delivers 194.8mAh/g in the first cycle at C/5 rate in 2.5-4.3V potential range.

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